Ieee Switchgear

IEEE Guide for Switchgear—Unit Substation—Requirements

IEEE Power and Energy Society

Sponsored by the Switchgear Committee

IEEE 3 Park Avenue New York, NY 10016-5997 USA

IEEE Std C37.121™-2012 (Revision of IEEE Std C37.121-1989)

22 February 2013

Authorized licensed use limited to: University of Missouri-Kansas City. Downloaded on October 08,2015 at 19:06:07 UTC from IEEE Xplore. Restrictions apply.


IEEE Std C37.121™-2012 (Revision of IEEE Std C37.121-1989)

IEEE Guide for Switchgear—Unit Substation—Requirements Sponsor

Switchgear Committee of the

IEEE Power and Energy Society

Approved 5 December 2012

IEEE-SA Standards Board Approved 28 October 2014

American National Standards Institute


Abstract: The basis for the coordination of equipment in unit substations by assisting in the selection of components is intended as the use of this guide. A variety of designs for unit substations are possible using various combinations of incoming sections, transformer sections, outgoing sections, and transition sections. It is intended that the incoming, outgoing, transformer, and transition sections included in a unit substation meet the basic requirements of applicable industry standards for those sections. This guide covers three-phase unit substations for stepdown operation in the range of 112.5 kVA or greater at primary voltages of 601 V through 38 kV. Keywords: control, dead-front switchboard, distribution, fuse, IEEE C37.121™, metal-clad switchgear, metal-enclosed switchgear, metering, mobile unit substation, molded-case circuit breaker, motor control center, power circuit breaker, primary unit substation, radial substation, rectifier-type substation, secondary selective substation, secondary unit substation, spot-network substation, substation, surge protection, switchgear, transformer, transition section, unit substation

x

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Introduction This introduction is not part of IEEE Std C37.121-2012, IEEE Guide for Switchgear—Unit Substation—Requirements.

C37.121-1989 was originally developed by a working group sponsored by the Power Switchgear Assemblies Technical Committee of the Switchgear Section (8SG) of the National Electrical Manufacturers Association (NEMA/SG/5). The document was transferred from NEMA to the IEEE Power and Energy Society Switchgear Committee, Switchgear Assemblies Subcommittee, in January of 2003. IEEE Std C37.121 was reaffirmed by the IEEE Standards Association Standards Board in 2006. The Switchgear Assemblies Subcommittee Task Force, created to review this document, determined that this document did not meet the intent of a standard as it references applicable IEEE Standards for all requirements that must be met by each component of a Unit Substation. Based on this review, the Task Force recommended that this document be changed from a Standard to a Guide. The recommendation was accepted by the Switchgear Assemblies Subcommittee. In the revision of this document from a standard to a guide, the document has been revised to reflect needed technical changes and to update the reference documents to the latest revisions. Other significant changes are as follows: ⎯

Subclauses 1.1 and 1.3 of IEEE Std C37.121-1989 have been combined to form the Scope and subclauses 1.2 and 1.4 have been combined to form the Purpose of the new document.

⎯

Clause 2, Normative references, has been changed to remove dates and all informative standard references have been moved to Annex A.

⎯

Clause 3, Definitions, has been arranged in alphabetical order.

⎯

Table 1 has been redrawn and Table 2 through Table 5 have been combined into a new Table 2– Primary unit substation transformers and Table 3–Secondary unit substation transformers.

⎯

Metal-enclosed bus as described in IEEE Std C37.23 has been added to Clause 6—Incoming section, Clause 7—Outgoing section, 11.2—Unusual service conditions, and 11.5.2—Loading guides.

⎯

All of the existing referenced figures in Clause 6, Clause 7, and Clause 10 have been redrawn, and moved into their respective sections. Figures that had previously shown a fused and unfused figure have now been combined to show a figure with a fuse (when used) designation.

⎯

Clause 8, Ratings, has been updated to reflect the latest rating names and definitions.

vi Copyright © 2013 IEEE. All rights reserved.


Participants At the time this guide was submitted to the IEEE-SA Standards Board for approval, the C37.121 Working Group had the following membership: James Smith, Chair Douglas Edwards, Vice-Chair P. Barnett Paul Barnhart J. Baskins Ted Burse L. Farr M. Flack Keith Flowers S. Gohil

D. Hrncir A. Jivanani Harry Josten M. Lafond D. Lemmerman A. Livshitz D. Mazumdar S. Meiners

A. Morgan Charles Morse Ted Olsen R. Parthasarathi A. Patel P. Sullivan C. Tailor J. Toney

The following members of the individual balloting committee voted on this guide. Balloters may have voted for approval, disapproval, or abstention. William Ackerman Peter Balma Paul Barnhart Robert Beavers George Becker Steven Bezner Wallace Binder Ted Burse William Bush William Byrd Stephen Conrad Gary Donner Edgar Dullni Douglas Edwards Gary Engmann Patrick Fitzgerald Keith Flowers Frank Gerleve David Gilmer Mietek Glinkowski James Graham Randall Groves Timothy Hayden Jeffrey Helzer Gary Heuston

Scott Hietpas Andrew Jones Harry Josten John Kay Chad Kennedy Yuri Khersonsky Joseph L. Koepfinger Jim Kulchisky Saumen Kundu Chung-Yiu Lam Albert Livshitz Frank Mayle Kenneth McClenahan Gary Michel Georges Montillet Charles Morse Jerry Murphy K. R. M. Nair Dennis Neitzel Arthur Neubauer Michael S. Newman Joe Nims Ted Olsen Lorraine Padden Mirko Palazzo

Bansi Patel Christopher Petrola Iulian Profir Robert Puckett Reynaldo Ramos John Roach Michael Roberts Thomas Rozek Bartien Sayogo Gil Shultz Veselin Skendzic James Smith James Smith Jeremy Smith Jerry Smith Gary Stoedter James Swank David Tepen Wayne Timm Joe Uchiyama John Vergis Yingli Wen Kenneth White Larry Yonce Jian Yu

vii Copyright © 2013 IEEE. All rights reserved.


When the IEEE-SA Standards Board approved this guide on 5 December 2012, it had the following membership: Richard H. Hulett, Chair John Kulick, Vice Chair Robert Grow, Past Chair Konstantinos Karachalios, Secretary Satish Aggarwal Masayuki Ariyoshi Peter Balma William Bartley Ted Burse Clint Chaplin Wael Diab Jean-Philippe Faure

Alexander Gelman Paul Houzé Jim Hughes Young Kyun Kim Joseph L. Koepfinger* David J. Law Thomas Lee Hung Ling

Oleg Logvinov Ted Olsen Gary Robinson Jon Walter Rosdahl Mike Seavey Yatin Trivedi Phil Winston Yu Yuan

*Member Emeritus

Also included are the following nonvoting IEEE-SA Standards Board liaisons: Richard DeBlasio, DOE Representative Michael Janezic, NIST Representative

Catherine Berger IEEE Standards Program Manager, Document Development Erin Spiewak IEEE Program Manager, Technical Program Development

viii Copyright © 2013 IEEE. All rights reserved.


Contents 1. Overview .................................................................................................................................................... 1 1.1 Scope ................................................................................................................................................... 1 1.2 Purpose ................................................................................................................................................ 2 2. Normative references.................................................................................................................................. 2 3. Definitions .................................................................................................................................................. 4 4. Service conditions ...................................................................................................................................... 5 4.1 General ................................................................................................................................................ 5 4.2 Usual service conditions ...................................................................................................................... 5 4.3 Unusual service conditions .................................................................................................................. 6 5. Transformer section .................................................................................................................................... 6 5.1 Primary unit substation transformers ................................................................................................... 6 5.2 Secondary unit substation transformers ............................................................................................... 7 6. Incoming section ........................................................................................................................................ 7 6.1 High-voltage (or primary) bushings on the transformer cover ............................................................ 7 6.2 Primary terminal chamber on the transformer ..................................................................................... 8 6.3 Metal-enclosed bus .............................................................................................................................. 8 6.4 Metal-clad or metal-enclosed switchgear ............................................................................................ 8 6.5 Metal-enclosed interrupter switchgear ................................................................................................. 9 6.6 Cutout, fuse, or fuse link.....................................................................................................................10 7. Outgoing section........................................................................................................................................11 7.1 Metal-clad switchgear .........................................................................................................................11 7.2 Metal-enclosed interrupter switchgear ................................................................................................11 7.3 Metal-enclosed bus .............................................................................................................................11 7.4 Metal-enclosed, low-voltage, power circuit breaker switchgear ........................................................11 7.5 Molded-case, circuit-breaker, dead-front switchboards ......................................................................11 7.6 Motor control centers..........................................................................................................................12 8. Ratings .......................................................................................................................................................12 8.1 Rated power frequency .......................................................................................................................12 8.2 Rated kVA ..........................................................................................................................................12 8.3 Rated high voltage (or primary voltage) and rated low voltage (or secondary voltage) .....................12 8.4 Rated continuous current ....................................................................................................................12 8.5 Rated short-time withstand current .....................................................................................................12 8.6 Rated momentary withstand current ...................................................................................................13 8.7 Rated power frequency withstand voltages ........................................................................................13 8.8 Rated lightning impulse withstand voltage (BIL) ...............................................................................13 9. Construction ..............................................................................................................................................13 9.1 Phase and polarity arrangements ........................................................................................................13 9.2 Phase sequence ...................................................................................................................................14 9.3 Metal barriers......................................................................................................................................14 9.4 Interlocks ............................................................................................................................................14 9.5 Grounding ...........................................................................................................................................14 9.6 Nameplates .........................................................................................................................................14 9.7 Drawings – Diagrams – Instructions ..................................................................................................15 ix Copyright © 2013 IEEE. All rights reserved.


9.8 Coordination .......................................................................................................................................15 10. Typical arrangements ..............................................................................................................................16 10.1 Primary unit substations ...................................................................................................................16 10.2 Secondary unit substations ...............................................................................................................18 11. Guide for selection, application, installation and maintenance of unit substations .................................22 11.1 Application considerations ...............................................................................................................22 11.2 Unusual service conditions ...............................................................................................................22 11.3 System conditions .............................................................................................................................22 11.4 Location – transformer selection ......................................................................................................23 11.5 Load requirements ............................................................................................................................23 11.6 Miscellaneous design considerations ................................................................................................24 11.7 Installation, field-testing, operation, and maintenance .....................................................................26 Annex A (informative) Bibliography ............................................................................................................29

x Copyright © 2013 IEEE. All rights reserved.


IEEE Guide for Switchgear—Unit Substation—Requirements IMPORTANT NOTICE: IEEE Standards documents are not intended to ensure safety, health, or environmental protection, or ensure against interference with or from other devices or networks. Implementers of IEEE Standards documents are responsible for determining and complying with all appropriate safety, security, environmental, health, and interference protection practices and all applicable laws and regulations. This IEEE document is made available for use subject to important notices and legal disclaimers. These notices and disclaimers appear in all publications containing this document and may be found under the heading “Important Notice” or “Important Notices and Disclaimers Concerning IEEE Documents.” They can also be obtained on request from IEEE or viewed at http://standards.ieee.org/IPR/disclaimers.html.

1. Overview

1.1 Scope This guide covers three-phase unit substations for step-down operation in the range of 112.5 kVA or greater at primary voltages of 601 V through 38 kV. This guide does not cover the following installations: a)

Substations in which the transformer section includes load-tap-changing equipment.

b) Substations in which the transformer section is described and defined as “network,” “subway,” “vault,” or “underground” in IEEE Std C57.12.24™ [B14] and IEEE Std C57.12.40™ [B18]. c)

Substations in which the transformer section is described and defined as “pad-mounted” in ANSI C57.12.22 and IEEE Std C57.12.27™ [B16].

d) Gas-insulated substations as described in IEEE Std C37.122™ [B13]. e)

Rectifier-type substations.

f)

Mobile unit substations.

g) Installations in ships, watercraft, railway rolling stock, aircraft, or automotive vehicles. h) Installations for mines.

1 Copyright © 2013 IEEE. All rights reserved.


IEEE Std C37.121-2012 IEEE Guide for Switchgear—Unit Substation—Requirements

i)

Installations of railways for generation, transformation, transmission, or distribution of power used exclusively for operation of rolling stock, or for installations used exclusively for signaling and railway communication purposes.

j)

Installations of communication equipment that is under the exclusive control of communication utilities, located outdoors or in building spaces used exclusively for such installations.

k) Installations under the exclusive control of electric utilities for the purpose of communication, or metering; or for the generation, control, transformation, transmission, and distribution of electric energy located in buildings used exclusively by utilities for such purposes or located outdoors on property owned or leased by the utility or on public highways, streets, roads, etc; or outdoors by established rights on private property.

1.2 Purpose The guide is intended for use as the basis for the coordination of equipment in unit substations by assisting in the selection of components. A variety of designs for unit substations are possible using various combinations of incoming sections, transformer sections, outgoing sections, and transition sections. It is intended that the incoming, outgoing, transformer, and transition sections included in a unit substation shall meet the basic requirements of applicable industry standards for those sections. In addition, this guide provides suggested requirements when used as part of a unit substation.

2. Normative references The following referenced documents are indispensable for the application of this document (i.e., they must be understood and used, so each referenced document is cited in text and its relationship to this document is explained). For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments or corrigenda) applies. ANSI C37.51, American National Standard for Switchgear—Metal-Enclosed Low-Voltage AC Power Circuit Breaker Switchgear Assemblies—Conformance Test Procedures. 1 ANSI C84.1, American National Standard for Electric Power Systems and Equipment—Voltage Ratings (60 Hz). 2 ANSI/UL 845, Motor Control Centers. 3 ANSI/UL 891, Dead-Front Switchboards. IEEE Std C37.010™, IEEE Application Guide for AC High-Voltage Circuit Breakers Rated on a Symmetrical Current Basis. 4, 5 IEEE Std C37.20.1™, IEEE Standard for Metal-Enclosed Low-Voltage Power Circuit Breaker Switchgear.

1

NEMA publications are available from Global Engineering Documents, 15 Inverness Way East, Englewood, CO 80112, USA. (http://global.ihs.com). 2 ANSI publications are available from the Sales Department, American National Standards Institute, 25 West 43rd Street, 4th Floor, New York, NY 10036, USA (http://www.ansi.org ). 3 UL Standards are available from Comm-2000, 1414 Brook Drive, Downers Grove, IL 60515, USA (http://www.comm-2000.com ). 4 IEEE publications are available from the Institute of Electrical and Electronic Engineers, Service Center, 445 Hoes Lane, Piscataway, NJ 08854, USA (http://www.standards.ieee.org ). 5 The IEEE standards or products referred to in this clause are trademarks of the Institute of Electrical and Electronics Engineers, Inc.




IEEE Std C37.20.2™, IEEE Standard for Metal-Clad Switchgear. IEEE Std C37.20.3™, IEEE Standard for Metal-Enclosed Interrupter Switchgear. IEEE Std C37.23™, IEEE Standard for Metal-Enclosed Bus. IEEE Std C37.24™, IEEE Guide for Evaluating the Effect of Solar Radiation on Outdoor Metal-Enclosed Switchgear. IEEE Std C37.40™, IEEE Standard Service Conditions and Definitions for High-Voltage Fuses, Distribution Enclosed Single-Pole Air Switches, Fuse Disconnecting Switches, and Accessories. IEEE Std C57.12.00™, IEEE Standard General Requirements for Liquid-Immersed Distribution, Power, and Regulating Transformers. IEEE Std C57.12.01™, IEEE Standard General Requirements for Dry-Type Distribution and Power Transformers Including Those with Solid Cast and/or Resin Encapsulated Windings. IEEE Std C57.12.10™, IEEE Standard Requirements for Liquid-Immersed Power Transformers. IEEE Std C57.12.51™, IEEE Standard for Ventilated Dry-Type Power Transformers, 501 kVA and Larger, Three-Phase, with High-Voltage 601 V to 34 500 V; Low-Voltage 208Y/120 V to 4160 V—General Requirements. IEEE Std C57.12.52™, Standard for Sealed Dry-Type Power Transformers, 501 kVA and Larger, ThreePhase, with High-Voltage 601 to 34500 Volts, Low-Voltage 208Y/120 to 4160 Volts—General Requirements. IEEE Std C57.91™, IEEE Guide for Loading Mineral-Oil-Immersed Transformers. IEEE Std C57.94™, IEEE Recommended Practice for Installation, Application, Operation, and Maintenance of Dry-Type General Purpose Distribution and Power Transformers. IEEE Std C57.96™, IEEE Guide for Loading Dry-Type Distribution and Power Transformers. IEEE Std C57.142™, IEEE Guide to Describe the Occurrence and Mitigation of Switching Transients Induced by Transformers, Switching Device, and System Interaction. IEEE Std C62.22™, IEEE Guide for the Application of Metal-Oxide Surge Arresters for Alternating Current Systems. NEMA C37.57, Switchgear—Metal-Enclosed Interrupter Switchgear Assemblies—Conformance Testing. NEMA C37.55, Switchgear—Medium-Voltage Metal-Clad Assemblies—Conformance Test Procedures. NFPA 70, National Electrical Code® (NEC®). 6 NFPA 70B, Recommended Practices for Electrical Equipment Maintenance. UL 1562, Transformers, Distribution, Dry-Type—Over 600 Volts.

6

The NEC is published by the National Fire Protection Association, Batterymarch Park, Quincy, MA 02269, USA (http://www.nfpa.org ). Copies are also available from the Institute of Electrical and Electronics Engineers, 445 Hoes Lane, Piscataway, NJ 08854, USA (http://standards.ieee.org ).




3. Definitions For the purposes of this document, the following terms and definitions apply. The IEEE Standards Dictionary: Glossary of Terms & Definitions should be referenced for terms not defined in this clause. 7 articulated unit substation: A unit substation in which the incoming, transforming, and outgoing sections are manufactured as one or more subassemblies intended for connection in the field. barrier: A partition within the enclosure and part of the contained equipment, used for the insulation or isolation of electric circuits or electric arcs. conformance tests: Certain performance tests to demonstrate compliance with the applicable standards. The test specimen is normally subjected to all planned routine tests prior to initiation of the conformance test program. NOTE—The conformance tests may, or may not, be similar to certain design tests. Demonstration of margin (capabilities beyond the standards) is not required. 8

design tests: Tests performed to determine the adequacy of the design of a particular type, style, or model of any unit of equipment, or its component parts, to meet its assigned ratings and to operate satisfactorily under normal service conditions or under any specified conditions. Such tests may also be used to demonstrate compliance with applicable standards of the industry. NOTE 1—Design tests are performed on representative apparatus or prototypes to verify the validity of design analysis and calculation methods, and to substantiate the ratings assigned to all other apparatus of basically similar design. These tests are not intended to be performed on every design or during normal production. The applicable portion of these design tests may also be used to evaluate modifications of a previous design to assure that performance has not been adversely affected. Test data from previous similar designs may be used for current designs when appropriate. Once made, design tests need not be repeated unless the design is so changed as to modify performance. NOTE 2—Design tests are sometimes called “type tests.”

enclosure: A surrounding case or housing used to provide a degree of protection to the enclosed conductors or equipment, and to provide a degree of protection to personnel against incidentally contacting live parts. high voltage: A general term that pertains to the primary voltage, or primary-voltage side, of a transformer or of a unit substation. incoming section: Equipment that includes necessary mechanical and electrical connecting parts for coordination in a unit substation on the high-voltage (or primary) side of a transformer section. low voltage: A general term that pertains to the secondary voltage, or secondary-voltage side, of a transformer or of a unit substation. other tests: Tests, so identified in individual product standards, that may be specified by the user in addition to routine tests. (Examples: Impulse; insulation power factor; audible sound) outgoing section: Equipment that includes necessary mechanical and electrical connecting parts for coordination into a unit substation on the low-voltage (or secondary) side of a transformer section. primary unit substation: A unit substation in which the low-voltage section is rated above 1000 V.

7 8

The IEEE Standards Dictionary: Glossary of Terms & Definitions is available at http://shop.ieee.org. Notes in text, tables, and figures are given for information only and do not contain requirements needed to implement the standard.




production tests: Tests performed during production for quality control by the manufacturer(s) on every device, or on representative samples, or on parts or materials, as required to verify that the manufactured product meets the design specifications and applicable standards. NOTE 1—Certain quality assurance tests on identified critical parts of repetitive high-production devices may be performed on a planned statistical sampling basis. NOTE 2—Production tests are sometimes called “routine tests.”

secondary unit substation: A unit substation in which the low-voltage section is rated 1000 V and below. substation: An assemblage of equipment in which the incoming, transforming, and outgoing sections are manufactured as one or more subassemblies, through which electric energy in bulk is passed for the purpose of switching or modifying its characteristics. transformer section: A three-phase power transformer used for step-down operation that includes necessary mechanical and electrical connecting parts for coordination in a unit substation. transition (throat) section: A mechanical, electrical, and coordinated connection between a transformer section and an incoming section, or between a transformer section and an outgoing section, or between different types of incoming sections, or between different types of outgoing sections. A transition (throat) section may be: a)

Integral parts of two adjacent sections,

b)

An integral part of one section, or

c)

A separate section.

unit substation: A substation consisting primarily of one or more transformers that are mechanically and electrically connected to, and coordinated in design with, incoming and outgoing equipment. NOTE—For this guide, the term “unit substation” shall be limited to mean “articulated unit substation” only.

4. Service conditions

4.1 General A variety of designs for unit substations are possible using various combinations of incoming sections, transformer sections, and outgoing sections. The design of individual sections of a unit substation must be compatible with the service conditions in which they are applied.

4.2 Usual service conditions Unit substations conforming to this guide should be suitable for operation at their nameplate ratings under the following usual conditions: a)

Temperature 1)

The effect of solar radiation is negligible. (The principles stated in IEEE Std C37.24 may be used for guidance.)

2)

qC except that, when the transformer is liquidimmersed, the minimum temperature of the liquid’s uppermost layers is qC. 5 Copyright © 2013 IEEE. All rights reserved.



b)

3)

The maximum ambient air temperature is +40qC.

4)

The average ambient air temperature in any 24-hour period is not more than +30qC.

Altitude. The maximum altitude is 1000 m (3300 ft). See IEEE Std C37.20.1, IEEE Std C37.20.2, IEEE Std C37.20.3, and IEEE Std C57.12.00 or IEEE Std C57.12.01 for corrections to dielectric strength and continuous-current rating at altitudes greater than 1000 m (3300 ft).

4.3 Unusual service conditions For unit substations that are to be applied under conditions other than those in 4.2, see 11.2 for guidance.

5. Transformer section Transformer sections should meet the requirements of this guide and shall comply with the requirements of their applicable standards, including the standard kVA ratings listed in Table 1. Furthermore, the rated high voltage and rated low voltage shall be used in combination with the standard kVA ratings that are listed in Table 2 and Table 3. Primary unit substation transformers should be of the types in 5.1. Secondary unit substation transformers should be of the types in 5.2.

5.1 Primary unit substation transformers 5.1.1 Liquid-immersed without load-tap-changing These transformers shall meet the following requirements: a)

Voltage and kVA combinations as indicated in Column 1, Column 2, and Column 5 of Table 2

b)

The requirements of IEEE Std C57.12.10 and IEEE Std C57.12.36™ [B17]

5.1.2 Liquid-immersed with load-tap-changing These transformers are not covered in this guide.

5.1.3 Ventilated dry-type, including those with solid-cast or resin-encapsulated windings These transformers shall meet the following requirements: a)


b)

The requirements of IEEE Std C57.12.01 and IEEE Std C57.12.50 and the requirements for solid cast-resin units

5.1.4 Sealed dry-type These transformers shall meet the following requirements: a)


b)

The requirements of IEEE Std C57.12.01, IEEE Std C57.12.52, and UL 1562 6 Copyright © 2013 IEEE. All rights reserved.



5.2 Secondary unit substation transformers 5.2.1 Liquid-immersed without load-tap changing These transformers shall meet the following requirements: a)


b)

The requirements of IEEE Std C57.12.10 and IEEE Std C57.12.36 [B17]

5.2.2 Ventilated dry-type, including those with solid-cast or resin-encapsulated windings These transformers shall meet the following requirements: a)


b)

The requirements of IEEE Std C57.12.51

5.2.3 Sealed dry-type These transformers shall meet the following requirements: a)


b)

The requirements of IEEE Std C57.12.01 or IEEE Std C57.12.52, and UL 1562

6. Incoming section Incoming sections should meet the requirements of this guide and shall comply with the requirements of their applicable specifying standards. Incoming sections may include the components described in 6.1 to 6.6. NOTE—Figure 1 to Figure 10 are shown with the high-voltage section on the left of the figures and the low-voltage section on the right.

6.1 High-voltage (or primary) bushings on the transformer cover These bushings shall meet the thermal, mechanical, and dielectric requirements of the applicable transformer standard. A typical example is shown in Figure 1.

Figure 1 —Bushings on transformer cover 9

9

Figure 1 to Figure 10 are shown with the high-voltage section on the left of the figures and the transformer section on the right.




6.2 Primary terminal chamber on the transformer This chamber shall meet the thermal, mechanical, and dielectric requirements of the applicable transformer standard. A typical example is shown in Figure 2.

9

Figure 2 —Terminal chamber

6.3 Metal-enclosed bus Metal-enclosed bus shall meet the requirements of IEEE Std C37.23.

6.4 Metal-clad or metal-enclosed switchgear This switchgear shall meet the requirements of IEEE Std C37.20.2 and NEMA C37.55 or IEEE Std C37.20.1 and ANSI C37.51 as applicable. Typical Metal-Clad or Metal-Enclosed Switchgear examples are shown in Figure 3 through Figure 6.

Figure 3 —Metal-clad or metal-enclosed switchgear – For one incoming line

9




9

Figure 4 —Metal-clad or metal-enclosed switchgear – For two incoming lines

Figure 5 —Metal-clad or metal-enclosed switchgear – 9 For two incoming lines, selector function

Figure 6 —Metal-clad or metal-enclosed switchgear – For one incoming line, looped

9

6.5 Metal-enclosed interrupter switchgear This switchgear shall meet the requirements of IEEE Std C37.20.3 and NEMA C37.57. Typical examples are shown in Figure 7 through Figure 9.




Figure 7 —Interrupter or disconnect switches – Single circuit

Figure 8 —Interrupter or disconnect switches – Dual circuit

9, 10

9, 10

Figure 9 —Interrupter or disconnect switches – Selector circuit

9, 10

6.6 Cutout, fuse, or fuse link This equipment shall meet the applicable service requirements of the components covered in IEEE Std C37.40. A typical example is shown in Figure 10.

10

Metal-Enclosed Interrupter Switchgear, the switching devices and fuses may be non-draw-out.




Figure 10 —Interrupter cutouts – Fused or unfused

9, 10

7. Outgoing section Outgoing sections should meet the requirements of this guide and shall comply with the requirements of their applicable specifying standards. Because of the complexity of outgoing arrangements, it is not practical to present typical examples here. Outgoing sections may include the components listed in 7.1 through 7.6.

7.1 Metal-clad switchgear This switchgear shall meet the requirements of IEEE Std C37.20.2 and NEMA C37.55.

7.2 Metal-enclosed interrupter switchgear This switchgear shall meet the requirements of IEEE Std C37.20.3 and NEMA C37.57.

7.3 Metal-enclosed bus Metal-enclosed bus shall meet the requirements of IEEE Std C37.23.

7.4 Metal-enclosed, low-voltage, power circuit breaker switchgear This switchgear shall meet the requirements of IEEE Std C37.20.1 and ANSI C37.51.

7.5 Molded-case, circuit-breaker, dead-front switchboards These switchboards shall meet the requirements of ANSI/UL 891.




7.6 Motor control centers These control centers shall meet the requirements of ANSI/UL 845.

8. Ratings The rating of each section of a unit substation shall comply with the applicable standards for its components (referenced in Clause 5, Clause 6, and Clause 7) and shall be equal to or greater than the rating of the unit substation. The kVA, high-voltage, and low-voltage ratings of the transformer section shall be the basis for those ratings of the unit substation. Other sections shall be coordinated with those ratings. The unit substation shall have the ratings listed in 8.1 through 8.3.

8.1 Rated power frequency The rated power frequency of a unit substation shall be the frequency of the circuit for which it is designed.

8.2 Rated kVA The rated kVA of a unit substation shall be the maximum rated kVA of the three-phase power transformer in accordance with Table 1. The kVA rating of a double-ended unit substation shall be the total kVA of the two transformers.

8.3 Rated high voltage (or primary voltage) and rated low voltage (or secondary voltage) In combination with the rated kVA of a unit substation, the rated voltages shall be as follows: a)

For primary unit substations, as indicated in Table 2

b)

For secondary unit substations, as indicated in Table 3

8.4 Rated continuous current The rated continuous current for high-voltage and low-voltage equipment of a unit substation shall be equal to the respective high-voltage and low-voltage full-load currents of the transformer section.

8.5 Rated short-time withstand current The rated short-time withstand current of a unit substation is the rms short-circuit current that is intended to be carried for a specified period of time without causing electrical, thermal, or mechanical damage. The current shall be the rms value determined over the specified period of time. The rated short-time withstand current rating of a unit substation shall be the rated short-circuit current (carrying) rating of the high-voltage interrupting device. If no high-voltage interrupting device is present, the rated short-time withstand current rating of the unit substation shall be the through-fault current of the transformer, in terms of primary amperes. 12 Copyright © 2013 IEEE. All rights reserved.



8.6 Rated momentary withstand current The rated momentary withstand current of a unit substation is the maximum rms total current that it is required to withstand. The current is the rms value, including the dc component, at the major peak of the maximum cycle as determined from the envelope of the current wave of the maximum offset phase during a test period of at least 10 cycles. The symmetrical current is the rated short-time current and the peak current value is 2.6 times its rated short-time current at the major peak of the maximum cycle (this is also referred to as the peak withstand current). The rated momentary withstand current of a unit substation shall be the rated short circuit current withstand rating of the high-voltage interrupting device. If no high-voltage interrupting device is present, the rated momentary withstand current rating of the unit substation shall the through-fault current of the transformer, in terms of primary amperes.

8.7 Rated power frequency withstand voltages The rated power frequency withstand voltage of a unit substation is the maximum alternating-current voltage that it is intended to withstand for one minute. The alternating-current voltage shall have a crest value equal to 1.41 times the rms value, shall be as close to a sine wave as practical, and shall have a frequency not less than the rated frequency. The rated power frequency withstand voltage of the unit substation, on its high-voltage end, shall be the lesser rating of adjacent high-voltage sections. The rated power frequency withstand voltage of the unit substation, on its low-voltage end shall be the lesser rating of adjacent low-voltage sections.

8.8 Rated lightning impulse withstand voltage (BIL) The rated lightning impulse withstand voltage of the unit substation on its high-voltage end shall be the lesser rating of adjacent high-voltage sections. The rated lightning impulse withstand voltage of the unit substation on its low-voltage end shall be the lesser rating of adjacent low-voltage sections. Lightning impulse voltage ratings levels are not applicable to low-voltage equipment below 1000 V.

9. Construction The construction of all sections of a unit substation should be coordinated and the sections shall be compatible with each other.

9.1 Phase and polarity arrangements As viewed from the main switching-device side of the operating mechanism, the phase arrangement on buses and primary connections of all sections should be 1, 2, 3 counting from front to back, top to bottom, or left to right. However, the following exception should be noted. For other arrangements of unit substations, the transformer bushing phasing may be other than 1, 2, 3 counting from front to back, top to bottom, or left to




right. With these arrangements, a phase transposition shall be made at the connection to the outgoing and incoming sections so that 1, 2, 3 phasing is maintained in these sections. Panel devices should be mounted with 1, 2, 3 phasing counting from left to right and top to bottom, as viewed from the front of the panel.

9.2 Phase sequence The phase sequence on connection diagrams (see 9.7) should be such that, when considering voltages to neutral on a polyphase system with respect to the element of time, the voltage of phase 1 will reach a maximum before the voltage of phase 2, phase 2 before phase 3, and so forth, in numerical order. This sequence should be designated as “phase sequence in the order 1, 2, 3” and so forth.

9.3 Metal barriers Metal barriers should be provided to segregate the incoming section from the transformer and the outgoing sections from the transformer.

9.4 Interlocks Where transformer line currents exceed the load-interrupting capability of the incoming line-section equipment, interlocking should be provided to prevent opening the equipment on currents in excess of its rating. Such interlocking should be effected either mechanically or by a combination of mechanical and electrical devices.

9.5 Grounding The ground bus for each section of the unit substation should have a provision for connection to a station ground by suitable conductors.

9.6 Nameplates Each incoming, outgoing, and transformer section shall have a nameplate in accordance with its applicable standard. The nameplate should be mounted so as to be visible after normal installation.




9.7 Drawings – Diagrams – Instructions The drawings, diagrams, and instructions supplied with each unit substation should include, as applicable, all or a combination of the following drawings, depending on the type and complexity of the equipment: a)

General arrangement (outline) and foundation plan

b)

One-line and/or three-line diagram 11

c)

Schematic/elementary diagram11

d)

Connection/wiring diagram11

e)

Interconnection diagram11

f)

Terminal diagram

g)

Control-metering-relay panel arrangement and bills of material

h)

Instruction books containing information about receiving, handling, storage, installation, operating, and maintenance, covering all sections and all devices mounted on or within the substation

9.8 Coordination 9.8.1 Mechanical coordination and connection If the transition (throat) section is connected to a metal-enclosed bus, it should be the responsibility of the manufacturer of the bus duct to match the termination facilities provided by the manufacturers of the transformer and incoming or outgoing section, unless otherwise mutually determined by the affected manufacturers, with the approval of the purchaser. If the transition (throat) section consists of a close-coupled throat arrangement, it should be the responsibility of the transformer manufacturer to match the termination facilities provided by the manufacturers of the incoming and outgoing sections unless otherwise mutually predetermined by the affected manufacturers, with the approval of the purchaser. If the transition (throat) section is a compartment between equipment, such as low-voltage metal-enclosed switchgear, metal-clad switchgear, or metal-enclosed-interrupter switchgear, the responsibility for matching should be mutually determined by the affected manufacturers of this equipment, with the approval of the purchaser. Flexible connections should be provided for the connection between the incoming, outgoing, or transition (throat) sections and the bushings of the transformer except for exposed cover-mounted transformer bushings.

9.8.2 Secondary and control wire interconnections between sections For adjacent and close-coupled sections, wiring and necessary details should be provided, and wire should be isolated from power circuits rated over 600 volts ac, nominal. Isolation should be by grounded metal enclosures, metal barriers, metal conduit, electrical metallic tubing, or other approved means, except for short lengths of wire at, for example, instrument transformer terminals, temperature-measuring terminals, secondary devices, and fan-control equipment.

11

These diagrams are defined in IEEE Std 315™ [B9].




For remote sections, each section should be provided with terminal blocks and terminal-block details for users’ external interconnections.

10. Typical arrangements Because of the varied ratings and types of equipment, there are many possible arrangements for unit substations. These are listed in10.1 and 10.2, and illustrated in Figure 11 through Figure 23.

10.1 Primary unit substations A primary unit substation is usually one of the following types: a)

Radial (see Figure 11)

b)

Distributed-Network (see Figure 12)

c)

Spot-Network (see Figure 13)

d)

Secondary (low voltage) selective (see Figure 14)

e)

Duplex (see Figure 15)

Also see Figure 16 for typical alternate arrangements of two-transformer sections.

Figure 11 —Primary unit substation – Radial type

12

12

Figure 11 and Figure 12 are shown with the transformer section on the left of the figure and the outgoing section on the right of the figure.




12

Figure 12 —Primary unit substation – Distributed network type

Figure 13 —Primary unit substation – Spot network type

13

Figure 14 —Primary unit substation – Secondary selective type

13

13

Figure 13 to Figure 15 are shown with the transformer sections on the left and right of the figure and the outgoing section in the middle of the figure.




Figure 15 —Primary unit substation – Duplex type (breaker-and-a-half scheme)

13

Figure 16 —Primary unit substation – Transformer unit substation (alternate arrangements)

10.2 Secondary unit substations A secondary unit substation is usually one of the following types: a)

Radial (see Figure 17 and Figure 18)

b)

Distributed-Network (see Figure 19)

c)

Spot-Network (see Figure 20)

d)

Secondary (low voltage) selective (see Figure 21, Figure 22, and Figure 23)




Figure 17 —Secondary unit substation – Radial type

Figure 18 —Secondary unit substation – Radial type with reverse arrangement




Figure 19 —Secondary unit substation – Distributed network type with indoor-outdoor arrangement

Figure 20 —Secondary unit substation – Spot network type

Figure 21 —Secondary unit substation – Secondary select type




Figure 22 —Secondary unit substation – Secondary select type with common rrawout aisle arrangement

Figure 23 —Secondary unit substation – Secondary select type with indoor-outdoor arrangement




11. Guide for selection, application, installation, and maintenance of unit substations

11.1 Application considerations In applying unit substations, the following subjects may require consideration: a)

Service conditions, that is, environmental considerations

b)

System conditions, for example, voltage, frequency, and available short-circuit currents

c)

Installation conditions, for example, restricted access or exposure to the general public

d)

Load requirements, including duty cycles if applicable

11.2 Unusual service conditions a)

Significant solar radiation

b)

Ambient temperature outside the limits in 4.2

c)

Altitudes above 1000 m (3300 ft)

d)

Surrounding environment containing volatile organic compounds, moisture and dust.

e)

Exposure to abnormal vibration, natural or man-made

f)

Local conditions affecting grounding resistance

For metal-enclosed switchgear equipment (which may be used as the incoming or outgoing sections of unit substations) guidelines and requirements for responding to unusual service conditions are given in IEEE Std C37.20.1, IEEE Std C37.20.2, IEEE Std C37.20.3, and IEEE Std C37.23. Information concerning unusual service conditions for transformers is included in IEEE Std C57.12.00 and IEEE Std C57.12.01.

11.3 System conditions 11.3.1 Voltage and frequency The voltage operating ranges of a unit substation are dependant on the high-voltage and low-voltage ratings of the included transformer. When the voltage variation is greater than acceptable for the application, then the use of equipment load regulation should be considered. (The application of that equipment is not covered in this guide.)

11.3.2 Short-circuit considerations Short-circuit current values—short-time and momentary—must be calculated for the incoming and outgoing sections to permit the selection and coordination of switching and protective devices, and also to provide proper protection for the transformer. Procedures for making the calculations are included in standards such as IEEE Std C37.010 and IEEE Std 141™ [B6].




The “E/X Simplified Method,” described in IEEE Std C37.010, is usually satisfactory. Short-circuit values for common substations and conditions are given in IEEE Std 141[B6]. While interrupting ratings of protective devices are based on symmetrical current, it is only necessary when applying these devices to consider the maximum symmetrical short-circuit current, since the product standards covering testing take into account the maximum possible asymmetry. The short-time withstand current and momentary withstand current ratings of a unit substation are defined in Clause 8. In planning the unit substation, its rating should be made at least equal to the calculated available short-circuit current values. Due consideration should be given to possible future system changes that might demand increases in the calculated available values.

11.4 Location—transformer selection The physical location of the unit substation is of major importance in determining the type of transformer to be used for a particular installation.

11.4.1 Indoor and outdoor locations Less-flammable liquid-insulated transformers, nonflammable fluid-insulated transformers and sealed transformers are, in general, suitable for use both indoors and outdoors. Liquid-immersed transformers insulated with flammable liquids are normally suitable only for outdoor locations. They may be installed indoors only when located in fireproof vaults and where local codes permit. See electrical code information in NFPA 70 and NFPA 70B. Ventilated dry-type transformers are normally suitable only for indoor locations, except when mounted in a specifically designed enclosure for outdoor application.

11.4.2 Environmental conditions Environmental conditions such as dust, moisture, and fumes may be important factors in the selection of transformer types.

11.4.3 Audible sound level If the normal sound level is a factor at the location and operation of any transformer, special consideration should be given to the sound abatement in the form of barriers or low-noise transformers.

11.4.4 Grounding It is necessary to take grounding considerations into account when installing unit substations. Refer to IEEE Std 141 [B6] and IEEE Std 142™ [B7] for grounding instructions.

11.5 Load requirements The load capacity of a unit substation is determined by the kVA rating of the included transformer(s).




11.5.1 Transformer kVA rating The kVA rating of the transformer section should, at a minimum, be sufficient to handle the immediate required load. Consideration should be given to any future load growth that might be required by expanding or changing facilities. When substantial load growth is anticipated, it is usually desirable to install, initially, a single transformer substation with a main circuit breaker that can be expanded readily to a twotransformer (double-ended) substation when the additional capacity is needed. For application of demand factors and diversity factors to the total connected load, refer to IEEE Std 141 [B6] and IEEE Std 142 [B7]. Fan-cooling may be used to provide higher kVA ratings to meet load growth. For secondary-selective systems or network systems, fan-cooling is often used to provide higher ratings during periods when one or more transformers are out of service. Other requirements for the selection and rating of equipment could involve unusual loading conditions, for example, the starting of large motors, or the operation of welding equipment or sensitive loads such as computers and scientific instruments.

11.5.2 Loading guides Consult the following: a)

For liquid-immersed transformers, consult IEEE Std C57.91.

b)

For dry-type transformers, consult IEEE Std C57.96.

c)

For metal-enclosed switchgear assemblies, consult IEEE Std C37.20.1, IEEE Std C37.20.2, IEEE Std C37.20.3 and IEEE Std C37.23.

11.6 Miscellaneous design considerations 11.6.1 Incoming section In unit substation applications, it is desirable to be able to electrically isolate the transformer from the incoming circuit. An exception occurs when the transformer of the unit substation is the only load on the incoming circuit; in this case the switching device at the source of the circuit may serve to isolate the transformer electrically. However, the switching device, whether a fused switch or a relayed circuit breaker, must provide proper protection for the transformer to prevent damage from short-circuit current (short-time withstand or momentary withstand) due to abnormal secondary fault conditions.

11.6.2 Transformer section The selection of transformers for unit substations is based on such factors as location (see 11.4) and load requirements (see 11.5). Other considerations include surge protection, supplementary cooling, and maintenance requirements.

11.6.2.1 Surge protection When connected to circuits that are subject to lightning or other transients, surge protection should be considered. Surge protection should limit voltage surges to values below the impulse-withstand ratings of 24 Copyright © 2013 IEEE. All rights reserved.



the unit substation. See IEEE Std C62.22 for specific information concerning surge protection. See IEEE Std C57.142 for information on mitigation of switching transients. If the unit substation is to operate in an environment that requires a greater lightning impulse-withstand capability, surge arresters should be used to ensure that the equipment is properly protected at the required lightning impulse level.

11.6.2.2 Forced-air cooling The forced-air cooling rating of the transformer is often a factor in determining the transformer to be selected. For single-ended unit substations, the forced-air cooling rating of the transformer is based on the system total load. For double-ended unit substations, the load conditions when each transformer may have to supply the total load of the substation during an emergency or during maintenance should be considered.

11.6.2.3 Maintenance requirements For information on maintenance requirements and techniques, see the manufacturer’s literature and the following guides: a)

For liquid-immersed transformers: IEEE Std C57.93™ [B22], IEEE Std C57.104™ [B23], and IEEE Std C57.106™ [B24].

b)

For dry-type transformers: IEEE Std C57.94.

Differences in the maintenance requirements of the various types of transformer sections may be a factor in determining the type of transformer to be used for a particular application. Maintenance of liquid-immersed transformers should at least include periodic checking of the tank for pressure-tightness, and sample-testing of the liquid for dielectric strength and other characteristics. Dielectric strength can sometimes be restored by filtering. Maintenance of sealed transformers should include periodic inspections for pressure-tightness. An indication of positive pressure on the transformer pressure gauge is generally sufficient, since these units are usually sealed with positive gas-pressure. If a unit substation component, such as switchgear or dry-type transformer, is to be stored or, after installation, deenergized for a significant period of time in humid conditions, a space-heater should be provided within the housing, and left energized from a suitable power source.

11.6.3 Outgoing section

11.6.3.1 Selection of low-voltage protective devices Circuit breakers are generally recommended for circuit protection for flexibility in operation. They can be reclosed quickly where a sustained interruption of power cannot be tolerated. Current-limiting devices can be utilized where reenergizing speed is not critical, or where high interrupting capability (up to 200 000 A) is needed, or both. Their speed of operation and current-limiting action can provide protection to coordinate equipment in circuits that have high available short-circuit currents. When current-limiting devices are used, the ratings of protected equipment must be coordinated with the




maximum let-through energy and the peak let-through current of the device. Where there may be damage from single-phasing, the protective device needs to open all three phases.

11.6.3.2 Transformer main secondary fused switch or circuit breaker A transformer main secondary protective device should be used for the following reasons: a)

In case of emergency, it is quicker and simpler to deenergize the entire load by opening a transformer main secondary protective device at each substation than to open each feeder’s protective device. Conversely, in case of trouble in the primary cable or transformer, it is often desirable to disconnect the low-voltage bus from the transformers and to supply the bus from an alternate source.

b)

It provides fault-protection for the bus and backup-protection for the feeder devices. In addition, where a main secondary protective device is present, it may provide overload protection for a transformer, and less-sensitive primary protection may be used. This is particularly true for groundfault protection.

c)

Where interlocking is used, it provides for, and simplifies, key-interlocking between the primary switch and secondary switchgear.

d)

When a transformer main secondary relayed circuit breaker is used, coordination with primary protective devices is more readily obtainable.

e)

It provides flexibility. Note that a main secondary protective device is essential for several of the circuit arrangements in Figure 11 through Figure 23. A radial-type unit substation that includes a main fused switch or circuit breaker can later be expanded into one of the more elaborate circuit arrangements without extensive field modification.

11.6.3.3 Continuous-current rating of transformer secondary protective devices and connections The transformer main secondary circuit breakers, or fuse switches and connections, should have continuous-current ratings that are approximately 25 percent greater than the continuous-current rating of the transformer. This is recommended because transformers often carry short-time loads above their nameplate ratings due to short duty cycles or low-ambient temperatures. When selecting the continuous-current rating of the transformer’s main secondary protective devices and connections, consideration should also be given to whether the transformer has, or will have, a continuous supplementary-cooled rating.

11.6.4 Protective relaying See IEEE Std C37.90™ [B10] and IEEE Std C37.91™ [B11], for general guidance in the applications of protective relays for unit substations.

11.7 Installation, field-testing, operation, and maintenance The installation and field-testing of unit substations should, in general, be performed in accordance with manufacturer’s instructions (refer to NFPA 70B and IEEE Std C37.20.1, IEEE Std C37.20.2, and IEEE Std C37.20.3. Meggering is recommended when equipments have been stored in damp and dirty locations. If the megger readings are less than the manufacturer’s recommendations, a drying-out and cleaning of the




insulation system is recommended. When dielectric testing is performed, it should be conducted at the reduced values specified for field- testing in the applicable referenced standards. When various sections of the unit substation have to be assembled in the field, the connections should be made in strict accordance with the manufacturer’s drawings and instructions. Operation and maintenance instructions are also furnished by the manufacturer and should be followed. Note that additional maintenance may be required when equipment is installed in unusual service environments (see 11.2). General maintenance requirements for transformers are shown in 11.6.2.3. Table 1 —Standard three-phase transformer kVA ratings from 112.5 kVA – 10 000 kVA b

LiquidImmersed Col. 1 112.5 150 225 300 500 750 1 000 1 500 2 000 2 500 3 750 5 000 7 500 10 000

Self-Cooled (kVA) Ventilated DryType Col. 2 112.5 150 225 300 500 750 1 000 1 500 2 000 2 500 3 750 5 000 7 500 10 000

Sealed DryType Col. 3 — — — — — 750 1 000 1 500 2 000 2 500 3 750 5 000 7 500 10 000

LiquidImmersed Col. 4 — — — — — 862 1 150 1 725 2 300 3 125 4 687 6 250 9 375 12 500

Forced-Air-Cooled (kVA) Ventilated DryType Col. 5 — — — 400 667 1 000 1 333 2 000 2 667 3 333 5 000 6 667 10 000 13 333

a

c

Sealed DryType Col. 6 — — — — — — — — — — — — — —

a

Based on an average winding temperature rise, due to resistance, of: 65 °C rise for liquid-immersed transformers; 150 °C rise for dry-type transformers. (“Other” rises of 115 °C and 80 °C are also available for ventilated-dry-type transformers.)

b

For transformers rated above 2500 kVA, the forced-air-cooled rating is generally 125% for liquid immersion, and 133% for ventilated dry-types.

c

When a future forced-air-cooled rating is planned, self-cooled transformers shall be specified to have provision for future addition of equipment for fan-cooling.




Table 2 —Primary unit substation transformers Voltages (V) Rated HV

Rated LV

Col. 1 6 900 7 200

Col. 2 2 400 4 160 4 160Y/2 400 2 400 4 160 4 160Y/2 400

Ventilated DryType Col. 3 ------750–7 500 750–7 500 750–7 500

2 400 4 160 4 160Y/2 400 2 400 4 160 4 160Y/2 400

1 500–7 500 1 500–7 500 1 500–7 500 1 500–7 500 1 500–7 500 1 500–7 500

12 000 12 470 13 200 13 800 23 000

34 500

abc

Transformer type (kVA) Sealed Dry-Type Col. 4 ------750–5 000 750–5 000 750–5 000

LiquidImmersed Col.5 1 000–3 750 1 000–3 750 1 000–3 750 1 000–7 500 1 000–7 500 1 000–7 500

1 500–5 000 1 500–5 000 1 500–5 000 1 500–5 000 1 500–5 000 1 500–5 000

1 000–7 500 1 000–7 500 1 000–7 500 1 000–7 500 1 000–7 500 1 000–7 500

a

Voltages listed are as shown in ANSI C84.1. Voltages in individual transformer product standards may differ.

b

All voltages are delta unless otherwise indicated.

c

When a dash connects kVA ratings, include all intervening kVA ratings as shown in Table 1.

Table 3 —Secondary unit substation transformers Voltages (V) Rated HV

Rated LV

Col. 1 2 400

Col. 2 208Y/120 480 480/277 208Y/120 480 480/277 208Y/120 480 480/277 208Y/120 480 480/277

Ventilated DryType Col. 3 112.5–1 000 112.5–1 500 112.5–1 500 112.5–1 000 112.5–1 500 112.5–1 500 112.5–1 000 112.5–2 500 112.5–2 500 112.5–1 000 112.5–2 500 112.5–2 500

208Y/120 480 480/277 208Y/120 480 480/277

300–1 000 300–2 500 300–2 500 300–1 000 300–2 500 300–2 500

4 160 4 800 6 900 7 200 12 000 12 470 13 200 13 800 23 000

34 500

a

abc

Transformer type (kVA) Sealed Dry-Type Col. 4 750–1 000 750–1 500 750–1 500 750–1 000 750–1 500 750–1 500 750–1 000 750–2 500 750–2 500 750–1 000 750–2 500 750–2 500

LiquidImmersed Col.5 112.5–1 000 112.5–2 000 112.5–2 000 112.5–1 000 112.5–2 500 112.5–2 500 112.5–1 000 112.5–3 750 112.5–3 750 112.5–1 000 112.5–3 750 112.5–3 750

750–1 000 1000–2 500 1000–2 500 750–1 000 1 000–2 500 1 000–2 500

112.5–1 000 112.5–3 750 112.5–3 750 112.5–1 000 112.5–3 750 112.5–3 750

Voltages listed are as shown in ANSI C84.1. Voltages in individual transformer product standards may differ.

b

All voltages are delta unless otherwise indicated.

c

When a dash connects kVA ratings, include all intervening kVA ratings as shown in Table 1.




Annex A (informative) Bibliography [B1] ANSI C57.12.22, American National Standard for Pad-Mounted, Compartmental-Type, Self-Cooled, Three-Phase Distribution Transformers With High-Voltage Bushings, 2500 kVA and Smaller; High Voltage, 34 500 GrdY/19 920 Volts and Below; Low Voltage, 480 Volts and Below. [B2] ANSI C57.12.50, American National Standard Requirements for Ventilated Dry-Type Distribution Transformers, 1 to 500 kVA, Single-Phase, and 15 to 500 kVA, Three-Phase, with High-Voltage 601 to 34 500 Volts, Low-Voltage 120 to 600 Volts. [B3] ANSI C57.12.55, American National Standard for Transformers—Used in Unit Installations, Including Unit Substations—Conformance Standard. [B4] ANSI C57.12.57, American National Standard for Transformers—Ventilated Dry-Type Network Transformers 2500 kVA and Below, Three-Phase, with High-Voltage 34500 Volts and below, LowVoltage 216Y/125 and 480Y/277 Volts—Requirements. [B5] IEEE Std 4™, IEEE Standard Techniques for High-Voltage Testing. [B6] IEEE Std 141, IEEE Recommended Practice for Electric Power Distribution for Industrial Plants. [B7] IEEE Std 142, IEEE Recommended Practice for Grounding of Industrial and Commercial Power Systems. [B8] IEEE Std 241™, IEEE Recommended Practice for Electric Power Systems in Commercial Buildings. [B9] IEEE Std 315, Supplement to Graphic Symbols for Electrical and Electronics Diagrams. [B10] IEEE Std C37.90, IEEE Standard for Relays and Relay Systems Associated with Electric Power Apparatus. [B11] IEEE Std C37.91, IEEE Guide for Protecting Power Transformers. [B12] IEEE Std C37.100™, IEEE Standard Definitions for Power Switchgear. [B13] IEEE Std C37.122, IEEE Standard for High-Voltage Gas-Insulated Substations rated above 52 kV. [B14] IEEE Std C57.12.24, IEEE Standard for Submersible, Three-Phase Transformers, 3750 kVA and Smaller: High Voltage, 34 500 GrdY/19 920 Volts and Below; Low Voltage, 600 Volts and Below. [B15] IEEE Std C57.12.26™, IEEE Standard for Pad-Mounted, Compartmental-Type, Self-Cooled, ThreePhase Distribution Transformers for Use with Separable Insulated High-Voltage Connectors (34 500 GrdY/19 920 Volts and Below, 2500 kVA and Smaller). [B16] IEEE Std C57.12.27, IEEE Conformance Requirements for Liquid-Filled Distribution Transformers Used in Pad-Mounted Installations, Including Unit Substations. [B17] IEEE Std C57.12.36, IEEE Standard Requirements for Liquid-Immersed Distribution Substation Transformers. [B18] IEEE Std C57.12.40, IEEE Requirements for Secondary Network Transformers Subway and Vault Types (Liquid Immersed). [B19] IEEE Std C57.12.70™, IEEE Standard Terminal Markings and Connections for Distribution and Power Transformers. [B20] IEEE Std C57.12.80™, IEEE Standard Terminology for Power and Distribution Transformers.




[B21] IEEE Std C57.13™, IEEE Standard Requirements for Instrument Transformers. [B22] IEEE Std C57.93, IEEE Guide for Installation and Maintenance of Liquid-Immersed Power Transformers. [B23] IEEE Std C57.104, IEEE Guide for the Interpretation of Gases Generated in Oil-Immersed Transformers. [B24] IEEE Std C57.106, IEEE Guide for Acceptance and Maintenance of Insulating Oil in Equipment. [B25] IEEE Std C62.1™, Surge Arresters IEEE Standard for Gapped Silicon-Carbide Surge Arresters for AC Power Circuits. 14 [B26] NEMA ICS-2, Industrial Control and Systems Controllers, Contactors and Overload Relays Rated 600 Volts. [B27] NEMA SG2, High-Voltage Fuses.

14

IEEE Std C62.1-1989 has been withdrawn; however, copies can be obtained from Global Engineering, 15 Inverness Way East, Englewood, CO 80112-5704, USA, tel. (303) 792-2181 (http://global.ihs.com/).



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