ger-4223 - ge generator fleet experience and … generator fleet experience and available...

GE Generator Fleet Experience andAvailable Refurbishment Options

Alex LembergGE Energy ServicesAtlanta, GA

Karl TornroosGE Energy ServicesAtlanta, GA

g

GE Energy

© 2004 General Electric Company.

All Rights Reserved

GER-4223 (01/04)

GE Generator Fleet Experience and Available Refurbishment Options

GE Energy ■ GER-4223 ■ (01/04) i

Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

GE Generator Fleet Demographics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Reasons for Generator Upgrades and Rewinds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Generator Reliability and Aging. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

How to Improve the Reliability of Aging Generators. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Rewinding for Higher Output and Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Rewinding for Reliability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Generator Service Issues and GE Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Generator Monitoring. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Appendix. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

IntroductionSince the 19th century GE has manufacturedand placed in service over 8000 medium andlarge power generators, many of them still inservice today. By utilizing progressive designsand developing reliable materials that have beenproven in a large number of installations, GEhas amassed reliability records for GE genera-tors that have provided decades of sustainedservice.

The 1980s saw a dramatic growth in the rebuild-ing and upgrading of turbine-driven generatorsdriven by the need to reduce maintenance onaging fleets—while also adding reliable powerat minimal cost. As today’s operators face thesame urgent requirements, the pace of therebuild and upgrade activity continues to accel-erate.

GE Generator Fleet DemographicsDespite a sharp increase in the number of thenew generators placed in service during the pastfew years, many GE generators currently in serv-ice are 30 years old or older. Figure 1 representsall GE turbine-generators in service, regardlessof design or size, grouped according to age seg-ments.

All GE turbine generators can be subdividedinto two main groups: large and medium tur-bine- generators designed and manufactured byGE factories in Schenectady, NY and Lynn, MA.GE has manufactured a number of large steamturbine driven generators (LSTG), rated from100 to 1600 MVA. The nucleus of this fleet arethe liquid-cooled stator winding design genera-tors, which have been in service since the late1950s.

Reasons for Generator Upgrades andRewindsWhen evaluating generator upgrade alterna-tives, plant operators must consider many alter-natives, including:

■ Planned service life

■ Base-load or start-stop cyclic duty

■ Load requirements (megawatts andmegavars)

■ Reliability requirements

Using these critical parameters to establish thetype and extent of the required upgrade, GEperforms a comprehensive review of the totalgenerator design and offers a complex of


GE Energy ■ GER-4223 ■ (01/04) 1

Figure 1. GE generator fleet demographics

upgrades that can meet the objective. Thisreview includes the requirements for the gener-ator coolers, excitation system, auxiliaries andmonitoring systems, as well as the stator andfield windings.

While the intended use of the unit will provideguidelines for the rebuild, the existing condi-tion of the equipment is usually an equallyimportant factor in determining the extent ofthe rebuild that is necessary. Proper mainte-nance on a regularly scheduled basis as recom-mended by the OEM will help retain the excel-lent reliability of GE turbine-generators.Conversely, lack of regular maintenance, not fol-lowing the manufacturer’s instructions, or oper-ating the generator beyond the prescribed limitscan result in accelerated wear and the need formore extensive rebuild at a later date.

This paper also refers the reader to relevant GEpublications that address generator reliabilityconcerns in more detail—including GER-4212(Generator Rotor Design, Operational Issues andRefurbishment Options) and GER-3751A (Under-standing, Diagnosing and Repairing Leaks in Water-Cooled Generator Stator Windings). In addition tothese reference publications, GE maintains acontinually expanding knowledge base of best

practices and advanced technology proce-dures—based on our up-to-date experience withworldwide fleets—that can be applied to gener-ator upgrades and rewinds. This enables GE toprovide customers with coherent and compre-hensive generator protection systems as part ofour full service offerings.

In recent years there has been a noticeableincrease in the number of generator forced out-ages. While a variety of reasons contribute to thisincrease, two key causes have been clearly iden-tified: operational incidents and aging of thegenerators. Since age is the most common causeof generator failures, this paper primarily focus-es on aging generators and optimum solutionsto improve their reliability.

Generator Reliability and AgingOlder units constitute an increasingly higherpercentage of installed industry capacity andreserve margins on typical systems—and theyrepresent an important segment of the industry.Examination of industry data reveals severalimportant facts about this segment.

Figure 2a illustrates a typical trend of componentfailure rates with age for one manufacturer.Though highly reliable, turbine-generator units


GE Energy ■ GER-4223 ■ (01/04) 2

Figure 2a. Turbine-generator reliability trend Figure 2b. Turbine-generator reliability improvement trend

are not immune to age deterioration. During itsnormal life expectancy most technical equip-ment exhibits a basic pattern of failure rate,which is commonly referred to as a “bathtub”curve. For example, after an initial operatingperiod called the “debugging” stage, the powergenerator has a normal operating period whereunit reliability remains fairly constant. However,after many years of service the failure rate tendsto increase in the “wear-out” period.Replacement of the worn components willimprove reliability of the generator, resettingthe failure rate, as shown on Figure 2b.

Consistent with the increase in the number ofolder generators in service, there has been anincrease in the number of forced outages for GEgenerators. Currently the generator forced-out-age frequency is approximately one a week. Thisincrease in the number of forced outages notice-ably coincides with the aging segment of GE’sgenerator fleet as it moves towards the risingedge of the "bathtub" curve. The following datarepresents some examples of types of forced out-ages that occurred in 2003:

■ Generator key-bar failure

■ Field shorted turns, vibration

■ Field winding ground

■ Field shorted turns, vibration

■ Field top turn break

■ Field winding failure due to H2Scorrosion

■ Generator stator winding and coredamage

■ Stator winding insulation failure

■ Field winding failure

■ Stator winding ground failure, coredamage

■ Field motoring incident, shaft damage

■ Broken stator key-bar

■ Generator rotor failure due tooverspeed incident

■ Stator phase to phase short

■ Stator winding failure due to coolerleak

While there are a number of reasons that cancause generator forced outages—such asimproper maintenance and catastrophicevents—failures caused by worn generator com-ponents can be clearly distinguished. Figure 3reproduces GE data for water-cooled statorwinding failure frequencies for the affected gen-erators listed in TIL-1098 (Inspection of Generators


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Figure 3. Water-cooled winding failures (TIL-1098)

With Water-Cooled Stator Windings). Many of thesestator windings have already been replaced withthe new, improved design windings.

How to Improve Reliability of AgingGeneratorsThe preceding information leads to the ques-tion, "What is needed to prevent a forced outageand to extend the operating life of a generator?" Toanswer this question, and make a meaningfulassessment of the condition of an operatingunit, a thorough inspection and test must beperformed. In addition to these procedures, GEalso reviews inspection reports from prior yearsto look for evidence of mechanical or electricalwear, distress, and aging. By comparing theinspection results of a particular generator withour database of information for similar units, wecan identify components likely to impact thegenerator’s future reliability and make correc-tive recommendations.

If a unit has not had an inspection for severalyears, or there has been a recent incident thatpotentially affected the condition of the gener-ator, it would be prudent to perform an inspec-tion before making any final decisions onrebuild workscope. This could avoid a forcedoutage and an extended rebuild workscope. Ifa customer has several GE generators we mayalso perform a fleet study, addressing theupgrade and reliability options applicable to allof them.

Rewinding for Higher Output andEfficiencyWhile nearly all of the generator componentsmay be upgraded during the service life, statorrewind and field rewind are by far the mostconvenient and powerful means of achievingboth a higher efficiency and a higher output.Rewinds always present an opportunity for the

original equipment manufacturer to enhancethe performance of the machine and support aturbine uprate. The economics of such designupgrades can often help to justify the cost ofthe rewind activity. By considering the vintageand type of the original machine design, tur-bine output, and uprate objectives, GE candevelop an optimized solution that is specific tothe generator.

Rewinding for Reliability

Stators

Advances in the area of non-metallic materials,insulation systems and composites allow signifi-cant reliability improvements and life extensionto be achieved by replacing old materials thatare approaching the end of their useful lives. Anexample of this type of enhancement is thereplacement of an asphalt-insulated stator wind-ing with a modern epoxy-based insulation sys-tem. Since the insulation is life-limited, byreplacing the stator winding with a new one—often of a higher thermal class insulation sys-tem—it is possible to reset the "time clock" onthe stator winding. Beyond simple replacementof materials, significant reliability enhancementcan be obtained through upgrading the designof the winding insulation and the winding sup-port system. With the new winding GE willdesign and supply the new stator slot support sys-tem as well as the endwinding support.Depending upon the generator design, a newwedging system may include pressure wedgesthat are made of non-shrinkable non-abrasivematerial, top and side ripple springs. Thesecomponents will effectively secure winding inthe slot, while allowing certain axial movementof the endwinding basket due to the normalthermal growth or abnormal currents.

One goal of this paper is to detect a trend in thestator rewinds, based on GE rewind experience.


GE Energy ■ GER-4223 ■ (01/04) 4

Figure 4 represents the experience data for con-ventionally-cooled stator rewinds performed byGE for the last decade, using Class F epoxy-glassinsulation systems. Major drivers for theserewinds were output increase and reliabilityincrease. Other reasons included test failures,operational incidents, system faults, and envi-ronmental causes.

Though a variety of reasons forced these statorsto be rewound, the histogram in Figure 5 clearlyshows the peaks at two distinct age groups with-in the total lot of data. Further breakdown by agenerator-cooling medium detects the sub-

groups of the air- and hydrogen-cooled genera-tors, suggesting that hydrogen-cooled genera-tors sustain a longer time between rewinds(TBR). Though hydrogen gas indeed provides acleaner environment, this is partly due to themode of operation. Most of these hydrogen-cooled generators are base load steam turbinedriven generators, whereas some of the air-cooled generators were the gas turbine driven,cycling generators.

The same main objectives—reliability and/oruprates—were pursued by GE customers effect-ing liquid-cooled stator rewinds. Figure 6 repre-


GE Energy ■ GER-4223 ■ (01/04) 5

Figure 5. Hydrogen-cooled stator rewind orders

Figure 4. Air-cooled stator rewind orders

sents the frequency of liquid-cooled rewinds per-formed by GE for its customers in the pastdecade. An age histogram of the water-cooledgenerators rewound by GE shown below indi-cates that currently, the peak rewind frequencyoccurs mostly in the generator age group from20 to 30 years in service.

Many generators referenced in TIL-1098 andrecommended for inspection and rewind arestill operating with the original winding in place.GE recommends that inspection of these gener-ators should be performed. GE publicationGER-3751A (Understanding, Diagnosing andRepairing Leaks in Water-Cooled Generator StatorWindings) provides details regarding recom-mended maintenance, inspection and testing,and test data.

Field Rewinds

Experience has shown the generator field is acomponent that requires maintenance. This isnot surprising considering that it is operatingunder very high centrifugal load and thermalcycling. Also, typical operating incidents havethe greatest impact on the field (motoring, con-tamination, etc.). Rebuild of the field normallyfocuses on re-insulation of the field winding.

However, owners should not lose sight of otherconsiderations. Load level, type of duty, andnumber of stop-start cycles are the main factorsaffecting the wear of the generator field. Otherfactors include prime mover type (gas or steamturbine), ambient air conditions (for air-cooledgenerators), cooling and maintenance of a gen-erator.

It is common for older units to be operated atlower power factors to carry more reactive power.Frequent load cycling common for the peakingunits also may contribute to accelerated wear anddistortion of the field winding, and, at times, leadto a field current sensitive vibration – thermal sen-sitivity. (GER-3809 [Generator Rotor ThermalSensitivity: Theory and Experience] provides adetailed description of this phenomena). A com-plete replacement of the old field winding may bepreferred as a retrofit option in such cases.

Reliability of the generator field is increasedwith a rewind. New modern insulating materialwill replace the original worn out insulation andaddress the latest service concerns. The newcopper coils would usually have a higher crosssection, reducing the current density and heat-ing. Conversion from indirect to direct coolingof the rotor may also be effected in order to per-

GE Energy ■ GER-4223 ■ (01/04) 6


Figure 6. Liquid-cooled stator rewind orders

mit uprating the generator. GE publicationGER-4212 may serve as a good guide to selectionof a proper field retrofit option. The followinglist of recent examples of field refurbishmentjobs performed by GE Energy Services repre-sents some popular retrofit options selected byGE customers.

■ Gas turbine drive, peaking unit,shipped in the 70s.(Forced outage. Field ground due toend turn distortion. Rewind with newcopper coils).

■ Large steam turbine drivenconventionally-cooled generator.(Planned field rewind with new copper,main leads and bore copper).

■ Gas turbine drive.(Forced outage. End turn migrationper TIL-1308. Field exchange).

■ LSTG conventionally-cooled generator.(Field rewind with top turn isolationper TIL-1005).

■ Medium steam turbine generator.(Field rewind with new copper to effectthe generator uprate).

■ Gas turbine drive.(Shorted turns, thermal sensitivity.Field rewind reusing the originalcopper).

■ Medium steam turbine generator.(Shorted turns, vibration. Field rewindreusing the existing copper).

■ Gas turbine drive.(Exchange field to effect a generatoruprate).

■ Large steam turbine generator.(Field rewind with layer separators toprevent copper dusting).

■ Air-cooled steam turbine drivengenerator, frequent load cycling, end

turn migration.(Field rewind with the new insulatingmaterials).

■ Large steam turbine generator.(Rotor wedge replacement per TIL-1292).

■ Steam turbine driven generator. Steelmill, load cycling.(Field rewind reusing the existingcopper).

■ Medium steam turbine drivengenerator.(Forced outage due to the overspeed.Field rewind with new copper,replacement of compromisedcomponents. Shaft stress analysis).

■ Medium steam turbine generator.(Contamination of the field winding,erosion of brazed joints. Field rewindwith the new copper coils, brazeprotection).

■ Medium steam turbine generator, late60s vintage, peaking unit.(Forced outage. Distortion of endcopper turns, shorted insulation. Fullfield rewind with new copper coils).

Due to the multiple causes for the field degra-dation, the age of a generator may not serve as aprimary factor to determine the time to re-furbish. Distribution of the medium generatorfield rewind frequencies is presented by age inFigure 7.

Monitoring the generator condition, testing andinspections performed on regular intervals asrecommended in TIL-1154 and other GE publi-cations will determine the actual condition ofthe field and other generator components.

If a generator is due for an upgrade—which maynot be performed immediately—a good prac-tice would be to stock a rewind kit. This willreduce the downtime in the event of emergency.


GE Energy ■ GER-4223 ■ (01/04) 7

If not used for an emergency, the kit may beused later at the time of scheduled outage.

Generator Service Issues and GERecommendationsNot all generator service concerns may be solvedwith rewinds. Careful attention must be paid tothe generator auxiliaries, exciter, collector andbrushes, hydrogen seals, frame, end shields,water-cooling system, and hydrogen system.Time and wear of the generator componentshas a combined effect on the generator avail-ability. Based on statistics for recent months, the

Pareto charts shown in Figure 8 and Figure 9 mayillustrate the contribution of various stator andfield components to the overall number of thegenerator stator and generator field serviceissues.

Generator MonitoringMonitoring generator condition and parame-ters on-line provides the opportunity to detect atrend in behavior of a monitoring parameter;assess the rate of deterioration and possibly pre-dict the time to failure; and detect faults of thegenerator components. While an array of gener-


GE Energy ■ GER-4223 ■ (01/04) 8

Figure 7. Medium generator rewinds

Figure 8. Stator components service issues

ator monitoring schemes and devices are usedby the industry, the following three areemployed most widely: Generator Flux Probe,Stator Leak Monitoring System, and PartialDischarge Analysis:

Generator Flux Probe

In order to provide an effective early-detectionsystem, GE developed the Flux Probe to detectshorted turns that might exist in the field duringoperation. The permanent Flux Probe permitscontinuous on-line monitoring of the field. Thepickup coil is mounted to a stator wedge; norewedging is required. Electrical leads from thepickup probe are brought out through the endwindings to an electrical pressure connectorthat is welded to the wrapper. This allows condi-tions in the field coils to be monitored while thegenerator is operating, so problems can be dis-covered early enough to avoid major opera-tional issues—such as rotor vibration caused bylinear thermal sensitivity.

Stator Leak Monitoring System

To help prevent catastrophic stator winding fail-ure, GE developed the Stator Leak MonitoringSystem (SLMS). This system has two functions:on line detection of water-cooled stator windingleaks and maintaining cooling water oxygen

content. It consists of a flow meter, gas analyzer,data acquisition and control system and a systempiping modification package. Since on-line leakdetection is important in avoiding catastrophicstator winding failure from wet insulation and inoutage planning, the SLMS is designed to detectdeveloping water leaks in a water-cooled statorwinding and maintain the cooling water's oxy-gen content.

As described in TIL-1098, GE has identified thepotential for water leaks to develop in this classof generators. When a leak develops, higherpressure hydrogen escapes into the water systemand can accumulate in the water storage tank onthe cooling water skid. As the hydrogen accu-mulates, it creates a "blanket" effect, keepingatmospheric oxygen from entering the waterand leading to deoxygenated water and theproblems described above.

Addition of an SLMS will require a modificationto the Stator Water Cooling System (SWCS).The SLMS module will be mounted to the SWCShydrogen detraining tank and will connect to agas analyzer and a flow meter which are addedto the existing piping. The system will inducefresh filtered air into the cooling water, whichprovides a measurable gas flow and maintains


GE Energy ■ GER-4223 ■ (01/04) 9

Figure 9. Field components service issues


GE Energy ■ GER-4223 ■ (01/04) 10

water oxygen content. Measurement of thehydrogen content and gas flow will provide anaccurate measurement of hydrogen leakagethrough the stator winding. The level of hydro-gen leakage is directly related to a leak in thewater cooled stator winding. Recent upgradesincluded the on-line oxygen monitoring andupdated data acquisition system.

Partial Discharge Analysis

High frequency (40 KHz – 100 MHz) low voltage(micro volts) partial discharge activity exists inessentially all high voltage equipment. PhaseResolved Partial Discharge Analysis (PRPDA) isa powerful tool to monitor this activity on-lineand identify trends on specific machines and/orcompare activity in identical machines that canbe used for condition- based maintenance andforced outage avoidance. Recent developmentsin measurement hardware, software and analysistechniques show great potential for identifyingthe specific sites of partial discharge activity with-in generators and quantifying the partial dis-charges at each site in order to discriminatebetween normal and destructive activity.

There are several conditions which can occurwithin a generator that can generate PD activitythat is of interest and relates to the condition ofthe generator:

■ Stator bar vibration

■ End winding contamination

■ Damage to the end winding voltagesuppresser system

■ Connection ring vibration

■ Broken conductors

■ Insulation delamination/damage

■ Slot discharge

■ Collector brush sparking

These are some typical conditions that would be

investigated during a maintenance outage testand inspection program. On-line PDA testinggives a relative assessment of the generator con-dition that can augment more conventional testsand inspection methods in order to plan condi-tion-based maintenance outages and to helpavoid forced outages. The PRPDA method de-tects discharges with sophisticated signal pro-cessing, noise gating and pulse shaping, and dis-plays the activity as it occurs in relation to the50/60 Hz power sine wave. The resulting phase-resolved patterns allow for discriminationbetween internal discharge activity, external dis-charge activity, and noise activity. The superiorsignal discrimination of PRPDA simplifies meth-ods for coupling to the generator, while theenhanced signal presentation of PRPDA simpli-fies using partial discharge for condition- basedmaintenance and forced outage avoidance.

ConclusionA recent increase in the number of forced out-ages can be attributed to the aging of GE’s gen-erator fleet. With many of these generator units30 years or older, early diagnosis and correctionof a problem is important for reliable operation.The best approach in preventing forced outagesis a proactive one.

Based on the expertise and knowledge baseaccumulated from our worldwide fleet of gener-ators, GE has the ability to help customers deter-mine the optimum reliability solution for theirspecific units—with a comprehensive range ofofferings that provide everything from mainte-nance and monitoring through upgrades andrewinds.

Though there is no hard data pointing to a datewhen a generator must be rewound, GE recom-mends to follow relevant publications such asTechnical Information Letters and referencemanuals that correspond to a particular unit.


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(GE Recommended Test and Inspection sched-ules are included in the Appendix. See Table B-1and Table B-2.)

Some data material presented in this paper mayalso be used as a trend indicator. The most com-mon and proven generator upgrades and repairsolutions offered by GE have been formalized inour Generator Source Book offerings. A list ofthese Generator Source Book articles (alongwith a sample article) is presented in the appen-dix for your reference. These articles are avail-able through your area sales representative orthrough the Outage Optimizer tool on gepow-er.com.

The authors express special thanks to the fol-lowing individuals who contributed to this pub-lication: Ron Zawoyski, Rod Rumer, and MichaelKavney.

References1. Worden, J.A., and Mundulas, J. M.,

"Understanding, Diagnosing and RepairingLeaks in Water-Cooled Generator StatorWindings," GE Reference Library, GER-

3751A, August 2003.

2. Zawoysky, R.J, and Genovese, W.M.,

"Generator Rotor Thermal Sensitivity:

Theory and Experience," GE Reference

Library, GER-3809, April, 2001.

3. Zawoysky, R.J, and Tornroos, K., "Generator

Rotor Design, Operational Issues and

Refurbishment Options," GE Reference

Library, GER-4212, August, 2001.

4. TIL-1005, "Fatigue Cracks (Top Turn Breaks)

in Generator Field Coils," GE Technical

Information Letter, 1987.

5. TIL-1098, "Inspection of Generators with

Water-Cooled Stator Windings," GE

Technical Information Letter, 2001.

6. TIL-1154, "Generator Test and Inspection,"

GE Technical Information Letter, 1994.

7. TIL-1292, "Large Steam Turbine Generator

Dovetail Inspection Recommendation," GE

Technical Information Letter, 2000.

8. TIL-1308, "Generator Field Endwinding

Insulation Migration," GE Technical

Information Letter, 2002.

Appendix

A. 1) Generator Source Book ArticlesMany of the following Generator Source Book articles may be accessed online at www.gepower.com byselecting the Online Tools page and choosing Outage Optimizer—or by contacting your GE sales rep-resentative.


GE Energy ■ GER-4223 ■ (01/04) 12

• Temporary flux probe

• Permanent flux probe

• Generator gas monitoring system

• Exchange gas monitoring system

• Gas analyzer

• Deionizing resin

• Stator cooling water filters

• Shaft voltage monitor

• Collector brush holder retrofit

• Excitation ventilate modification

• Ex2000 + modifications

• Field balance weights

• Collector terminal stud kit

• Replacement field

• Full field rewind with Copper

• Exchange field

• Field rewind w/o Condal

• Full field rewind w/o Copper

• Field high-speed balance

• Main terminal stud kit

• Partial field rewind

• Retaining ring install kit

• Retaining ring non-destructive test

• Field shipping-storage bag

• Thru stud install kit

• Alterrex oil deflectors

• 7A6 oil leak modifications

• Bearing ring insulation kit

• End shield oil leak mod

• Retaining ring TIL-1097

• Liquid-cool bar TIL-1098

• Core ring test

• Test for copper dust per TIL--965

• El Cid test

• In-situ test

• Major inspection of liquid-cooled generator

• Minor inspect of liquid-cooled generator

• Test main lead TIL-1002

• Field non-destruct test

• Partial discharge test

• Field shorted turn test

• End winding freq test

• Telephone influence test

• Thermal sensitivity test

• Stator wedge tight test

• Gen tagging compounds

• Generator uprate analysis

• High voltage bushing repair kit

• Liquid-cooled bar repair kit

• Corona resistant paint

• Full stator rewind

• Gegard 600 stator rewind

• Partial stator rewind

• Liquid flow conversion

• Stator leak monitoring system

• Series loop insulation kit

• Stator re-wedge


• Collector brush holder retrofit per TIL-813

• TIL-962, space block migration prevention

• Copper dust rewind TIL-965


• 7H2 end wedge modifications

• Main lead TIL-1002

• Top turn isolation per TIL-1005

• Alterrex cool tube TIL-1027

• Field re-wedge TIL-1035/1036

• Kopflex cplg TIL-1037

• TIL-1093 5/6a3 limit switch

• Ret ring TIL-1097

• Liquid-cool bar til-1098

• 7H2 end wedge mod

• TIL-1161 9H2 term stud

• TIL-1164 9H2 bore seal

• TIL-1173 9H2 stdoff insul

• TIL-1187 6A3 stator rewdg

• TIL-1195 5/6A3 conn strap

• Liq-cooled stator bar abrasion

• 7FH2 belly band mod

• TIL-1226 strainer basket

• SLMS EPROM upgrade

• H2 detector kit

• 6A3 pedestal vibration mod

• Generrex CPS disabling

• Major inspection of conventionally-cooled

generator

• Minor inspection of conventionally-cooled gen

• Performance curve lookup

• Hydrogen seal ring retrofit

• Hydrogen seal ring replacement

• Hydraulic test-winding

• Top turn isolation TIL-1005

• Alterrex cool tube TIL-1027

• Field rewedge TIL-1035/1036

• Kopflex coupling TIL-1037

A. 2) Sample Generator Source BookArticle CODE: GFFRCU64

DESCRIPTION: FULL FIELD REWIND WITHCOPPER

INTRODUCTION:

A full field rewind with a new copper windingreplaces the old, worn ground and turn insula-tion with the latest systems and provides for anew field winding. Since these new insulationsystems are typically thinner than what they arereplacing, additional space is made availableand optimized by designing the new field coilswith a larger cross-section. This provides anuprate potential for the generator. Even if thecustomer is not interested in an uprate at thistime, a full field rewind with copper will typical-ly reduce the operating temperatures of thefield, which will improve machine reliability andthe life expectancy of the machine.

APPLICABLE UNITS:

All generators.

TECHNICAL DESCRIPTION:

A full field rewind with copper allows for the fullimplementation of the latest ground and turninsulation systems, along with the latest fieldwinding design technology. Technically, thisrewind option provides the greatest potential forimproved generator output when the field islimiting. A stator rewind, cooler upgrade orexcitation upgrade may be required in additionto the field rewind if their capability is also lim-iting.

By rewinding the field with new copper, the reli-ability of the field is greatly increased. New hardcoils are installed to reduce coil distortion dur-ing operation, while Class "F" insulating materi-als are installed to improve the temperaturecapability of the winding design. When the coilsare replaced, the field winding design can be

optimized to lower its resistance and net operat-ing temperatures for the same output level. Byreplacing the old coils with new ones, the designof the winding is improved. Class "F" insulationsystems are used to improve the insulation sys-tem's temperature capability.

BENEFITS:

■ New Class "F" insulation systemsimprove temperature capability

■ Existing shorted turns can beeliminated

■ Possible uprate potential

■ Field operating temperature can bereduced

■ Reduced down-time, increasedreliability

■ Increased life expectancy of theinsulation system

REFERENCES:

GER-3707, Generator Upgrades and Rewinds

SCOPE OF SUPPLY:

■ New field coils (100%)

■ Slot armors (100%) plus twocontingency spares for coil #1 above

■ Turn insulation - slot and end winding(105%)

■ New distance blocks when existingblocks are asbestos or unit is a mediumgenerator (100%)

■ Pole-to-pole connectors (100%)

■ Coil-to-coil connectors (100%)

■ Fan lock plates for axial flow fans(100%)

■ Main terminal nuts (50%)

■ One retaining ring installation kit (seeGFRRIK63)

■ Temporary wood (international ordersonly)


GE Energy ■ GER-4223 ■ (01/04) 13

■ Temporary wood drawing (domesticorders only)

■ Rewind accessories and miscellaneousmaterials needed to perform rewind(100%)

NOTES:

A field high-speed balance is strongly recom-mended (SEE GFHSBN62).

SCOPE OF WORK:

This Scope Of Work lists the required steps toperform the subject installation only. It assumesthat generator disassembly is for no other pur-pose than the installation. Typically, conver-sions, modifications and uprates are scheduledby a customer to coincide with other turbine-generator maintenance activity.

■ Remove field from the stator

■ Remove retaining rings

■ Strip field of coils and insulation

■ Rewind field with new coils and newinsulation

■ Install retaining rings

■ Insert field into the stator

SITE INFORMATION REQUIRED:

■ Turbine, generator and field serialnumbers

■ Notification of any modificationspreviously performed on the fieldforging or winding

OPTIONS:

■ Retaining Ring Replacement (SeeGFRRRP67)

■ Field High-Speed Balance (SeeGFHSBN62)

■ Generator Tagging Compounds (SeeGRTGCP52)

■ Main Lead Replacement (SeeGFMLRP63)


GE Energy ■ GER-4223 ■ (01/04) 14

B) GE Recommended Generator Inspections and Standard Tests

VISUAL INSPECTION AREAS


GE Energy ■ GER-4223 ■ (01/04) 15

Stator All Components X X X X X XBars X X X X X XEW Support System X X XSlot Support System X X XConn. Rgs & Lower Lds. X X X X XHigh Voltage Bushings X X X X

Core All Components X X X X X X X X XCore End X X XVentilation Ducts XLaminations X X XKey Bars X

Field All Components X X X X X X X XBody & Wedges X X X XRetaining Rings X XFans XSpindles X XWinding X XCollectors X X

Fore

ign

Mat

eria

l/Con

tam

inat

ion

Corr

osio

n

Surf

ace

Cond

ition

and

Wea

r

Wat

er L

eaks

(Wat

er-C

oole

d)

Crac

ks

Loos

e or

Dis

plac

ed P

arts

Wor

n Pa

rts

Bur

ning

Blo

cked

Ven

tilat

ion

Bar

Spa

rkin

g

Tape

Mig

ratio

n

Bro

ken

Tile

s

Clea

nlin

ess

Core

Tig

htne

ss

Shor

ted

Core

Pun

chin

gs

Det

erio

ratio

n (G

ener

al)

Mec

hani

cal D

amag

e

Mov

emen

t

Table B-1. Recommended generator inspections


GE Energy ■ GER-4223 ■ (01/04) 16

STATORAIR HYD LCSW MINOR MAJOR

Test Component Inspection ObjectivesRTD Element Res Gas & Winding RTDs Checks for calibration & poor connection X X X X X RTD Ground Insulation Stator Winding RTDs Insulation condition of RTD X X X X XWinding Copper Res Stator Winding Checks for calibration & breaks X X X X XInsulation Resistance CE Bearing Contamination and/or deterioration of insulation X X X X X(aka Megger) Hydrogen Seal Casing Contamination and/or deterioration of insulation X X X XPolarization Index Stator Winding Contamination and/or deterioration of insulation X X X X XDC Leakage Current Stator Winding Contamination and/or deterioration of insulation X X X X XOver Potential/Hipot Stator Winding Groundwall insulation integrity X X X X XWedge Tightness Map Stator Wedges Detect wedge tightness deterioration X X X XMagnetic Scalar Potential (ElCid) Stator Core Insulation Weak or damage core enamel X X X XVacuum Decay Water Cooled Stator Wdg Hydraulic integrity of entire winding X* X XPressure Decay Water Cooled Stator Wdg Hydraulic integrity of entire winding X* X XCapacitance Mapping Water Cooled Stator Wdg Wet groundwall bar insulation X* XHelium Tracer Gas Water Cooled Stator Wdg Detect minute leaks in the hydraulic circuit X* X

OPTIONAL TESTSPartial Discharge Analysis Stator Winding Insulation Localized deterioration X X X R RWater Flow Verification Water Cooled Stator Wdg Restrictions in hydraulic circuit X OCore Ring Test Stator Core Insulation Weak or damage core enamel X X X ODynamic Freq Response Stator End Winding Potentially damaging resonance X X X OBar Jacking Slot Support System Check slot clearance X O

FIELD AIR HYD LCSW MINOR MAJORTest Component Inspection ObjectivesWinding Copper Resistance Field Winding Checks for poor connections & breaks X X X X XPolarization Index Field Winding Contamination and/or deterioration of insulation X X X X XAC Impedance Field Inter-turn Insulation Turn shorts & speed sensitive turn shorts X X X X X

OPTIONAL TESTSOverpotential/Hipot Field Winding Groundwall insulation integrity X X X O OAir Gap Flux Probe Field Inter-turn Insulation Shorted turns at operating speed X X X R RBore Pressure Test Chevron Seals Sealing capability of Chevron seals X X O O

O – Optional testX* – Pertains only to water-cooled unitsR – These tests are performed while the unit is running

Table B-2. Recommended generator standard tests


GE Energy ■ GER-4223 ■ (01/04) 17

List of FiguresFigure 1. GE generator fleet demographicsFigure 2a. Turbine-generator reliability trendFigure 2b. Turbine-generator reliability improvement trendFigure 3. Water-cooled winding failures (TIL-1098)Figure 4. Air-cooled stator rewind orders Figure 5. Hydrogen-cooled stator rewind ordersFigure 6. Age of rewound liquid-cooled generatorsFigure 7. Medium generator rewindsFigure 8. Stator components service issuesFigure 9. Field components service issues

List of TablesTable B-1. Recommended generator inspectionsTable B-2. Recommended generator standard tests

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