DOBLE High Voltage Bushings

Reference Book on High Voltage Bushings A Project of the Doble Client Committee on Bushings

Doble Engineering Company 85 Walnut Street Watertown, Massachusetts 02272-9107 (USA) Telephone: (6 17) 926-4900 Fax: (617) 926-0528

wm7u~.doble.com

72A-1973-01 Rev. I3 7/04

Reference Book on High Voltage Bushings

NOTICE This Reference Publication (the "Reference Book") is solely the property of the Doble Engineering Company (~oble@) and, along with the subject matter to which it applies, is provided for the exclusive use of Doble Clients (the "Client") under contractual agreement for ~ o b l e @ test equipment and services. In no event does the Doble Engineering Company assume liability for any technical or editorial errors of commission or omission; nor is Doble liable for direct, indirect, incidental, or consequential damages arising out of reliance, inaccurate third party information or the inability of the Client to use this Reference Book properly. Copyright laws protect this Reference Book; all rights are reserved. No part of this Reference Book shall be reproduced, stored in a retrieval system, or transmitted by any means, electronic, mechanical, photocopying, recording, or otherwise without written permission from the Doble Engineering Company. Doble and the Doble logo are registered in the U.S. Patent and Trademark Office and are trademarks of the Doble Engineering Company. ~oble@ is providing the information contained herein for reference purposes only. ~ o b l e @ makes no warranty or representation that the Reference Book will meet the Client's requirements. This Reference Book is intended to provide a basic understanding and general application of the principles set forth herein. Comments contained herein relating to safety represent minimum guidelines, and should never be compromised; however, it is foreseeable that the minimum safety guidelines may be supplemented in order to conform to Client's company safety and compliance regulations. Client is responsible for applying the information contained herein in strict accordance with industry as well as Client's company compliance and safety regulations. The techniques and procedures described herein are based on years of experience with some tried and proven methods. However, the basic recommendations contained herein cannot cover all test situations and there may be instances when ~ o b l e @ should be consulted directly. ~ o b l e @ is not responsible for the MISUSE OR RELIANCE ON THlS PUBLICATION; ANY OPINIONS CONTAINED HEREIN OR AS A RESULT OF MODIFICATION BY ANYONE OTHER THAN DOBLEB OR AN AUTHORIZED DOBLE REPRESENTATIVE. THERE ARE NO WARRANTIES, EXPRESSED OR IMPLIED, MADE WlTH RESPECT TO THlS REFERENCE BOOK INCLUDING, BUT NOT LIMITED TO, ANY IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. DOBLE@ EXPRESSLY DISCLAIMS ALL WARRANTIES NOT STATED HEREIN. IT IS UNDERSTOOD THAT MUCH OF THlS INFORMATION (ALTHOUGH OWNED BY DOBLE~)HAS BEEN COMPILED FROM OR CONVEYED BY THIRD PARTIES WHO IN DOBLE'S REASONABLE ASSESSMENT ARE LEADING AUTHORITIES IN THE INDUSTRY, ALTHOUGH DOBLE HAS REVIEWED THE INFORMATION WlTH REASONABLE CARE, THE VERACITY AND RELIABILITY OF THE INFORMATION AND IT'S APPLICATION IS NOT ABSOLUTE. UNDER NO CIRCUMSTANCES WILL DOBLE BE LIABLE TO CLIENT OR ANY PARTY WHO RELIES IN THE INFORMATION FOR ANY DAMAGES, INCLUDING WITHOUT LIMITATION, PERSONAL INJURY OR PROPERTY DAMAGE CAUSED BY THE USE OR APPLICATION OF THE INFORMATION CONTAINED HEREIN, ANY INCIDENTAL OR CONSEQUENTIAL DAMAGES, EXPENSES, LOST PROFITS, LOST SAVINGS, OR OTHER DAMAGES ARISING OUT OF THE USE OF OR INABILITY TO USE THlS INFORMATION SUCCESSFULY. Some states do not allow the limitation or exclusion of liability for incidental or consequential damages, so the above limitation or exclusion may not apply.

0Copyright, 2004 By DOBLE ENGINEERING COMPANY

All Rights Reserved

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72A-1973-01 Rev. B 7104

Preface It is the purpose of this guide to assemble and place in the hands of operating personnel, a concise assembly of the most frequently desired information on the inspection and maintenance of bushings. An index of items covered in the Doble Client Conference Papers and digests of manufacturers' material also are included for situations, which may be beyond the scope of this guide. In some cases tin the guide; the names of manufacturers of test equipment devices and instruments have been included for the convenience of Clients. Such inclusion is for the purpose of giving examples and does not imply that the particular device is recommended or that there are not other equally suitable devices. It is apparent that there may be other manufacturers of equal or superior devices. This guide is a project of the Doble Client Committee on Circuit Breakers and Bushings, but does not offer any recommendation of either the Committee or the Doble Engineering Company. At the time the revision of this Guide was approved, the Doble Client Committee on bushngs consisted of the following members:

A. J. Herry, Chair C. A. Rogas, Jr., Vice Chair M. Launer, Secretary W. Andrle J. J. Arneth J. W. Brown E. J. Chiginsky P. Cotrone A. L. Davidson P. J. Dempsey J. B. Duffus G. B. Edwards B. N. Egan A. G. Felice J. W. Gannon R. Garland R. T. Garris D. M. Giles K. E. Gill S. Gonzales R. B. Hagen

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W. L. Henry D. L. Hines M. E. Horning W. G. Hutchnson J. C. Isecke E. I. Jacobson M. C. Jenson J. Kay R. W. Kimball G. L. Kuntz D. G. Langseder R. B. Lewis V. J. Lukasiak W. W. Lynn G. F. MacDonald D. E. McConnell G. N. Medich, Jr. P. S. Melluzzo

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K. L. Millard R. C. Morse, Jr. V. N. Nguyen J. K. O'Connor S. C. Palandri C. L Pankratz R. E. Pankratz W. J. Penner S. J. Petruit W. L. Przyuski S. Raoufi J. S. Reiter, Jr. R. E. Rozek H. A. Ruggles E. G. Sanchez D. C. Schauwecker W. D. Shead J. E. Short

W. E. Sipe V. V. Sokolov T. W. Spitzer K. W. Swain J. F. Troisi P. L. Vaillancourt R. Van Haeren M. D. VanDoren W. B. Wallace P. M. Wasacz R. Wasson L. Weathington F. R. Winnard L. Worthngton D. G. Wray G. de Radigues

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TABLE OF CONTENTS

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1

Introduction to Bushings

2

Apparatus Bushing Standards

2.1 2.2

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....................................................................................................... 3

.............................................................................................................3 Apparatus Bushing Standards ...............................................................................3 Introduction

EEMAC Standard for Power Transformer and Reactor Bushings .................................................... 4

IEC Publication No . 137 (1984) ....................................................................................................... 4 British Standard Specification for Bushings for AC Voltages Above lOOOV .................................. 4

2.3

2.4

2.5

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Service Conditions 5 Altitude ......................................................................................................................................... 5 Operating Temperatures.................................................................................................................... 5 Mounting Angle ................................................................................................................................ 5 Operating Pressure of Parent Equipment ......................................................................................... 6 Bushing Ratings 6 lRated Maximum Line-to-Ground Voltage.......................................................................................6 Rated Frequency ............................................................................................................................... 7 Rated Continuous Current................................................................................................................. 7 Rated Thermal Short-Time Current .................................................................................................. 8 Rated Dynamic Current .................................................................................................................... 8 Rated Dielectric Strength ..................................................................................................................8 Rated Density of Insulating Gas ................................................................................................... 8 Bushing Tests 8 Test Conditions .................................................................................................................................9 9 Design Tests - Dielectric ...................................................................................................................

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Dry Low-Frequency Withstand Voltage Test with 9 Partial Discharge Measurements....................................................................................................... 9 Wet Low-Frequency Withstand Voltage Test .................................................................................. 10 Full-Wave Lightning-Impulse Withstand Voltage Test .................................................................. Chopped-Wave Lightning-Impulse Withstand Voltage Test ..........................................................10 Wet Switching-Impulse Withstand Voltage Test..........................................................................

10

Dielectric Withstand Test Failure Modes ....................................................................................... 11

2.6

Design Tests - Thermal

................................................................................ ........11

Temperature Rise - Hottest Spot Test ............................................................................................. 11 Thermal Short-Time Current Withstand Test ................................................................................. 11 Thermal Stability Test .....................................................................................................................

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2.7

Design Tests .Mechanical 12 Cantilever-Load Strength Test ........................................................................................................ 12 Draw-Lead Bushing Cap Pressure Test 12 Tightness Test for Liquid-Filled and Liquid-Insulated Bushings ................................................... 12 Check Tests 13

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2.8

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2.9

Power Factor - Dissipation Factor ..................................................................................................13 Capacitance.....................................................................................................................................13 Partial Discharge ............................................................................................................................ 13

2.10

Production Tests - Dielectric ............................................................................ 14 Dry Low-Frequency Withstand Voltage Test with 14 Partial Discharge Measurements..................................................................................................... 14 Power Factor - Dissipation Factor ................................................................................................. Capacitance................................................................................................................................... 1 5 Partial Discharge ............................................................................................................................. 15 16 Potential Tap Withstand Voltage Test ............................................................................................ Test Tap Withstand Voltage Test....................................................................................................16

2.1 1 2.1 2

2.1 3

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Production Tests .Mechanical 16 Bushing Tightness Test ..................................................................................................................1 6 Bushing Flange Tightness Test .......................................................................................................17 Mechanical Design Specifications 17 Creepage Distance .......................................................................................................................... 17 Bushing Potential Tap Dimensions ................................................................................................. 17 Bushing Dimensions ....................................................................................................................... 17 Bushing Nameplates 18

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3

Apparatus Bushing Storage and Handling

4

Apparatus Bushing Application

...................................................................................21 3.1 Introduction ...........................................................................................................21 3.2 storage ....................................................................................................................21 3.3 Handling .................................................................................................................21

4.7 4.2

....................................................................................23

........................................................................................................... 23 Electrical Application Criteria ............................................................................. 23

Introduction

Rated Maximum Line-to-Ground Voltage ...................................................................................... 23 Rated Frequency .............................................................................................................................

23

Rated Continuous Current............................................................................................................... 23 Apparatus Bushing Inspection and Maintenance Practices ............................................................ 24

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4.3 4.4

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Mechanical Application Criteria 24 Mounting Flange .............................................................................................................................25 Lower End....................................................................................................................................... 25 Other Application Considerations 26

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Terminal Connections ..................................................................................................................... 26 External Current Transformers ....................................................................................................... 26

5

Apparatus Bushing Inspection & Maintenance Practices

5. I

...........................................................27

~nspection...............................................................................................................27 ....................................................................................................................................... 27 Gaskets ........................................................................................................................................... 27

Cement

Oil-Level......................................................................................................................................... 27 Porcelain Insulating Envelope ........................................................................................................ 28 Solder Seals..................................................................................................................................... 28 Structural Parts ................................................................................................................................ 28 Apparatus Oil Level ........................................................................................................................ 28

5.2

Maintenance

...........................................................................................................28

.............................................................................................................................28 Gaskets ............................................................................................................................. 28 Oil-Level .......................................................................................................................... 29 Porcelain Insulating Envelope ........................................................................................ 29 Solder Seals....................................................................................................................... 29 Structural Parts .................................................................................................................. 29

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Cement

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29 Terminal Caps ................................................................................................................... Potential Taps and Power-Factor Test Taps ..................................................................... 30

6

...........................................................................................................33 6.1 General ...................................................................................................................33

Apparatus Bushing Testing

6.2 6.3

........................................... ................................

Power FactorIDissipation Factor. and Capacitance 33 34 Power-Factor Test Types and Testing Recommendations Overall Test (GST-Ground Test Circuit) ........................................................................................34 Modified Overall Test (UST Test Circuit) ......................................................................................36 Main Insulation C, Test (UST Test Circuit) ................................................................................... 36 Tap-Insulation (C2) Test (GST-Guard Test Circuit) ....................................................................... 38 Alternate Tap Test Method (GST-Ground Circuit) ........................................................................ 40 Inverted C1Test (UST Circuit) ....................................................................................................... 42 Hot-Collar Test (GST or UST Test Circuit) ................................................................................... 43 Hot Guard Test (GST-Guard Circuit) ............................................................................................. 47 72A-1973-01 Rev. B 7104

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6.4

Main Insulation (CI) Power-Factor Limits For Bushings 49 Federal Pacific Electric ...................................................................................................................49 General Electric ..............................................................................................................................49 Lap ................................................................................................................................................. 50 Ohio Brass....................................................................................................................................... 50 Pennsylvania Transformer ............................................................................................................. 51 Westinghouse................................................................................................................................ 5 1

ASEA Brown Boveri (ABB) .......................................................................................................... 52 ASEA ............................................................................................................................................ 52 Passoni & Villa ............................................................................................................................... 53 Micanite & insulators (M&I), English Electric, Ferranti ................................................................53 Bushing Company (Reyrolle Limited) .......................................................................................... 5 3 Haefeley Trench .............................................................................................................................. 53

6.5 Radio-Influence-Voltage (Riv) .............................................................................54 6.6 DC ~nsulationResistance ......................................................................................54 6.7 Moisture Measurement Of Gas In Sf6Bushings .................................................54 6.8 Thermal Imaging (Infrared).................................................................................55 6.9 Comments on Testing of RTV Coated Bushings and Insulators ......................55 6.10 Comments on Abnormal Test Results .............................................................56 Transformer Windings Not Short-circuited ..........................................................56

6.1 1

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Typical Bushing Troubles

7.1 7.2 7.3 ..

Negative Power Factor ~ f f e c t .............................................................................. ' 56 Circulation of Contaminants .................................................................................. 56 Resistive Coatings on Bushings ............................................................................. 57 References 57

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61

................................................................................................................... 61 Mechanical Troubles .............................................................................................61 Electrical Troubles ................................................................................................ 62 General

...............................................................................................................................69

Repair Practices

8.1

...................................................................................69

General Electric Company Type A ............................................................................................................................................ Type B ............................................................................................................................................

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69 69

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Type F ............................................................................................................................................ 70 Type I, ............................................................................................................................................

70

Type LC ..........................................................................................................................................70

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Type OF ....................................................................................................................................... 71 71 Type U ............................................................................................................................................

8.2 8.3

.....................................................71 Ohio Brass Company ............................................................................................71 Locke Division of General Electric Company

Bulk ............................................................................................................................................... 71 Class ODOF (or OF) ..................................................................................................................... 71 Class L ........................................................................................................................................... 72 Class G ........................................................................................................................................... 72 Class LK ....................................................................................................................................... 72 Class GK ......................................................................................................................................... 72

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8 . 4 ~ a p ~nsulator p company 72 Dry Type ....................................................................................................................................... 72 Type ERC ....................................................................................................................................... 72 Types POC and POC-A .................................................................................................................. 73 Types PRC ............................................................................................................. 73 8.5 Allis-Chalmers, Moloney, Pacific, PINCO,

8.6

9

Safety Considerations

9.1 9.2 9.3 9.4

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73 Pennsylvania. Standard. and Wagner Bushings Westinghouse Electric Corporation 73 Types A. B. C.D.E. F. H-1 andH-2 .............................................................................................73 Type J-1 ........................................................................................................................................ 73 Type 5-2 ....................................................................................................................................... 73 Type G, including modifications G- 1, GI, G2, OG, and OG2 .......................................................73 Type K, including modifications K-1 and OK-1 ............................................................................ 74 Type M .......................................................................................................................................74 ....................................................................................................................................... Type N 74 Type 0 .......................................................................................................................................... 74 Type RJ ....................................................................................................................................... 74 Types S and OS............................................................................................................................... 75

..................................................................................................................77

.................................................................................................................77 Static Charges ........................................................................................................77 Field Testing........................................................................................................... 77 Shop Testing...........................................................................................................78 Handling

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10

Catalog of Apparatus Bushing Design

10.1 10.2

......................................................................................79

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ALLIS-CHALMERS APPARATUS BUSHINGS 79 Allis-Chalmers Dry Type: Solid Porcelain Bushings .....................................................................79 GENERAL ELECTRIC APPARATUS BUSHINGS 79 Type "A"Bushings ........................................................................................................................ 79 Type "B" Bushmgs ......................................................................................................................... 82

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Type " F Bushings .......................................................................................................................... 84

Type "L" Bushings ......................................................................................................................... 85 Type "LC" Bushings ....................................................................................................................... 86 Type "OF" Bushings ...................................................................................................................... 87 Type "S" Bushings (Rigid Core) .................................................................................................... 88 Type "U" B u s h g s ......................................................................................................................... 89

10.3 10.4

10.5 10.6

General Electric Dry Type: Solid Porcelain Bushings

.................................................................................... .............................................................................................

(Other than Type "A") 90 LAPP BUSHINGS 91 Type "ERC" Bushings ....................................................................................................................91 Type "POC" Bushings .................................................................................................................... 92 93 Type "PRC" B u s h g s .................................................................................................................... Lapp Dry Type: Solid Porcelain Bushings ..................................................................................... 94 LOCKE INSULATOR COMPANY APPARATUS BUSHINGS 94

................. MOLONEY ELECTRIC COMPANY APPARATUS BUSHINGS .............94

Moloney Dry Type: Solid Porcelain Bushings ...............................................................................94

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10.8 10.9

Cum

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OHIO BRASS BUSHINGS 94 Class "G" Bushings.........................................................................................................................94 Class "GK" Bushings......................................................................................................................96 97 Class "L" Bushings ......................................................................................................................... Class "LK" Bushings ...................................................................................................................... 98 Type "ODOF" Bushings ................................................................................................................ 99 Ohio Brass Dry Type: Solid Porcelain Bushings ............................................................................99 PENNSYLVANIA TRANSFORMER APPARATUS BUSHINGS 100 Type "P, " P A and "PB" ..............................................................................................................100 Pennsylvania Transformer Dry Type: Solid Porcelain Bushings .................................................. 100 STANDARD TRANSFORMER COMPANY APPARATUS BUSHINGS 100 Standard Transformer Dry Type: Solid Porcelain Bushings......................................................... 100

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10.10

WESTINGHOUSE BUSHINGS

ELECTRIC

CORPORATION

APPARATUS

................................................................................................... 100

4

Westinghouse Dry Type: Solid Porcelain Bushings .....................................................................100 Type "G' Bushings ...................................................................................................................... 102 103 Types "J-1" and "J-2" Bushings ...................................................................................................

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Type "K" Bushings ....................................................................................................................... 104 Type "M" Bushings ...................................................................................................................... 105 Type "N" Bushings ....................................................................................................................... 106 107 Type "0"Bushings 1942 to 1957................................................................................................. Type "RJ" Bushings...................................................................................................................... 109 Type "S" Bushings Solid Stud, Bare Cable Connection ...............................................................110

11

Index of Conference Papers

11.1

Papers

..................................................................................................113

...............................................................................................................113

Adapters ..................................................................................................................................... 113 Air Circuit Breaker Bushings ........................................................................................................ 113 Application.................................................................................................................................... 113 Askarel-Filled Bushings................................................................................................................ 113 Capacitance Taps ..........................................................................................................................114 Circuit-Breaker Bushings ..............................................................................................................114 Corona (see Testing and Maintenance).........................................................................................114 Design and Construction.............................................................................................................. 1 1 5 Direct Current, Bushings for ......................................................................................................... 118 EHV Bushings .............................................................................................................................. 118 Faults and Failures ........................................................................................................................118 Gasket ........................................................................................................................................... 118 General Electric Bushings............................................................................................................. 119 Ground Sleeves ............................................................................................................................. 121 Interchangeable Bushings ............................................................................................................. 122 123 Maintenance (see Reconditioning & Repair) ................................................................................ Ohio Brass Bushings..................................................................................................................... 124 ............................................................................................................................................... Oil 124 ..................................................................................................................................... Operation 125 ................................................................................................ Power Factor Versus Temperature 125 Power Factor Versus Voltage ....................................................................................................... 125 Purchasing .................................................................................................................................. 1 2 5 Reconditioning and Repairing (see Maintenance) ........................................................................ 126 Records ........................................................................................................................................ 127 Solder-Seal Bushings .................................................................................................................... 127

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Solid-Porcelain Bushings ............................................................................................................. 1 2 8 Spares .......................................................................................................................................... 128 Standardization(see Interchangeability)....................................................................................... 128 Storage and Handling .................................................................................................................... 128 Surface Contamination..................................................................................................................129 129 Test Data ..................................................................................................................................... Testing and Maintenance .............................................................................................................. 130 Transformer Bushings................................................................................................................... 134 134 Westinghouse ................................................................................................................................

LIST OF FIGURES

1 C

Figure 6-1 B u s h g Overall Power Factor Test ................................................................................. 35 Figure 6-2 Bushng Overall Power Factor Test Flange Isolated ....................................................... 36 37 Figure 6-3 Bushing C1 Power Factor Test ........................................................................................ Figure 6-4 Tap Insulation C2 Test ..................................................................................................... 40 Figure 6-5 Bushing C1 + C2 Test ...................................................................................................... 41 Figure 6-6 Inverted C1 Test ............................................................................................................... 42 Figure 6-7 Single Hot Collar Test GST Mode ................................................................................... 44 Figure 6-8 Single Hot Collar Test UST Mode ...................................................................................45 Figure 6-9 Multiple Hot Collar Test GST Mode ................................................................................46 Figure 10-1 General Electric Type A Bushings.................................................................................80 Figure 10-2 General Electric Type A Bushings .................................................................................81 Figure 10-3 General Electric Type B Bushings ................................................................................. 83 Figure 10-4 General Electric Type F Bushings ................................................................................. 84 Figure 10-5 General Electric Type L Bushings ................................................................................. 85 Figure 10-6 General Electric Type LC Bushings .............................................................................. 86 Figure 10-7 General Electric Type OF Bushings ..............................................................................87 Figure 10-8 General Electric Type S Bushngs .................................................................................88

LIST OF TABLES

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Table 2-1 Limits of Operating Temperatures for Standard Bushings ................................................. 5 Table 2.2 Apparatus Bushing Reference Voltages (kV)......................................................................7 Table 2-3 Acceptable Variations of Percent Power Factor and Dissipation Factor .......................... 13 Table 2-4 Acceptable Variations of Partial Discharge ....................................................................... 14 Table 2-5 Allowable Limits of Percent Power Factor and Dissipation Factor .................................. 15 Table 2-6 Allowable Limits of Partial Discharge ............................................................................... 16 Table 2-7 Standardized Bushing Dimensions .................................................................................... 18 Table 2-8 Standard Nameplate Information ...................................................................................... 19 Table 6-1 PERMISSIBLE TEST Potentlals ......................................................................................38

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Table 6-2 General Electric Bushings PF% Limits ............................................................................. 49 Table 6-3 Lapp Bushings PF% Limits ............................................................................................... 50 Table 6-4 Ohio Brass Bushings PF% Limits ..................................................................................... 50 Table 6-5 Westinghouse Bushings PF% Limits ................................................................................51 52 Table 6-6 ABB Bushings PF% Limits ............................................................................................... Table 6-7 ASEA Bushings PF% Limits.............................................................................................52 Table 6-8 Passoni & Villa Bushings PF% Limits............................................................................. 53 53 Table 6-9 Bushing Company PF% Limits ...................................................................................... Table 6-10 Haefeley Trench PF% Limits ......................................................................................53 Table 7- 1: Ceramic (Solid-Porcelain) Bushngs ............................................................................... 62 Table 7-2: Compound-Filled, Liquid-Filled, And Liquid-Insulated Bushings................................... 63 Table 7-3: Gas-Filled Bushngs ......................................................................................................... 64 65 Table 7-4: Epoxy Bushings................................................................................................................. Table 7-5: Ceramic (Solid Porcelain) Bushings .................................................................................65 Table7-6: Compound, Oil Or Askarel-Filled Bushings ...................................................................... 66 Table 7-7: Gas-Filled Bushings .......................................................................................................... 66 Table 7-8: Epoxy Bushings................................................................................................................ 67

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1

introduction to Bushings

The main hnction of a bushing is to provide insulation for an energized conductor where it passes through the grounded wall of an apparatus tank or chamber. At the same time a bushing may be used as a Support for other energized working parts of the apparatus, such as circuit-breaker contacts. The design and construction of apparatus bushings, particularly above 15 kV, have advanced considerably since around 1920, when first use of porcelain made them adaptable for all types of weather. Since that time, when the true bulk-type bushing relied upon the thickness of the solid material for dielectric strength, the art has progressed through solid porcelain, paper cylinders and cores to the present automatically wound paper core with spaced condensers, all of which are dried and impregnated under vacuum. The condenser principle, which was first used in 1909, has been advanced to where it has now been almost universally adopted by all manufacturers. The advent of bushing standardization has been a major step in the mechanical adaptability of a bushng of any manufacturer between various types of equipment and in another manufacturer's equipment. This has helped to reduce inventories and simplify ordering.

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As with any product, a high-voltage apparatus bushing must successfully, meet the expectations of the user, whch are a function of many factors that are the responsibility of and controlled by the manufacturer. The ultimate desire of the user is to obtain a piece of equipment that exemplifies the best quality of design, materials and workmanship. It is the goal of those who apply apparatus bushings to equipment that they will provide a safe, dependable and long service life under normal operating conditions and conditions of increased stress. To provide the means to prescribe to manufacturers the meaningful guidelines and methods of determining a bushing's compliance to them, industry experts have over time developed and revised apparatus bushing manufacturing standards. These published standards allow the production of bushings acceptable in all respects to the needs of the utility industry. While "standard" bushings constitute a vast amount of the utility industry's in-service and stock inventories, the requirements set forth for bushing designs in each of the existing standards may, by agreement between a manufacturer and user, be expanded or reduced. In this section of the Reference Book on High Voltage Bushings, the major apparatus bushing standards observed throughout the industry are reviewed in an effort to gain familiarization with the requirements for the electrical and mechanical performance characteristics and dimensional criteria for the application of standardized bushings. The test methods employed to determine the performance characteristics would also be outlined in order to gain a full understanding of the significant factors that influence the design of apparatus bushings.

2.2


.

The published national and international apparatus bushing standards that will be analyzed in this section are listed below along with the scope and exclusions noted in each:

IEEE General Requirements and Test Procedures for Outdoor Apparatus Bushings ANSI-IEEE C57,19.00- 198X IEEE Standard Performance Characteristics and Dimensions for Outdoor Apparatus Bushings ANSIIIEEE Std 24- 1984 These two United States standards, published jointly by the American National Standards Institute and the Institute of Electrical and Electronics Engineers (ANSIIIEEE), are intended to apply to outdoor power class apparatus bushings having Basic Impulse Insulation Levels of 110 kV and

72A-1973-01 Rev. 8 7104


above, and which are designed for use as components of oil-filled transformers and reactors, and oil circuit breakers. The scope of the combined ANSIIIEEE standards excludes gas-filled and gas-insulated bushng designs and the following bushing applications: Cable Terminations

Instrument Transformers

Test transformers

Distribution Transformers

Automatic Circuit Reclosers

Distribution Breakers

Line Sectionalizers

Oil-Less Apparatus

"

Class Class and

Circuit Oil-Poor

Gas-Filled Equipment

EEMAC Standard for Power Transformer and Reactor Bushings EEMAC GL1-3-1988 The current Canadian standard established by the Electrical and Electronic Manufacturers Association of Canada indicates in its scope that it applies to outdoor apparatus bushings having lightning impulse test levels of 110 kV through 1950 kV. It further stipulates that the standard bushings are for use as components of liquid-filled power transformers and reactors in the 15-765 kV voltage class. IEC Bushings for Alternating Voltages Above 1OOOV

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IEC Publication No. 137 (1984) Developed by the Insulated Bushng sub-conunittee of the International Electrotechnical Commission's committee on Insulators, this standard, as its title notes, is applicable to bushngs intended for use at voltages of 1000V (three-phase, 15 to 60Hz) and above. The standard is not applicable to bushings used for the following applications: Cable Terminations Test Transformers Rotating Machinery Rectifiers British Standard Specification for Bushings for AC Voltages Above 1000V BSI 223-1985 The bushing manufacturing standard sanctioned by the British Standards Institute is identical to the IEC standard and information discussed in this section regarding these two standards will be referred to as IECIBSI. The analysis of the bushing standards listed above will be divided into the major topics that comprise each of the standards and are outlined below: Service Conditions Bushng Ratings

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Bushing Tests Mechanical Design Specifications Bushing Nameplate Requirements

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Each of the standards includes definitions of specific terms used therein. For this analysis of the standards, brief definitions are given when that term or topic is discussed.

2.3

Servioe Conditions

Guidelines and limits for operating or service conditions that a bushing design may be exposed to specified in the standards and are established on the basis of the various dielectric, thermal and mechanical ratings of the design.

Altitude Each of the standards stipulates that the rated dielectric strength of bushings is based on an operating altitude not to exceed 100 meters above sea level. At high altitudes the dielectric strength of air is reduced, and for bushings, which depend on air for insulation (i.e. outdoor bushngs), the air clearance or arcing distance may not be sufficient for application of the bushings at those altitudes. The arcing distance is defined as the shortest external "short-string" distance measured over the insulating envelope, between the metal parts at line-potential and ground.

A guideline is given in the standards that recommend a one-percent increase in the insulation level, upon which the arcing distance is based, for each 100 meters in excess of 1000 meters above sea level. Operating Temperatures The thermal ratings established in the standards are based on the limits of operating temperature of components of the bushing, the ambient air and the immersion media and are outlined below: Table 2-1 Limits of Operating Temperatures for Standard Bushings Ambient Air Immersion Media External Terminal

ANSUIEEE 40°C max -30°C min 95°C max 30°C rise

EEMAC 40°C max -50°C min 95°C max 70°C max

IEClBSl 40°C max -60°C min 95"'C max

1

Mounting Angle The specification of the mounting angle of bushings in their parent equipment is established in the standards to insure that for liquid-filled and liquid-insulated bushings; the major insulation, which includes the liquid, is maintained at a level that will provide the desired insulating characteristics. For liquid-filled bushings it is desirable to maintain the level of the insulating liquid such that the internal insulation, which may be impregnated with the same liquid, will continue to be in complete communication with the fill liquid.

72.41 973-01 Rev. B 7104


The ANSIIIEEE standard provides a general application guideline of a mounting angle that should not exceed 20" from vertical. The EEMAC standard's specified mounting angle is a maximum of 30" from vertical for liquid-filled bushings and 90" from vertical for bushings which do not depend on self-contained insulating liquid. The value set down in the IECIBSI standards is based on the actual physical arrangement that the bushing will be applied. For bushings that are to have one end immersed in an insulating medium other than ambient air, the required mounting angle may not exceed 30" from vertical. For, all other methods of applying a bushing to the parent equipment there is no specified limit for the mounting angle.

" *

-

Operating Pressure of Parent Equipment As noted in the IECIBSI standards, for gas-filled and gas-insulated bushings that are applied to equipment where the insulating gas is in communication with that of the bushing, the operating gas pressure of the parent equipment is considered to be a service condition that should adhere to established standard levels.

2.4

Budhifig Ratings

-

The electrical insulation performance characteristics of apparatus bushings, which are based on specific operating and factory test conditions, are categorized by the standard ratings assigned to bushing designs.

. *

iRated Maximum Line-to-Ground Voltage This rating is defined as the highest rrns power frequency voltage between the center conductor and the mounting flange at which the bushng is designed to operate on a continuous basis. While a bushng design can be generally classified by the Rated Maximum Line-to-Ground Voltage, it is the practice of manufacturers and users to reference bushings on the basis of the phase-to-phase system voltage. The bushing standards differ on the terminology employed for the voltage based designation and in the actual voltage values categorized. The ANSIIIEEE applies the term Insulation Class to b u s h g s with ratings of 15 to 196 kV; however, for bushings rated 362, 550 and 800 kV these ratings are classified as the Maximum System Voltage. The term Voltage ClassiJication is employed in the EEMAC standard and in the IECIBSI publication the system voltage for which a bushing is intended is termed its Nominal Voltage (W).An outline of the voltage values used to classify bushings in the various standards appears below: &

72A-1973-01 Rev. B 7/04

-


Table 2.2 Apparatus Bushing Reference Voltages (kV) ANSWIEEE Insulation Class Max System Voltage -

15 25 34.5 46 69 92 115 138 161 196

EEMAC Voltage Class A

A

A

15 27.5 35 50 72.5

3.6 7.2 12 17.5 24 36 52 72.5

-

-

123 145

123 145 170 245 300 362 420 525 765

-

362

245 300 362

-

-

550 800

550 765

-

IECIBSI Nominal Voltage

Rated Frequency This is the frequency at which the bushing is designed to operate. Both the ANSIIIEEE and EEMAC standards expressly indicate in their tables of characteristics that the bushings listed are intended for use on 60 Hz system voltages. The IECIBSI standards do not indicate a specific frequency, in that system voltages of 50 and 60 Hz may be encountered. The particular tests that involve the power frequency are required to be performed with the appropriate frequency. Rated Continuous Current The Rated Continuous Current is the rms current at Rated Frequency, which a bushng is required to carry continuously under specified conditions without exceeding permissible temperature limitations. Since the temperature limits encompass the operating temperature of the immersion media that a bushng may be subjected to, different continuous current ratings for the same bushing design may be specified. The ANSIIIEEE standard specifies dual ratings of continuous current for b u s h g s in the 115 through 196 kV insulation class based on their intended application in transformers or circuit breakers. The EEMAC standard provides a graphical representation of current carrying capacity correction factors based on the temperature of the immersion media and a specified top terminal temperature of 70°C. For bushings utilized in a draw-lead application it should be noted that the bushing center conductor does not carry current; therefore, the bushing continuous current rating is not associated with the current rating of the draw-lead itself. The hot-spot temperature of the draw-lead conductor limits the draw-lead continuous current rating.

724-1973-01 Rev. B 7/04


Rated Thermal Short-Time Current Only the IEC/BSI standards specifl a short-time (one second) rated current which is designated as 25 times the Rated Continuous Current. For bushings with a continuous current ratings of 4000 Amperes and above the Rated Thermal Short-Time Current is 100 kA. This current level is defined as the rms value of a symmetrical current, which the bushing can withstand thermally for the specified duration.

L*

Rated Dynamic Current This is the specified peak value of current that a bushing should withstand mechanically. Again this specification is unique to the IECIBSI standards. The standard value of the dynamic current has amplitude of the first peak of 2.5 times the Rated Thermal Short-Time Current. Presently a test has yet to be developed which can simulate the stresses encountered by a bushing during a transformer short-circuit test. Rated Dielectric Strength A bushing's Rated Dielectric Strength is expressed in terms of specified values of factory performed Voltage Withstand Tests. The withstand test ratings listed below are not necessarily included in each of the standards:

-

Rated Dry and Wet Low-Frequency, Test Voltage Rated Full-Wave Lightning-Impulse Voltage

w

Rated Chopped-Wave Lightning-Impulse Voltage Rated Wet Switching -Impulse Voltage

The voltage levels for the Rated Full-Wave LightningImpulse Voltage are used to express the Basic Impulse Insulation Level (BIL) of a standard bushing.

Rated Density of Insulating Gas This is the density of the insulating gas designated by the manufacturer at which the bushng is to be operated in service. This rating is specified in the IECIBSI standards and is intended to apply to gasfilled or gas-insulated bushings in which the gas is in communication with that of the parent equipment.

2.5

Bushing Tests

In the course of the design and manufacture of apparatus bushings, the applicable standard stipulates that tests of dielectric, mechanical and thermal characteristics be performed and that the results conform to the required levels. The tests that bushings are subjected to in the factory are separated into two categories; Design or Type Tests and Production or Routine Tests. The series of Design Tests performed in the factory are intended to determine if the overall design of a particular type or model bushing is adequate to meet the standard specifications as well as to note

72A-1973-01 Rev. B 7/04

-

- -


if the methodology of manufacture is acceptable. These tests are performed on representative or prototype bushings as part of new bushing development or modification of existing designs. 4

%

Production Tests are performed to assure that each individual bushing produced has been properly manufactured according to the design, that it has been properly assembled and processed, and that the quality of the materials used is acceptable. Test Conditions Each of the bushing standards outlines the conditions under which each of the design and production tests are conducted. The physical arrangement of the specimen under test is critical as is the environmental conditions. Each standard specifies ranges of desired environmental conditions for design and production tests, which include temperature, humidity, and barometric pressure and in the case of wet withstand tests, the rate, angle and resistivity of artificial precipitation. The voltage level of a disruptive discharge or flashover of the external insulation is dependent upon the prevailing atmospheric conditions. When the actual test conditions deviate from the standard test conditions, atmospheric correction factors are utilized to correct the applied withstand voltages to voltage levels at standard conditions. Atmospheric correction factors are provided for humidity and air density, which is derived from the relationship between temperature and barometric pressure. The values of the correction factors are also based on the type and polarity of the withstand voltage applied and the flashover distance of the particular bushing under test.

Design Tests - Dielectric The dielectric withstand voltage tests that fall into the category of design tests are listed below along with a brief description: Dry Low-Frequency Withstand Voltage Test with Partial Discharge Measurements The low-frequency withstand tests are intended to determine a bushing's ability to operate properly at the power frequency conditions it was designed for. This dry withstand test is only required as a design test by the ANSIIIEEE standard. The specified voltage is applied to a clean and dry bushing for one minute, if the bushing withstands the voltage for that specified time it is considered to have passed this phase of the test. If a single flashover occurs, the test may be repeated. The bushing is considered to have failed if the repeat test also results in a flashover. The ANSIIIEEE standard then requires that partial discharge measurements (RIV or Apparent Charge) be taken at five minute intervals while the bushing under test has 1.5 times its rated maximum line-to-ground voltage applied for one hour. The partial discharge measured must remain below the specified maximum values.

Wet Low-Frequency Withstand Voltage Test The wet withstand test duration presently differs between the standards. The IECIBSI and EEMAC standards specify that the low-frequency withstand voltage must be applied for 60 seconds, while the ANSIIIEEE requirement is 10 seconds. The grading criteria of the wet test is the same as the dry.

A wet low-frequency withstand test is not, according to the particular standard, applicable to the following buslung voltage designations:

7%-1973-01 Rev. B 7104


ANSIIIEEE EE'MAC IECBSI

362 kV and above 245 kV and above 300 kV and above

Full-Wave Lightning-Impulse Withstand Voltage Test Lightning-Impulse tests are, understandably, intended to determine if a bushing design is capable of withstanding the effects of voltage levels and wave shapes that simulate environmental lightning surges. For the full-wave lightning-impulse withstand test, bushings are subjected to specified crest values of a standard wave shape impulse voltage. The current standardized wave shape is designated is one of 1.2150 microseconds. The value of 1.2 microseconds is the time required for the voltage wave to reach its crest value from an initial value of zero. The wave shape is also defined by the time, measured from the initial zero voltage, for the crest value to decay to one-half. That time is 50 microseconds for the standard wave.

-

.

The procedures for this test, outlined in the standards, require that a number of both positive and negative impulse voltage waves be applied to the bushing under test. The use of both positive and negative impulse voltage waves is intended to account for differences in flashover characteristics due to the geometry of the test specimen. The results of the test are graded on the basis of no internal punctures of the internal insulation of the bushing and a maximum of two flashovers per series of fifteen tests at either polarity. -

Chopped-Wave Lightning-Impulse Withstand Voltage Test The ANSIIIEEE and EEMAC standards both call for a chopped-wave lightning-impulse test, * whereas IECIBSI does not include it in their requirements. A standard 1.2150 microsecond impulse wave, which is applied to the bushing under test, is "chopped" at a specified time after reaching its - crest value, by the use of a parallel rod gap. The rod gap's physical characteristics achieve the shorting to ground via a sparkover of the impulse voltage at the desired time following wave crest. The chopping or shorting of the impulse voltage is intended to test the bushings ability to withstand surge voltages that change very rapidly, such as those developed when equipment in close proximity to the bushing experiences an insulation failure. For the chopped-wave test, a minimum of three impulses of either positive or negative polarity, at the specified voltage level, is applied and the bushing must withstand that voltage for the specified time duration.

Wet Switching-Impulse Withstand Voltage Test As its name implies, this design test is intended to observe a bushing designs ability to withstand voltages that have the characteristic levels and wave shapes of what is generally termed switching surges. For system voltages of 300 kV and above the operation of circuit breakers and occurrences _ -of flashover associated with transmission lines may, depending on the system configuration, generate such surges. The generalized wave shape that has been adopted by the standards to simulate switching impulses is one of 25012500 microseconds.

-

Each of the standards requires that for bushings rated above 300 kV, a wet switching-impulse test be performed. The bushing under test is exposed to artificial precipitation prior to and during the test. The ANSIAEEE and EEMAC standards require only positive polarity impulses, however, both

10

72A-1973-01 Rev. B 7104

'--


.

-

positive and negative polarity tests are required in the IECIBSI standards. As with the full-wave lightning-impulse withstand voltage test, the passing of the bushing is judged on its ability to withstand punctures and is limited to two flashovers per series of fifteen tests.

Dielectric Withstand Test Failure Modes Each of the dielectric design and production withstand voltage tests have established criteria for grading I bushing design or produced unit. A review of the terminology used to classify the failure modes of insulation resulting from the electrical stress of the dielectric withstand tests is provided below: Disruptive Discharge - The failure of insulation under electrical stress, which completely bridges the insulation, reduces the test potential to, or nearly to zero. This term applies to electrical breakdown in solid, liquid and gaseous dielectrics and to combinations thereof Spark-Over - A disruptive discharge occurring in a liquid or gaseous medium. Flashover - A disruptive discharge occurring over the surface of a solid dielectric in a liquid or gaseous medium. Puncture - A disruptive discharge occurring through a solid dielectric, producing permanent loss of dielectric strength. These definitions are derived from those outlined in IEEE Standard Techniques for High-Voltage Testing-IEEE Std 4-1978.

2.6

-

Design Tests Thermal

Each of the standards require thermal tests of bushing designs in order to note the ability of a bushing to carry its rated continuous current under the specified conditions and not to exhibit a reduction in the life of the internal insulation.

Temperature Rise - Hottest Spot Test The purpose of Temperature Rise, Hottest Spot or, as it is sometimes called, the Heat Run Test is to match the bushing against standard values of the hottest spot or point on the center conductor while its rated continuous current and frequency are applied. The temperatures of the center conductor and mounting flangelground sleeve are measured with the use of thermocouples mounted on or built into the bushings internal insulation. The IECIBSI standards outline the calculation &he hottest spot for bushngs where the installation of thermocouples is prohbitive. Specification of the hottest spot values is dependent upon the standard range of ambient air temperature and the temperature of immersion media during the test.

Thermal Short-Time Current Withstand Test As specified by the IEC/%SI standards the ability of the bushing design to withstand the Rated Thermal Short-Time Current can be demonstrated by a calculation based on the composition, the

7214-1973-01 Rev. B 7104


geometric configuration of the center conductor and the temperature of the conductor while operating at the rated continuous current. If the result of the calculation does not meet the established standard value, an actual withstand test is required.

L

The results of an actual test are graded on the basis of visual evidence of damage and if the bushing can withstand a repetition of all production tests, without significant change from previous results.

-

Thermal Stability Test Each of the standards require a test of thermal stability for bushings that have internal insulation of an organic material (i.e. oil-impregnated, resin-bonded or resin-impregnated paper) and which are intended to be installed in apparatus filled with an insulating medium with an operating temperature of 60" and above. Thermal stability is achieved if the dissipation factor remains at a level value for a specified period of time, under specified thermal conditions. A bushing design that attains thermal stability must then pass all production tests without change from previous results. The Thermal Stability Test is intended to be applied to bushing designs rated 500 kV and above as noted in the ANSIIIEEE standard. EEMAC and IECIBSI standards require that bushings in the reference voltage ratings of 300 kV and above be subjected to this test.

2.7

-

Design Tests Mechanical

-

The mechanical integrity of a bushing design is observed using the tests discussed below.

Cantilever-Load Strength Test The Cantilever-Load Strength Test indicates a bushing's ability to withstand transverse forces applied to the terminals at each end of the bushing. Strength of the materials employed in the bushing, the method of assembly and the resiliency of the gasketing material utilized in the design, are all aspects focused upon by this test. The specified levels of static force are applied perpendicularly to the bushing terminals, individually, for a period of time while the bushing is rigidly mounted and has a specified internal pressure. The standards limit permanent deflection and prohibit leakage after removal of the load. The IECIBSI standards further require that a bushing withstand a repetition of all production tests without significant change.

2.8

* -

Draw-Lead Bushing Cap Pressure Test

The bushing cap assembly associated with draw-lead application designs must withstand a specified level of internal pressure.

Tightness Test for Liquid-Filled and Liquid-Insulated Bushings The IECIBSI standards require an internal pressure test of liquid-filled and liquid-insulated bushings as part of the design tests.

72A-1973-01 Rev. B 7/04

-


2.9 4

.

Check Tests

In the course of performing the design tests which have been discussed, in particular the dielectric withstand voltage tests, what may be classified as "check tests" are employed to determine if puncture damage to the internal insulation has resulted. In order to monitor the potential damage to the bushing under test, limits for the degree of change in the measured values obtained for the check tests have been established by the standards.

Power Factor - Dissipation Factor ANSIIIEEE and EEMAC standards specify the measurement ofpercentpowerfactor as a means of monitoring the possible deleterious effects of the withstand voltage tests. The IECIBSI standards require measurement of the dissipationfactor. The applied test potential for the percent power factor measurement as stipulated in the ANSIIIEEE standard is the rated maximum line-to-ground voltage of the bushing. The EEMAC standard require a test potential of not less than 8 kV. Test potentials used in measuring the dissipation factor required by the IECIBSI standards are 1.05 times the rated nominal voltage for bushings rated 36 kV and below, and values of 0.5, 1.05 and 1.5 times the rated nominal voltage for bushings rated 52 kV and above. The acceptable variation in the percent power factor and dissipation factor of the major insulation for particular types of bushings is outlined below: Table 2-3 Acceptable Variations of Percent Power Factor and Dissipation Factor

Bushing Type Oil-impregnated paper Resin-bonded paper Resin-impregnated

Percent Power Factor ANSIIIEEE EEMAC +.02 +.02, -.06 +.08, -.08 +.04, -.04

-

+.02

Dissipation Factor IECIBSI +.01 (.5 to 1.05 X UN) OR +.003 (.5 to 1.50 X U)'

Capacitance Each of the standards requires that capacitance measurements of the major insulation of bushings be performed in conjunction with the withstand voltage tests. The test potential specified by each standard is the same test potential as that used for the power factor or dissipation factor tests except in the IECIBSI standards where just one test potential is required; 1.05 times the maximum line-toground voltage rating. ANSIIIEEE and EEMAC standards dictate an acceptable change in measured capacitance of +I%. The IEC/BSI standards state that the value should not differ by more than the amount that can be attributed to the puncture of one layer of internal insulation.

Partial Discharge The measurement ofpartial discharge in the major insulation of a bushing prior to and following the withstand voltage tests is accomplished by one of two methods. The ANSIIIEEE and EEMAC standards require that changes in the Radio Influence Voltage (RIV) in terms of microvolts, or


changes in the Apparent Charge quantity measured in picocoulombs, be monitored. The IEC/BSI standard recognizes only the apparent charge measurement. A test potential of 1.5 times the rated line-to-ground is specified in each standard and the acceptable variations are outlined below:

*

b

Table 2-4 Acceptable Variations of Partial Discharge (RIV in microvolts or Apparent Charge in picocoulombs)

Bushing Type

1

Percent Power Factor

I

Dissipation Factor

/

I

I

lEC'BS=

I

ANSI/IEEE

I

I

Resin-bonded paper

2.10

I

EEMAC

+lo0 pV

I

+15 yV

+250 PC

-

Production Tests Dielectric

As noted previously, the Production or Routine Tests are performed on each bushing which is manufactured as a method of quality control and to establish factory test data that can be used as reference for analyzing field-test results.

'.

-

-

Dry Low-Frequency Withstand Voltage Test with Partial Discharge Measurements The ANSI/IEEE standard requires that partial discharge measurements be performed on each completed bushing prior to and following a one-minute dry withstand test at the specified withstand voltage. The partial discharge level of the bushing is measured with an applied test potential of 1.5 times the rated maximum line-to-ground voltage. The standard states that for oil-impregnated paper bushings that are to be applied to circuit breakers, the partial discharge measurement may be substituted with a power factor and capacitance measurement of the Main Insulation (CI) at the maximum line-to-ground voltage before and after the dry low-frequency withstand voltage test.

Power Factor - Dissipation Factor The percent power factor or dissipation factor, depending on whch standard is observed, is measured between the bushing center conductor and the bushing potential or test tap before and after the dry low-frequency withstand voltage test. A test potential of 10 kV is specified by ANSUIEEE and EEMAC, and IEC/BSI standards recommend that the test be performed at a test potential of 2.5 to 10 kV. The maximum values of percent power factor and dissipation factor that are prescribed in the standards are outlined below:

- --

.- -


Table 2-5 Allowable Limits of Percent Power Factor and Dissipation Factor

Percent Power Factor Bushing Type

Dissipation Factor

ANSIIIEEE

EEMAC

IECIBSI

Oil-impregnated paper

.5%

.7%

.007

Resin-bonded paper

2%

1.5%

.015

Resin-impregnated

-

1.5%

.015

Cast-resin(cap. graded)

-

1.5%

.O 15

Cast-resin(non graded)

-

2%

.02

cap.

The reference temperature for the power factor and dissipation factor limits given in each of the standards is 20°C. .

-

The EEMAC standard also requires a power factor measurement ofthepotential or test tap insulation. It specifies a limit of 10% for this test, for all types of bushings.

Capacitance The Main Insulation (C1) capacitance and the Tap Insulation (Cz) capacitance are also measured before and after the low-frequency withstand voltage tests at the same test potential as that used for the power factor or dissipation factor tests. The same tolerances discussed previously under design tests apply. Partial Discharge Each o f standards provides specified allowable limits of the partial discharge generated within bushngs. As noted previously measurements can be in terms of the RIV levels or the apparent charge. An outline of the limits in the standards for a test potential of 1.5 times the maximum lineto-ground voltage rating is given below:

Cm

72A-1973-01 Rev. B 7104


.

Table 2-6 Allowable Limits of Partial Discharge RIV in microvolts or Apparent Charge in picocoulombs Bushing Type

ANSIDEEE

EEMAC

IECIBSI

Oil-impregnated

10 pV

25 pV112 PC

10 PC

Resin-bonded paper

100 pV

I

250 PC

-

I

Potential Tap Withstand Voltage Test Low frequency withstands voltage tests on the insulation associated with the bushing potential tap are required by each of the standards. ANSIIIEEE and EEMAC standards specie a test potential of 20 kV, in oil or in air, for duration of one minute. A one-minute withstand test is also specified in the IECIBSI standards and that the applied test potential be twice the rated voltage of the potential tap, but at least 2 kV. IECIBSI further requires that prior to and following this test, the capacitance of the potential tap insulation be measured at its rated voltage with no significant change.

n

Test Tap Withstand Voltage Test A low-frequency withstand voltage test on the insulation associated with the bushing test tap is required by each of the standards. EEMAC, 2 kV by IECIBSI and 5 kV by ANSIIIEEE specify tests of one minute duration at voltage levels of 500 V. The IECIBSI standards stipulate that following the withstand voltage test on bushing test tap insulation. a capacitance measurement on that insulation is performed with a test potential of 500 V. For test taps associated with dedicated transformer bushings, capacitance and dissipation factor measurements are required at 500 V. The measured results are to comply with the specified maximum values of 5000 picofarads and a 0.1 dissipation factor.

2.1 4

-

Production Tests Mechanical

All of the standards require mechanical tests of assembled bushings that relate to the integrity of the sealing system.

-Bushing Tightness Test Liquid-filled and liquid-insulated bushings are tightness or pressure tested by applying internal - pressure to the bushing for period of time. The IECIBSI standards provide specifications for tightness tests intended for gas-filled and gas-insulated bushings.

72A-1973-01 Rev. B 7104

a 'm


Bushing Flange Tightness Test The IEC/BSI standards provide specifications for tightness tests of the mounting flange seal where it contributes to the sealing of the parent equipment.

2.12

Mechanical Design Specifications

In addition to the ability of bushing designs to meet pre-established electrical insulation characteristics determined through the factory-performed design and production tests, another equally important aspect of the bushing manufacturing standards that is advantageous to the user is the specification of mechanical characteristics. In the context of the mechanical design characteristics, it is the standardization of the dimensional attributes of bushings that is of great importance when determining a bushings applicability and its interchangeability. The mechanical design characteristics for standardized bushings are discussed below:

Creepage Distance The distance between the terminal of a bushing, operating at line-potential, and the grounded mounting flange as measured along the contour of the insulating envelope is a specified in the standards and is termed the Creepage Distance. This is a mechanical requirement that is based on the dielectric ratings of the bushing design. Both the ANSI/IEEE and EEMAC standards provide specified minimum creepage distances for bushings that comply. The IEC/BSI standards provides their specified minimum creepage distance values in the form of a distance per unit of the nominal voltage rating, for various degrees of polluted atmospheres. Bushing Potential Tap Dimensions Standard dimensions for bushing potential taps of the normally grounded and normally ungrounded tap designs are provided in the ANSI/IEEE standard. The EEMAC standard complies with the dimensions specified by ANSIJIEEE. Both potential and test taps are required by the standards to be positioned midway between mounting flange bolt holes and in line with the oil-level gauge, if one is incorporated in the design. Bushing Dimensions The standardized bushing dimensions provided by the ANSI/IEEE and EEMAC standards are the prime consideration for the proper application of bushings to the parent equipment and for interchanging bushings of different manufacture but with similar ratings. The critical dimensions included in the standards are outlined below:

72A-1973-01 Rev. B 7/04


Table 2-7 Standardized Bushing Dimensions

Terminals-

Lower End-

Mounting Flange-

Length Minimum Usable Thread Thread Dimensions Minimum Tube ID Bottom Terminal Configuration Total Length - Flange to End Minimum Insulation Length Depth of Current Transformer Pocket Distance from Flange to Minimum Oil Level Ground Sleeve Diameter Lower Washer Diameter Gasket Space Dimensions Bolt Circle Diameter Number of Bolts Bolt hole Size

The IECIBSI standards do not provide standard dimensions, but it may be construed that manufacturers employ uniform dimensions for various bushing ratings that are intended to meet the standard specifications.

_

-

One particular development of note in the ANSIIIEEE standard was that of specifications for Transformer Breaker Interchangeable bushing designs. By adopting standardized dimensions for bushings of various voltage classes, in particular the minimum insulation length, that would allow proper application in either an oil circuit breaker or a transformer and by incorporating a top terminal design that could be used with or without a draw-lead, a bushing could be manufactured that had flexibility with regard to its application. Use of TBI bushings also allows users to reduce inventories and minimize outage time due to failures or troubles.

2.13

Bushing Nameplates

The various bushings standards have established requirements for the information, supplied by the bushing manufacturer that appears on the nameplate(s) affixed to apparatus bushings. The objectives of the information provided by a bushing nameplate is to provide a means for the identification of particular units, to aid in the analysis of field test results and by inclusion of some of the specified ratings, ensure the proper application of the bushing. The specified nameplate information that is required by the ANSIIIEEE and EEMAC standards is outlined below:

72A-1973-01 Rev. I3 7/04

--

---


Table 2-8 Standard Nameplate Information

Manufacturer's Name Bushing Type Serial Number Power Factor referred to 20°C Capacitance of Main Insulation (CI)

Voltage or Insulation Class Rated Maximum Line-to-Ground Vo Rated Continuous Current Rated BIL Capacitance of Potential Tap Insulati

The information specified for bushing nameplates in the IECIBSI standards is similar to the other standards outlined above; however, production test results for capacitance and dissipation factor are not required. The IECIBSI standards are also unique in that the switching-impulse withstand voltage rating, for bushings whch that test applies, is to be included on the nameplate and for gas-filled and gas-insulated bushings the type of insulating gas along with the minimum operating density is noted. While this section of the the Reference Book on High Voltage Bushings has provided a thorough review of the currently observed apparatus bushing standards, complete details and information pertaining to Definitions, Requirements, Test Procedures, Ratings and Dimensions should be obtained through reference to the actual publications. In order to obtain copies of the published apparatus bushing manufacturing standards, contact the appropriate agency. ANSIIIEEE Standards-

EEMAC Standards-

IECIBSI Standards-

72A-1973-01 Rev. B 7/04

ANSI Publication Sales 1430 Broadway New York, New York 10018 2 12- 642-4900 EEMAC 10 Carlson Court Rexdale, Ontario Canada M9W 6L2 4 16- 674-74 10 ANSI Publication Sales 1430 Broadway New York, New York 10018 212- 64 2-4900


7214-1973-01 Rev. B 7/04

r!~m

3 3.1

Apparatus Bushing Storage and Handling

Introduction

Bushings in stores are generally for emergency use to replace those, which are found to be defective through visual inspection, test, or which have failed in service. Spare bushings as well as those intended for new installations must therefore be stored in such a manner that they can be readily identified and easily removed from the stores location for transportation to the parent equipment.

3.2

Storage

The following are some principle considerations with regard to the proper storage of apparatus bushings: Bushings should be stored where they will not be subjected to mechanical damage. Bushings having exposed paper insulation on the lower-end should be kept dry. The storage area should be such that the humidity can be controlled and preferably be low, and a suitable moisture barrier applied to the lower-end of bushings may prove helphl. Completely sealed bushings may be stored outdoors. To prevent the possibility of introducing voids or air bubbles into bushing insulation systems, it is important that compound and liquid-filled bushings never be stored in a horizontal position. Manufacturers may prescribe minimum limits of the angle from horizontal that the top-end of particular bushings may be stored. Fifteen degrees from horizontal would normally be acceptable. Stock bushings may be mounted on storage racks or left in the crates in which they were delivered. Bushings left in shipping crates should be stored in accordance with the instructions provided by the manufacturer.

The condition of stored apparatus bushings should be checked periodically. Visual inspection of oil level or signs of leakage and mechanical damage should be conducted on a regular basis. Periodic power-factor tests are also advisable. Power-factor tests are recommended prior to placing a bushing into service. Bushings stored in shipping crates MUST be removed for power-factor testing.

3.3

Handling

Care should be used in the handling of bushings to avoid damage. Bushings should be handled in a manner that maintains the top-end at the recommended angle above horizontal.

724-1973-01 Rev. B 7/04


Although some bushings may be lifted from the top-end, it is generally a preferred practice to lift at the mounting flange. Due to the weight and dimensions of many bushings it is advisable to use additional slinging at the upper end of the bushing to guide it or hold it in a desired position. The use of non-metallic slings is preferable when, in the process of lifting, they would come in contact with insulating envelopes (weathersheds)) made of porcelain. Manufacturers may provide suggestions as to preferred methods of slinging particular types of bushings.

7214-1973-01 Rev. B 7/04

*


Apparatus Bushing Application

4. 1

Introduotion

In order to maintain apparatus bushings in a safe and satisfactory operating condition, the user should be familiar with their function, design, construction, testing and repair, as well as the application of all styles of bushings. Apparatus bushings have a wide variety of applications. Most modern bushings can be applied to more than one kind or type of apparatus, and often more than one type of bushing can be applied to a given apparatus. There are certain fundamental criteria that must be observed to avoid potential operating troubles with bushings and their parent equipment. In order to properly apply a given bushing to a piece of apparatus, attention must be focused on the electrical and mechanical characteristics of the bushing that are the most critical to its compatibility to the apparatus and the system.

4.2

Electrical Application Criteria

The electrical characteristics, which are observed in the application of apparatus bushings, are the electrical insulation performance ratings that are associated with the bushing design. The applicable bushing ratings are discussed below:

Rated Maximum Line-to-Ground Voltage Thls voltage rating of a bushing should equal or exceed the line-to-ground voltage rating of the parent equipment and the system voltage which both are applied to. Rated Frequency A bushing designed for a particular operating frequency is intended to be applied to a system of the same frequency. Rated Continuous Current As defined in Section Two of tlvs guide, the Rated Continuous Current is the rrns current at rated frequency, which a bushing is required to carry continuously under specified conditions without exceeding permissible temperature limitations. In applying apparatus bushings it is obvious that the coqt~uouscurrent rating, also expressed as the current carrying capacity of the bushing, should equal or exceed the anticipated load current associated with the parent equipment.

7%-1973-01 Rev. I3 7104


It must also be recognized, that as the definition notes, the continuous current rating of a bushing has thermal limitations incorporated in it. As outlined in the IEEE General Requirements and Test Procedures for Outdoor Apparatus Bushings ANSIIIEEE C57.19.00-198X what is termed the Thermal Basis of Rating is associated with a hottest-spot temperature rise in the current-carrying components of a bushing in contact with temperature index 105 insulation, not exceeding 65°C over ambient air and a total temperature limit of 105°C for non-current-carrying metallic components in contact with temperature index 105 insulation. This thermal rating is established with the temperature of the immersion-oil at a rise of 55°C over ambient air for transformer applications, and a rise of 40'C over ambient air for circuit breaker applications.

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Apparatus Bushing Inspection and Maintenance Practices Bushings intended for transformer application that meet the above thermal requirements, specified in the standard, at rated current are applicable to 55°C or 65°C rise transformers. A limit for the oil temperature in these transformers of 95°C averaged over a 24-hour period is further stipulated in the standard. The proper application of apparatus bushings, in particular transformer bushings, with respect to the current carrying capacity therefore should also address the planned or anticipated loadingltemperature rise requirements of the transformer. As noted in the IEEE Guide for Application of Power Apparatus Bushings ANSIIIEEE C57.19.101-19XY, under conditions of high ambient temperature, bushings operating at rated current in transformers exhibiting top oil rise of 65°C can exceed the thermal limit. Bushings may also be subjected to thermal overload in transformers that are loaded to the limits recommended in the IEEE Guidefor Loading Mineral OilImmersed Transformers Up To and Including 100 MKA With 55OC or 65°C Winding Rise ANSIIIEEE C57.92-1981.

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The higher operating temperatures that a bushing may experience will result in a shortened life expectancy. Application of bushings having a continuous current rating some degree greater than that of the transformer current rating will minimize the possible loss-of-life in the bushing. The loss-of-life of a bushing subjected to thermal overload is not only manifested in the increased thermal degradation of the liquid and solid insulation, but additional problems such as internal pressure build-up leading to loss of liquid filler, gasket deterioration, gassing of the liquid and solid insulation, and increase in dielectric-loss1power factor due to thermal runaway may result. These detrimental aspects of overloading bushings are discussed in the IEEE application guide as well as recommended limits for loading bushings beyond the nameplate current rating. For transformer bushings applied with a draw-lead connection, the relevant continuous current rating is that of the draw-lead itself, which is limited by its hot-spot temperature. Rated Full-Wave Lightning Impulse Voltage I Basic Impulse Insulation Level

4.3

Mechanical Application Criteria

The other vital aspect of the application of apparatus bushings is the proper mechanical fit of the desired bushing in the parent equipment. The significant mechanical dimensions of bushing components that are observed in their application are discussed below:

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Mounting Flange The bushing mounting flange provides the means of securely affixing a bushing to the parent equipment, but also must provide the efficient sealing of the equipment against external contaminants and in some instances the loss of liquid or gaseous insulant/coolant. The gasket space dimensions of a bushing must conform to the opening in the parent equipment to insure proper seating of the gasket. In the application of bushings with respect to the mounting flange, there must be compatibility between the bolt circlepattern(diameter, bolt number, bolt size) of the bushng and that of the parent equipment. The use of mounting flange adapters to install replacement bushings in equipment is a common practice when the mounting flange characteristics of the bushing do not conform to those of the parent equipment.

Lower End Of all the dimensions associated with the lower end, or the portion of the bushing below the mounting flange, the total length is the most crucial in terms of application. The bottom terminal of the bushng must be positioned such that proper connection to the terminals of the parent equipment is possible. In transformers or reactors, the length of the lower end should be such that no part of the bushng is in contact with terminal boards or studs and the bottom terminal should have sufficient clearance from the core, coils and other energized parts of the windings. For circuit breaker application the lower end length is crucial to the proper positioning of stationary contacts and interrupters. Also of importance in the application of bushings in the context of the dimensional characteristics of the lower end of bushings, is the observation of the recommended minimum oil level. The normal and anticipated low level of the oil in parent equipment should meet or exceed the minimum oil level of the applied bushing for proper operation. The minimum oil level recommended by bushing manufacturers relates to the length below the mounting flange of the outer portion of the bushing, which operates at ground potential. Generally this dimension is based on the length below the mounting flange of the bushing ground sleeve, but it can also relate to the length below the flange of the outer-most grounded layer of the capacitance-grading system, which is employed in most highvoltage bushings. The prime objective is to have the parent equipment oil level extend above the bottom of the bushing's "ground layer" in order to relieve the stress of the high-voltage gradient which occurs at that point. For non-capacitance-graded designs, the metallic ground sleeve must extend below the parent equipment oil level and for capacitance-graded bushings it is necessary that the bottom end of the ground layer extend below the oil level. In addition to the voltage gradient stress occurring at the bottom of the grounded sleeve or layer, whch would be detrimental to the bushing insulation system, static discharges between the bushng ground layer and the surface of the equipment oil can result if the minimum oil level of a bushng is not accommodated. The bushng lower end dimension identified as the depth of current transformerpocket and diameter belowflange/ground sleeve diameter should be noted in the application of bushings which will be operated in conjunction with doughnut or slip-over type current transformers, in order to ensure proper fit.

72A-1973-01 Rev. B 7/04


4.4

Other Application Considerations

In addition to electrical and mechanical characteristics of bushings that should be observed in their application, other points worthy of note are discussed below:

Terminal Connections Care should be taken to ensure that all terminal connections are tight both mechanically and electrically. The external leads or bus connections applied to a bushing must be such that the bushing does not furnish the mechanical support or be subjected to abnormal mechanical loading. Terminal connection hardware for draw-lead bushing application and transformer breaker interchangeable bushing designs should be installed properly, according to manufacturer's instructions. External leads connected to terminals of bushings installed in parent equipment which may be subjected to vacuum treatment, must be removed before the procedure.

External Current Transformers Certain care and considerations are necessary in the use of external slip-over type bushing current transformers. The bushing mounting flange should not be used to support the transformer. Provisions should be made to support the transformer from the apparatus case, taking care that potential taps or test taps are accessible for test purposes. Placing the transformer so as to affect the external flashover distance must be avoided.

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3 5.1

Apparatus Bushing Inspection 8 Maintenance Practices

Inspection

Bushings should be systematically and periodically inspected to insure that they are in an acceptable operating condition. Bushings should be inspected during any routine or emergency substation inspection. The frequency of routine inspections is usually determined by user. practice. The following should be considered when determining the inspection frequency: Construction, condition, and age of bushings. Opportunity for de-energized inspection. Importance of parent equipment. Normal operating conditions and unusual conditions such as contaminated environment or ovemoltages. User experience and/or manufacturer's recommendations with particular bushing types. Availability of qualified inspectors.

Upon receipt of new bushings or equipment supplied with bushings, a visual inspection should be made in order to observe any damage, which may have been incurred in shpment. Items requiring visual inspection are:

Cement Cement may be used for attachng metal parts to the porcelain or may be used to connect the porcelain pieces of a multiple section bushings the cement joints should be inspected for signs of chipping and/or crumbling.

Gaskets Most gaskets deteriorate with age. Deteriorated gaskets may leak or permit moisture to enter the bushings. Oil-Level Low oil-level can result in reduced dielectric strength. The oil-level in bushings with sight-glasses, gauges or of other types of level indicators should be checked during any inspection of the substation and/or parent equipment.

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724-1973-01Rev 8 7104


Oil-level is not generally checked for bushings without sight-glasses or gauges. Evidence of a leak dictates that the level be checked. This may be accomplished in the shop or field via a comparative analysis of capacitance values obtained by the Hot-Collar Test method, for the suspect bushing and similar bushings in stock or in the parent equipment. Gauges should be inspected for proper operation.

Porcelain Insulating Envelope Porcelain insulating envelopes (i.e. weathersheds) are sometimes chpped or cracked. This may be caused by lightning, stones (rocks), bullets, or mechanical stresses. Minor imperfections may not cause problems, while larger ones can appreciably affect the creepage distance.

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Solder Seals Solder sealing methods are used to seal metal to porcelain joints. Gaskets are not used in these joints. Solder seals may also be used to seal the fill plug on some bushings. This type of seal should be examined for cracks and leaks. Structural Parts Bushing parts such as clamping rings and washers should be inspected for cracks or breaks. Apparatus Oil Level The proper oil level must be maintained in the parent equipment to insure that the bushing is properly immersed to the correct operating point with respect to the ground sleeve.

5.2

Maintenance

Maintenance of apparatus bushings is generally performed in conjunction with inspection, testing or maintenance of the parent equipment. The extent of the repairs required would be the determining factor in maintaining or replacing a bushing. The items that fall into the realm of field maintenance are:

Cement Crumbling or chipping cement should be repaired. Minor erosion is not necessarily serious, but should be repaired during the next scheduled outage. The bushing should be replaced when complete removal and replacement of the cement is required. The bushing can then be repaired in the shop. There are several new epoxy compounds that may be used to repair or replace cement. Gaskets Replacement of gaskets, which form an integral part of the bushings, should be done in the shop. Gaskets between bushing flanges and the parent equipment may be replaced in the field. Care must be taken to insure that the material and shape are right for the application. Some designs require semi-conducting material to assure proper grounding. Gaskets with the proper thickness must be used to insure correct compression. Cork or cork composition gaskets should be painted with Glyptal or an equivalent to eliminate porosity. Silicone grease applied to one surface will aid in future removal.

7%-1973-01 Rev. B 7104

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Oil-Level The first thing that should be done on bushings with low oil-level indication is to determine the reason for the low oil. Possibilities include external leaks through cracked or deteriorated gaskets; loose clamping, or an internal leak of bushing oil into the apparatus. An internal bushing leak will contaminate the oil in the parent equipment with oil from the bushing. Many older bushings contain PCB contaminated fluid and this may cause contamination of the parent equipment. Manufacturer's instructions should be followed when adding oil to a bushing. Extraordinary care should be taken to be certain that the oil being added is acceptable; that it is kept uncontaminated during the addition process; and that seals are properly reestablished. Amber colored glass should be used when replacing the oil-level indicator and expansion chamber of an oil-filled bushing utilizing glass accessories. Inoperative oil-level gauges should be replaced or repaired. The phenomenon of oil agitation and wax formation in the sight glasses of some bushngs has been observed. This wax does not cause a hazardous condition. It will discolor the sight glass. This condition can be corrected by venting the dome to eliminate the vacuum condition that causes the wax formation. The vent hole must be adequately resealed after the venting process is completed. It is often prudent to replace a bushing rather than attempting a field repair. Shop repair may be feasible under controlled conditions. Porcelain Insulating Envelope Small chips may be repaired by painting with a porcelain repair and sealing paint such as Glyptal. Large chips, sections of missing skirts, etc. may be repaired with one of the commercially, available bushing repair kits. In some locations, the atmosphere contains contaminants, which deposit on and adhere to the porcelain surface. These contaminants may cause an external flashover. In such cases, a periodic cleaning program should be established. The bushings may also be treated with one of the commercially available compounds for preventing flashovers of contaminated bushings and insulators. Examples are: Silguard (A.B. ChancelDow Corning), DC-5 (Dow Corning); Insuljel or Insulgrease (General Electric). The nature of the deposit and its rate of accumulation will influence the frequency of and the type of corrective action. Solder Seals Solder seals may be repaired by utilizing soldering techniques. controlled shop conditions.

This technique may require

Structural Parts Damaged structural parts should be replaced. Painting may be required if corrosion is not severe. Care must be taken to avoid painting the porcelain parts and the nameplate. Information on the bushing nameplate(s) such as the type, serial number and year of manufacture are utilized in identifying a particular bushing. Factory performed power-factor and capacitance test results found on nameplates are necessary for analyzing maintenance test data. Terminal Caps Top terminals, draw lead nuts and caps and other external connectors can loosen in service. If these parts loosen, overheating of the threaded joints can take place. Resulting deterioration of the threads

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72A-1973-01 Rev. I3 7104


and gaskets can lead to serious problems. Infrared tests can detect these problems or the caps can be checked during maintenance periods. Potential Taps and Power-Factor Test Taps These devices should be examined for proper gasketing to prevent the entrance of moisture. Gaskets should be replaced when conditions warrant. Whenever a tap cover is removed, the surface of the tap insulator should be examined for cleanliness and signs of cracks or other damage. Bushings having potential taps and no potential device connected should have the tap compartment filled with an insulating compound (insulating oil, petrolatum or the manufacturer's recommended material). Bushings with a grounded potential tap should be inspected to determine that the tap electrode is properly grounded. Bushings having potential taps to which a bushing potential device is attached should be filled in accordance with the manufacturers' recommendations. Power-factor test taps should be inspected to determine that the grounding of the electrode is adequate.

72A-1973-01 Rev. B 7104

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Tapped Capacitance-Orading Layer

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Center Conductor

Test Tap

I Potential Tap

b)

(b)

Bask Constructian Diffennws Distinguishing Bushings with Ten Taps fran Bushings with Potential Tap$


7%-1973-01 Rev. B 7D4

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Apparatus Bushing Testing

The Bushing Field Test Guide will address the following methods utilized in the shop andlor field testing: A. Power FactoriDissipation Factor, and Capacitance B. Radio Influence Voltage (RIV) C. DC Insulation Resistance D. Moisture Measurement of Gas in SF6 Bushings

E. Thermal Imaging (Infrared)

For each test type, this guide will provide information regarding test procedures and connections, routine versus investigative tests, special considerations, benefits and drawbacks of individual tests, and evaluation of test data. New items have been added, which include sections on evaluation of abnormal test results and the testing of RTV silicone coated bushings. Whenever possible, references have been given which will provide additional detailed information regarding specific methods of testing. These references will be given in each section and in the reference section of the guide.

6.2

Power FactorfDisslpatlon Factor, and Capacitance

The power-factor test is the most effective field test procedure known for the early detection of bushng contamination and deterioration. This method also provides measurement of ac test current, which is directly proportional to bushing capacitance. -

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This section will cover the following test methods:

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1. Overall test (GST-ground test circuit)

2. Modified overall test (UST test circuit) 3. Main insulation (C1) test (UST test circuit)

4. Tap insulation (C2) test (GST-guard test circuit)


5. Alternate tap (C1+C2)test method (GST-ground circuit) 6. Inverted UST (Inv C1)test (UST circuit) 7. Hot-collar test (GST-ground & UST test circuit)

8. Hot guard test (GST-hot guard circuit)

6.8

PodwetdFactor T6in Typi. and TeCting FPecarntJBanClatlons

One or more of seven methods, depending upon the type of bushing and the power-factor test set available, may test apparatus bushings. When the bushings being tested are located in a transformer, all of these tests are made with the windings short-circuited to avoid capacitive coupling between adjacent windings and the lower portion of the bushings5. Spare bushings allow for an overall test to be performed, but an overall test on a bushing installed in an apparatus should only be performed as an investigative test. The two standard tests, Main Insulation (C1) and Tap Insulation (C2) Tests, should be performed on all bushings equipped with test taps. These tests should be performed on a routine basis determined by client experience. Hot-Collar Tests should be performed routinely on the following bushings: 1. Bushings without taps. 2. Compound-filled bushings.

3. Oil-filled bushings not equipped with a sight glass or level gauge. 4. Gas-filled bushings. 5. Solid porcelain bushngs. There are additional investigative situations for which the hot-collar test may provide additional information. One such situation would be investigating a bushing with a suspect liquid level gauge. The Alternate Tap (C1 + C2) Test and the Inverted UST (Inv-C1) Test are recommended as investigative tests, which should only be performed on, suspect bushings. The C1+Cztest can also be utilized to mitigate the influence of electrostatic interference in an energized switchyard. The Hot Guard Test is only performed on draw lead bushings, which are not equipped with taps. T h s test method is no longer widely performed in the United States due to the fact that most bushngs are now equipped with taps, but other countries, particularly Canada, have used and continue to utilize this techruque in their routine testing. Overall Test (GST-Ground Test Circuit) This is a measurement of the condition of the insulation between the current-carrying or center conductor and the grounded mounting flange of a bushing. The application of this test is limited to

72A-1973-01 Rev. B 7/04

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spare bushings out of apparatus. For bushings without taps, which are installed in apparatus, please refer to item 2, Modified Overall Test (UST Test Circuit). The bushing should be mounted vertically in a grounded metal rack for this test, not tested in a wooden crate or lying horizontally. A sling may be used to support the bushing, but care should be taken not to let the sling material come near the center conductor. If the distance between the energized centers conductor and the sling material is very small, surface leakage current or capacitive coupling returning to ground through the sling may influence the test results. A bare wire sling is preferable; leather or nylon slings may contain moisture or other contaminants, which will affect test results. Energizing the bushing conductor and grounding the flange perform the test. These test connections are illustrated in Figure 6- 1.

Bushing Overall Test

Apparatus Ground

Figure 6-1 Bushing Overall Power Factor Test

7%-1973-01 Rev. I3 7104


Modified Overall Test (UST Test Circuit) For bushings installed in apparatus and which are not equipped with Potential or Test Taps, a modified Overall Test may be performed. In order to perform this test, the normally grounded flange must be isolated from the grounded tank in which it is installed. This requires that the flange gasket have an adequate resistance value of at least 50,000 a. Prior to removing the bushing flange bolts, . thus isolating the bushing from ground, valves should be closed to any conservator tanks andlor gas bottles. Care should be taken not to disturb the bushing mounting, which may lead to additional problems. It is also required that the bushings be short circuited, in order to eliminate the influence of winding inductance on this test. After the tests are completed, the bushing flange bolts should be tightened evenly and to the prescribed torque.

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The test is performed in the UST Test Mode, by energizing the bushing conductor and measuring to the isolated flange, via the low voltage lead. These test connections are illustrated in Figure 6-2.

Hiah-Voltage Cable

Figure 6-2 Bushing Overall Power Factor Test Flange Isolated

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Main Insulation C1 Test (UST Test Circuit) This test is a Doble-recommended routine procedure, which should be performed on a regular basis. It is a measurement of the condition of the insulation between the current-carrying or center conductor and the potential or test tap. This test may be applied to any bushing in or out of apparatus, which is equipped with a tap.

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72A-1973-01 Rev. I3 7104

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Main-Insulation/C1 Test Standard Method

6-gp

High-Voltape Cable

Test Mode: UST

Apparatus Ground

Figure 6-3 Bushing C1 Power Factor Test While any insulation whlch may be attached to the bushing (such as contact assemblies, transformer windings, etc.) would also be energized, only the insulation of the bushng between the center conductor and the ungrounded tap would be measured. In order to connect the low voltage lead to the tap, an adapter may be needed, such as that which is supplied with the Doble test sets. When the bushings being tested are located in a transformer, all of these tests are made with the windings short-circuited to eliminate the effects of the induction of the windings and subsequent capacitive coupling of those out-of-phase components between the adjacent windings and the lower portion of the bushings. For more complete, detailed instructions on the method of test and test procedure, please see the Test Set Instruction Manual. The C1 capacitance should always be measured along with the percent power factor, as changes in the capacitance reading will indicate physical deterioration within the bushing, such as shortcircuited condenser layers. Doble recommends that changes in C1 capacitance of 10% or more warrant the removal of the bushing fiom service.

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72A-1973-01 Rev. B 7104


The nameplate values for the C1percent power factor and capacitance should be used as benchmarks for future testing. Any significant change from nameplate values should be investigated. Please refer to the listing of Bushing Maufacturers' Main Insulation (CI) Power-Factor Limits later in this section, which lists typical and questionable power factors for individual bushing types. The test is performed in the UST Test Mode by energizing the bushing conductor with the low voltage lead attached to the bushing tap and the flange grounded. These test connections are illustrated in Figure 6-3.

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During an investigation of a suspect bushing, it may be beneficial to obtain CI results for tests performed at various voltages. Significant differences in these results may indicate the presence of a voltage sensitive problem. Refer also to Inverted UST (Inv-C1) Test in Item 5. Tap-Insulation (C2) Test (GST-Guard Test Circuit)

It is the recommended practice to perform a bushing tap insulation (C2) test whenever the main body of the bushing (C1)is tested. This is a measurement of the condition of the insulation in the potential or test tap area, including the portion of the bushing oil or compound in this area. It can also be used to examine the condition of the connection of the tap to the capacitive layer of the bushing. In the case of bushings with potential taps, where the tap itself is connected to one of the bushing's inner condenser layers, the connection of the outermost condenser layer to ground will also be tested. Some tap connections may be damaged if proper care is not taken when tightening the connector at the top of the bushing or when re-aligning the interrupter assembly on the bottom of the bushing conductor. If the bushing is allowed to twist within its shell, the effect may be to sever this outermost layer's connection to ground. This was a condition found on some Type 0 bushings in Westinghouse type GM, GMA, and GW power circuit breakers, 121- 362 kV, in the late '70s and early '80s.

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The C2 capacitance should always be measured along with the percent power factor, as changes in the capacitance reading will indicate physical changes in the bushing tap area, such as settling debris, shorted layers between the potential tap and last layer of the condenser core, a floating ground sleeve, or a poor connection. The nameplate values for the C2 percent power factor and capacitance, when available, should be used for comparison to all field testing. On bushings equipped with test taps, typically bushings rated 69 kV and below, the recommended test voltage is 0.5 kV. Some manufacturers recommend higher test voltages, but 1 kV should be considered the maximum. On bushings equipped with potential (capacitance) taps, which typically includes bushngs rated 92 kV and above, tests are performed at 2 kV. If the nameplate indicates that the~potentialtap is rated for a higher voltage, then that voltage may be used, but no test voltage greater than 5 kV should be applied to any potential tap. Some manufacturers also recommend a lower test voltage for some specific bushings. Table 1 shows the recommended tap test voltage for a selection of commonlyused bushings. Table 6-1 PERMISSIBLE TEST Potentlals

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To Be Applied To Power-Factor Taps (69 kV and Below) Manufacturer ABB ASEA BBC Canadian General Electric General Electric Haefely Lapp Micafil Micanite & Insulators Ohio Brass Ohio Brass Passoni & Villa Pennsylvania (Federal Westinghouse

Bushing Type or Class O+C All GO Types CTF, CTKF U LC, U All POC WtxF All L GK, LK All P S, 0s

Test Voltage 1000 500 500 1000 500 500 1000 500 500 250 500 500 500 500

Some of these voltages are lower than previously prescribed. They reflect current manufacturer's recommendations, and have been revised accordingly. This test is performed in the GST-Guard Test Mode, by energizing the bushing tap and measuring to the grounded flange, with the bushing conductor connected to Guard, via the low voltage lead. These test connections are illustrated in Figure 6-4. The connection from the high voltage hook to the tap may require an adapter, such as those included with the Doble test set, as mentioned in Item 2.

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Figure 6-3A Tap Adapters for Power Factor Measurements

The small clip-lead included with the Doble test set can be used to connect the hook to the tap or to the adapter. The power factor of the potential or test tap insulation for all paper-oil-condenser core bushings will generally be on the order of 1.0 or less. The power factors obtained for non-paper-oil-condenser

72A-1973-01 Rev B 7104


core bushings may be somewhat higher, due to the higher loss materials used in the design and construction of the tap layer. However, such high power factors make the job of the tester more difficult, since they may mask the symptoms of tap-insulation deterioration. It is Doble's position that the CZpower factor for non paper- oil-condenser core bushings be limited to 2%.

L

v

Dielectric Circuit - Tap Insulation C2 Test

-

m e -

Low Voltage Lead n

High Voltage Lead

T

, a -

Test Mode: GST-Guard

2

Test Ground --*-----------

I & W Meter

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Figure 6-4 Tap Insulation C2 Test

Alternate Tap Test Method (GST-Ground Circuit) If excessive interference is experienced, an alternate test can be made, using the same cable connections as with the C2 test. The circuit is changed from GST-Guard to GST-Ground. In this test, the measurement is Cl+C2 (see Figure 6-5). C2 can then be calculated by subtracting the current and watts results of the C1 (UST) test as described in (2).This is usefi-il with Doble Type MH test sets, not equipped with an Interference Cancellation Device (ICD), or for Doble Type MH or M2H Test Sets where interference cancellation techniques are not adequate. The Doble Type M4000 Insulation Analyzer will not be affected by electrostatic interference.

7214-1 973-01Rev. B 7104

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When energizing the tap, do not exceed the recommended test voltage. Potential Taps should be energized at 2 kV and Test Taps at 0.5 kV. For additional information, please refer to Table 6- 1. This test is.performed in the GST-Ground Test Mode, by energizing the bushing tap and measuring to the grounded flange and to the buslung conductor, connected to Ground via the Low Voltage Lead. These test connections are illustrated in Figure 6-5.

C1 + C2 Test LVL HVL

Test Mode: GST-Ground

L-Guard

--I--------Test ~ r o u n d d

Figure 6-5 Bushing C1 + C2 Test

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72A-1973-01 Rev. B 7104


Inverted C1 Test (UST Circuit) An "inverted" C1 test may be utilized as an investigative test on suspect bushings. These values should be identical to test results obtained by the standard UST (C1) test, which may also include tests performed at various voltages.

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Using this method, as in the standard C1 (UST) test, the test is performed in the UST mode, but the test connections used for the standard C1 test are reversed. The bushing tap is energized, and the bushing conductor is connected to the UST Circuit via the low voltage lead, with the bushing flange grounded. These test connections are illustrated in Figure 6-6.

Test Mode: UST

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Figure 6-6 Inverted C1 Test

When energizing the tap, please do not exceed the recommended test voltage. Potential Taps should be energized at 2 kV and Test Taps at 0.5 kV. For additional information, please refer to Item 3.

72A-1973-01 Rev. B 7X)4

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Hot-Collar Test (GST or UST Test Circuit)

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This is a measurement of the condition of a specific small section of bushing insulation between an area of the upper porcelain weathershed and the bushing conductor. It is performed by energizing one or more electrodes (Hot-Collars) placed around the bushing porcelain, with the bushing center conductor grounded for a GST-Ground Test, or connected to the low voltage lead for the UST Test. While both methods measure between the hot collar and the bushing center conductor, there are significant differences between the two configurations. Both types of hot collar tests are performed at 10 kV and the condition of the bushing is evaluated on the basis of current and watts-loss. The total currents are typically low, therefore power factor calculations are not recommended. In the GST-Ground configuration, the following components are measured: a) The insulation between the hot collar and the grounded center conductor. This measurement would include a small portion of the weather shed, the insulating medium (oil, air, gas, or compound) within the bushing, and the bushing core material(s). This component gives an indication of the internal condition of the bushing. b) The surface leakage current from the hot collar to the grounded center conductor. This component is not typically significant in evaluating the condition of the bushing, as is can mask internal problems and is affected by external contaminants, such as moisture and pollution.

c) The surface leakage current from the hot collar to the ground flange. This component is not typically significant in evaluating the condition of the bushing, as it can mask internal problems and is affected by external contaminants, such as moisture and pollution. The GST-Ground Test obtains accurate results even under conditions of moderate electrostatic interference. The electrostatic interference current is shunted to ground prior to the metering network of the test set and does not affect the measurements. These test connections are illustrated in Figure 6-7

7M-1973-01Rev. B 7104


Low Voltage Lead

I F

-

1Iig

Test Mode: GST-Ground Ground Lead r---1

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Figure 6-7 Single Hot Collar Test GST Mode In the UST configuration, the following components are measured: a) The insulation between the hot collar and the center conductor, which is connected to UST via the low voltage lead. This measurement would include a small portion of the weathershed, the insulating medium (oil, air, gas, or compound) withn the bushing, and the bushing core material(s). This component gives an indication of the internal condition of the bushing. b) The surface leakage current from the hot collar to the center conductor (UST). This component is not typically significant in evaluating the condition of the bushing, as it can mask internal problems and is affected by external contaminants, such as moisture and pollution. The UST test does not measure the surface leakage current from the hot collar to the grounded flange. This test does have an increased susceptibility to electrostatic interference, and this may require the use of interference cancellation techniques. These test connections are illustrated in Figure 6-8.

7%-1973-01 Rev. B 7104

Cm -

-.


I

Single Hot Collar Test - UST Mode

! (

Test Mode: UST ------------------Ground Lead I

Figure 6-8 Single Hot Collar Test UST Mode

In general, use the GST mode for Hot-Collar tests on capacitance-graded bushings. Hot-Collar UST measurements on capacitance-graded bushings may produce misleading results due to the shielding effect of the internally grounded capacitance-graded layer of the main insulating core. That is, if the Collar is not placed on the porcelaidepoxy at a level hgher than the internally grounded layer of the capacitance-graded core, the test will not measure anything beyond this grounded outer layer. Another "Collar" technique involves the use of several Collars simultaneously. This is referred to as the Multiple-Collar method. Doble advocates the use of several single hot collar tests rather than the use of a single multiple hot collar test. Refer to Figure 6-9.

Cm -

72A-1973-01 Rev. €3 7104


MULTIPLE-COLLAR TEST TECHNIQUES

For bushings and cable potheads on which more than one Single Hot-Collar test is required, there is the option of performing one Mdtiple Hot-Collar test instead, as iUWated in Figure D-1: LOW-VOLTAGE LEAD

CURRENT & LOSS

BUSHING AND

-..

Test Mode GST-GROUND

Multiple Hot-Collar Test Technique (GST-GROUND Test Method) FICTlPC h

l

Figure 6-9 Multiple Hot Collar Test GST Mode

The Hot-Collar test is used as a supplemental test or to test bushings in apparatus when C1 and C2 tests are either inapplicable or impractical. Hot-Collar tests are effective in locating cracks in porcelain, deterioration or contamination of insulation in the upper section of a bushing, low compound or liquid level, voids in compound, and so forth. This can be a handy way to verify the operation of a liquid level gauge. If the liquid level is below the point of application of the collar in one of several similar bushings, the test results will be different for that bushing (principally, the current will be lower).


Since the internal configuration of the bushing is not uniform, tests taken at each skirt may yield different results. For proper comparison to previous tests and among similar bushings, this test should be repeated with the collar under the same skirt each time, and using the same test circuit (GST-Ground or UST).

Hot Guard Test (GST-Guard Circuit) This is a measurement of the insulation between the current-carrying or center conductor and the mounting flange of a bushing. The test was designed specifically for "draw-lead type bushings but is applicable to any bushing in apparatus which can be isolated from connected windings, bus, etc., but not rated to withstand test potential. This test requires the Doble Type M Hot Guard Attachment and Hot Guard High Voltage Cable (MHMIHG Cable), which has four conductors, rather than the three in the standard High Voltage (M2) Cable. The first conductor is the hook, or center conductor. It is the high voltage conductor. The insulation between t h s point and ground is measured by the metering network. The second conductor is the first shield (ring), which is connected to the Hot Guard circuit. This is a high voltage connection but the metering network does not measure the insulation between this point and ground. The third conductor is the second shield (ring), which is connected to the guard circuit. The fourth and final conductor is the third sheld (ring), which is connected to the ground circuit. Prior to testing a bushing, that bushing draw lead is isolated from the bushing top tenninaI (center conductor). The hook of the MHM/HG cable is connected to the top terminal of the draw lead bushing. The first shield (ring), is connected to the draw lead of the bushing. The draw lead and the hollow bushing center conductor are both energized at our recommended test voltage, typically 10 kV, so that there is no potential between the draw lead and the bushing center conductor. The test is made on the insulation system between the energized center conductor and the grounded flange of the bushing. The remaining bushngs must have the draw leads connected to the bushing center conductor. They should also be jumpered together with the draw lead of the bushing under test via the hot guard, or first shield (ring), connection of the MHMIHG cable, for the duration of the test. The winding insulation (including the bushings not under test) is stressed to ground, but with the Hot Guard Attachment these values are not measured by the metering network. The test connections are illustrated in Figures 6- 10 and the Doble Type M Hot Guard Attachment is illustrated in Figure 6- 10A.

em

72A-197341 Rev B 7104


Figure 6- 10 Hot Guard Test Connections

Figure 6-10A Hot Guard Test Set and Cable

72A-I 973-01Rev. B 7104

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6.4

Main Insulation (C1) Power-Factor Limits For Bushings

The following tabulations of factory power factors and power-factor limits are as published by the manufacturers or otherwise listed by them. Please note, however, that many bushings have the factory power factor listed on the nameplate. This nameplate value should be used to rate the field measurements. In general, any bushing that exhibits a hstory of continued increase in power factor should be questioned and scheduled for removal from service. The Table of Multipliers at the end of this section include temperature correction multipliers for converting measured bushing power factors to power factors at 20°C. -

Federal Pacific Electric See item number 6.4.5, Pennsylvania Transformer.

General Electric Table 6-2 General Electric Bushings PF% Limits

Description

Type

Through Porcelain (1) High Current, Solid Porcelain (2) Flexible Cable, Compound-Filled (1) Oil-Filled Upper Portion, Sealed Oil-Filled, Sealed Oil-Filled Upper Portion, Sealed Oil-Filled Upper Portion, Sealed Oil-Filled, Expansion Chamber Forms C & CG, Rigid Core, CompoundOil-Filled, Sealed Oil-Filled, Sealed

A A B D F

L LC OF S U T

Typical % Power Factor 3.0 1.O 5.0 1.O 0.7 1.5 1.5 0.8 1.5 0.5 0.5

Questionable if % P. F. More 5.0 2.0 12.0 2.0 1.5 3.0 3.0 2.0 6.0 1.O 1.O

Notes:

(I)

Type S, Forms F, DF and EF (flexible cable) redesigned as Types B, BD and BE, respectively. Type S, no form letter (through porcelain redesigned as Type A.

(2)

Modern hgh-current oil-filled solid-porcelain design

72A-1973-01Rev B 7/04


Lapp Table 6-3 Lapp Bushings PF% Limits

Bushing Type

Typical % Power Factor @, Type PA and POC (Paper-oil 0.5% condenser-type; totally enclosed), Type PRC and PRC-A(paper-resin0.8% condenser core) Type ERC (paper-epoxy hard core0.8% m e ; no lower porcelain), 15-23 kV

Questionable if % P. F. More Than 1.5% 1.5% 1.5%

Ohio Brass Table 6-4 Ohio Brass Bushings PF% Limits

Bushing Type

Initial P.F., New, Dangerous

2O0C ODOF, Class G and Class I, Oil-Filled Bushings: a) Manufactured prior to 1926 and after 1938 b) Manufactured 1926 to 1938, inclusive Class GK-Type C, 15 to 196 kV--oil-impregnated Paper condenser core, oil-filled. Class LK-Type A, 23 to 69 kV-resin-paper condenser core, oil-

Values,

2O0C

0.4%

Initial P.F. + 22% P.F. Initial P.F. + 16% P.F. 1.O%

0.4%

1.O%

1-5% 2-4%

General Notes: Initial values of power factor for new bushings from the 1944 Doble Client Conference Minutes, Sec. 4603 and 4-604.

-.

Dangerous values of power factor for bushings in service from the 1946 Doble Client Conference Minutes, Sec. 4-303.

-z

Refer to Ohio Brass Co. for recommendations for reconditioning bushings before power factor reaches dangerous value.

72A-1973-01 Rev. B 7104

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Starting approximately in 1940, Ohio Brass bushing nameplates give over-all power factor and watts-loss at 10 kV as measured at the factory in air. Bushings tested in good oil will usually have lower power factor. Ohio Brass Condenser-Type Bushings have normal power factors from 0.5 to 1.0% at 20°C. See 0 . B. Publication No. 1354-H. The reasons for differences between power factors measured by the grounded and ungrounded-specimen test methods on certain OB bushings are discussed in the 1954 Doble Client Conference Minutes, Sec. 4501.

Pennsylvania Transformer Types P, PA or PB (paper-oil condenser-type, totally enclosed) 69 to 196 kV. The manufacturer's literature states that the normal power factor for these bushings is approximately 0.5% at 20°C. All bushings leaving the factory have power-factors less than 0.65%. In addition the manufacturer has suggested that a bushing showing a power factor above 1% be checked carefdly.

Westinghouse Table 6-5 Westinghouse Bushings PF% Limits

Semi-condenser Type All Type D Transformer Bushings Types S and OS On OCB & Inst. Trans. 69 kV and below (except types S and 0 s ) On OCB & Inst. Trans. 92 kV to 138 kV, except Type 0 ) On Power & Dist. Trans. of all ratings, and OCB & Instrument Transformers 161 kVto 288 kV Type 0 and 0-AL bushrngs 92 kV to 288 kV (oil filled) Type 0 Plus Bushings Type RJ

Typical % P. F.

Questionable % P. F.

1.5 0.8 1.5

3.O 2.0 3.0

1.5

3.0

1.O

2.0

0.3

1.O

0.3 1.O

1.O 2.0

General Note: Increase in capacitance of 15% (10% for Type 0) indicates short-circuited condenser sections.

72A-1973-01 Rev. 8 7104


ASEA Brown Boveri (ABB) Table 6-6 ABB Bushings PF% Limits

Typical % P. F.

Type

l o+c IT

Questionable % P. F. I

I

I

0.5 0.5

1 Double name~late

1 Double nameplate

1

General Notes: Contact the manufacturer if the capacitance increase to 110% of original installed value This information obtained from the ABB instruction leaflet 44-666Edated July 1, 1990.

ASEA Table 6-7 ASEA Bushings PF% Limits

GOH GOM GOA OTHER

YES YES NO

0.25 0.45 0.45

0.45 0.65 0.65

...

General Notes: Up to a 3% change from nameplate capacitance is considered acceptable.

.)

Remove from service when the difference between nameplate and measured C1 percent power factor exceeds 75%. Type GOBL has no test tap.

7214-1973-01 Rev. B 7/04

e@ -

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This information obtained from ABB Components bulletin #2750 5 15E-56, dated 1990.

Passoni & Villa Table 6-8 Passoni & Villa Bushings PF% Limits

L

Typical %P.F. 0.4 0.4

Type PNO PA0

Doubtful %P.F. 0.7 0.7

General Note: This information taken from P&V bulletin #1005, dated 1992.

Micanite & Insulators (M&l), English Electric, Ferranti Questions on bushings originally made by the above manufacturers should be referred now to Reyrolle Limited Company.

Bushing Company (Reyrolle Limited) Table 6-9 Bushing Company PF% Limits

Type OTA

Typical %P.F. 0.35

Doubtful %P.F. 0.6

i

General Note: This information received from The Bushing Co. by fax dated 9/1/1993.

Haefeley Trench Table 6-10 Haefeley Trench PP% Limits

Type

Typical %PF

Doubtful %PF

0.30 0.35

Double Nameplate Double Nameplate

COTA (Under 1400 kV BIL) COTA (1400 kV BIL and above) General Notes: C1 capacitance is doubtful if 10% over nameplate

72A-1973-01 Rev. B 7/04


CI capacitance is doubtful if 5% over first measurement in field after installation

CZcapacitance may vary by 20%. The above information is based on a fax from Haefely dated April 5, 1994 Some Haefely bushings, 115 kV and above, which have potential taps, have C1 nameplate capacitance based on factory tests made on the test tap. The test tap is then buried and unavailable to the user. The user instead tests the bushing using the potential tap, and the capacitance appears to be high compared to nameplate values. The capacitance obtained in the field must be modified as follows:

-

-

C1 (Doble Field Test) = (CI (Haefely) * C2 (Haefely))/(Cz (Haefely) - C1 (Haefely)), where C1 (Haefely) and C2 (Haefely) are the nameplate capacitances. Based on information in a fax from Haefely dated April 3, 1995.

This method of test is covered by NEMA Publication #I07 dated 1987, "Methods of Measurement of Radio Influence Voltage (RIV) of High-Voltage Apparatus". Both ANSI C57.19 and IEC 137 specify partial discharge limits of 10 pC for Oil-Impregnated Paper Insulated Bushings when tested at 1.5 x maximum L-G voltage.

6.6

DC INSULATION RESISTANCE

Of these methods the use of d-c insulation resistance generally cannot be relied on to detect early contamination. When bushing deterioration can be detected by DC insulation resistance it is generally in an advanced stage requiring immediate attention.

6.7

MOtdSTURE MEASUREMENT OF GAS IN SFs BUSHINGS

Bushings of this design are not equipped with special test electrodes or facilities, so the only Doble Tests applicable are Power-Factor tests by the Overall method, conductor to mounting flange, and the Hot Collar test. A h g h watts reading may indicate moisture in the SF6 gas, or tracking along the interior surface of the porcelain. Tests may also be made on the SF6 gas for moisture, pressure, and dew point. Not only will loss of gas pressure affect the operation of the apparatus, but also the presumed escape into the atmosphere may have unforeseen consequences.

7%-1973-01 Rev. B 7104

L

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6.8

THERMAL IMAGING (INFRARED)

This method can distinguish between overheating due to external connections to the bushing and internal heating. Relative comparisons can be made with adjacent bushings, as well as point-bypoint measurements. These "spot" measurements can complement the effect of the visual display by allowing for the assessment of temperature gradients.

6.9

Comments on Testing of RTV Coated Bushings and Insulators

The outline of the procedures and special consideration for the Doble Testing of RTV coated bushings and insulators is as follows: Knowledgeable, experienced personnel should perform the actual application of the RTV silicone. This will ensure that the application was performed under suitable weather conditions, that the RTV coating was applied to the correct thckness evenly around the entire porcelain surface, and that any other applicable considerations will be taken into account. Prior to Application of RTV Silicone to the Bushing or Insulator Porcelain Surface. 1. The surface of the bushing or insulator should be cleaned and dried. 2.

Doble Tests should be performed.

After the Application of RTV Silicone to the Bushing or Insulator Porcelain Surface. 1. The RTV silicone should be allowed to cure. This typically requires a minimum 48 hours, depending upon temperature conditions. 2 . Doble Tests should be performed so that a benchmark data set can be obtained for the coated bushing or insulator.

SpeciaI Considerations for Routine Doble Testing of KTV Silicone Coated Bushing or Insulators. 1. Weather conditions, especially high humidity, can cause significant increases or decreases in measured wattsloss or power factor values. While Doble would recommend the use of Guard Collars as a method by which the effects of increased surface leakage could be reduced, it is likely that acceptable results would not be obtained until the weather conditions have improved (i.e., lower humidity).

2 . If testing cannot be postponed, then consideration should be given to enclosing and applying heat to the test specimens. This will become less practical as the voltage rating of the test specimen increases. 3.

The use of water as a cleaner prior to Doble testing should be discouraged, as there will be a time delay during which the RTV silicone will regain its hydrophobic properties. Additionally the used of alcohol based cleaners should also be avoided, because they can cause moisture to condense on the surface of the RTV coated surface.

7214-1973-01 Rev. I3 7104


During any of the bushing power factor testing, abnormally high or low percent power factors may be experienced which are due to influences, which are not immediately obvious. We can be alerted to such results if they vary significantly from any of the following, on the high or low side:

-

&

A

P Limits set forth in the Doble Test Data Reference Book P Nameplate data > Previous test results P Results on other similar specimen tested at the same time It should be emphasized that an unusually low power factor, such as an inter-winding insulation test (CHL)on a transformer of 0.03%, should cause concern equally as much as an unusually high percent power factor. The causes of these abnormal test results can be categorized as follows:

Transformer Windings Not Short-circuited When bushings installed in a transformer are tested, the tests will be inconclusive if the transformer winding attached to these bushings is not short-circuited. The usual result is unusually high CI percent power factors. This may be accompanied by a significant tip-up, and even higher percent power factors on the center bushing5. Negative Power Factor ~ffect' Due to contamination, a too-low watts reading is "seen" by the test set, causing very low or negative power factors. The remedy is to find the source of the contamination. These are some typical sources: 0 0 O

-

.

.

The outside surface of upper bushing watersheds is not clean and dry The inside surface of a bushing shell where tracking has occurred Lower bushing surfaces coated with contaminated oil from the parent apparatus

It is sometimes possible to remedy the lower bushing surface problem if the bushing is located in an oil circuit breaker. Operating the breaker several times may disturb the continuity of the coating enough to enable successful testing.

Circulation of Contaminants The oil in a bushing can become contaminated from incompatible bushing components, such as solder or gasket material, or from leaks. If a bushing whose oil is contaminated is tested after moving it, the percent power factor of both the C1 and C2 tests may change as the particles in the contaminated oil settle to a resting place. Their relative changes may help determine where these particles are settling. An increase in the C2 percent power factor may indicate settling of contaminants in the tap or bushing flange area. A simultaneous decrease in the C1 percent power factor would confirm the "settling out" of the contaminants away from the main condenser core area included in the C1test.

72A-1973-01 Rev. B 7104

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Resistive Coatings on Bushings A semi-conductive glaze is used on some insulators to control voltage distribution and reduce flashover problems under contaminated conditions. This may result in high CH and Cal power factors in transformers equipped with these bushings, due to the highly resistive surface leakage. Tests on the bushings themselves may also be affected, but the transformer intertwining insulation test, CHL,will not. Test results should be compared to previous results.

6.I1

References

Several papers are recommended for reference to test techniques and phenomenon: 1. Kopaczynski, D. J. and Manifase, S. J. "Negative Power Factor on Doble Insulation Test Specimens (An Analysis)" Doble Client Conference Minutes, 1987, Sec. 2-501 2. Kopaczynski, D. J. and Manifase, S. J. "The Doble Tap-Insulation Test for Bushings (A Review)", Doble Client Conference Minutes, 1990, Sec. 4-3.1 3. "The Hot-Collar Test (A Review)", 1992, Doble Test-Data Reference Book 4. "Dry-Type Porcelain Bushings", 1992, Doble Test-Data Reference Book 5. Levi, Raka and Brusetti, Robert C. "Doble Testing of Transformer Bushings - Abnormal Results Due to Incorrect Proceedures", Doble Client Conference Proceedings Book, 1995, Sec. 3-3.

72A-197201 Rev. I3 7104

Reference Book on Bushings Table 6-11: Power Factor Temperature Correction Multipliers

*

1

Reference Book dn High vbltage Bushings

BUSHINGS ASEA

ABB

Type T 1.02 1.02 1.02 1.01 1.01 1.01 1.01 1.01 1.OO 1.OO 1.OO 1.OO 1.00 .99 .99 .98 $97 .97 .96 .95 .94 .93 .91 .89 .87 .86 .84 .82 .79 .77 .75

Type O+C .87 .89 .91 .92 .93 .94 .95 .96 .98 .99 1.OO 1.01

1.02 1.03 1.04 1.05 1.06 1.07 1.07 1.08 1.08 1.09 1.10 1.10 1.11 1.11 1.11 1.1 1 1.11 1.12 1.12

All GO TYpes 25-765 kV .79 .8 1 .83 .85 .87 .89 .92 .94 .95 .98 1.OO 1.03 1.05 1.07 1.09 1.12 1.14 1.17 1.19 1.21 1.23 1.26 1.28 1.30 1.31 1.33 1.34 1.38 1.37 1.37 1.38

DOBLE ENGINEERING COMPANY

BROWN BOVERI

Types CTF, CTKF 20-60 kV

---1.24 -------1.22 1.20 1.17 1.15 1.12 1.10 1.06 1.05 1.03 1.OO .98 .96 .94 .91 .88 86 .84 .82 .80 .78 .76 .74 .72 .70 ,68 .66 .64 .62 .60 .58

Types CTF, CTKF 85-330 kV 1.OO

1.OO

1.00

GENERAL ELECTRIC TEST TEMPERATURES OC OF 0 32.0 2 35.6 4 39.2 6 42.8 8 46.4 10 50.0 12 53.6 14 57.2 18 60.8 18 64.4 20 68.0 22 71.8 24 75.2 26 78.8 28 82.4 30 86.0 32 89.6 34 93.2 36 96.8 38 100.4 40 104.0 42 107.8 44 111.2 46 114.8 48 118.4 50 122.0 52 125.6 54 129.2 56 132.8 58 136.4 60 140.0

Page 59 -

-

Type Type F B 1.09 .93 1 0 9 .95 1.09 .97 1.08 .98 1.08 .99 1.07 .99 1.06 .99 1.05 1.00 1.04 1.00 1.02 1.00 1.00 1.00 .97 .99 .97 .93 .96 .90 .94 .85 .92 .81 .89 .77 .87 .73 .69' .84 .65 .81 .61 .78 .74 .70 .64 .58 .52

Types L,LC, LI LM 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 .99 .99 .98 .97 .96 .95 .94 .93 .91 .89 .87 .85 .83 .82 .80 .79 .78 .77 .76 .74

Types OF,OFI, OFM 1.18 1.16 1.15 1.13 1.11 1.10 1.08 1.06 1.04 1.02 1.OO .97 .94 .91 .88 .86 .83 .80 .77 .74 .70 .67 .63 .6 1 .58 .56 .53 .5 1 .49 -46 .44

Types S,SI,SIM Types Cpd,-,Filled) T.& U 1.26 1.02 1.24 1.02 1.21 1.02 1.19 1.01 1.16 1.01 1.14 1.01 1.11 1.01 1.08 1.01 1.06 1.OO 1.03 1.OO 1.OO 1.OO .97 1.OO .93 1 .OO .90 .99 .87 .99 .84 .98 .81 .97 .77 .97 .74 .96 .70 .95 .67 .94 .93 .63 .60 .91 .56 .89 .53 .87 .50 .86 .47 .84 .44 .82 .41 .79 .38 .77 .36 .75

HAEFELY Types s COT, COS, SOT -

0.88 0.90 0.93 0.95 0.98 1.OO 1.02 1.04 1.07 1.09 1.11 1.13 1.15 1.17 1.19 1.21 1.22 1.24 1.25 1.26 1.27 1.28 1.29 1.30 1.29

.I .27


72:-1973-01

Rev. I3 7104


Typical Bushing Troubles

Bushings which are deteriorating, if found in time, may cause no significant loss of service of the equipment on whch they are used. Bushings may be subject to many different stresses which eventually could cause failure. Bushings used on transformer or other static equipment are for the most part subject only to the stresses due to thermal expansion and occasionally to those due to internal faults in the equipment on w h c h they are mounted. Bushings used in circuit breakers additionally serve as the mechanical support for holding contacts and interruption devices in place. Further mechanical stresses are introduced by high speed operation and high interrupting capacities required. In this section therefore an attempt has been made to outline troubles of a mechanical or electrical nature most frequently found in certain types, design or manufacture of bushngs. Tests that may be expected to reveal each are suggested.

7.2

MECHANICAL TROUBLES 1 2 3 4

Ceramic (Solid Porcelain) Bushings Compound, Oil or Askarel-Filled Bushings Gas-Filled Bushings Epoxy Bushings

Table 7-1 Table 7-2 Table 7-3* Table 7-4

72A-1973-01 Rev. 8 6104


Table 7- 1: Ceramic (Solid-Porcelain) Bushings

( Insulation

/

moisture from air.

1

I Hot-Collar Tests.

7%-1973-01 Rev. B 7104

I


Table 7-2: Compound-Filled, Liquid-Filled, And Liquid-Insulated Bushings Type of Trouble Cracked Porcelain

Trouble Due To Non-uniform tightening of holddown bolts. Projectiles (rocks, bullets, etc.) Heating of filler causes expansion. May rupture porcelain.

Deterioration of Cemented Joints

Cement deteriorates. Moisture enters interstices; freezes and expands. Cement growth eventually destroys joint.

Gasket Leaks

Gasket material deteriorates absorbing moisture. Poor installation of gaskets; uneven comparison due to non-uniform tightening of hold-down bolts. Poor gasket material. Gasket too thin.

Solder Leaks

Result of Trouble

Method of Detection

Allows moisture to enter.

Visual inspection. Power-Factor and/or Hot-Collar Tests. Filler leaks out; moisture Visual inspection. enters. Filler leaks out; moisture Visual inspection. Power-Factor and/or enters. Hot-Collar Tests. Filler leaks out; moisture Visual inspection. enters Power-Factor and/or Hot-Collar Tests. Filler leaks out; moisture Visual inspection. Power-Factor and/or enters. Hot-Collar Tests. Top gasket leaks allowing Power-Factor and/or moisture to enter. Hot-Collar Tests. Hot-wire test for moisture.

Bottom gasket leaks Visual inspection. Top Hot-Collar Test allowing filler to leak out. for voids. Detection of compound in equipment oil. Mounting flange gasket Visual inspection. Monitor leaks. gas pressure of parent equipment. Leak detector. Potential or test tap Visual inspection. receptacle gasket leaks Power-Factor Test. allowing moisture to enter Insulation and liquid filler to leak out. resistance. Seal Failure of solder seals generally due Terminal solder seal leaks Power-Factor andlor to poor workmanship, poor factory allow moisture to enter. Hot-Collar Tests. inspection or rough handling in the Solder seal at flange leaks Hot-Wire Moisture allow filler to leak. Tests. Leak detector. field. Visual inspection.

72A-1973-01 Rev. B 7/04

-


Table 7-2 (continued): Compound-Filled, Liquid-Filled, And Liquid-Insulated Bushings Trouble Due To

Result of Trouble

Method of Detection

Rough handling in field or poor workmanship in factory. Vibration or repeated shock in service.

Sparking in apparatus tank or within the bushing. Discolored oil.

Power Factor (low current or fluctuating meter readings).

Leaks through gaskets. Poor workmanship in pouring compound into bushing.

Internal corona.

Oil Migration

Poor seals.

Contaminates filler.

Displaced Grading Shield

Fragile shield mounting. Rough handling. Excessive apparatus vibration. Loss of protective coating. Corrosion of rust deteriorate metal.

Internal sparking discolors oil.

Hot-Collar Tests (10% or more decrease in current). Power-Factor Tip-Up Visual inspection. Power-Factor and Hot-Collar Tests. Hot-Collar Test (top porcelain area).

Type of Trouble Broken Connection Between Ground Sleeve and Flange Voids in Compound

Deterioration of Metallic Surfaces Discolored Oil Level Sight Glass

Allows moisture to enter. Bushing oil or filler to leak.

Material used during manufacturing Cannot determine oil level process susceptible to ultraviolet light. without an outage. X-wax generation at surface of oil.

Visual inspection. Power-Factor and/or Hot-Collar Test. Visual.

Table 7-3: Gas-Filled Bushings

72A-1973-01 Rev. B 7104


Table 7-4: Epoxy Bushings

7.3

ELECTRICAL TROUBLES 1 2 3 4

Ceramic (Solid Porcelain) Bushings Compound, Oil or Askarel-Filled Bushngs Gas-Filled Bushings Epoxy Bushings

Table 7-5 Table 7-6 Table 7-7 Table 7-8

Table 7-5: Ceramic (Solid Porcelain) Bushings

72A-197501 Rev. €3 7104


Table7-6: Compound, Oil Or Askarel-Filled Bushings

Table 7-7: Gas-Filled Bushings Type of Trouble Electrical Flashover

Lightning

Corona

Trouble Due To Contamination built up on epoxy or porcelain. Rain (wet flashover too low). Improper application. Defective improperly applied associated surge arrester. Moisture or contaminate in gas.

Result of Trouble Method of Detection Cracked or broken epoxy or Visual inspection. porcelain. Complete bushing Hot-Collar Test. failure. Cracked or broken epoxy or Visual inspection. porcelain. Complete failure Test arresters. causes damage to other apparatus. Radio interference. RIV. Hot-Collar Test Overheating of epoxy or Gas Moisture Test Visual Inspection porcelain.

72A-1973-01 Rev. B 7/04


Table 7-8: Epoxy Bushings

Oil Leaks

Felt spacer pads become moisture laden or displaced, disoriented. Apparatus vibration breaks epoxy under mounting flange.

72A-1973-01 Rev. B 7104

Radio interference. Loss of oil.

Visual inspection. RIV Power-Factor Test. Hot-Collar Test. Low chargmg current with lack of oil.


72A-1973-01 Rev.8 7104


Repair Practices Over the years there have been many varieties of entrance bushings, ranging from a porcelain tube to the modern condenser bushing. Maintenance practices have necessarily changed to keep pace with improved design and construction techniques. The principal causes of bushing failures are deteriorated insulation, resulting from moisture and foreign deposits, and mechanical damage from external sources. Open-breathing type bushings are particularly susceptible to moisture damage. modern bushings are of sealed construction, which practically precludes the ingress of moisture. Maintenance practices will, of necessity, vary widely between companies based on the number of bushings in service, the area covered, the proximity to manufacturers' service shops, etc. Other than visual observation for leaks and broken porcelain, the principal method of determining the need for corrective maintenance is the power factor test, which is performed at specified intervals. When corrective action is indicated, it generally requires disassembly, oven dry-out of the insulation, and regasketing the bushing. Details covering the repairing of various makes of bushings are listed below.

8.1

General Electric Company

Type A This bushing was introduced in 1924, has undergone many modifications; but all designs have in common the use of a one-piece porcelain, which extends through the apparatus cover and provides the major insulation of the bushing. Deteriorated gaskets, deteriorated cement, or cracked porcelain are the most common problems encountered with Type "A" bushings. In some cases, it may be practical to renew the gaskets in the field. The porcelain and cement can be replaced in a repair shop; however, this is usually only economical in the case of bushings with the higher current ratings. The older designs, particularly with non-detachable cable terminals, are generally more economically replaced with a newer design Type "A" bushing. Type B This bushing consists of a one-piece porcelain assembled with clamping ring, a support flange, a terminal cap, providing a weather-tight structure around the upper portion of a flexible, varnishcambric-insulated cable. The space between the porcelain and the insulated conductor is filled with insulating compound. In addition to deteriorated gaskets, deteriorated cement, and cracked porcelain the Type "B" bushing is subject to high power factors resulting from the entrance of transformer oil into the compound chamber of the bushing. The Type "B" bushing can often be

72A-1973-01 Rev. I3 7/04

69


economically repaired in a properly equipped repair shop. If moisture has entered the bushing, it may be easier to replace the insulated cable than to try to dry it out. In the case of the older design, Type "B" bushings (one-piece cap design) it may be more practical to scrap the bushing and replace it with a modern bushing.

-

This bushing can usually be readily and economically repaired in the shop. The center clamped type construction of this bushing requires a simple jig to relax the compression springs for disassembly and reassembly. The entrance of moisture into the bushing may make it necessary to dry the Herkolite cylinders in an oven. High power factor of a Type "F" bushing may sometimes be improved by flushing the bushing with clean, dry transformer oil if the trouble is due to moisture which has not yet penetrated into the Herkolite cylinders or to leaching of hydrated calcium sulfate from the cylinder paper. The latter is most prevalent in bushings manufactured during 1947 - 1950. The improvement, however, may be only temporary and should not be considered a permanent repair where moisture is concerned. Several utilities have experienced serious trouble and in-service failures because of ionization in the cylinders of bushngs of this type. Deterioration of t h s nature has been detected by increased or abnormally low (negative) UST power factors. For this reason these bushings should be carefully watched by a regular test schedule. Any case of steadily increasing or suddenly increased power factors above 1.5% warrants removal from service for investigation and consultation with the manufacturer.

This bushing can readily be repaired in the shop. The presence of water in the parent apparatus may be due to defective bushing top cap gaskets of holIow conductor-type bushings. These can be replaced in the shop or In the field, Should a high power factor indicate moisture within the core, the manufacturer recommends that the core be dried uniformly in a heated oven for a period not exceeding 3 hours at a temperature of approximately 100°C (105°C must not be exceeded), The Herkolite core of the Type "L" bushing is susceptible to corona damage. A radio noise or corona test should be considered before repairs are made. The General Electric Company has made a special bushing "trade-in" offer (a modern Type "U" bushing at a price substantially below the net to replace the Type "L" bushings) which make it uneconomical to repair the Type "L" bushings.

Type LC This bushing is basically the same as the Type "L"except that they are center-clamped with a heavy Bellville spring washer at the top. It is extremely easy to repair in the shop. It is particularly important to keep the oil filling plug at the-top sealed to prevent the ingress of moisture. The bushing core is also susceptible to corona damage, and a radio noise or corona test should be considered before repairs are made. The General Electric Company "trade-in" offer made for the Type "L" bushings also applies to the Type "LC" bushings. Care should also, be taken to insure that power-factor tap housings are properly sealed to prevent entrance of moisture.

72A-1973-01 Rev. B 7104

...


Type OF This bushing can usually be economically rebuilt. When Type "OF" bushings are rebuilt, it should be determined that they have all the latest features, i.e., sump-type washer, bellmouth breathers, amber glass, and thermal-seal features. Bushings with broken porcelains, particularly the top porcelain, may not be economical to repair. The presence of water in the parent apparatus may be due to defective bushing top cap gaskets of hollow conductor type bushings. These can be replaced in the shop or in the field. High power factor on a Type "OF" bushing can sometimes be temporarily reduced by removing the drain plug in the bottom washer of the bushing and flushng with clean dry transformer oil. The improvement, however, is usually only temporary and should not be considered a permanent repair. The bushing can, be restored to its original dielectric condition by rebuilding after drying or replacing the cylinders and core insulation. Detailed recommendations for repairing these bushings are covered in GEI-9187 (Repairs on Types "OF" and "OFI" Bushings). For older bushings, replacement is recommended in cases where high power factor has developed.

Type lJ This bushing can be repaired. The presence of water in the parent apparatus may be due to defective bushing top cap gaskets of hollow conductor-type bushings. These can be replaced in the shop or in the field. No extensive work has yet been required on this type bushing; however, it appears that any properly equipped repair shop will be in a position to economically repair these bushings when required. Detailed recommendations for repairing these bushings are covered in GEI-63707A (Repairs on Type "U" Bushings) -

8.2

Locke Division of General Electric Company

Locke Division bushings are the same as the equivalent General Electric Company bushings; therefore, the above comments also apply for any particular type Locke bushing.,

8.3

Ohio Brass Company

Bulk The bulk-type bushing, consisting of porcelain tubes, either single or in concentric assembly with cement between the various tubes, was built for 7.5 to 73 kV up to about 1932. The principal trouble encountered with this type of bushing is oil leaks at the cemented joints. This variety of bushng is repairable; however, it may not always be economical. Class ODOF (or OF) T h s bushing consists of a number of concentric porcelain tubes enclosed in a porcelain housing which is oil filled. It was manufactured from about 1924 to 1932. This class can be repaired by replacement of broken porcelain, recementing joints, regasketing, etc; however, it will usually be more economical, where extensive rebuilding is necessary, to replace damaged bushings.

7%-1973-01 Rev. 6 7104


Class L (See Section 12 Page ?) Manufacture of this bushing was started about 1932 for 8.6 to 69 kV. It is of the porcelain-core, oil- filled, center-clamped construction. The earlier models breathed into the apparatus in which they were installed. The later models are completely sealed. This bushing is economically repairable. Power-factor values are shown on the nameplate and should be used as a guide when rebuilding and testing. Flushing with hot oil and refilling can usually improve h g h power factor.

"

-

Class G Manufacture of this bushing was started about 1932 for 46 kV and up. It is of the concentric porcelain-tube, oilfilled, centerclamped construction. Like the Class "L," the earlier model Class " G bushings breathed into the apparatus in which they were installed. The later models are completely sealed. Flushing and refilling will usually improve high power factor readings. Class LK This bushing for 15 to 69 kV consists of a thermosetting, resin-coated paper-wound condenser core, enclosed above the flange in an oil-filled porcelain. Below the flange the ground sleeve is shrunk on to assure tight contact with the core. Below the ground sleeve multiple coatings of moisture-proof varnish protect the exposed core. These bushings can be used with adapters to replace older model obsolete bushings. Although no extensive repairs have been necessary on this type of bushing, it should be readily-repairable in a well equipped shop. Class GK This bushing for 15 kV and up consists of an uncoated-paper-wound core, which is totally oil impregnated and is completely encased with oil-filled porcelain housings above and below the flange. As with Class "LK" bushings, the Class "GK" bushing can be used with adapters to replace obsolete bushings. These bushings should be readily repairable in a well equipped shop.

8.4

Lapp Insulator Company

Dry TYpe This bushing for 7.5 to 34.5 kV consists of one-piece porcelain, with cemented-on mounting flange, and draw lead or through-rod conductor accessories. The only repairs that are practical are the maintaining-of a weather-tight seal ' at the mounting flange and terminal cap and the replacement of complete porcelains. Type ERC This bushing is available in 15 and 23 kV ratings, meeting only the NEMA electrical standards. It has a condenser epoxy-paper, hard-core insulating structure. Early bushings were plastic filled; however, this was later changed to oil-filling.

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dm

*

-

:


Types POC and POC-A These bushings are constructed for 15 kV and up and consist of a condenser core composed of oilimpregnated paper and aluminum foil, totally enclosed in an oil-filled, sealed housing. The latest version for 15 to 69 kV has a glass oil reservoir to facilitate oil-level determination. It has not been necessary to perform any extensive maintenance on these bushings; however, they should be readily repairable in a well equipped shop. Types PRC This condenser bushing is available for 15 kV through 69 kV. The design consists of an epoxypaper core with an epoxy filler instead of oil. T k s bushng is new; hence there is no field maintenance experience as yet.

These bushings, 23 kV and below, are basically a one-piece, bulk porcelain variety and require only occasional replacement of gaskets or deteriorated cement. (See Section 12, Pages 1, 18,25 & 26).

8.6

Westinghouse Electric Corporation

Types A, B, C, D, E, F, H-I and H-2 (See Section 12 Page ?) These bushings were manufactured for various intervals between 1909 and 1934. All of them are substandard when compared with modern bushings. Any remaining in service should be scrapped at the first opportunity and replaced with modern bushings. Type J-I This is a single-piece porcelain tube, bulk-type bushing with heavily insulated cable lead, manufactured from 1922 to 1930, for 4.3 kV to 23 kV. As long as the porcelain is intact, the gaskets and insulated lead can be replaced as necessary to continue this bushing in service. Type J-2 This is a single-piece porcelain tube, bulk type bushing, with solid stud lead, the manufacture of which was started in 1922 for 4.3 kV to 23 kV. Periodic regasketing is all that is required to keep this bushing in good operating condition.

-.

Type G, including modifications G-I, G I , G2, OG, and OG2 These bushngs, whch are basically the same, were manufactured from 1934 until about 1943. They consist of a condenser-type core and a one-piece porcelain weather casing, which is end-clamped between the cap and the mounting flange. It is not practical to perform field maintenance on these bushngs; however, when found bad by power-factor test, they should be removed from service for rebuilding. Before rebuilding, the condenser assembly should be checked for power factor and dried

72A-197361 Rev. 8 7104


in an oven if necessary. A capacitance check should be made at the same time as the power-factor test to determine that the capacitance is not more than 15 percent above the average for bushings of the same design. When replacement is necessary, ASA bushings and adapters, where necessary, should be used.

-

Type K, including modifications K-I and OK-l These bushings, which are basically the same, were manufactured from 1937 to 1941 for 34.5 to 230 kV. They consist of a condenser-type core and a one-piece porcelain weather casing, which is endclamped between a cast cap and a pressed-on fabricated flange. Type "K" is plastic encased, and Type "OK" is oil-encased. Type bbOK-l"has an oil filled weather casing and is designed for use in askarel-filled apparatus. Recommendations for rebuilding or replacement are the same as for Type "G." Type M This is a bushing manufactured for oil circuit breakers only from 1937 to 1941 for 46 to 230 kV. It is of the oil-encased type and has an oil sight-glass between the porcelain and the expansion chamber. Bushings of ths type are economically repairable, and recommendations for rebuilding or replacement are the same as for Type "G'." Type N This bushing was manufactured from 1940 through 1942 for 92 through 228 kV. It has a spun or drawn cap section with multiple-coil springs to place a definite pressure on all gasketed joints. Bushings of this type are apparently more susceptible to short-circuited condenser sections than other similar bushings. Power-factor tests should always include a UST test and any bushing with a C1 capacitance value 10 percent above normal should be investigated. if power factor and capacitance tests are satisfactory, this bushing is economically repairable; and recommendations for rebuilding or replacement are the same as for Type "G." Type 0 (See Section 12, Pages ?) Manufacture of ths bushing was started in 1942 for 92 kV and above. It is now produced from 69 kV up. The Type "0" bushing has an oil-impregnated Krafi paper condenser inside an oil-filled chamber, consisting of a cap, upper porcelain, mounting flange, and lower porcelain, all of which are held under pressure from springs in the cap. This is the current design bushing for 69 kV up and requires no routine maintenance except for occasional cleaning of the porcelain and observation of the oil level. This bushing is used in its ASA version with appropriate adapters to replace obsolete bushings. Field repairs on this type of bushing are not practical; however, any well equipped shop should be capable of rebuilding it.

Type RJ This bushing is made up of a single-piece porcelain with a flange sleeve rolled into grooves in the porcelain over silastic gaskets. As these bushngs have been manufactured only since 1955

7%-1973-01 Rev. B 7104

-w '

-

..


experience is limited; however, the construction appears to preclude any repair other than the cap gasket.

Types S and OS Manufacture of this bushing was started in 1941 for 15 to 69 kV. It is plastic-filled (Type S) or oilfilled (Type OS), hermetically-sealed, with all joints sealed by brazing or soldering, eliminating the use of cement and gaskets. No routine maintenance is required, except for occasional cleaning of the porcelain. Field repairs are not practical, and rebuilding should be performed in a well equipped shop. This bushing is used, in its ASA version, with appropriate adapters, to replace obsolete bushmgs.

7214-197361 Rev. 6 7104


7ZA-1973-01 Rev. B 7/04

fm


9

Safety Considerations

At all times, either in the shop or field, safety is the most important consideration. Proper location of equipment in the design stage of an installation is an element that can never be omitted. Training of personnel in the use of rubber gloves, equipment clearance, equipment grounding, proper use of tools and test equipment, and adequate supervision are the other elements that must be present to insure that a job is done safely. The following are minimum suggestions for safety and are not intended to supersede safety practices established by individual companies.

9.1

Handling

When handling bushings, care must be taken to be sure that rigging is applied properly to prevent damage to the bushing andlor to adjacent equipment and personnel. This is covered more fully in Section 10 - Storage and Handling. Cracked or chipped porcelain produce sharp edges, which can result in severe cuts on the hands and arms of personnel working around them.

9.2

Static Charges

Static charges induced by test potentials, while not always an electrical hazard in bushings, provide a source for serious accidents through falls caused by reflex action. High static voltages may be encountered at the bushings installed in apparatus during cold weather and oil-handling operations. Protective or safety grounds should be used to bleed off static charges. High static charges may also be encountered at the bushing capacitance taps if the covers are removed. These also should be grounded before being handled. Induced voltages from nearby energized lines can cause serious accidents if they are not handled properly. Employees should be constantly reminded of the possibility of induced charges and the dangers involved. An electrical clearance on bushings does not assure safe working conditions. Induced voltages of steady state nature are often encountered when the de-energized circuit closely parallels another energized circuit. In such instances protective grounds should be applied to the circuit at the bushings to be inspected. If electrical tests are to be conducted, the grounded leads may be removed which would prevent such tests.

9.3

Field Testing

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77


Field testing generally requires work in the proximity of energized equipment. A short safety meeting on the site should be conducted prior to beginning field tests on bushings. The job supervisor should point out equipment, which is energized, and give specific instructions concerning safe work areas. Rope or other company approved physical barriers are very effective in preventing accidental contact with energized equipment. For further specific details on Field Tests see Section 7 - Test Methods, Procedures, and Limits.

Equipment may be placed on the test floor and tests accomplished in accordance with standard shop safety procedures. In addition, all safety procedures prescribed by the test equipment manufacturers should be observed. Static and induced charges may be present, and precautions should be taken to prevent falls and other injuries which result from sudden movement. For further specific details on Shop Tests see Section 7 - Test Methods, Procedures, and Limits.

72A-1973-01 Rev. B 7/04

.


10

Catalog of Apparatus Bushing Design

A synopsis of manufacturers' literature listed alphabetically by manufacturer and bushing type.

10.1

ALLIS-CHALMER APPARATUS BWSWINOS

Allis-Chalmers Dry Type: Solid Porcelain Bushings These single-piece porcelain bushings, rated 23 kV and below, are produced in a variety of types and sizes for either a spade or clamp-type solderless connector. Bushings rated 23 kV are the oil-filled, sealed type, while those rated 15 kV and below are the dry type. For details on the internal construction of any specific bushing, reference should be made to the manufacturer's literature.

10.2

GENERAL ELECTRIC APPARATUS BUSHINGS

Type "A" Bushings The Type "All bushings introduced in 1924 have been modified many times, but all designs have in common the use of a single-piece porcelain which extends through the apparatus and provides the major insulation of the bushing. Type "All detachable cable conductor bushings manufactured prior to 1941 used a mounting support flange bolted to a clamping ring which, in turn, is cemented to the porcelain. In some older modifications of this construction, the support flange is cemented directly to the porcelain. From 1941 to 1952 a modification of the detachable-cable bushing eliminated the support flange by gasketing the ground-porcelain surface of the bushng against the apparatus housing. In 1952 a more modern design, having a detachable cable conductor, was made by using a threesection mounting clamp and washer. This same design is also built with a solid conductor. The majority of Type "A" bushings in service use no liquid filler. However, some designs, particularly high current ratings, have been manufactured with No. 10-C oil in the bushing, or with provisions for self-filling the bushing with oil from the transformer to improve radio-influencevoltage characteristics.

C~m

72A-1973-01 Rev. I3 7104


Figure 10-1 General Electric Type A Bushings

7%-1973-01 Rev. B 7104

em -

S r ~ o l r i qnut

-

lead,

- - - - --

n, tnn -11 burh~nqlor 100-amo rotlna

.-

.One-plcce po~celarrrshell

Ccmentlesr-typo clump

1952 t o P r e s e n t Detachable Cable Type

1952 t o P r e s e n t S o l i d Conductor Type


Type "B"Bushings The Type "B" bushings were in active Production from 1916 to 1930, and continued in limited application to 1945. The Type "B" bushings are compound-filled bushings but are characterized by a flexible cable conductor, rather than a rigid core. The bushing consists of a one-piece porcelain assembled with clamping rings, a support flange and terminal cap providing a weather-tight structure around the upper portion of a flexible, varnished-cambric-insulated cable conductor. The space between the porcelain and the insulated conductor is filled with a pliant insulation compound. A typical bushing of this design is shown. These bushings were also furnished as double conductor (Type BD) and as triple conductor (Type BE).

72A-1973-01 Rev. B 7/04

-. A


Figure 10-3 General Electric Type B Bushings

7%-1973-01 Rev. I3 7104


Type "F"Bushings Type "F" bushings were in use from 1948 to approximately 1955 on G. E. power, distribution and instrument transformers, and oil circuit breakers, in voltage ratings from 92 to 330 kV. They were furnished in 69-kV ratings for special application. The Type "F" bushing design is a completely sealed, oil-filled construction with Herkolite insulating cylinders and concentric oil ducts around a central metal tube or rod. To provide a voltage supply for potential devices, some Type "F" bushings rated 92 kV and above were built with a capacitance tap. All oil-circuit-breaker bushings, 115 kV and above are provided with a capacitance tap.

I

Part I

n

j

3 4

5 6 7 8

Gasket Compression-spring assembly Gasket Casket Magn~ticliquid-lrvcl gage with garket Expansion chamber

II I2

I5 I

I

6 7

22

23 24 -.

Terminal cap Cable stud Pi Casket Intermediate cap Casket

g lo

13 14

Name of Part

Gasket

1

I ,

Terminal shield Top porcelain Central tube or rod Herkolite cylindrrs with conduct in^ stress q u a i izers

'

Gaskrt

: I

Bottoln was11rr

Drain plug . . ..-

- -- -

--

-

-

Figure 10-4 General Electric Type F Bushings

72A-1973-01 Rev. I3 7104

-.


.

Type "L" Bushings Types "L," "LI" and "LM" bushings were manufactured from 1932 to 1951. They were used on power, distribution and instrument transformers, and oil circuit breakers in ratings of 15 to 73 kV inclusive. The Type "L" bushings consists of one-piece porcelain assembled to provide a liquid-tight structure around the upper portion of the core. The core is Herkolite insulation wound on a central metallic tube or rod. The space between the core and the porcelain is oil filled.

Hekol~tscore inwldion

Central metallic tube

PART 1 2

3

16

17

~ u ~ p oianl(c rt

6 7 8 9 Metal ground sleeve

Embedded st-

eqwlizer

Terminal cap Cable aud Pin Gdd Buahing cap Core-seal gasket Bushing-cap gasket Top washer Corc+eal watlher Core-seal spring Clamping bolt and washer Gasket Top clamping ring Porcelain Bottom clamping ~g Clampin bolt and washer

4 5

Flange gasket surface

NAMOP PART

10 11 12 13 14 15

Figure 10-5 General Electric Type L Bushings

Cm -

72A-1973-01 Rev. B 7104


Type "LC"Bushings Type "LC" bushmgs have been in production since 1951 for applications in the range of 15 to 69 kV.

The Type "LC" bushing core consists of resin-impregnated Herkolite insulation, wound on a central metallic tube or rod. The upper porcelain is center-clamped; the space between the porcelain and Herkolite is oil-filled and completely sealed.

7 1

2 3

""OF

PART

--

Terminal cap

10

Gasket

Pin

12

Cdet

Cable-tcnninalstud Garket

Gdct

Filling plug with1 gasket GasLet

Bushing cap &Ilcvilk washer

13 Sup rt flange 14 . G Z ~ 15 Corc ~rscglbly, which in. cluder central metal tube, Hatolire inrulation, and p p u d dteve

Figure 10-6 General Electric Type LC Bushings

72A-1973-01 Rev. B 7104


Type "OF" Bushings Type "OF" and "OFI" buslvngs were manufactured from 1918 to 1948 and were used on power, distribution and instrument transformers, and oil circuit breakers rated 92 to 230 kV. For special applications they were also used down to 34.5 kV. The bushings are of the open-type construction with glass expansion chambers for observing the oil level. The Type "OF" bushing consists of two or more porcelains assembled so as to provide an oil-tight structure around the series of spaced, concentric, Herkolite insulating cylinders and a central copper tube or rod. To provide a voltage supply for potential devices some Type "OF" bushings rated 73 kV and above were built with a capacitance tap.

Breather pipe Gage-glass washer Gage-glass bolt S ring washer PEin washer Gage-glau gaskets Gage glass Plug I.ock nut Plain washer Spring washer Collar Slecvc gasket Threaded slnve Top-washer bolt Hcavy sprin washer Top washcr$assembly includes U-tube and drain valve) Top-washer gasket Top-washer drain plug Top clamping ring Terminal shield Clamping nut Spam Fiber waaher Spacing block Top porcelain Hcrkolite cylinder Central conductor Gmund shield r intermediate c amping ring Bolt Heavy spring w a h c r Star washcr Gaskct support Bolt Hcavy spring washer Gasket Lower intcrmediate clamping ring Bottom porcelain Bottom clamping ring Gaskct Bolt Heavy spring washer Bottom washer Bottom-washer drain plug

"'f"

Figure 10-7 General Electric Type OF Bushings

72A-1973-01 Rev. B 7104


Type "S" Bushings* (Rigid Core) Types "S", "SI", and " S M bushings were manufactured from 1916 to approximately 1932 for transformers and oil circuit breakers in ratings from 15 to 73 kV. The general construction of the Type "S" bushing embodies a rigid core, consisting of a metal tube or rod covered with Herkolite insulation. The upper part of the core is enclosed by porcelain, the space between the porcelain and core being filled with a solid insulating compound.

Compound hllc,

Ground r

*

-------i

e

e

r

*

J

]

Figure 10-8 General Electric Type S Bushings

* Type "S' (Forms F, DF and EF) is flexible cable bushings and has been redesignated as Types " B , " B D and "BE". Description of these bushings is listed under Type "B" bushings. Type "S" bushings with no form letter have been redesignated Type "A".Description is listed under Type "A" bushings.

724-1973-01 Rev. B 7104

em -


Type "U" Bushings Type "U" bushings are designed for applications between 23 and 700 kV on power, distribution and instrument transformers, and on oil circuit breakers. They are of the completely sealed oil-filled type.

Figure 10-9 General Electric Type U Bushings

The fundamental principle of design of the Type "U" bushing is the proper combination of voltage stress equalizers and oil-impregnated paper on a central metal tube or rod.

.. -.*

w9icc -u' ECWZW;;

Production of these bushings in the 69 through 138 kV ratings has included both magnetic liquid level gages and transparent glass expansion chambers. To provide a voltage supply for potential devices all Type "U" bushings, 92 kV and above, are built with a

capacitance

8

72P1973-01 Rev. I3 7/04

tap, which can also be used for power factor tests. All Type "U" bushings below 92 kV are provided with a power factor test tap to facilitate field-testing.


These bushings are produced in a variety of types and sizes for fixed hollow or solid conductors as well as cable-type construction. For details on the internal construction of any specific bushing, reference should be made to the manufacturer's literature.

90

72A- 1973-01 Rev. B 7/04

m -'

-


*

Type "ERC" Bushings The Type "ERC" bushing is a hard-core bushing introduced in 1962. This bushing has an epoxy paper insulating structure and is of the condenser type. It is oil-filled at the top end only. The Type "ERC" bushing is available in a 15-kV and a 23-kV rating meeting only the NEMA electrical standards

Figure 10-10 Lapp Type ERC Bushings

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91


Type "POC" Bushings The Lapp Type "POC" bushings, manufactured since 1956. meet the ASANEMA standards. Available in the 15-kV to 500-kV range, the Type "POC" bushing has a paper oil condenser core. It is completely sealed. At 69 kV and below, these bushings have power-factor taps. From 92 kV to 500 kV all models have oil gauges and capacitance taps as standard equipment. The Type "POC" bushing is a standard transformer bushing. The Type "POC-A" is an interchangeable bushing for use in both circuit breakers and transformers. The Type "POC-T" bushings are for use in test transformers or similar applications.

15 kv to 69 kv

9 2 kv and above

Figure 10-11 Lapp Type POC Bushings

72A-1973-01 Rev. B 7/04

-


Type "PRC" Bushings The Type "PRC" bushing introduced in 1964, incorporates a void free paper-epoxy insulation system. This line of bushings is available in ratings from 15 kV through 69 kV. They are oil-filled at the upper end only, and have sight glass tops for checking oil level. The application of these bushings is specifically in the area of distribution equipment such as distribution breakers and large distribution or small power transformers, reclosers and replacements for bulk-type bushings, or porcelain and copper-stud assemblies.

Figure 10-12 Lapp Type PRC Bushings

72A-1973-01 Rev. B 7104


Lapp Dry Type: Solid Porcelain Bushings Lapp dry type, solid porcelain bushings are produced in a variety of types and sizes for either draw lead or with a fixed hollow or solid conductor. For details on the internal construction of any specific catalog number, reference should be made to the manufacturer's literature.

-

See General Electric Apparatus Bushings.

Moloney Dry Type: Solid Porcelain Bushings These bushings rated 15 kV and below are produced in a variety of types and sizes. For details on the internal construction of any specific bushing, reference should be made to the manufacturer's literature. All Moloney bushings are made with a rod or tube permanently installed in the bushing and solidly attached to the top bushing cap and connection lug and to the bottom sealing nut and lug.

Class "G" Bushings Class "G" bushings were introduced about 1930 and manufactured until 1958. These bushings covered the 46-kV through 230-kV voltage classes. A significant change in design occurred in 1940 when the construction was changed from a freebreathing to a completely sealed style.

The Class "G" bushing consists essentially of a central conductor or supporting member, surrounded by one or more concentric porcelain tubes with some varnish-cambric insulation. This is then encased in an outer porcelain shell and filled end-to-end with transformer oil. The "G" classification designates a bushing with an oil-level indicator.

72A-1973-01 Rev. B 7104

Cm -

-

-


Illll~rc.hslw~~l,lc. q , p r lrrminal I~rmc~roblr plu~

(hl expawion rhnmbrr M m r t i c oil kvrl indirahrr Srlrmal oil l r r d

Carnprrssiana p r i n ~ TrplmJ for nttwhin(l vultlyc limitinr mp Gdalicla rmpnmd lrtatrtl m u h i n d end Ctmlcriw allarer

I'oM1 oil-pnnl-e~mrntjoints I'orcrlain ooalrr shrll Purcrlnin inlwr rrm I ~ r w l b l i woil I n t ~ m g uruunll l altield

Cork Cakeb-bsnncd be; kern M u h ~ n c dnd Ground

Surfun

)lwhimJ barr

dm

\Isrhiorrl frrr m>on,li~,l: wkel

/

(i,rtnl curniurlor

( : ~ , ~ ~ pom-l:tin t c d luwckr aIr.11 m t t e r cow a ~ ~ > r w ~ r t (;rsdinr[ drit4d stld hmrr vnd lr.rilw plak Drain ph&a Int~~rclu~tamldr l n r r r terminn1

b w n M r h i n c d nd Ground

SuAm

Free Breathing Type

Completely Sealed Type

Figure 10-13 Ohio Brass Class G Bushing

7%-1973-01 Rev. B 7104


Class " G K Bushings The Class "GK" bushings introduced in 1956 fully complies with ASA standards extending from 23 kV to 196 kV. A 15-kV bushing is also available. This type bushing is completely sealed with an oil-impregnated paper core, equipped with porcelain on both upper and lower ends. Class "GK" bushings rated 92 kV and above are provided with a capacitance tap outlet. The 69-kV rating and below are equipped with power-factor test-electrode terminals.

GROUND PORCELAIN

CONDENSER MPE INSUUTlNG CORE

FOIL CONDENSER

WITANCE TAP

ALUMINUM GROUND SLEEVE

GROUND PORCELAIE;

Figure 10-14 Ohio Brass Class GK Bushing

72A-1973-01 Rev. B 7104

'--

--


Class "L" Bushings Class "L" bushings were inboduced around 1930 and were manufactured as late as 1958 in voltage ratings available in the 8.7-kV to 69-kV range. A significant change in design occurred in 1940 when the construction was changed from a free breathing to a completely sealed style.

The Class "L" bushing consists essentially of a central conductor or supporting member, surrounded by one or more concentric porcelain tubes with some varnish-cambric insulation. This is then encased in an outer porcelain shell and filled end-to-end with transformer oil. The "L" classification designates a bushing without an oil-level indicator.

1 Ieahuyaldc upwr m

3 Y-I

d d

to mrmi @&~trrljutnt

3 1Ln,D*DItlrplt~g 4 (8I czfxsnnonehdrr

a Xo-l

'GI k u d

8 C'fwl~tw&ntu~winlr 7 TaMfd fur ntwrhc*

d:w !in+In#lrt;lp

lwcx,~." r~mtltat
B.1.7-I.C.22 Dntlkffr#nnmtr-l II Fnntorio*ymerr

IQ F d d n m k r %k*U 11 1'01n4Sin inmv r n

12-19 bdutise mt 13

I a t d mu& hiwid

w 3iwai:d fa mwzaiUi~us+t ~k

>?

I~FEGRRI LIWI

LR

Rir~.Ltntnwer sMl

20 t . . n t d rsndut*ec 21 C m t P r n m c ~

23 fhwm i hmngpktilr.

Wee Breakhkng Type

24

Dnin lllue

25

h~ten.hmmdtlcbwcr4vrn1r11?l

Completely sealed Type

Figure 10-15 Ohio Brass Class L Bushing

72A-1973-01 Rev. 8 7/04


Class " L K Bushings Class "LK" bushings introduced in 1955 are ASA standard bushings. This class covers ratings from 23 kV to 69 kV inclusive ' 'A 15-kV bushing is also available. These bushings have a resin paper core encased in oil above the flange only. Stendord k m l n d

YDdod b l t Cad.

mlly I*.rad Rung. and m d tkm

kCbnwamcr)l. ond pmvnd *rm

Rt bw l. ""

-

StQhtardwy.afi *ngh bd* h g r

Stdod kmkal

eamiwd

a*.&

kn(iHI

Figure 10-16 Ohio Brass Class LK Bushing

7%-1973-01 Rev. B 7104

m -'


Type "ODOF Bushings The Type "ODOF" bushing first manufactured in 1910 is an outdoor, oil-filled, porcelain-shell bushing with some varnish-cambric insulation between shells. They do not differ appreciably from the Class "L" and " G bushings. In the Type "ODOF" bushings, the external metal components were either cemented directly, or bolted to, metal flanges which were cemented directly to the ends of the upper and lower porcelain weathersheds.

Figure 10-17 Ohio Brass Class ODOF Bushing

Ohio Brass Dry Type: Solid Porcelain Bushings These Class " R bushings are produced in the 8.66 kV to the 25-kV range, for either draw lead or with a fixed conductor. For details on the internal construction of any specific Catalog Number, reference should be made to the manufacturer's literature. Figure 10-18 Ohio Dry Type Solid Porcelain Bushing

72A-1973-01 Rev. I3 7104


Type "P, "PA" and "PB" The present Types "P", "PA" and "PB" Pennsylvania Transformer Company bushings in ratings of 69 kV and above were first manufactured in 1956 by the Federal Pacific Electric Company. These bushings meet the ASA and NEMA standards. The bushng is oil-filled and is completely sealed. The 69-kV bushing is equipped with a power-factor tap. Ratings 115 kV and above are equipped with a capacitance tap.

Pennsylvania Transformer Dry Type: Solid Porcelain Bushings These bushings are produced in a variety of types and sizes with and without a draw lead. For details on the internal construction of any specific bushing, reference should be made to the manufacturer's literature.

10.9

STANDARD BUSHINGS

TRANSFORMER

COMPANY

-

APPARATUS

Standard Transformer Dry Type: Solid Porcelain Bushings These bushings rated 22 kV and below are produced in a variety of types and sizes usually with a stud terminal. For details on the internal construction of any specific bushing, reference should be made to the manufacturer's literature.

10.10 WESTINGHOUSE

ELECTRIC

CORPORATION

APPARATUS

BOBHI~OS Westinghouse Dry Type: Solid Porcelain Bushings These bushings rated up to 15 kV are produced in a variety of types and sizes with or without a draw lead. For details on the internal construction of any specific bushing, reference should be made to the manufacturer's literature.

72A-1973-01 Rev. B 7/04

em -

-

*.

--


WESTXNGHOUSE APPARATUS BUSHINGS

Bushings manufactured from 1909 to 1933

(

-pa "C" slud brought hmqh

cop nut COUlrd kDd

setl tRllnq compound ,3172 thin multr-

=m-r cou f k q 8

-emmm R mdrnlv

kypisrrl eondzu&on of

c~nrtructiosd

"B" bumhing- manufmtured 1922 to lB2B for 48 k r to 187 h

tvp. "A'%b\uhln$- r a n d a c t r r d leOB to 1922 for 23 h to 184 h

typo

~includm)

(iclud*.)

tppiorl coastruction of typm "C" bushlag-nranufrcturmd l@aaLO 19SB for 28 ko to 66 kv (includwf

69 t v a d -low c gaskets od nwpenr witti

c o w &oldend

stop gasXan

mta untHrdulr

MccUI

2 2

earl* nm Cammad lo porcrfotn sot1 fi11lng

COmPlnJna

+3122 me

w

w-wn

curt mounnng *nge camnfrd to

C U r n M C d C0&t

condenser

ring

~n f411og

cable W

compound *3172

cast ftange cnmsntsQ tu conaenser

typical construction of 'OD" bushing - manufaehud Eer eanrfonnara only. 1922 to 1932 Im 33hutd44Lv typ

typical construotion of

typical conrtru~fion04

1922 to 1929 for 33 Lv to 181 ku

"F" buahing -manufactured 1929 to 1934 for 13.8 kv to 230 kv

~incluaivo)

(inclusive)

type

"E" bushing - manuiactuzad

type

Figure 10-19 Westinghouse LV Dry Type Solid Porcelain Bushings

72A-1973-01 Rev. 8 7/04


Type "G'Bushings The Type "G" bushing, manufactured from 1934 to 1942 for 15 kV through 288 kV, is used on transformers and oil circuit breakers. On all voltage ratings below 288 kV, a one-piece porcelain weather casing is used, while at 288 kV a two-piece porcelain weather casing is used. This bushng has a shellac paper wound condenser core. Before June 1938 the filler was a soft compound; after June 1938 the filler was a plastic. A bushing of this design is shown below. Type " O G bushings are the same as described above, but have the porcelain casing filled with oil instead of a plastic. Type "1G bushngs have the weather casing filled with Inerteen instead of plastic. Types "GI," "OGI" and "IGI" bushings are the same as described above, but are designed for use in Inerteen filled apparatus. Types "GI" and"G2," for voltages 15 kV to 46 kV were designed when aluminum became unobtainable for spring caps, which were used on Type " G bushings. With the exception of the cap, all other parts of these bushings are identical with those of the Type " G bushings.

Figure 10-20 Westinghouse Type G Bushings

7%-1973-01 Rev. B 7104

m -'

-

.


Types "J-I" and "J-2" Bushings The Type "5-2" bushing is a bulk type bushing manufactured from 1922 through 1955, which is used in transformers for voltages 4.3 kV through 23 kV. This bushing is a single-piece porcelain tube with a solid stud lead through the tube. The porcelain is cast with a collar below the rainsheds; this collar fits over the gasketed mounting of the transformer cover.

wbdtsd

hporcekln

--ma

porwloin tube

~ l o t e cd o b leod

extansion tube spacirrg cellor

lock nut washer lock nut

Type "J-1" Bushing 1922 to 1930

Type "5-2" Bushing 7923

+n 1 9 5 S

Figure 10-21 Westinghouse Type J- 1 and 5-2 Bushings

72A-1973-01 Rev. B 7104


Type " K Bushings The Type "K" bushings, manufactured from 1937 to 1942 for voltages 34.5 kV to 230 kV, for use in transformers and oil circuit breakers, can either be oil or plastic encased. It is recognized by a cast cap with bolted cover and one piece porcelain under spring pressure. This bushing has a shellac paper wound condenser core. Most of the Type "K" bushings produced were in the higher voltage ratings above 69 kV. Type " O K bushings have the porcelain weather casing filled with oil. Type "OKI" bushings, having this same construction, have an oil-filled weather casing. The bushing is designed for use in Inerteen-filled apparatus. Type "K-1" and "OK" bushings are modifications of the Type "K" bushing, used in all cases when special requirements of the customer cannot be met with the standard type.

TYPE "K-l" BUSHIW 1939 to 2942

Figure 10-22 Westinghouse Type K and K1 Bushings

72A-1973-01 Rev. B 7104

m -'

*

-


Type "M" Bushings The Type " M bushing, manufactured from 1937 to 1941 for 46 kV through 230 kV, is of the oil encased type for use in transformers and oil circuit breakers. The one-piece porcelain, construction is sealed by a gasket to a gauge which is resistant to active rays. Thls bushing has a shellac paper wound condenser core. A sump and sampling connection are supplied at the bushing flange.

cork-neoprene gasket matol to metal stop

oil level indkotor

circult brso her and bevel aasket Figure 10-23 Westinghouse Type M Bushings

72A-1973-01 Rev. B 7104


Type "N" Bushings The Type "N" bushing, manufactured from 1940 to 1942 for 92 kV to 288 kV, for use in transformers and circuit breakers, has a plastic filler. Below 288 kV a one-piece porcelain casing is used, while at 288 kV a two-piece porcelain casing is used. T h s bushing has a shellac paper wound condenser. Type "ON" bushings use an oil filler instead of a plastic an oil filler instead of a plastic. odapter nut-

I

, -

terminal cup

circuit breaker and washer

Figure 10-24 Westinghouse Type NBushings

72A-197501 Rev. B 7104


Type "0" Bushings 1942 to 1957 The Type "0" bushing, introduced in 1942 for 69 kV and above voltage ratings, for use in transformers and oil circuit breakers, is an oil impregnated condenser bushing. The chamber between the porcelain and the paper condenser is oil filled. For voltage ratings up to and including 345 kV, a one-piece porcelain casing is used. As the Type "0" bushings are completely sealed, they may be stored indoors or outdoors. A typical construction of ASA Standard Type "0" bushing manufactured from 1957 is shown.

f 942 to 1957

Figure 10-25 Westinghouse Type 0 Bushings

m -'

72A-1973-01 Rev. B 7104


Type "0" Bu

TYPE "0" BUSI3ING 1957 to Present

Figure 10-26 Westinghouse Type 0 Bushings 1957 to present

72A-1973-01 Rev. B 7/04

dm -


Type "RJ" Bushings The Type bushing, manufactured since 1955, is a bulk type bushing used in transformers for voltages 15 kV and below. This bushing is made up of a single piece wet process porcelain with a flange sleeve rolled into grooves in the porcelain over silastic gaskets. 6 6 R J

Three types of leads are used in these bushings: a solid stud which goes through the cap, a solid stud which screws into the cap, and a hollow tube with a cable conductor inside of it.

porceloin

. 4

cushion ?Ii' ring gcl sket

I

cork neoprene for oil: krna "N" cork for fnerteen

a

bushing f longe

sleeve

,

- sealing gasket:

u

r

silostic sealing gasket rolled compression

micoria tube stud clamping flange

= . - >* -

L c o v e r boss

cushion washer

brass washer

brass nuts

Figure 10-27 Westinghouse Type RJ Bushings

C-w

72A-1973-01 Rev. B 7/04


Type "S" Bushings Solid Stud, Bare Cable Connection The Type "S" bushing has been manufactured since 1941 for 15 kV through 69 kV, for use in transformers and oil circuit breakers. These bushings consist of a shellac paper wound condenser core. The chamber between the porcelain and the condenser core is filled with a plastic. Since 1956, these bushings have been manufactured to conform to ASA Standards. Type "0s" bushings use a filler of "Wemco C" transformer oil instead of plastic.

WPE

"S "

BUSHING

1956 to Present

Figure 10-28 Westinghouse Type S Bushings

72A-1973-01 Rev. B 7/04

*


confined cork neoprem gorkst

read fsrmlnel and locking nut

Serw-in vent tor filltng (soldered over)

solder wof ta pererlaln waathrr casing

N d s r 1.01 to porcsloln

mounling flonge

cable lead covrrrd with top4

Figure 10-29 Type "S" Bushings Taped Lead, Solid Stud

72A-1973-01 Rev. I3 7104


72A-1973-01 Rev. B 7104


,

11

Index of Conference Papers

The following index is of bushing topics and subjects covered by the Minutes of the Annual Conference of DobIe Clients. Under each topic or subject is listed, by year, all pertinent Conference papers.

11.1

Papers

Title, Discussion

Author

Date

Section

Adapters ASA Bushings (Transformer-Breaker Interchangeable)

G. R. Deinema

1961

4-701

Improper Bushing Adapter Design Causes Transformer G. R. Deinema Failure

1952

6-201

1955

4-1201

1956

2-101

1954

2-401

Air Circuit Breaker Bushings Westinghouse Circuit Breaker Bushings

J. H. Frakes

Application Trends in Specifications and Factory Tests for Station P. L. Bellaschi Apparatus Notes on Electrical Clearances in Station Apparatus, For the P. L. Bellaschi Maintenance Engineer Use of Ground Sleeves for Bushings

L. W. Smith

1945

4-101

Classification of Bushings

F . C. Doble

1935

5-1

Askarel-Filled Bushings Failure of 115-kV Askarel-Filled Bushings

R. P. Gale

1958

4-101

Contamination of Askarel in 15-kV Bushings

M. J. Kramer

1951

4-101

113

7214-1973-01 Rev. B 6104

m -'


Title, Discussion

Author

Date

Section

Capacitance Taps Installing Replacement of Capacitance-Tap Assemblies Associated wit1 General Electric Type F 115-kV Bushings

H. A. Vasil

Replacing Capacitance-Tap Insulators in 345-kV Bushings ir Place

1

I

safety Safety Practice Applied to Capacitance Taps

I

Testing Bushing Tap-Voltage Measurements with a Hot stick Voltmeter,

L. E. Humbard

Testing Bushing Capacitance Tap Outlet Cables

J. H. Merriman

G. W. Early W. J. Bridgegam

I Circuit-Breaker Bushings

/ Operation of Bushings in Carbonized Oil I Westinghouse Electric Circuit-Breaker Bushings

W. W. Thompson J. H. Frakes

Ungrounded-?Specimen Tests on a Westinghouse 138-kV Type 0 Bushing

J. B. Finnell

Minimizing Moisture Hazards in Oil Circuit Breaker Bushings

M. A. Saeault

Westinghouse Circuit Breaker Bushings

J. H. Frakes


A. W. Hill

Westinghouse Bushings

H. J. Lingal

I Corona (see Testing and Maintenance)

I

Bushing Corona Testing by the Pulse Detection Method Corona Pulses and Their Measurement

C. R. Goodroe L. E. smith E. H. Povey

Radio-Influence-VoltageTests in the Presence of Interference,

E. H. Povey

Corona on Cable in Wall Bushings

V. S. McFarlin H. A. Vasil P. L. Bellaschi

Corona Characteristics of Dry-Type Apparatus (Survey of the Problem)

724-1973-01 Rev. B 7104

em


Title, Discussion

Author

Date

Section

-

1

Design and Construction

Allis-Chalmers

1 Allis-Chalmers "Positive Seal" Transformer Bushings I Bushings in Allis-Chalmers Transformers

I/

I P. S. Castner

Federal Pacific Electric Federal Pacific Electric High-Voltage Apparatus Bushings,

I

General Electric General Electric Bushings

P. S. Castner

I/

1962

I

4-801

I

I

N. E. Dillow

1965

4-601

General Electric Bushing Quality (The Total Concept)

J. W. Albright

1964

4-301

500-kV Co-Ordinated Design Bushing

J. K. Easley

1963

4-701

Par;tial Failure of a Type F Semi-condenser Bushing R. G. A. Brearley Detected by Power-Factor Tests,

1961

4-201

General Electric Bushings,

J. W. Albright

1961

4-401

General Electric Bushings

J. A. VanLund

1960

4-401


J. A. VanLund

1958

4-701


J. A. VanLund

1957

4-701


E. V. DeBlieux

1954

4-101


E. A. Elge

1953

4-501


L. Wetherill

1952

4-101


L. Wetherill

1950

4-601


L. Wetherill

1949

4-501


L. Wetherill

1948

4-801


L. Wetherill

1947

4-601


L. Wetherill

1946

4-101


L. Wetherill

1945

4-601

Discussion of General Electric Bushings

E. D. Eby

1944

4-501


L. Wetherill

1943

4-101


L. Wetherill

1942

4-401


L. Wetherill

1939

4-49

Maintenance of Type OF Bushings

L. Wetherill

1938

3-23

General Electric Bushing Developments During 1936

L. Wetherill

1937

12-3

7%-1973-01 Rev. 6 7/04

I1

1 1948 1 6-701 I

M. G. Mathers

I

I

1950 14-501


Title, Discussion

Author

I E. D. Eby

General Elecric Bushing Developments During 1935

Section

Date I

I

1

L. Wetherill Outline of theory of Design and Construction of Bushings E. D. Eby Manufactured by General Electric Company L. wetherill

I

I

I

1

1935 1935

I

13-3 7-1

Lapp Lapp Bushing Developments

G. L. Atkinson

1965

4-401

New Developments in Lapp Bushings

G. L. Atkinson

1964

4-401

Lapp POC Bushings

G. L. Atkinson

1963

4-501

Developments in High-Voltage Bushings

G. L. Atkinson

1962

4-901

Lapp High-Voltage Bushings

G. L. Atkinson

1961

4-801


G. L. Atkinson

1960

4-501

Lapp POC Bushings

G. L. Atkinson

1959

4-901


G. L. Atkinson

1958

4-801

Lap POC Bushings

R. S. Lapp

1957

4-501

Ohio Brass Field Testing of Ohio Brass Class L and G Bushings

N. W. Richards

1963

4-801

Ohio Brass Condenser Bushings

N. W. Richards

1962

4-1001

Extension of Ohio Brass Class GK Oil Paper Bushings in the N. W. Richards Lower-Voltage Applications

1961

4-901

1959

1I 4-1001 1 4-701

I

Ohio Brass Bushings

II T. F. Brandt I T. F. Brandt

Ohio Brass Bushings

P. M. Ross T. F. Brandt

Ohio Brass Company Bushings

I

Ohio Brass Bushings

I

I

I

I

I

I

I

I

I

I

I T. F. Brandt I T. F. Brandt I T. F. Brandt I

New Developments in Ohio Brass Company Bushings

I

1 T. F. Brandt I

Ohio Brass Bushing Developments

I

I

I

Ohio Brass Bushings

I

I

I

Ohio Brass Bushings

I

(

I

Ohio Brass Bushings

I

T. F. Brandt

I


4-701

1953 I

(

1 T. F. Brandt I T. F. Brandt I

Ohio Brass Bushings

1958

I T. F. Brandt I T. F. Brandt

T. F. Brandt

I

Ohio Brass Bushings

I

1 1952 ( 4-301 1 1951 14-801 1 1949 1 4-601 1 1948 1 4-701 1 1947 1 4-501

(

I

Ohio Brass Bushings

I

1I 1

I

I

I

1946

(

4-301

1 1943 1 4-201 1 1942 1 4-301 1 1941 1 4-31 1 1940 1 4-27

72A-1973-01 Rev. B 7/04

C!~m


-

Title, Discussion

Author

Date

Section

Notes on Ohio Brass Company Bushings

T. F. Brandt

1939

4-59

Ohio Brass Busing Developments

F. L. Brandt

1938

3-13


F. L. Brandt

1937

11-3

Commentary on the Operating Characteristics of Certain Ohio F. L. Brandt Brass Bushings

1936

12-3

Outline of Theory of Design and Construction of Bushings F. L. Brandt G. V. Smith Manufactured by Ohio Brass Company

1935

8-1

Westinghouse A Philosophy of Bushing Design

E. C. Wentz

1959

4-201

Westinghouse Condenser Bushings

C. F. Sonnenberg

1958

4-601

Westinghouse Electric Circuit-Breaker Bushings

J. H. Frakes

1957

4-1001


J. H. Frakes

1955

4-1201


J. H. Frakes

1954

4-301


J. H. Frakes

1953

4-601

Westinghouse Bushings, H. L. Cole and

J. H. Frakes

1952

4-201


J. H. Frakes

1950

4-401


A. W. Hill

1949

4-401

Westinghouse Transformer Bushings

H. L. Cole

1949

4-301

Notes on Westinghouse Transformer Bushings

H. L. Cole

1948

4-501

Westinghouse Condenser Type Bushings

H. J. Lingal

1948

4-601

Recent Developments in Transformer Bushings

H. L. Cole

1947

4-301


H. J. Lingal

1947

4-401


H. J. Lingal

1946

4-201


H. J. Lingal

1943

4-301


H. J. Lingal

1942

4-201

Condenser Bushing Developments

R. C. Bergvall

1941

4-17

Condenser Bushing Developments

R. C. Bergvall

1940

4-13

Westinghouse Bushing Plastic No. 7399-1

H. L. Cole

1939

4-=67

Westinghouse Bushing Developments

G. A. Burr

1938

3-1

Outline of Theory of Design and Construction of Bushings G. A. Burr Manufactured by Westinghouse Electric and Manufacturing Company

1935

6-1

Cm -

72A-1973-01 Rev. B 7/04

-


Title, Discussion

Author

Date

Section

Direct Current, Bushings for Bushings for High-Voltage Direct Current

P. L. Bellaschi

1965

4-301

EHV Bushings General Electric Bushings

N. E. Dillow

1965

4-601

Lapp Bushing Developoments

G. L. Atkinson

1965

4-401

New Developments in Lapp Bushings

G. L. Atkinson

1964

4-401

500-kV Co-Ordinated Design Bushing

J. K. Easley

1963

4-701

(345-kV) J. E. Beehler R. A. Byron

1963

2-301

1961

4-201

1961

4-301

Progress on Corona Detection Tests of High-Voltage C. A. Duke Bushings on the Tennessee Valley Authority System

1960

4-101

Manufacturing Defect in a New 161-kV Type "U" Bushing R. G. A. Brearley Detected by Field Power Factor Tests

1959

4-401

Faults and Failures Field Experience with Equipment,

Extra-High-Voltage

Partial Failure of a Type F Semi-condenser Bushing Detected R. G. A. Brearley by Power-Factor Tests Experiences with Type LC Bushings

J. M. Upperman

Failure of 115-kV Askarel-Filled Bushings

R. P. Gale

1958

4-501

Failure of a 161-kV Bushing

1958

4-501

Failure of Cemented Porcelain Bushings on 12-kV Draw-Out Type Circuit Breakers

M. Fischer W. W. Thompson L. A. Bateman J. W. Bree

1955

4-401

Failure of a Type L 34.5-kV Bushing

R. Beatty

1955

4-401

Bushing Problems

T. A. Wolfe

1955

4-801

Bushing Failures in Service During Extreme Heat

M. A. Sareault

1950

4-101

Bushing Troubles Caused by Conditions Above the Oil Level in Apparatus

E. W. Whitmer

1947

4-101

Gaskets General Electric Bushings

L. Wetherill

1951

4-501

Gasketing Methods and Materials (A Progress Report),

W. A. Rey

1951

2-101

Ohio Brass Bushings

T. F. Brandt

1951

4801


R. G. A. Brearley J. H. Brakes

1951

4-601

72A-19'73-01 Rev. B 7104

m -'


Title, Discussion

General Electric Bushings Westinghouse Bushings General Electric Bushings

Author

I L. Wetherill I J. H. Frakes I L. Wetherill

General Electric Bushings Capacitance Taps General Electric Bushings

J. A. Van Lund

General Electric High-Voltage Bushings,

E. V. DeBlieux


L. Wetherill

Comments on Experience General Electric Bushings

J. A. Van Lund

General Electric High-Voltage Bushings

E. V. DeBlieux


L. Wetherill


L. Wetherill

Corona (RIV) RIV Tests on 69-kV Type L Bushings

A. C. Wilson

RIV Tests on Type L and LC Bushings

C. M. McCoy


E. V. DeBlieux

Special Tests on Bushings

F. S. Oliver

Gauge Glass Type L Bushings (Locating Defective Solderseals),

C. M. McCoy

Negative UST on Bushings General Electric Bushings (Effect of Leakage Currents on UST Power Factor and Capacitance Tap Voltage), Application and Significance of Ungrounded-Specimen Tests

D. L. Johnston A. L. Rickley R. E. Clark

Power Factor Taps General Electric Bushings

J. W. Albright

Experiences with Type LC Bushings

J. M. Upperman


E. V. DeBlieux


E. V. DeBlieux

-

7214-1973-01 Rev. B 7/04

Date

Section


Date

Section

Types A & B Field Power-Factor Tests Point Out Design Fault in New 14.4- J. A. Mahan kV Bushings,

1955

4-301


L. Wetherill

1952

4-101


L. Wetherill

1945

4-601

Bushing Reconditioning,

E. L. Schlottere

1944

4-701

Type F Operating Experience of 115-kV and 138-kV Type F Bushings

J. W. Albright

1963

4-601

), D. L. Johnston

1961

4-101

1961

4-201

Title, Discussion

General Electric Bushings (Effect of Leakage Currents on UST Power Facor and Capacitance Tap Voltage

Author

Partial Failure of a Type F Semi-condenser Bushing Detected J. H. Frakes by Power-Factor Tests General Electric Bushings,

J. A. Van Lund

1957

4-701

Audible Noises Emanating from 115-kV Type F Bushings,

P. A. Stemmler

1957

4-101

1956

4-401

Recent Experience with General Electric 161-kV Type F Bushings, C. A. Duke General Electric Bushings,

E. V. DeBleiux

1955

4-501


L. Wetherill

1952

4-101


L. Wetherill

1950

4-601

Types L, LC, LI and LM General Electric Bushings

J. W. Albright

1961

4-101

Experiences with Type LC Bushings

J. M. Upperman

1961

4-301

Progress on Corona Detection Tests of High-Votlage Bushnigs on the Tennessee Valley Authority System

C. A. Duke

1960

4-101

RIV Tests on 69-kV Type L Bushings,

A. C. Wilson

1959

4-101

RIV Tests on Type L and LC Bushings,

C. M. McCoy

1959

4-701


J. A. Van Lund

1957

4-701


E. V. DeBlieux

1956

4-301

Failure of a Type L 34.5-kV Busing,

R. Beatty

1955

4-401


E. V. DeBlieux

1955

4-501

Bushing Problems,

T. A. Wolfe

1955

4-801

General Elecric Bushings, E

V. DeBlieux

1954

4-101


Title, Discussion

Author

Date

Section


F. S. Oliver

1954

4-401

Bushing Problems,

T. A. Wolfe

1953

4-301


E. A. Elge

1953

4-501


L. Wetherill

1952

4-101


L. Wetherill

1950

4-601


L. Wetherill

1947

4-601

Field Testing Experiences - 1942, V

. W. Brust

1943

5-401

Type OF General Electric Bushings

L. Wetherill

1947

4-601


L. Wetherill

1945

4-601

Bushing Replacement Index GET-906

L. Wetherill

1941

4-25


L. Wetherill

1938

3-23

Experience with OF Bushing on Property of American Gas F. D. Brook and Electric Company,

1937

1-3

1944

4-701

1944

4-301

Type S, SI and SM Bushing Reconditioning

E. L.Schlottere

Experience in Pressure Impregnating Bushing Stems,

A. Sears

Field Testing Experiences - 1942, V.

W. Brust

1943

5-401

Bushing Replacement Index, GET-906

L. Wetherill

1941

4-25

Reconditioning of Bushings,

R. A. Anderson

1193 5

4-20

TypeU (TBI) General Electric Bushings

J. W. Albright

1961

4-401

1959

4-401

Manufacturing Defect in a New 161-kV Type "U" Bushing J. H. Frakes Detected by Field Power-Factor Tests

-


J. A. Van Lund

1957

4-701


E. V. DeBlieux

1955

4-50


E. A. Elge

1953

4-501

Ground Sleeves Use of Ground Sleeves for Bushings

,L. W. Smith

1945

4-101

'--

72A-1973-01 Rev. B 7104


Title, Discussion

Author

Date

Section

E. L. Schlottere

1964

4-501

1963

4-201

Interchangeable Bushings

General High-Voltage Bushing Standardization (A Progress Report), High-Voltage Bushing Standardization (A Progress Report), E. L. Schlottere Purchase, Testing, Operations and Maintenance of Bushings,

H. E. Stockwell

1962

4-501

Purchasing, Testing, and Maintenance of Bushings

A. J. Devereaux

1962

4-301

1962

4-101

Bushing Maintenance and Testing, R. H. Peterson HighOVoltage Bushing Standardization (A Progress Report),

E. L. Schlottere

1961

4-601

High-Voltage Bushing Standardization (A Progress Report),

E. L. Schlottere

1959

4-501


E. L. Schlottere

1958

4-301


E. L. Schlottere

1957

4-901

High-Voltage Bushing Standardization (A Progress Report)

W. F. Dunkle

1955

4-701

High-Voltage Bushing Standardization (A Progress Report)

W. F. Dunkle

1954

4-601

Report on Bushing Standardization

W. F. Dunkle

1953

4-401

1941

11-4

Doble Committee of Standard Abbreviations for Bushing Structual Features Effect of Tentative AIEE Bushing Standards

L. Wetherill

1940

4-23

Bushing Nomenclature,

J. A. Kaup

1938

3-8

General Electric General Electric Bushings,

N. E. Dillow

1965

4-601

ASA Bushings (Transformer-BreakerInterchangeable),

G. R. Deinema

1961

4-701


,J. A. Van Lund

1959

4-701


L. Wetherill

1949

4-501


L. Wetherill

1945

4-601

1961

4-701

Lapp ASA Bushings (Transformer-Breaker Interchangeable), G. R. Deinema Lapp High-Voltage Bushings

G. L. Atkinson

1960

4-501

Lapp POC Bushings,

R. S. Lap

1957

4-501

72A-1973-01 Rev. B 7/04


Title, Discussion

Author

-

Ohio Brass ASA Bushings (Transformer-Breaker Interchangeable), Extension of Ohio Brass Class GK Oil Paper Bushings in the Lower-Voltage Applications

G. R. Deinema N. W. Richards

Extension of Low-Voltage Class GK Bushings Down to 15 N. W. Richards kV Ohio Brass Company Bushings

T. F. Brandt

Westinghouse ASA Bushings (Transformer-BreakerInterchangeable),

G. R. Deinema

A Philosophy of Bushing Design,

E. C. Wentz


J. H. Frakes

Westinghouse Bushings, 1

H. J. Linga

Lapp Bushings, Comments on Experience Lapp High-Voltage Bushings

G. L. Atkinson

Lapp POC Bushings,

R. S. Lapp

Maintenance (see Reconditioning & Repair) General Computer and Manual Card Systems for Inventory and Maintenance Schedules, S. H. Osborn, Jr. Discussion of Maintenance Practices at the 1962 Doble Conference Device for Preventing Transformer Oil Leaks to Compound Chamber of Compound Filled Bushings

W. J. Bridegam

Oil Conservators,

B. H. Dorman

Instructions for Installing Oil Reservoirs on Circuit Breaker Bushings,

J. M. Geiger

Effect of Oil and Compound Mixture on Solid and Condenser Type Bushings

,

E. L. Schlottere

zed Operation of ~ u s h i n ~ i n ~ a r b o n i Oil

,

W. W. Thompson


L. Wetherill

* General Electric

7W-1973-01Rev. B 7104


Title, Discussion

Author

Date

Section

Ohio Brass Field Testing of Oil Brass Class L and G Bushings

N. W. Richards

1963

4-801

Ohio Brass Company Bushings,

T. F. Brandt

1952

4-301


T. F. Brandt

1946

4-301

H. L. Cole J. H. Brakes

1952

4-201

Capacitance Taps Ohio Brass Company Bushings

T. F. Brandt

1949

4-601

General Ohio Brass Bushings

T. F. Brandt

1957

4-1101

Ohio Brass Bushings

T. F. Brandt

1956

4-601

Ohio Brass Bushings,

A. R. Morelli

1955

4-1301


T. F. Brandt

1952

4-301


T. F. Brandt

1947

4-501

Ohio Brass Bushings

,G. V. Smith

1945

4-801

Discussion of Ohio Brass Bushings

T. F. Brandt

1944

4-601

Notes on Ohio Brass Company Bushings

T. F. Brandt

1939

4-59

Mechanical Loading Ohio Brass Condenser Bushings

N. W. Richards

1962

4-1001

Ohio Brass Bushings,

0. L. Allanson

1954

4-501

Ohio Brass Bushings

T. F. Brandt

1951

4-801


T. F. Brandt

1950

4-801

Testing Field Testing of Ohio Brass Class L and G Bushings

N. W. Richards

1963

4-801

1956

10-F

1940

10-3

1935

2-18

Westinghouse Westinghouse Bushings, Ohio Brass Bushings

Oil Questionnaire - Inhibited Oil in Bushings E. W. Whitmer

Performance of Bushing Oils in Service, -

-

--

~ f f e c of t Oil and compoundMixture on Solid and condenser

EX~ c h l s e r e

p p

72A- 1973-01 Rev. B 7/04

'Y)


Title, Discussion

Author

Date

Section

1957

4-801

Type Bushings, Operation Current Ratings of Westinghouse Condenser Bushings for E. C. Wentz Transformers, Power Factor Versus Temperature Lapp Bushing Developments

G. L. Atkinson

1965

4-401


G. L. Atkinson

1961

4-801

Variation of Power Factor with Temperature

1958

3-101


A. L. Rickley R. E. Clark E. V. DeBlieux

1956

4-301

Comments on Westinghouse Bushings,

J. H. Rakes

956

4-501

1948

4-101

1946

3-301

Variation of Power Factor with Temperature

E. W. Whitmer R. E. O'Leary H. A. Walsh

1941

2-5

Revised Bushing Temperature Conversion Tables

H. A. Walsh

1939

4-35

Power-Factor-Temperature Characteristics of Insulation,

L. W. Smith

1936

7-3

Temperature Characteristics of Solid Type Bushings,

E. A. Walker

1936

7-3

Westinghouse Condenser Bushings,

A. C. Burr

1936

14-3

Power Factor Versus Voltage Lap Bushing Developments

G. L. Atkinson

1965

4-401

Purchasing Purchase, Testing and Maintenance of Bushings on the Union Electric System,

J. B. Finnell

1962

4-201

Purchase, Testing, Operation and Maintenance of Bushings,

H. E. Stockwell

1962

4-501

Purchasing, Testing, and Maintenance of Bushings

A. J. Devereaux

1962

4-301

1962

4-101

1962

4-401

162

4-B,C,D

Power Factor-Temperature Curves on Selected Bushings 0. E. Fawcett Heated to Elevated Temperatures (A Progress Report), Temperature Corrections for Field Power Factor Readings,

Bushing Maintenance and Testing, R. H. Peterson Bushing Procurement and Handling Practices on TVA System, Discussion of Maintenance Practices at the 1962 Doble Conference

72A-1973-01 Rev. 8 7104

M. Fischer W. W. Thompson


Title, Discussion

Author

Date

Section

Drying Ovens Purchasing, Testing, and Maintenance of Bushings

A. J. Devereaux

1962

4-301

Comments on Ovens and Drying Methods,

C. White

1943

11-201

Construction and Operation of Drying Ovens,

G. W. Early

1943

11-101

Description of New Vacuum Ovens for the Alabama Power Company,

W. H. McClure

1943

11-301

1943

11-501

1939

4-27

1950

4-201

Compounds for Repairing Bushings Selected by Critical E. W. Whitmer Study,

1944

4-101

Rebuilding and Reconditioning of Insulation

F. S. Oliver

1942

4-101

Reconditioning Bushings During 1940 (A Progress Report),

1941

4-13

Insulation Reconditioning,

C. F. von Herrmann, Jr. E. L. Schlottere

1937

8-3

Application of Oil Conservator to Bushings,

B. H. Dorman

1936

8-3

Recent Experience with General Electric 161-kV Type F Bushings

C. A. Duke

1956

4-401


L. Wetherill

1951

4-501

Bushing Practices and Policies of the Connecticut Light and A. E. Davidson Power Company,

1962

4-601


L. Wetherill

1951

4-501

Converting Bushings to Permit Ungrounded-Specimen Tests,

M. E. Willis

1951

4-401

Purchase, Testing, Operation and Maintenance of Bushings,

H. E. Stockwell

1962

4-501

Bushing Practices and Policies of the Connecticut Light and Power Company,

A. E. Davidson

1962

4-601

Reconditioning and Repairing (see Maintenance)

Discussion on Drying Ovens Apparatus Reconditioning,

C. B. Wisbon

General Maintenance Methods and Equipment Used for Repairing J. C. McCoy Transformer Oil Circuit Breaker Bushings,

General Electric Bushings Twe F

Twe L

Tvpe OF

72A-1973-01 Rev. B 7/04


I

( Title, Discussion

I

Author

I

Date

I

Section


L. Wetherill

1951

4-501


L. Wetherill

1947

4-601

Experiences in Re-Assembling General Electric Company, A. Sears 132-kV Type OF High-Voltage Bushings,

1945

4-401

Bushing Replacement Index GE T-906

L. Wetherill

1941

4-25


L. Wetherill

1938

3-23


L. Wetherill

1951

4-501

Converting Bushings to Permit Ungrounded-Specimen Tests

M. E. Willis

1951

4-401


L. Wetherill

1946

4-101

Bushing Reconditioning

E. LSchlottere

1944

4-701

Experience with Compounds for Filling Bushings

,A. Sears

1944

4-201

Field Testing Experiences - 1942,

V. W. Brust

1943

5-401

Apparatus Reconditioning,

C. B. Wisbon

139

4-27

Reconditioning Type SI Bushings (A Blackborad Talk),

E. L. Schlottere

1939

4-25

Reconditioning of Bushings

,R. A. Anderson

1935

4-2

Statistics Reconditioning Bushings (A Progress Report),

T. A. Wolfe

1955

4-1001

Preventive Bushing Maintenance Earns Dividends

W. F. Dunkle

1948

4-301

Westinghouse Bushings Apparatus Reconditioning

C. B. Wisbon

1939

4-27

Tpme S

]

Records Computer and Manual Card Systems for inventory and Maintenance Schedules,.

I

I S. H. Osborn, Jr I

Bushing Maintenance and Testing

I R. H. Peterson I A. R. Conde I

Spare Bushing Problems for Power Apparatus

1 1 1963

I

I

I

I

(

I

Solder-Seal Bushings Maintenance of Solder-Seal Bushings

'--

72A-1973-01 Rev. B 7/04

J. A. Kaup

I

I W. C. Whitfield

2-201

1

1 1962 1 4-101 ( 1950 1 4-301

Committee Report on Standard Abbreviations for Bushing Structural Features Bushing Nomenclature,

I

I

1940

4-21

1938

3-8

I

I [

1959

[

I 4-601

(


Date

Section

1955

4-901

1953

4-301

Improper Bushing Adapter Design Causes Transformer G. R. Deinema Failure

1952

6-201

Control of Corona in Porcelain Bushings (Supplementary G. R. Deinema Information)

1951

4-201

Title, Discussion

Author

Solid-Porcelain Bushings Failure of Cemented Porcelain Bushings on 12-kV Draw-Out L. A. Bateman Type Circuit Breakers J. W. Breed

T. A. Wolfe

Bushing Problems,


L. Wetherill

1951

4-501


H. L. Cole

1951

4-701

Allis-Chalmers "Positive Seal" Transformer Bushings

P. S. Castner

1950

4-501

Effect of Corona on Metals

1950

2-501

Control of Corona in Porcelain Tubes

J. C. Parker R. D. Barrett G. R. Deinema

1948

4-201

Conducting Paint on the Inside Surface of Porcelain Bushings

J. H. Merriman

1945

4-301

Bushing Reconditioning

E. L. Schlottere

1944

4-701

Spares Purchase, Testing and Maintenance of Bushings on the Union Electric System,

J. B. Finnell

1962

4-201

1962

4-301

Bushing Practices and Policies of the Connecticut Light and Power Company

A. E. Davidson

1962

4-601

Spare Bushings

H. A. Walsh

1936

3-19

1957

2-1101

Standardization (see Interchangeability) Station Apparatus - Developments Specifications, Testing

in

Insulation P. L. Bellaschi

Storage and Handling Purchase, Testing Operation and Maintenance of Bushings,

H.E. Stockwell

1962

4-501

Purchasing, Testing and Maintenance of Bushings

A. J. Devereaux

1962

4-301

Bushing Maintenance and Testing,

R. H. Peterson

1962

4-101

1962

4-401

Bushing Procurement and Handling Practices on TVA M. Fischer W. W. Thompson Systems,

72A-197341 Rev. I3 7/04


Title, Discussion

Author

Date

Section

Surface Contamination Removing Surface Moisture from Bushing Porcelain

W. J. Bridegam

1957

4-301

Controlling Surface Leakage During Bushing Tests

E. H. Povey

1952

3-301

W. B. Landers Accessory for Hot-Collar Testing During Unfavorable W. J. Bridegam Weather Conditions

1952

3-101

Multiple Hot-Collar Testing of Outdoor Bushings

W. J. Bridegam

1950

4-701

Mitigating Surface Leakage During Tests on Bushings

H. A. Walsh

1948

4-401

Hot-Collar Tests on Bushings in Humid Weather

R. C. Bacon H.A. Cornelius

1947

4-201

Review of the Collar Test Technique

H. A. Walsh

1946

3-301

W. J. Bridegam

1939

4-41

Corona Progress on Corona Detection Tests of High-Voltage C. A. Duke Bushings on the Tennessee Valley Authority System

1960

4-101

E. H. Povey

1964

3-101

Corona Detection in Transformer Bushings and R.H. Peterson 0 . W. Green

1963

4-101

Progress on Corona Detection Tests of High-Voltage Bushing C. A. Duke on Tennessee Valley Authority System

1960

4-101

Corona Measurement by the RIV Method

1958

3-201

1949

3-301

Test Data

Collar Hot Collar Tests on Oil Filled Bushings,

Corona Pulses and their Measurement,

E. H. Povey

Corona Characteristics of Dry-Type Apparatus (Survey of the P. L. Bellaschi Problem) Leakage Current Testing and Maintenance of Bushings

C. M. McCoy

1962

4-701

Porcelain Porosity Determination of Porcelain Porosity

J. C. Parker

1953

4-101

Power Factor Field Testing of EHV Apparatus Insulation

A. L. Rickley

1965

2-101

A. L. Rickley R. E. Clark

1960

3-201

1960

1A-301

Application and Significance of Ungrounded-Specimen Tests Doble Activity in Insulation Testing, E. H. Povey

-

72A-1973-01 Rev. I3 7/04


Title, Discussion

Author

Date

Section

Latest Developments in Testing Bushings Equipped with Special Test Electrodes,

E. H. Povey

1949

3-101

J

Tap Voltage Bushing Tap-Voltage Measurements with Voltmeter,

a Hotstick L. E. Humbard

UST Helpful Hints in the Testing of Certain Capacitance Tapped W. J. Bridegam Bushings by Use of the Ungrounded specimen Circuit

I

Testing and Maintenance

Cold Collar Review of the Collar Test Technique

H. A. Walsh

1946

3-301

Compound Bushings Experience with Westinghouse Type N Bushings

V. W. Brust

1957

4-201

1963

4-101

Early Detection of Corona in Substation Bushings

0. W. Gruen R. H. Peterson J. 0 . Lang

1963

4-401

Radio-Influence-Voltage Tests in the Presence of Interference

E. H. Povey

1963

3-101

1963

3-101

1959

1 4-801

1959

4-101

Corona Corona Detection in Transformer Bushings

Progress on Corona Detection Tests in the Presence of H. Povey Interference, I

Effects of Ionization in Condenser Bushings,

I R. E. O'Leary

RIV Tests on 69-kV Type L Bushings, RIV Tests on Type L and LC Bushings,

1

A. C. Wilson C. M. McCoy I

Corona Measurements by the RIV Method

I

I E. H. Povey

I

1959 I

(

4-701 I

1958

( 3-201

Audible Noises Emanating from 115-kV Type F Bushings,

P. A. Sternrnler

1957

4-101

Corona Testing of Bushings (A Progress Report)

E. H. Povey

1955

4-1101


E. V. DeBlieux

1955

4-501


F. S. Oliver

1954

4-401

Effect of Corona and Ionization on the Maintenance of L. W. Smith Electrical Apparatus,

1951

2-201

Effect of Corona on Metals,

1950

2-501

1949

3-301

J. C. Parker R. D. Barrett Corona Characteristics of Dry-Type Apparatus (Survey of the P. L. Bellaschi


Author

Date

Section

Control of Corona in Porcelain Tubes,

G. R. Deinema

1948

4-201

Conducting Paint on the Inside Surface of Porcelain Bushings,

J. H. Merriman

1945

4-301

Factory Federal Pacific Electric High-Voltage Apparatus Bushings,

M. G. Mathers

1962

4-801

Developments in High-Voltage Bushings

G. L. Atkinson

1962

4-901

Trends in Specifications and Factory Tests for Station P. L. Bellaschi Apparatus

1956

2-101

Title, Discussion Problem)

Effect of Tentative AIEE Bushing Standards

L. Wetherill

1940

4-23

Field Federal Pacific Electric High-Voltage Apparatus Bushings,

M. G. Mathers

1962

4-801

1934

29

Interchange of Field Experience General Purchase, Testing and Maintenance of Bushings on he Union Electric System,

J. B. Finnell

1962

4-201

Purchase, Testing, Operation and Maintenance of Bushings

H. E. Stockwell

1962

4-501


H. E. Stockwell

1962

4-501


A. J. Devereaux

1962

4-301

Testing and Maintenance of Bushings,

C. M. McCoy

1962

4-701

Bushing Maintenance and Testing

R. H. Peterson

1962

4-101

Bushing Procurement and Handling practices on TVA System

M. Fischer W. W. Thompson A. E. Davidson

1962

4-401

1962

4-601

Safety Practice Applied to Capacitance Taps, G. W. Early and

W. J. Bridegam

1958

4-201

Detection of Distributed and Localized Deterioration in Electrical Apparatus Insulation

L. W. Smith

1958

2-901

Maintenance L. W. Smith

1954

4-301

Bushing Practices and Policies of the Connecticut Light and Power Company

Planning on Program,

Electrical

Power-Apparatus

Preventive Bushing Maintenance Earns Dividends

W. F. Dunkle

1948

4-301

Insulation Testing of the Subsidiary Companies of the American Gas and Electric Company

F. D. Brook

1935

2-1

-

72A-1973-01Rev. B 7/04

131


Title, Discussion

Author

Date

Section

General Electric Recent Experience with General Electric 161-kV Type F Bushings

C. A. Duke

1956

4-401

Minimizing Moisture Hazards in Oil Circuit Breaker Bushings M. A. Sareault

1956

4-101

Field Power-Factor Tests Point Out Design Fault in New 14.4- J. A. Mahan kV Bushings

1955

4-301

Bushing Problems,

T. A. Wolfe

1953

4-301

Hot Collar Removing Surface Moisture from Bushing Porcelain

W. J. Bridegam

1957

4-301

E. H. Povey W. B. Landers Accessory for Hot-Collar Testing During Unfavorable W. J. Bridegam Weather Conditions

1952

3-301

1952

3-101

Multiple Hot-Collar Testing of Outdoor Bushings

W. J. Bridegam

1950

4-701

Mitigating Surface Leakage During Tests on Bushings

1948

4-401

Hot-Collar Tests on Bushings in Humid Weather,

H. A. Walsh R. C. Bacon H. A. Cornelius

1947

4-201

Review of the Collar Test Technique

H. A. Walsh

1940

3-301

Testing Transformer Bushing

H. A. Walsh

1940

4-3

Hot Collar Tests on Oil Filled Bushings

W. J. Bridegam

1939

4-41

Hot and Cold Collar Tests

H. A. Walsh

1938

3-7

Power Factor Testing of Bushings - Hot Collar Tests

F. Brook

1938

3-3

1937

3-3

Controlling Surface Leakage During Bushing Tests

New Test for Solid Type Insulation, Compound Embedded H. A. Walsh Bushings - Cold Collar and Hot Collar Tests Hot Collar Bushing Tests

J. H. Merriman

1937

1-17

In Service Testing Bushings in Service

E. H. Povey

1957

3-101

1965

4-501

1963

2-301

1961

4-101

Power Factor Solid-Porcelain Bushings Used in Low-Voltage Oil Circuit W. Lajousky Breakers (Comments on Experience) Field Experience Equipment

with

Extra-High-Voltage

(345-kV) J. E. Beehler R. A. Byron

General Electric Bushings (Effect of Leakage Currents on D. L. Johnston UST Power Factor and Capacitance Tap Voltage)

72A-1973-01 Rev. B 7104


Title, Discussion

Author

Date

Section

Tap-Insulation Tests on Bushings

A. L. Rickley R. E. Clark A. L. Rickley R. E. Clark E. H. Povey

1961

4-501

1960

3-201

Application and Significance of Ungrounded-Specimen Tests Doble Activity in Insulation Testing

Bushing Tests by the Ungrounded-Specimen Test Method E. H. Povey (Supplementary Remarks) I

Ohio Brass Bushings

(

Problems in Testing 330,000-Volt Equipment Westinghouse Transformer Bushings

I General Electric Bushings 1 Ohio Brass Bushings

I Transformer Bushing Testing

IA-301

1956

4-201

I E. H. Povey V. W. Bmst J. H. Campbell H. L.Cole

I L. Wetherill / T. F. Brandt I T. A. Wolfe

1 1954

/ 4-501 1 3-101

1954

2-201

1951

4-701

(

1954

I

I

1 1949 1 4-501 / 1 1949 1 4-601 1 1 1949 / 4-201 1

Latest Developments in Testing Bushings Equipped with E. H. Povey Special Test Electrodes

1949

3-101

E. H. Povey

1948

3-101

1947

4-101

Testing Bushings Equipped with Special Test Electrodes

Bushing Troubles Caused by conditions Above the Oil Level ,E. W. Whitmer in Apparatus Testing Bushing Capacitance Tap Outlet Cables

J. H. Merriman

1945

4-201

Discussion of Ohio Brass Bushings

T. F. Brandt

1944

4-601

Experience with Compounds for Filling Bushings,

A. Sears

1944

4-201

Operating Experience with Rebuilt and Regasketed Bushings

F. D. Brook

1941

4-3

Testing Transformer Bushings

H. A. Walsh

1940

4-3

Hot Collar Tests on Oil Filled Bushings,

W. J. Bridgegam

1939

4-41

General Electric Bushing Developments During 1936

L. Wetherill

1937

12-3

Temperature Characteristics of Solid Type Bushings,

E. A. Walker

1936

7-10

Spare Bushings

H. A. Walsh

1936

3-19

Testing of Transformer Bushings

0. E. Fawcet

1936

4-23

Effect of Oil and Compound Mixture on Solid and Condenser E. L. Schlottere Type Bushings,

1935

2-18

Insulation Testing of the Subsidiary Companies of the F. D. Brook American Gas and Electric Company

1935

2-1

1935

1-3

Power Transformer Bushing Testing

7%-1973-01 Rev. B 7/04

G. H. Browning

1

I

I

O.L. Allanson

I

Bushing Tests by the Ungrounded-Specimen Test Method

1 1 1960


Title, Discussion

Author

Date

Section

Further Points on Transformer-Bushing Tests

E. H. Povey

1935

3-2

UST Converting Bushings to Permit Ungrounded-Specimen Tests

M. E. Willis

1951

4-401

Transformer Bushing Tests Utilizing Insulation Provided by Mounting-Flange Gaskets

A. H. Ensor J. H. Bailey

1951

4-301

Helpful Hints in the Testing of Certain Capacitance Tapped Bushings by Use of the Ungrounded Specimen Circuit,

W. J. Bridegam

1949

4-101

J. B. Finnell

1957

4-601

E. W. Whitmer

1947

4-101

1954

3-101

Westinghouse Ungrounded-Specimen Tests on a Westinghouse 138-kV Type 0 Bushing, Transformer Bushings

General Bushing Troubles Caused by Conditions Above the Oil Level in Apparatus Power Factor Bushing Tests by the Ungrounded-Specimen Test Method E. H. Povey Transformer Bushing Testing

T. A. Wolfe

1949

4-201

Westinghouse Current Ratings of Westinghouse Condenser Bushings for Transformers,

E. C. Wentz

1957

4-801


H. L. Cole

1949

4-301

Notes on Westinghouse Transformer Bushings

H. L. Cole

1948

4-501


H. L. Cole

1947

4-301

V. S. McFarlin H. A. Vasil

1959

8-301

Capacitance Taps Comments on Westinghouse Bushings

J. H. Frakes

1956

4-501

Experience with 110-kV Condenser Bushings,

J. R. Bracewell

1956

4-501


J. H. Frakes

1954

4-301

Wall Bushings Corona on Cable in Wall Bushings Westinghouse

72A-1973-01 Rev. B 7104


Title, Discussion

Author

Date

Section


J. H. Frakes

1951

4-601

Westinghouse Bushings,

H. J. Lingal

1946

4-201

Comments on Experience Difficulties Experienced with Power Factor Test Taps

J. M. Upperman

1963

4-301

Effects of Ionization in Condenser Bushings

R. E. O'Leary

1959

4-801

Failure of a 161-kV Bushing, M. Fischer and

W. W. Thompson

1958

4-501

Westinghouse Condenser Bushings

C. F.Sonnenberg

1958

4-601

Experience with Westinghouse Type N Bushings

V. W. Brust

1957

4-201

Ungrounded-Specimen Tests on a Westinghouse 138-kV Type J. B. Finnell 0 Bushing,

1957

4-601

Experience with 110-kV Condenser Bushings

J. R. Bracewell

1955

4-201

Westinghouse Bushings, H. L. Cole and

J. H. Frakes

1952

4-201


H. L. Cole

1947

4-301


H. J. Lingal

1947

4-401


H. J. Lingal

1945

4-701

Experience with Compounds for Filling Bushings

A. Sears

1944

4-201


H. J. Lingal

1942

4-201


G. A. Burr

1937

10-3

Power-Factor Taps Westinghouse Circuit Breaker Bushings

J. H. Frakes

1955

4-1201


E. C. Wentz

1954

4-201

Power-Factor Tests Westinghouse Bushings

E. C. Wentz

1954

4-201


J. H. Frakes

1951

4-601

72A-1973-01 Rev. I3 7/04

DOBLE High Voltage Bushings

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