GE Generator Inspection

GE Energy

Generator In-Situ Inspections A Critical Part o Generator Maintenance Cost Reduction GER-3954C

Authors Christopher Markman

Product Line Leader Lie Extension Services Ronald J Zawoysky

Generator Engineering Leader Power Generation Services

Contents Introduction                                                                                                                              1 In-Situ Inspection – A Critical Part o Generator Maintenance Cost Reduction                                                           2 Guidelines or Choosing In-Situ Inspection Versus Pulling the Rotor                                                                    3 In-Situ Inspection Technologies                                                                                                           3 Miniature Air Gap Inspection Crawler (MAGIC)                                                                                         6 Remote Capacitance Probe                                                                                                          8 Retaining Ring NDE Scanner                                                                                                         8 Other Testing                                                                                                                        9 MAGIC Acceptance and Experience                                                                                                       9 Industry Acceptance                                                                                                                 9 System Design                                                                                                                      9 Traditional vs In-Situ Cost Analysis                                                                                                        9 Reducing Outage Duration                                                                                                          10 Reducing Disassembly Requirements                                                                                                10 Eliminating Consequential Damage                                                                                                 10 GE’s Position on In-Situ Inspection                                                                                                        11 Conclusions                                                                                                                             11 List o Figures                                                                                                                           12 List o Tables                                                                                                                            12

GE Energy | GER-3954C (3/12)

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Introduction

• Updatingequipmentmaintenancerecommendationsbasedon

GE’s feet experience

This paper compares in-situ inspection techniques that allow testing with the rotor still installed, to rotor-out inspections While in-situ inspections provide an alternative to pulling the generator rotor,

• Developinginspectiontoolsandservicesthatacilitaterapid

ofine assessment o equipment conditions

additional electrical testing is required, at a minimum, to provide a thorough inspection Other additional tests may be indicated via a

Industry insurers also have a vested interest in these objectives and

Technical Inormation Letter (TIL) or based on past unit history

are understandably reluctant to assume greater risks by deviating rom proven maintenance practices Consequently, insurers review

As the increasingly competitive marketplace orces the power

proposed plant maintenance protocol modications with operators

generation industry to reduce operating costs, equipment

and oten require supporting recommendations and other evidence

maintenance programs are under increased scal scrutiny Plant

rom Original Equipment Manuacturers (OEMs) that new protocols

maintenance programs, based on periodic disassembly and

are unctionally equivalent or superior to the traditional

inspection o critical turbine-generator components, have proven remarkably eective—as evidenced by the industry’s consistently

This paper oers a comparison o the results, advantages and

avorable plant reliability and availability statistics However,

limitations o GE’s modied inspection protocol or generators

many plant operators are looking or ways to lower cost while

utilizing in-situ inspection tools compared to a traditional inspection

maintaining reliability

with the rotor removed

As a leading manuacturer o turbine-generators and a major supplier o power generation services, GE is assisting operators in this objective by: • Developingimprovedmonitoringanddiagnosticinstrumentation

or online predictive maintenance, allowing or better outage planning and scope control


1

In-Situ Inspection – A Critical Part of Generator Maintenance Cost Reduction Visual and quantitative inspection techniques play an important role in assessing generator condition Online monitoring and diagnostic techniques are limited in detecting potential problems such as bar movement and vibration, component damage, copper dusting, coil distortion, and oreign object damage (FOD) Since many o these conditions can lead to a major equipment ailure i let unresolved or a period o time, periodic visual inspections are

During minor outages, in-situ inspections can be used to assess generator condition and help plan generator maintenance at uture outages The inspection results can indicate i the eld will need to be pulled and which components will require maintenance during current or uture outages I the generator condition is acceptable, the eld can remain in place and a uture in-situ inspection can be planned GE’s in-situ inspection techniques can also be used with traditional inspection and test techniques to provide a complete “major” inspection without eld removal

needed to supplement online monitoring and diagnostics I n-situ inspection oers an economical alternative to the traditional rotor

GE’s recommended standard tests or a major outage are described

pull inspection Table 1 lists typical generator-related inspections

in Technical Inormation Letter-1154 and GEK-103566 When

and when they occur in a traditional maintenance plan

generator problems are known or suspected to exist, applying

Continuous Online

Periodic Online

Minor Outage

Major Outage

STATOR

Stator Wedge Tightness

X

Bar Movement

X

Stator Winding Leaks

SLMS

X

Core Insulation Stator Winding Insulation Integrity

X X

ePDA

PD

X

Greasing

X X

Cracked Connections/Integrity

X

X

Oil Contamination

X

X

HV Connection Bolts

X

X

FIELD

Blocked Vent Ducts

X

RR NDT

X

Field Coil Distortion

X

X

Field Coil Loose Blocks

X

X

Field Wedge Migration Field Winding Insulation Integrity

X STMS

Thermal Sensitivity

X

X

X

X

Rotor Surace Heating

X

Table 1 Generator inspection items STMS: Shorted Turn Monitoring System – continuously monitors a fux probe and sends an alarm when a shorted turn is detected ePDA: Enhanced Partial Discharge Analysis – continuously monitors the generator and takes partial discharge data at specied intervals or later analysis PD:

Traditional Partial Discharge Testing where data is taken by a technician

SLMS: Stator Leakage Monitoring System – continuously monitors stator cooling water or the presence o hydrogen indicating a leak


2

periodic in-situ inspections can postpose the need or eld removal until a more convenient time When abnormal operation such

In-Situ Inspection Technologies

as a negative sequence event warrants a “suitability or service”

GE’s in-situ generator inspection capabilities (listed below) were

inspection beore the generator can be returned to service, the

developed to address areas requiring eld removal or inspection

in-situ inspection is a valuable tool or providing a quick, accurate,

(Figure 1)

documented inspection with minimal generator disassembly In-situ inspection reduces overall outage duration while gathering highquality condition assessment data

• GE’sproprietaryMiniatureAirGapInspectionCrawler(MAGIC)system

− MAGIC Visual Inspection − Stator Wedge Tightness Assessment

Guidelines for Choosing In-Situ Inspection Versus Pulling the Rotor

− Electromagnetic Core Imperection Detection (EL CID) − Borescope Inspection

One question requently asked is “What i the in-situ inspection nds something and I have to pull my eld? I wasted time and money on the in-situ inspection” The answer to this question can

• RemoteCapacitanceProbe • RetainingRingNon-DestructiveEvaluation(NDE)Scanner

be ound in previous inspection reports and the operating history o the unit I there is any indication that the rotor needs signicant repair (such as multiple shorted turns, a eld ground or thermal

• Othertestsandinspections,includingelectricaltestingand

hydraulic testing

sensitivity), then the rotor should be pulled Similar judgements should be made regarding the stator However, i the unit has had

The in-situ inspection consists o the basic MAGIC visual inspection

no known problems and previous inspections have not indicated

as well as one or more additional tests or inspections based on the

any issues, then an in-situ inspection is appropriate GE experience

circumstances and customer needs Table 2 lists critical generator

reveals that 1 percent o in-situ inspections uncover an issue which

components and the in-situ inspection techniques used or each

requires that the rotor to be pulled In many cases, conditions requiring repair are ound early enough to allow the repair to be postponed until the next planned outage Conditions ound by in-situ inspections that required the rotor to be pulled or repairs include oreign object damage, damage rom negative sequence

Note: While a borescope inspection is a normal part o a MAGIC

inspection, it may also be perormed independently This is typically done when a ast assessment o the generator, especially the end regions, is desired ater an event outside o normal operation

events, ailure o electrical testing indicating the need or rotor rewind, and loose wedges These conditions are listed in order o highest to least prevalence Since GE’s goal is to ensure the generator runs trouble-ree to the next outage, any signicant problem will bring a recommendation to pull the rotor and complete the necessary repairs For maximum benet, the in-situ inspection should be planned as early as possible during the outage so that any necessary repairs can be carried out during the planned outage, or at worst, the inspection will cause the minimum delay to restart 


3

Stator Wedge Tightness Assessment MAGIC Visual •CoreLaminations •SpaceBlocks •StatorBars,Wedges •FieldSurace,Wedges •RetainingRingNose

Electromagnetic Core Imperection Detection (ELCID) Stator Insulation Capacitance Measurement

Stator Clearance Measurement

Remote Access Cameras •FieldCoilEndturns •ConnectionRings •StatorBars •EndWindingsupportSystem •FluxShield •LowerFrameExtension

Retaining Rings •OutsideSurace

Eddy Current •InnerSurace Ultrasonic

Figure 1 Generator in-situ inspection capabilities


4

Component

Common Problems

MAGIC Visual

Borescope Visual

Wedge Tapping

ELCID

RR NDE

Capacitance

Clearance Meas

Stator/Core

Core Laminations

Foreign object damage, hot spots, evidence o movement

X

Space Blocks

Migration, cooling passage blockage

X

X

Gas Gap Bafe Studs

Cracked welds, looseness

X

X

Stator Wedges

Looseness, loss, sparking damage

X

Stator Bars

Foreign object damage, sparking, girth cracks, movement

X

X

X

X

X

Wet groundwall insulation

X

End Windings and Connection Rings

Bar movement, loose/broken ties, supports, etc, excessive corona activity

X

Copper Flux Shield

Overheating, looseness, general condition

X

Instrumentation

RTD, thermocouple wiring ties, fux probe, general condition

X

Field

Field Surace

Heating, arcing, oreign object damage

X

Body Weights

Looseness, staking

X

Field Wedges

Arcing, migration, cracking

X

X

Retaining Ring

Wedge contact , arcing, oreign object damage, material cracks, pitting

X

X

Coil End Turns

Blocked ventilation, damaged insulation, coil distortion, contamination

X

X

General

All

Lower Frame Ext Bus Leads and Connections

Excessive oil or other contamination, oreign object damage, blocked cooling Insulation condition, connection integrity (i exposed), high voltage bushing condition

X

X

X

Table 2 In-Situ Inspection capabilities


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Miniature Air Gap Inspection Crawler (MAGIC) The cornerstone o the MAGIC system is its visual inspection capability In addition, the system can perorm a stator wedge tightness assessment and ELCID testing

Stator Wedge Tightness Assessment – This test examines the

slot support system or any signs that the stator bars are ree to move A “tight” stator winding can last two or three times as long as a winding that is not rmly held in the stator core The test perormed by the MAGIC system is similar to the test used in the actory or new units

MAGIC Visual Inspection – Trained specialists can use GE’s exclusive MAGIC robotic devises to perorm a visual inspection o the generator stator and eld within the bore region GE now oers three dierent MAGIC robots that allow the inspection o generators in a variety o sizes

One component o this assessment is the wedge tightness or wedge tapping test that examines the tightness o the stator slot wedges The standard method used to determine when a stator rewedge is required is to perorm this test on the most critical wedges (the last 36 inches o each end o the generator) and then

Each crawler robot is a precision device that carries two high-

visually inspect the remaining wedges in the center o the core

resolution video cameras through the gap between the stator

When the rotor is removed, the tapping test can be perormed

core and eld Full inspection coverage o the core inner diameter

manually using a 2-inch hammer or a piece o equipment that

(ID) and eld surace is made possible by the crawler’s axial and

can mechanically evaluate wedge tightness During a MAGIC

transverse motion capability This capability also allows the crawler

inspection, a specialized test head is used to perorm a wedge

to navigate around the gas bafes p resent on many generator

tightness map o the critical areas The remaining wedges can

designs High-resolution video provides the specialist with a clear

then be visually inspected or any indications o looseness (such as

view o the stator core laminations, stator wedges, eld wedges a nd

dusting created by the wedge rattling in the dovetail)

surace on the inboard ends o the retaining rings Figure 2 shows some core damage captured using the wide angle and close-up cameras on the MAGIC robot

The MAGIC system determines wedge tightness by measuring the response o the wedge to a mechanical stimulus (impact) Inspection data is stored in a le and provided with the nal report that evaluates the winding condition to determine when repairs are needed The data is also used to generate a color-coded “wedge tightness map” that clearly shows the wedge tightness within the generator (Figure 3) Some generator designs limit access to all wedges and permit only a pa rtial inspection The most critical wedges, located closest to the slot ends, are inspected in all cases Note: The tapping test does not apply to units with asphalt stator

windings or the camelback wedge system For these units only a visual wedge assessment is perormed

Figure 2 View o core damage taken with MAGIC robot


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Core Lamination Insulation Core Laminations

Damaged Insulation

Core Vent Duct Stator Winding

Stator Core

Circulating Current

Figure 3 Generator Wedge Tightness

Figure 4 Circulating current due to damaged core insulation

Electromagnetic Core Imperfection Detection (EL CID*) Testing – One

Borescope Inspection – Our in-situ inspections also use the latest

o the optional tests that GE perorms during generator testing is

borescope technology to provide a high-resolution visual inspection

the ELCID test This test oers an accurate and economical way

o normally inaccessible areas on the generator, outside o the bore

to know the condition o the stator core lamination insulation

region While the MAGIC robots travel in the air gap between the

Damaged insulation can result in circulating currents that can

rotor and stator, the borescopes inspect the end windings and other

eventually lead to core overheating, stator damage, or even ailure

areas not associated with the air g ap To provide the most thorough

(Figure 4) GE typically recommends perorming EL CID tests as a

visual inspection possible with the eld in place, the normal scope

quality check to look or any possible sta tor core iron damage when

or a MAGIC robotic inspection includes a borescopic examination

generator repair work is perormed in the stator core, such as a

A complete inspection includes wedge tapping and any necessary

stator rewedge or stator rewind It can also optionally be perormed

electrical testing

during a minor or major test and inspection A borescopic examination o the generator can be made While the MAGIC crawlers have the ability to p erorm an EL CID

independent o a MAGIC inspection This is typically done when

inspection, there is little to no benet gained by perorming an EL

a ast assessment o the generator, especially the end regions, is

CID test during a routine MAGIC Inspection, because:

desired ater an event outside o normal operation

• Thegeneratorfeldisnotbeingremoved,sothereislittle

possibility o damaging the stator core iron during the inspection

To acilitate a complete inspection, both end shields must be removed Figure 5 shows a picture o eld coils taken by borescope

• Theunitwaspreviouslyrunningatratedux(vs.the4percent

o rated fux at which EL CID is perormed) and i there was any preexisting core iron damage o concern, there should be signs o overheating that can easily be spotted during the visual inspection • I there are any signs o the core iron overheating or mechanical damage, GE will recommend that the eld be removed and the core iron repaired It should be noted that i visual core damage is ound, then a core ring test at close to rated fux will be recommended


7

recommendation presented a roadblock to implementing an in-situ inspection program on water-cooled generators A tool recently developed by GE engineers now solves that problem, enabling capacitance testing to be perormed without removing the eld rom the stator As part o the in-situ inspection program, the new tool uses an infatable electrode, similar to that used with the eld removed, and a remote actuator arm or locating the probe

GE’s remote access camera is also used or positioning the probe and identiying its location This system is being used successully and provides results similar to those obtained during eld-out inspections 

Figure 5 Field coils picture taken by borescope

Test Area

Remote Capacitance Probe

Copper Conductors

GE water-cooled generators manuactured beore 1986 are

Ground-wall Insulation

susceptible to water leaks and the resulting concerns as described Test Electrode

in Technical Inormation Letter-1098 One o the periodic tests recommended in TIL-1098 is capacitance mapping o the stator

Figure 6 Stator bar capacitance test

bars This test has proven to be very reliable in identiying stator bars with deteriorated ground-wall insulation resulting rom a water leak

Retaining Ring NDE Scanner Stress Corrosion Cracking (SCC) o 18 Mn-5Cr generator retaining

Capacitance mapping requires placing a conductive electrode on the surace o the bar’s ground-wall insulation at the location where the bar exits the core slot (Figure 6) A meter is used to measure the capacitance across the insulation between the electrode and the stator bar conductor Each bar in the winding is measured on both ends o the core and statistical analysis is

rings is a well-documented industry-wide concern or generator maintenance SCC develops on the surace o the material in the presence o moisture and stress As a result o the stress concentration and geometry, which tends to hold moisture, the retaining ring inside diameter (ID) surace tends to be more susceptible to this phenomenon

used to identiy those bars with higher than normal expected capacitance High capacitance is a good indicator o moisture presence in the insulation

GE recommends replacement o 18 Mn-5 Cr rings with the improved 18 Mn-18 Cr alloy, which has not been susceptible to SCC However, or those customers who choose to periodically inspect

TIL-1098 recommends that a capacitance test be perormed at each major outage (approximately every ve years) Because perorming the capacitance test required eld removal, this


and repair the rings, GE oers a complete inspection program The most thorough NDE inspection can be per ormed with the rings removed rom the eld, permitting access to the ID surace

8

where eddy current testing is used to detect very small surace

O the more than 1,000 MAGIC inspections perormed by GE,

indications The rings can be tested while installed on the eld,

over 190 units have had two or more inspections, including

however, with less sensitivity to crack detection on the ID surace

several located at nuclear plants GE has also perormed nearly 100 inspections on generators built by other OEMs Ater more

Testing, similar to that perormed with the eld removed rom the

than a decade o experience, many insurers now accept MAGIC

stator, can now be completed on many units without removing the

inspections in lieu o major inspections Because the rotor is not

eld The NDE test equipment has been modied by miniaturizing

removed, the risk o consequential damage is reduced to the

the scanner assembly using the same signal processing system

benet o the insurer and utility alike

as that used with the eld removed The system provides an ultrasonic test (0050”/127 mm crack detection threshold) on the ring ID and an eddy current test (0050”/127 mm crack detection threshold) on the ring OD

System Design MAGIC robotic devices were designed to work without any negative impact to generator components Each crawler has emergency retrieval capability that is also designed to cause no damage to the generator

Other Testing In addition to the above tests and inspections, there are several

Because GE takes Foreign Material Exclusion (FME) very seriously,

others that are recommended during minor and major outages

GE’s technicians conduct a thorough inspection o the crawler

They include electrical testing o the stator and eld windings and

beore and ater the generator inspection to ensure no parts were

Resistance Temperature Detectors (RTDs), as well as hydraulic

let behind in the generator In addition, pictures o the crawler are

testing o water-cooled stator windings A complete description

taken beore and ater the inspection or reerence purposes

o GE-recommended tests is provided in Technical Inormation Letter-1154 and GEK-103566 In-situ inspection o the generator does not change the need or importance o these tests

Traditional vs In-Situ Cost Analysis Reduced cost to the equipment owner is a signicant actor in

MAGIC Acceptance and Experience Industry Acceptance

comparing in-situ inspection programs to traditional inspection programs Cost reduction is achieved due to three major actors: • ReducedOutageDuration–In-situinspectionreducesthetime

For many years, generator inspection consisted o a minor

required to complete a major generator inspection The duration

outage every two-and-a-hal years and a major outage with the

o a generator inspection includes the time required or removal

eld removed every ve years This practice proved to be quite

rom service, disassembly, inspection and reassembly, and

successul in maintaining a high level o reliability o the generator

preparation or service

feet As deregulation led the power generation industry to rethink its philosophy on equipment maintenance, GE developed generator

• ReducedDisassemblyRequirements–In-situinspection

in-situ inspection tools to help our customers reduce cost and cycle

signicantly reduces the time required or disassembly and

The in-situ inspection strategy has proven successul—providing

reassembly o the generator, although it does add some time to

similar accuracy, sensitivity, and thoroughness as a eld-removed

the actual inspection process

inspection In addition, in-situ inspection does not pose a signicant increase in the risk o ailure over traditional inspection techniques

• EliminationoConsequentialDamage–Sincetherotordoesnot

have to be removed, damage that could result rom the rotor removal process is eliminated


9

Net time savings vary based on the plant and generator design Table 3 below provides a good estimate o the time savings experienced or a typical large generator at a nuclear plant

Reducing Disassembly Requirements In-situ inspection oers signicantly reduced cycle time due to the greatly reduced level o generator disassembly required to complete the inspection However, reducing the level o

Type of Visual Inspection

Visual and Visual, Wedge Wedge Tightness Tightness and ELCID

disassembly has a number o benets beyond reduced cycle time, including cost savings that result rom reduced disassembly and

Traditional

14 Shits 16 Shits

18 Shits

reassembly labor, repair, and planning In addition, overhead crane

In-Situ

6 Shits

9 Shits

12 Shits

availability is not required or the inspection, reeing it up or use on

Savings

8 Shits

7 Shits

6 Shits

other parts o the outage

Table 3 Inspection time savings comparison

The total cost o eld removal and reassembly has been ound to be $50,000 to $250,000 or ossil plants and $250,000 to $500,000

Reducing Outage Duration When a generator is on an outage critical path, the ability to

or nuclear plants The cost associated with partial disassembly to allow in-situ inspection varies with the scope o the inspection, but generally runs about one-third the cost o complete disassembly

signicantly reduce generator inspection time is crucial Suitability or service inspections are generally recommended or generators ollowing an abnormal operating event that may have caused generator damage, including breaker ailures, short circuits, and loss o cooling Each o these can cause generator damage that can lead to an online major ailure i the damage is not repaired These circumstances provide an ideal application o in-situ inspection technology, where every hour saved directly aects the time spent ofine

Minimize Consequential Damage Another economic benet o in-situ inspection is the reduction o generator damage resulting rom rotor removal during the outage Rotor removal requires uncoupling the turbine-generator shats; careul disassembly o stator end shields on both ends o the generator; removal o bearings, hydrogen seals, oil defectors and exciter assemblies; and the skillul reassembly and realignment o these same components Improper end shield reassembly may result in: oil ingestion problems; expensive and time-consuming

In-situ inspection can also be used or advanced outage planning

oil cleanup; undesirable lubrication o the armature slot and

By perorming an in-situ inspection during a minor outage—prior to

endwinding restraining systems; increased armature motion; and

a planned major outage—you can help determine the necessity and

accelerated armature insulation wear (Reer to TIL-1098-3R2 or

scope o the major outage The major outage may be postponed

additional inormation on the adverse eects o oil ingestion)

altogether i the generator is ound to be in good condition I problems

In addition, rotor removal incurs risk o damage to the precision

are ound, the inormation gathered during the in-situ inspection can

components o the hydrogen seal oil assemblies and requires

be used to make preparations or repair at the next outage These

the heavy liting and temporary warm, dry storage o the rotor

preparations include planning the repair, identiying labor and material

Because the problems or damage resulting rom disassembly

needs and developing contingency plans When it comes to generator

can lead to very costly repairs, the best policy is to minimize

maintenance, experience has shown that preparation and planning

disassembly requirements

are critical to eciently executing an outage

The results are a result o the comparison o two dierent outage schedules or the same unit Length o the generator, stator diameter, and the number o slots in both the eld and stator are signicant variables GEII can work with each customer to develop time savings or each individual unit 1

2

Result o job cost estimations


10

GE’s Position on In-Situ Inspection

Conclusions

For many applications, GE’s MAGIC inspection provides generator

The power generation industry is undergoing major changes

component assessment capability comparable to that routinely

requiring power producers, OEMs, and insurers to adapt One

achieved by rotor removal inspections Close-up, detailed views o

way that GE has responded to these changes is through the

the core and rotor suraces, stator and rotor wedges, retaining ring

development o advanced-technology tools that enable in-situ

tips and vent ducts allow a generator specialist to detect and assess

inspection o generators In many cases, in-situ inspection oers

potential problems not generally discernible by electrical testing

an excellent, reduced cost alternative to traditional eld-out

or other online monitoring—oten prior to the occurrence o any

generator inspection GE continues to work to gain acceptance o

signicant generator damage

in-situ inspection techniques throughout the industry

Periodic in-situ inspections, together with electrical testing and hydraulic checks, can provide an excellent alternative to many traditional OEM maintenance protocols Skillul interpretation o in-situ inspection observations and related data can provide plant

GE is working on enhancing the capabilities o our in-situ inspection service and expanding the application to smaller generators In-situ inspection will play an increasing role in reducing power producers’ cost o generation

operators with cost-eective opportunities to deduce outages and outage duration while maintaining the outstanding reliability and availability o their generators Recommended maintenance schedules or traditional and in-situ inspection protocols are compared in Table 4

Traditional

MAGIC In-Situ

First year Inspection

Inspection Interval (years) 2.5

5

Major

Minor

Major

•Visual •Wedge

•Visual


In-Situ

In-Situ

In-Situ


•Visual


Table 4 Recommended generator inspection schedules Notes: Electrical and hydraulic testing continue at recommended intervals; NDE testing

and TILs may require rotor removal or completion


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List o Figures

List o Tables

Figure 1 Generator in-situ inspection capabilities                 4

Table 1 Generator inspection items                              2

Figure 2 View o core damage taken with MAGIC robot           6

Table 2 In-Situ Inspection capabilities                            5

Figure 3 Generator Wedge Tightness                            7

Table 3 Inspection time savings comparison                    10

Figure 4 Circulating current due to damaged core insulation      7

Table 4 Recommended generator inspection schedules         11

Figure 5 Field coils picture taken by borescope                   8 Figure 6 Stator bar capacitance test                             8


12

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GE Generator Inspection

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