주발전기경년열화관리기술동향 - KINS · 2018-01-01 · Generator Rotor Vibration • Correct problem diagnosis – Full train turbine-generator review – Field or stator

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주발전기경년열화관리기술동향

GEEnergy

2008년 4월 10일

하운식GE Energy Korea

This document and its contents are the property of General Electric. This copy is provided for GE Generator Technical Seminar attendee’s company internal use only, not to be copied or transmitted in any form to third parties.

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GE Company Proprietary

Generator Fleet Experience

• Generator field

• Generator stator

• Generator auxiliaries

• Generator maintenance

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Generator Rotor Rewinds

• Aging fleet- field rewinds are to be expected to maintain reliability

• In most cases rewinds can be done with existing copper and high speedbalancing is not necessary

• New copper may be necessary if –deformation or compression yielding

• Peaking units-more frequent rewinds than base load units ~ 2 to 1

• Insulation and winding components may be upgraded

• Design modifications may be possible to uprate unit

• Rewinds performed with rotor TILs >provide extended rotor life

• Fast rewinds have been developed to support shorter outages

• Partial field rewinds require special care

• Replacement rotors can be made to facilitate fleet rotor maintenance

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Generator Shorts and GroundsShorted turns• Difficult to find at standstill

• Flux probe provides best diagnosis– On-line at load– Stator short-circuit, no load

• Allows for planned maintenance

• Permanent and temporary flux probes available

• Shorts and grounds should be diagnosed prior to disassembly

• On-line shorted turn detector is available for continuous monitoring

• RSO (Recurrent Surge Oscillography) can detect shorted turns andpossibly speed sensitive and intermittent grounds

Rotor Grounds• Field ground circuitry includes field,

exciter, rectifier and ground detector

• Testing– Split voltage test– Current through forging test

• Most grounds found in end winding, bore copper or collector areas

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Generator Retaining Rings18 Mn-18 Cr retaining rings• No formal inspection recommendation to date• Some 18Mn-18Cr retaining rings found with corrosion pits/cracks

– Exposed to halides-iodine, bromine, chlorine, etc.– Retaining ring insulation used fire retardant

New TIL is in the works• Inspect 18Mn-18Cr retaining rings

– Florescent penetrant– Eddy Current

• Retaining ring insulation should not contain fireretardant or other potentially corrosive material

In situ retaining inspection now available• Primarily aimed at remaining 18 Mn-5 Cr fleet• Uses eddy current and UT

In Situ RR Inspection

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Generator Rotor Vibration• Correct problem diagnosis

– Full train turbine-generator review

– Field or stator

– Alignment/mechanical/operation

– What changed (maintenance, incident, operation, etc.)

– Resolution-GE expertise

• Thermal Sensitivity

– Testing outlined in GER 3809

• “No” low speed balance

30.0 PSIG H2

15.0 PSIG H

0.5 PSIG H

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40

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Meg

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412

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1

0.85 PF

0.95 PF

TEST POINT NO.

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GER

3809

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TIL 1292 Inspecting All Large Steam Turbine Generators for Cracks

• Mild to severe rotor tooth cracks have been observed on some long service generator rotors

• Cracks can lead to extended outages & ultimately to rotor failure

• TIL1292 applies to:– LSTG direct cooled fields– Large Schenectady-built

conventionally cooled fields– Model 324 fields

Large Crack Indication

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Disassembly:• Baseline inspection• Remove retaining rings, wedges• Measure #1 coil wedge top fits

Prepare for TIL 1292 Machining• Mfg New Aluminum Wedges• Clean/mask field• Perform TIL 1292 EC inspection• Evaluate EC data

Machining• Axial• Radial & 45/30 Degree

Re-assembly• Install wedges, retaining rings• Perform final inspection

TIL 1292 Machining

Mask Field

Radial & 45 Degree Cutter

Axial Cutter

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Generator Stator ExperienceTIL 1447-Water Cooled Stator Winding Update• Crevice corrosion still possible on phosphorus brazed bars despite stator bar

improvements

• Leaks may be found in other areas of the SWCS (connection rings, lower leads/HVB, rectifier circuit, etc.)

• On line monitoring and periodic leak testing are most effective methodto mitigate the occurrence of a wet bar

• Epoxy resin coating is an extremely effective method of halting the corrosion process

• GE water cooled fleet continues to be the most reliable in the industry –a controlled and scheduled monitoring and test plan will maintain this

• On line monitoring with SLMS-HP and liquid leak detector should be implemented

New stator bars have phosphorus freeBrazes and not subject to

Crevice corrosion

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Crevice Corrosion Process

1) Solution at braze surface = inlet water2) Water works its way into voids in braze and stagnates3) Crevice corrosion of braze (primarily Cu3P)4) Critical solution or surface area conditions met, and Cu corrodes5) Solution/surface area conditions change favoring braze corrosion6) Solution/surface area conditions change favoring Cu corrosion7) Leak drives down the bar to outer surface

Phosphorus Is Main Driver for Crevice Corrosion-Eliminate or Isolate

Water Box

Cooling Water(pH:7, low conductivity)

Copper Strand

Copper Strand

Voids in “Spongy”Area of Braze

Brazing Metal

Selective Attack of Cu3P

HH22OO

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GE Water Cooled Stator Winding Test and Monitoring Recommendations

Clip-Strand Braze: Phos Containing Global Epoxy or Clip-Strand Braze: Phos-Free

H2 Leak Monitoring Method

Orig SLMS, Bagged Vent, or No Monitoring SLMS-HP Installed Orig SLMS, Bagged

Vent, or No Monitoring SLMS-HP Installed

Test Minor 30 Months

Major 60 Months

Minor 30 Months

Major 60 Months

Minor 30 Months

Major 60 Months

Minor 30 Months

Major 60 Months

Vacuum Decay X X X XPressure Decay X X X XHelium Tracer Gas X X XCapacitance Mapping X X XWID - Wet Insulation Detector X X XWinding Electrical Testing X X X X X X X X

Notes: 1. If SLMS, SLMS-HP, or pressure or vacuum decay tests indicate a leak, then the helium tracer gas test, WID and capacitance mapping should be done.2. Refer to GEK 103566 for other testing and inspections not covered here.

Hydrogen Leakage -- Cu. Ft. per Day Recommended Action

1 to 5 Monitor weekly and trend (should be < 2 cu. Ft. per day)

5 to 50 Monitor daily and trend (leaks exists)

50 to 200 Monitor daily+ and trend (leak growing-plan to fix)

>200 Take unit off line and fix immediately (large leak)

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SLMS (Stator Leak Monitoring System)

• Water Leaks– Online monitoring at any time

• Maintains SWCS oxygen level >2ppm

• Minimizes risk of in-service stator failure– SLMS has diagnosed > 15 major

in-service leaks

• Periodic maintenance required

• Super sensitive SLMS-HP is available– Significantly reduces SWCS maintenance

SLMS-HP Unit

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Generator Stator ExperienceTesting for wet stator barsCapacitance mapping/WID• Test top and bottom bars independently

• Test turbine and collector ends separately

• If 3 standard deviations are in double figures, repeat test

Full set of recommended HIT skid tests• Vacuum and pressure decay, capacitance & WID, and helium leak test

Wedging• Tight end wedges are most important

• Upgrading to top ripple spring system provides robust design

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Generator Stator … Loose Wedges and End WindingInspections

-Wedge tightness -Loose ties

-Blocking -End winding hardware

-Dusting and greasing -Series loop damage-TIL 1045

Oil ingress-No damage to insulation

-Could accelerate bar and end winding wear

Maintenance-First year, then every 5 years

-Inspection with MAGIC or field out

Consequences-Bar abrasion -Stator ground/other electrical failure

-Broken hardware/plumbing -Rapid degradation once started

Key to maintaining stator integrity

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Generator Stator … End Winding Experience• Phase connections

– More complex than series loops• Connection rings• Water cooled HVB/neutral leads• “Impact” testing recommended

– Rewind– Partial Rewind– Evidence of end winding motion– Impact testing recommendations

being reviewed

Stator End Winding Components• Teflon hoses• Header nipples• Broken plumbing

Typical Liquid Cooled StatorPhase Connection

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Generator Stator … Water Cooling System ExperienceMaintenance

• Replace filters and resin• Inspect & replace strainers

– TIL 1226• Consider system acid flushing

Hardware• Strainers-appropriate mesh size• Duplex strainer system• Filters-cotton filters better• Resin-GE recommended• Install SLMS-HP

– Maintain proper O2 level>2 ppm– On-line leak detection– Minimize SWCS maintenance

Spare parts• Filters, strainers, resin, etc. Typical SWCS

TIL 1312-SWCS operationand maintenance

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Stator Water Cooling System Monitoring

• Cold and hot gas RTDs• Stator Bar RTDs and TCs

• Oxygen level >2 ppm• Conductivity• YTV vent hydrogen

– SLMS-HP• SWCS differential pressure and

flow• Strainers and filters• Monitoring/archiving/trending

data is invaluable in diagnosing in-service stator issues

If not maintained and monitored > stator bar plugging

PUMP

WATER COOLEDSTATOR

WATERSTORAGE TANK

COOLING WATER

WATERRETURN

SAMPLE IN

SAMPLEOUT

POWERIN(110VAC)

VENT GAS

6 CFD

PLANT COMPUTER

YTV

6 CFD

SLMSSystemPlant Air Supply

6.5 CFM @ 100 psi AIR INJECTION

DRAIN

SCWS ALARM

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Generator Stator Core Experience• Initial symptom-noise change from long term steady-state• Belly bands-provide contact between core and frame

– Round and square keybars-different parts and techniques

• Check torque on keybar nuts

• Loose inner core … can be tightened with shims

• Check for keybar to frame weld cracks

• Inspect at major outages or if significant change in noise or vibration is noted

• 7A6-A units (early units)

– TIL 1552-inspection, test and repair of 7A6 frame/core

– Isomode pad replacement at frame to base interface

Core Issues Are Uncommon in GE’s Generators

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RACER Trolley

Core Iron Inspection and RepairInspection and testing

-Before disassembly - After rewind/repair-After disassembly prior to rewind

Testing techniques-ELCID/RACER-for routine inspections-Core ring test-for burning and severe damage

Core iron repair-special techniques needed-Grinding - Acid cleaning-Significant damage could occur if repaired improperly

Vulnerability increases due to lack of scheduled maintenance

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Generator Auxiliary Experience

Collectors and Brushes• Maintenance, Maintenance

Maintenance!

• National Carbon 634 brushes

– Used on most units

• Carbone LFC554

– 330H

– 450H

• Don’t mix brushes!!!!!!!!!!!!!!!!!• Use brush originally supplied with

the generator

• Spare brushes and collector rings

High Voltage Bushings• Proper assembly required

• Proper gaskets and torquing

– Soft gasket-lower torque

– Hard gasket-higher torque

• Modified “Magic Dust repair” has provided extended operation for leaking HVB

• Spare HVB’s

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Collector Maintenance is VitalDaily Inspection by Operators Through Window• Check for sparking, chatter, burned pigtails, oil, wear, changes from

previous conditions (noise, vibration, etc.) …

Weekly Inspection and Maintenance by Electricians• Check for overheating, spot check vibration and record, examine

springs and brushes, check for brush hang up, inspect air filters …

Monthly Inspection and Maintenance• Observe rings with strobe light, plot and examine trends in vibration,

use of Infrared Thermography may be beneficial …

Shutdown Inspection and Maintenance• Take runouts in each brush track, examine worn parts and replace,

check for tightness, clean off dirt and oil, inspect air passages …

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Improved Magic Dust Repair

• Will repair all possible flange area leaks

• The level of the magic dust and sealing components raised approx. 2”

• Grind out solder and re-establishing seal with epoxy

• Patented solution

• Implemented successfully on several units

• Developed as a short term repair, but some units have operated for long periods of time

Improved Magic Dust Repair

ViscasilSilicone greaseMagic Dust

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Generator End Shield Sealing

This modification must be plannedfor prior to outage

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Generator Hydrogen Seals• Maintain H2 pressure and minimize

consumption

• CE insulation must be maintained

– Clean and “dry” oil

– Housing and bearing insulation

– Cracked insulation

– Megger insulation periodically

• Seal installation

– Different designs (bronze and steel babbitted)

– Clearances vary

– Lapping seals

• Oil feed must be maintained

• Proper parts and assembly necessary Typical Seal Assembly

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Hydrogen Leaks Require Immediate AttentionHydrogen leaks through the seal oil system

• Typically 300 to 1000 Cu. Ft. per day• Higher values indicate a system breakdown • Monitoring/corrective action is necessary

Hydrogen leaks up the YTV vent• Monitor-SLMS or the “old fashioned” way• <5 Cu. Ft. per day for tight winding• >200 Cu. Ft. per day-Immediate shut down to prevent catastrophic failure

Other generator hydrogen leaks• “Snoop” generator for leak location• SF6 has been used effectively, but long term generator effect unknown• Leak area should be well ventilated

All hydrogen leaks should be addressed immediately

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Generator Shaft Currents• Shaft grounding brushes must be operational

– Carbon or copper braid

– Regularly scheduled maintenance is necessary

• Bearing and Seal housing insulation

– Testing

– Cleanliness• Poor maintenance results in frosting and electrolysis on the journals

– Can result in degraded bearing and seal performance

– Journals, bearings and seals may require rework

• Exciter Coupling Insulation maintained

• Turbine / excitation induced currents

• Shaft magnetism could induce shaft currents

• Check station grounding

• TIL 1344-Generator Shaft Grounding Brush Maintenance

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Generator Maintenance-TIL 1154

• GER 103566-presently being revised

– Generator testing

– Generator inspections

• Overall generator fleet maintenance plan and recommendations are under constant review

• Condition based maintenance plan may be possiblefor selected units-requires GE study

• Generator TILs should be incorporated into maintenance plans to assure long term reliability

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Generator TILs• 747 &757-Generator Rotor Bore Inspections

• 854-Generator Temperature Monitoring

• 965-Copper Dust

• 1001-18Mn-5Cr Retaining Rings

• 1002-Generator Main Lead Replacement

• 1005-Generator Rotor Top Turn Breaks

• 1027-Rectifier Cooling Tube Concerns

• 1035 & 1036-Aluminum Field Wedges

• 1037-Generator Alterrex Flexible Couplings

• 1045-Generator Stator Series Loop Inspection for Medium Sized Units

• 1098-Inspection of Generators with Water Cooled Windings

• 1154-Generator Test and Inspection

• 1163-Lead Carbonate Contamination in Hydrogen Cooled Generators

• 1197-Liquid Cooled Stator Bar Abrasion

• 1226-Generator Y-Strainer Inspection or Replacement

• 1292-Rotor Dovetail Inspection

• 1308-End Winding Insulation Migration

• 1312-SWCS Maintenance, Monitoring and Operational Guidelines

• 1398-End Winding Support Hardware Issues

• 1447-Water Cooled Stator Winding Update

• 1515 & 1516-Nuclear Generator Coupling/shaft Inspection Rec.

• TIL 1552-Inspection, Test and Repair of 7A6 Frame/Core

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Diagnosing Generator In-Service IncidentsEvaluating the Incident Severity• Immediate action is necessary to address incident• Contact local GE Rep ASAP and enter PAC case• Obtain “vital data” immediately• Conference with GE experts when necessaryNeed “Vital” Unit Operating Data to Diagnose Problem

• Events or conditions preceding fault• Fault location• Duration• Stator phase currents• Field current• Which relays operated

• Generator terminal voltage• Speed changes• Load changes• Vibration changes• Main transformer impedance• Neutral grounding transformer

impedance

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Generator Fleet Experience Summary• Generator RTDs and TCs should be monitored on a scheduled basis

• The SWCS should not be operated with O2 < 2 ppm

• Do not operate with YTV H2 leakage > 200 ft3 per day

• Duplex strainers should be installed on all stator water cooling systems

• Tight stator wedges and end windings will assure long term reliability

• H2 leaks should be addressed immediately. This could be a safety issue!

• Hydrogen seals require the proper parts and assembly techniques

• Generator rotor copper leaf components should be replaced during rewinds

• Generators should not be operated with a field ground

• Rotors should not be pulled prior to troubleshooting shorts and grounds

• Use collector brushes supplied with unit. Do not mix brushes!

• A regularly scheduled collector maintenance plan should be set up

• Grounding brushes should be checked on a routine basis

• Install flux probes and SLMS-HP on all units

• Know your local GE Service Manager and Generator Specialists

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Save the date for GE's annual technical conference for steam turbines and generators. This conference has a long history as THE source of the latest information for steam turbine and generator owners and operators. New this year we are expanding the conference program to include Industrial and Small Steam Turbine Genenerators and Mechanical Drives.

2008 Steam Turbine Generator User’s Conference

We’re going back to New York for the 2008 conference!

Date: July 08-10, 2008Location: Crown Plaza-City Center, Albany, NY

A new look and feel

Scheduled for the week after the 4th of July holiday, we are inviting you and your families the opportunity to piggy back a family vacation in upstate NY with this years event. There are many things to do in the area for the family, while we have the conference and we have several tours of the GE facilities in the area and a tent event for the family, built into the agenda this year. So bring the family and see what Albany and upstate NY has to offer.

Bring your family

http://mailcenter.newmediagateway.com/accvb/sites/43/aboutalbany.htmlLink to the Albany Visitors Bureau

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7 / 1 0 / 2 0 0 8T h u r s d a y

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Agenda change We have adjusted the agenda in response to your feedback, to give you more time in the breakouts and your peers in similar power plants. Track groups will include users from fossil, nuclear, combined cycle and industrial. In addition we are adding break out sessions in some new categories to address the changing needs of our audience. Break out sessions will be in the categories of: training, operations, component design, and new technology.

Attendee Profile: GE steam turbine generator owners/users • plant operators/managers • maintenance managers • corporate turbine engineers/technical services

Agenda Topics include:• Generator Fleet Experience • Outage Experience • Hot Topics Discussions • Steam Path Audit Repairs • Multi-OEM Repairs • Repair Engineering • Boiler Feed Pump Upgrades • Startup Optimization • Vibration Analysis • Oil System Reliability

Online registration will begin in late April 2008

Documents

주발전기경년열화관리기술동향 - KINS · 2018-01-01 · Generator Rotor Vibration • Correct problem diagnosis – Full train turbine-generator review – Field or stator