ML17056B883

Summary of 920519 Meeting W/Util in Rockville,Md to Discuss Results of Failure Analysis Performed on B Phase Main Transformer from Facility That Failed on 910813.Attendees List & Licensee Handout Matl Also Encl

ML17056B883
Person / Time
Site:	Nine Mile Point
Issue date:	05/26/1992
From:	Menning J Office of Nuclear Reactor Regulation
To:	Office of Nuclear Reactor Regulation
References
NUDOCS 9206030260
Download: ML17056B883 (64)

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Docket No. 50-410 UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 Hay 26, 1992 LICENSEE:

Niagara Mohawk Power Corporation FACILITY:

Nine Mile Point Nuclear Station Unit 2

SUBJECT:

MEETING MINUTES REGARDING THE HAY 19,

1992, HEETING TO DISCUSS RESULTS OF THE FAILURE ANALYSIS PERFORMED ON THE "B" PHASE HAIN TRANSFORMER FROM NINE MILE POINT NUCLEAR STATION, UNIT 2, THAT FAILED ON AUGUST 13, 1991 A meeting was held at the NRC One White Flint North Office in Rockville, Maryland, with Niagara Mohawk Powe'r Corporation (NHPC) and NRC staff representatives to discuss the results of the failure analysis that was performed on the "B" phase main transformer from Nine Mile Point 2 that failed on August 13, 1991.

The failure of this transformer initiated events within the unit that eventually resulted in the declaration of a Site Area Emergency.

The subject meeting was requested by the NRC staff.

Enclosure 1 is a list of meeting attendees.

The handout material used by NHPC during the meeting is attached as Enclosure 2.

During the meeting NMPC initially provided a description of the transformer and discussed the preventive maintenance that had been performed prior to the failure.

Preventive maintenance involved daily rounds

checks, quarterly oil

sampling, and 18-month maintenance.

The licensee then described how the transformer was dismantled and the results of related visual examinations of the transformer internals.

The transformer was dismantled and examined by HagneTek Incorporated at its repair facility in Bradenton, Florida.

In

essence, the cause of the failure could not be conclusively determined since coils in the region of the transformer where failure most likely initiated were extensively damaged.

The licensee indicated that nothing discovered during the dismantling, unstacking, and visual examinations of the transformer would suggest or require changes in NHPC's operating procedures for similar generator step-up transformers.

The licensee stated that previous preventive maintenance on the transformer did not reveal any abnormalities that would have provided warning of an impending failure.

During a discussion of other, currently available techniques for monitoring transformer performance, NHPC pointed out that these techniques are often incapable of giving advanced warning of a sudden, rapidly propagating failure such as occurred on August 13, 1991.

Despite this limitation, NMPC is currently considering the use of an on-line monitoring system to enhance its transformer monitoring capability.

Such a system,.could provide an indication of deteriorating transformer performance sooner than the current preventive maintenance program.

A decision on whether to use an on-line system could be made in September or October of 1992.

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Hay 26, 1992 The licensee stated that the subject transformer will be rebuilt by HagneTek.

The transformer will subsequently be returned to. Nine Nile Point 2 and placed in service as the "B" phase main transformer.

Enclosures:

1.

List of Attendees 2.

Licensee Handout Haterial John E. Henning, Project Hanager Project Directorate I-I Division of Reactor Projects - I/II Office of Nuclear Reactor Regulation cc w/enclosures:

See next page

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May 26, 1992 The licensee stated that the subject transformer will be rebuilt by MagneTek.

The transformer will subsequently be returned to Nine Mile Point 2 and placed in service as the "B" phase main transformer.

Enclosures:

1.

List of Attendees 2.

Licensee Handout Material Original Signed By:

John E. Henning, Project Manager Project Directorate I-1 Division of Reactor Projects - I/II Office of Nuclear Reactor Regulation cc w/enclosures:

See next page DISTRIBUTION:

-Docket Fil e--,

NRC--8 Local PDRs PDI-1 Reading TMurley/FMirag 1 i a JPartlow SVarga JCalvo RCapra JHenning CVogan OGC

EJordan, 3701 JIbarra EBrown HWegner SAggarwal FAshe SMazumdar WLeschek ACRS (10)

RLobel, EDO 17G21 CCowgill, RGN-I OFFICE IIAME DATE PDI-1 LA CVOGAN 53 5/2t/92 PDI-1 PH JMENNING:t 6Qt 92 PDI-1 D

RCAPRA~

5 2492 OFFICIAL RECORD COPY FILENAME: NMP2.MTS

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B. Ralph Sylvia Niagara Mohawk Power Corporation Nine Mile Point Nuclear Station Unit No.

2 CC:

Mark J. Wetterhahn, Esquire Winston 5 Strawn 1400 L Street, NW.

Washington, DC 20005-3502 Hr. Richard Goldsmith Syracuse University College of Law E. I. White Hall Campus

Syracuse, New York 12223 Resident Inspector Nine Mile Point Nuclear Station P. 0.

Box 126

Lycoming, New York 13093 Gary D. Wilson, Esquire Niagara Mohawk Power Corporation 300 Erie Boulevard West

Syracuse, New York 13202 Mr. David K. Greene Manager Licensing Niagara Hohawk Power Corporation 301 Plainfield Road

Syracuse, New York 13212 Hs.

Donna Ross New York State Energy Office 2 Empire State Plaza 16th Floor

Albany, New York 12223 Supervisor Town of Scriba Route 8, Box 382

Oswego, New York 13126 Regional Administrator, Region I U. S. Nuclear Regulatory Commission 475 Allendale Road King of Prussia, PA 19406 Charles Donaldson, Esquire Assistant Attorney General New York Department of Law 120 Broadway New York, New York 10271 Hr. Richard H. Kessel Chair and Executive Director State Consumer Protection Board 99 Washington Avenue

Albany, New York 12210 Hr. Martin J.

HcCormick Jr.

Plant Manager, Unit 2 Nine Mile Point Nuclear Station Niagara Mohawk Power Corporation P. 0.

Box 32

Lycoming, New York 13093 Hr. Joseph F. Firlit Vice President Nuclear Generation Nine Mile Point Nuclear Station Niagara Mohawk Power Corporation P. 0.

Box 32

Lycoming, New York 13093

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ENCLOSURE 1

ATTENDANCE LIST Hay 19,

1992, Meeting with NHPC to Discuss Results of Failure Analysis Performed on "B" Phase Hain'ransformer that Failed on August 13, 1991 NAME John Henning Jose Ibarra Earl Brown Mary Wegner Satish Aggarwal Anil Julka Harold Light Matthew Gress W. David Baker Mark Lombard Frank Ashe Subinoy Hazumdar Walt Leschek POSITION Project Manager Senior 18C Engineer

Chief, Eng. Section Reactor Systems Eng.

Program Manager Elect./IEC Supervisor Senior Eng. Specialist Engineering Manager Licensing Prog. Dir.

Vice President Electrical Engineer Electrical, Engineer Plant Systems Engineer ORGANIZATION NRC/NRR/PD I-1 NRC/AEOD/PDNP NRC/AEOD/ROAB NRC/AEOD/ROAB NRC/RES Niagara Mohawk Niagara Mohawk HagneTek Inc.

Niagara Mohawk HDM Engineering NRC/NRR/DST NRC/AEOD/ROAB NRC/AEOD/TPAB

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ENCLOSURE 2

NIA A I H WEP O'R RP R4TI N NINE MILEPOINT UNIT2 B PHASE TRANSFORMER FAILURE ROOT CAUSE INVESTIGATION MEETING WITHNRC MAY19, 1992

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A EDA INTRODUCTIONS W. D. BAKER BACKGROUNDS)

Transformer Description Preventive Maintenance W. E. ADAMS ROOT CAUSE IIPi&STIGATION W. E. ADAMS H. F. LIGHT

TRA F R ER DE RIPTI RI INALM MCGRAW-EDISON ACTDlURR:

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SERIAL M.MBER:

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SHIPPED:

C-06607-5-2 MARCH 1984 IN T LLKD:

NINE MILEPOINT UNIT 2

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COMPONENT:

2MTX-XM1B

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"B"..PHASE OF THREE-PHASE BANK

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GENERATOR STEP UP TRANSFORMER RATIN SINGLE PHASE TRANSFORMER 350000 GRD. Y/202073 - 24300 VOLTS 408/457 MVACLASS FOA 55'/65'. RISE 60 HERTZ HV - 1050kv BIL, +/- 2-1 /o NO LOADTAPS LV - 150kv BIL

PRE E Tl E AI TE A E

DAILYR UI'A)

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PHYSICAL CHARACTERISTICS

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READINGS

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OPERATION OF FANS AND PUMPS

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NOISE QUARTERLYOIL SAMPLING 1S-MORPH PREVENTIVE NANCE

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A EI E TI ATI AU E EVAL ATED

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STATIC ELECTRIFICATION

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GEOMAGNETICALLYINDUCED CURRENTS

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INSULATIONDETERIORATION

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CORONA

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ORIGINALWORKMANSHIP

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DESIGN DEFICIENCY

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FREQUENCY RESONANCE

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SHIPPING DAMAGE

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N TOP AS STACKED ON FLOOR (L1)

LV COIL CORE STEEL LV X1 STATIC SHIELD (L2)

LV COILS I

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HV COILS (Hl)

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HV H1 12 13 (L3)

LV COILS I

HV COILS (H2)

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2 NO LOAD TAPS 6

19 HY Ha 14 BOTTOM 16 ORE STEEL FIGURE "1

SIMPLE, L'V, AND HV COIL CONFIGURATION LY X2

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DISMANTLING OF GENERATOR STEP UP TRANSFORMER FOR NINE MILE POINT ¹2 NUCLEAR STATION, AT MAGNETEK (OHIO TRANSFORMER)

BRADENTON, FLORIDA, REPAIR FACILITY PHASE "B" OF THREE SINGLE PHASE UNITS BANK ¹2MTX-XM1B MANUFACTURED BY MCGRAW-EDISON (COOPER INDUSTRY) 1984 SHELL TYPE TRANSFORMER SERIAL ¹C-06607-5-2 350kV gnd wye, 1050kU BIL,

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2Q% Taps 24.9 kV delta, 150 kV BIL 408/457 MVA, 55/65'C, FOA The electrical coil configuration diagram, see Figure 1, is arranged in the same manner as the physical arrangement of the coils when prepared for dismantling.

Low voltage coil 1 being on the top of the stack and low voltage coil 16 being the bottom.

This makes dismantling easy to follow from Figure 1, that is the electrical and mechanical arrangements are the same.

Photo 1 shows coil pack looking at bottom.

With the core steel removed and the coils removed from the lower tank section, one can see the external signs of the failure around the perimeter of the coil stack.

See Figure 2 - Areas 1 and 2 at the outside perimeter of the LV coils, area 2 at the inside perimeter also, and area 3 where some slight flash-over occurred between the LV and HV coils.

These appeared to be the areas where the.majority of damage had occurred.

Photo 2

shows perimeter; Photo 3, core steel damage; and Photo 5, flash-over area.

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2 Dismantling began by unstacking LV coil 1.

The first four low voltage windings for all practical purposes were in very ood ry goo condition.

No signs of any

nature, either electrical nor mechanical, that a failure had taken place, each coil was inspected very carefully.

High voltage coils 1 through 9 were also in very good condition.

Up to this point each coil removed from the coil stack looked to be in excellent condition.

Photo 4 is a typical coil, all in excellent condition.

HV coil 10 (area 3 on Figure 2) had a failure which occurred over and through the major insulation barriers of high to low voltage.

Zt appears that this is a failure which occurred from LV coil 5

to HV coil 10.

The failure in HV coil 10 is very superficial, there is a small area of electrical splash-over on HV coil 10.

The failur'e had to go through the major insulating board between the highs and lows.

This insulation included the crepe paper angles on the high voltage coil and the collars and washer barriers between the highs and lows.

Zt is suspected that near the

~I end of the failure process, the dielectric strength between the highs and lows in this area was greatly decreased, allowing this event to occur.

The upward and outward expansion of LV coil 5

along with all the combustible gases rising to the top of the unit greatly diminished the high to low dielectric strength and in all probability caused a flash-over from low to high.

LV coil 5 had serious electrical damage in this area, it showed damage to the extent of a large hole into the coil from the outside perimeter of HFL>NM2R020A.2JC

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3 the winding, but the damage was not as great as in areas 1 and 2.

Photo 5 shows flash-over on HV 10 and damage on LV 5.

LV coils 5,

6, 7,

8 and 9

were all involved with the electrical failure as shown on Figure 2.

Coil 5 and 6 were the most severely damaged coils, 'the magnitude then diminished from I

coils 7 to 9.

LV co..

9 has very little electrical involvement.

Both electrical and mechanical damage was extensive in LV 5 and 6.

Electrically, multiple turn-to-turn and coil-to-coil failures had occurred in the immediate failure areas with a large amount of burning and evidence of a large amount of energy and short circuit current caused by the failure of these coils.

Electrically, whatever caused the initiation of the failure in these areas was totally consumed in the tremendous magnitude of the failure. It is evident that the electrical energy from the decaying generator field and the rotating mass of the generator fed into this area of the failure.

Mechanically, outside of the electrical

areas, failure was widespread throughout each coil.

Extensive mechanical damage of beam strength and coil buckling was evident as these coils attempted to go in all directions, limited only by the confinements involved in a shell form constructed transformer.

Both area 1 and 2 failed to the outside core shield.

Area 2 also failed to the inside core shield and to the core steel.

Core steel damage occurred in area 2 on the inside perimeter.

Inspection of the remainder of the core steel showed no evidence of further damage.

See Photos 6 to 12, one can see extensive failure areas.

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LV coil 10 was mechanically involved with areas of deformation, but no electrical failure.

LV coils 11 and 12 showed no signs of failure.

HV coils 11 thru 19 all looked good.

LV coil 3.3 thru 16 looked good except for some slight mechanical deformation at the bottom of coils 15 and 16.

From all the evidence involved, one can only hypothesize as to the cause of this failure.

Somehow, in some way the dielectric integrity broke down in area 1 or 2

and ultimately caused a

catastrophic electrical failure.

Whichever area started first, either 1 or 2, it was most rapidly followed by thy other, since the magnitude of failure appears to be about equal in each area.

Outside of the electrical failure in LV coils 5 to 9

and the mechanical damage in 10, there is no other evidence throughout the unit that could lead to a cause for the failure.

The entire uzi4t was carefully inspected as each coil was removed.

There are no signs of static electrification anywhere.

Special care was taken to inspect coil spacer

areas, where possibly ',higg.~eelocity,".oil would flow, where thi.s-;event can'ave its..orig&. '"There'was not a t

single sign-of tracking, even near the: immediate area of"-the failure.

There is no sign of core steel overheating, other 'than area 2, or overheating of the tank.

The entire unit~s inspected for geomagnetically induced currents (GIC).

GIC causes saturation of the core steel, over excitation and possibly tank heating from the 'stray flux.

Not a single sign could be found anywhere on the transformer.

Removing the insulation from the high voltage no load HPLENM2R020A.2JC

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5 tap leads, it was found that lead 4 and 2

showed some signs of overheating.

Even though this was a non-contributing occurrence to the failure, it could account for the slight generation of CO and CO, in this unit.

Photo 13.

There has been absolutely nothing discovered during the dismantling and unstacking of this unit that would require a change in the operating procedures used in the operation of these generator step up transformers.

The failure was rapid and devastating, it totally consumed three areas of the low voltage coils with tremendous electrical energy and mechanical force.

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f~i LV 5-12 HV 11-19 LV 13-16 Coil pack as removed from tank and placed on floor for unstacking.

Looking at bottom of coil pack.

This end'goes into lower section of tank when uprighted.

LV 1,2,3,4 on top, down to LV 16 same arrangement as shown on Fig. II1.

PHOTO 1

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Area 2 where low voltage windings failed to core steel, inner side of coil pack.

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'rea 2, outer perimeter of LVcoil area.

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Core steel damage inhere LV failed to core steel. inside of area 2.

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Typical coils in upper section of.

coil pack before reaching LV 5.-

These are HV 2 & HV 5, coils are in excellent condition, every coil down to LV coil 5 was in excellent condition.

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HV coil 10 where LV 5 flashed over to HV 10 area 3 figure 2 iC LV 5 where flash over occurred to HV 10 area 3 figure 2 PHOTO 5 HFLiHFLPL028.~JC

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LV coil 5, area 2 on Figure II2 Extensive electrical and mechanical damage.

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4 LV coil 5.

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LV coil 5, area of electrical damage.

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LV coil 5 LV coil 5, area 1, at perimeter of coil.

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LV coil 6. area 2 extensive electrical and mechanical damage.

LV coil 6, area 2 extensive electrical and mechanical damage.

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LV 8, area 2 failure diminishes.

LV 8, area 2 failure diminishes.

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LV coil 9 PHOTO 12 HFL HFLPLOZS.JC

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HV tap 2, overheated tap lead HV tap 4, overheated tap lead PHOTO 13 HFL)HFLPL0"S.~JC

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