05000412/LER-1997-001, :on 970106,reactor Trip Occurred Due to Main Transformer Ground Protection Relay.Caused by Inadequate Design Implementation.Procedures 2OM-35.3C & 2OM-35.4L Revised

:on 970106,reactor Trip Occurred Due to Main Transformer Ground Protection Relay.Caused by Inadequate Design Implementation.Procedures 2OM-35.3C & 2OM-35.4L Revised

ML20134G007
Person / Time
Site:	Beaver Valley
Issue date:	02/03/1997
From:	Legrand R DUQUESNE LIGHT CO.
To:
References
LER-97-001, LER-97-1, NPD2VPO:0598, NPD2VPO:598, NUDOCS 9702100245
Download: ML20134G007 (7)

LER-1997-001, on 970106,reactor Trip Occurred Due to Main Transformer Ground Protection Relay.Caused by Inadequate Design Implementation.Procedures 2OM-35.3C & 2OM-35.4L Revised

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv), System Actuation
4121997001R00 - NRC Website

text

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'At5 Telephone (412) 393-6000 Nuclear Group Sh pp. port. PA 15077-0004 February 3,1997 NPD2VPO:0598 l

Beaver Valley Power Station, Unit No. 2 Docket No. 50-412 License No. NPF-73 LER 97-001-00 United States Nuclear Regulatory Commission Document Control Desk Washington, DC 20555 In accordance with Appendix A, Beaver Valley Technical Specifications, the following Licensee Event Report is submitted:

LER 97-001-00,10 CFR 50.73(a)(2)(iv), " Reactor Trip Due to Main Transformer Ground Protection Relay."

n R. L. LeGrand Division Vice President Nuclear Operations

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Attachment

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9702100245 970203 PDR ADOCK 05000412-S PDR

' February 3,1997 NPD2VPO:0598 l

Page 2 -

cc: Mr. H. J. Miller, Regional Administrator United States Nuclear Regulatory Commission Region 1 i

475 Allendale Road King of Prussia, PA 19406 Mr. D. S. Brinkman BVPS Licensing Project Manager United States Nuclear Regulatory Commission Washington, DC 20555 Mr. David Kern i

BVPS Senior Resident Inspector United States Nuclear Regulatory Commission Mr. J. A. Hultz Ohio Edison Company 76 S. Main Street l

Akron, OH 44308 Mr. Mark Burns Centerior Energy Corporation 6200 Oak Tree Boulevard Independence, OH 44131 INPO Records Center 700 Galleria Parkway Atlanta, GA 30339-5957 Mr. Robert Maiers Department of Environmental Resources P.O. Box 8469 State Office Building,13th Floor Harrisburg, PA 17105-8469 Director, Safety Evaluation & Controi Virginia Electric & Power Company 5000 Dominion Blvd.

Innsbrook Tech. Center Glen Allen, VA 23060

i NRC FORM 366 U.S. NUCLEAR REGULAT ORY COMMISSION APPROVED BY OMH SO. 3150-0104 (4 95)

EXPIRES 04 30 98 i

M ON E ON Q ST $0 0 HRS FOR A COMMENT $ REGARDING BURDEN EST! MATT.TOTHE INFORMAT10N LICENSEE EVENT REPORT (LER)

AND RECORD 5 MANAGEMENT BRANCH (MNiiB 77141. U S NUCL EAR REGULATORY COMMISSION WASHINCIUN.DC 20555 0001, ANDTD (See reverse for required number of digits < characters for each block)

[3N7$E R

F pr AS 3

F ALilJfY NAME tlJ DOCRt~1 NLMBER (b PAGE (3)

Beaver Vallev Power Station Unit 2 05000412 1 OF 5 Tm.E Reactor Trip Due to Main Transformer Ground Protection Relav Evf NT DATE(S) i ER NUMHER (6)

REPORT DATE (7)

OTitLR FACILITIES INv0LvED(H)

SEQUENEAL REVISION FACILffY NAME DUCKET NUMBER MONTr{

DAY YEAR YEAR NUMBER NUMBER MONTH DAY YEAR Beaver Valley Power Stanon Umt 1 05000334 01 06 97 97 001 00 02 03 97 N' ^

OPERATING

}

MODE (9) 20 402(b) 20.405(c)

X 50.73(aX2Xiv) 73.71(b) power 98'/o 20.405(aXI Xi) 50.36(cX:)

50.73(ax2Xv) 73.7)(c) t.EVEL (10) 20 405(aXIXn) 50.36(cX2) 50 73(ax2Xvn)

OTi!ER 20 405(aXIXiii) 50.73(aX2Xi) 50.73(aX2 XviiiX A)

(S eafy m sbseact P

20.405(aX1 Xiv) 50.73(aX2Xti) 50.73(aX2XviiiXB) below and m Text 20.405(aXI Xv) 50.73(aX2Xm) 50.73(aX2Xx)

NRC Form 306A)

IJCENSEE CONTACT FOR Tills 1.ER (12)

NAME TELEPilONE NUMBER (mclude AreaCode)

R. L. LcGrand. Vice President Nuclear Operations and Plant Manager (412) 393-7622 COMPI.ETE ONE I INE FOR EACll COMPONENT FAILt'RE DESCRIBED tr DilS REPORT (13)

CAUSE

$YSTEM COMPONENT MANUFACTURER REPORT ABLE

CAUSE

SY STEM COMPONENT MANUf ACitRER REPURTABLE 10 NPRDS TO NPRDS l

B EL 59 G182 Y

SUPPLEMENTAL REPORT EXPECTED (14)

EXPECTED MONTil DAY YEAR YES X

No st'BM!sSION 6 ryes. complete EXPECTED SUBMIS$lON DATT)

DATE (15) 1 ABSTR ACT (Limited to i 400 spaves, te., approximately 15 smgle-spaced typewntien imes) (16)

On January 6,1997, at 0556 hours0.00644 days <br />0.154 hours <br />9.193122e-4 weeks <br />2.11558e-4 months <br />, while in Mode 1 at 98% power, Beaver Valley Power Station Unit 2 experienced a reactor trip caused by turbine trip. The turbine trip was caused by the operation of Main Transformer Ground Protection Relay 59-202G which actuated Main Transformer Auxiliary Relay 87-202XI.

Relay 59-202G was functionally tested and found acceptable. Inspection of the potential transformer wiring and contacts revealed some vibration-induced v,:ar on the 22 KV potential transformer primary contacts. It is believed that this condition resulted in a small voltage drop across these contacts which resulted in an increased voltage to the 59-202G relay, causing it to actuate. Several other relays which should have responded had there been an actual 22 KV ground fault were tested with no anomalics noted. In addition, the results of post-trip startup testing, information from the switchyard fault recorder, the absence of other observed electrical protcetive circuit actuations, and the results of transformer oil samples, support that therc was no actual ground on the 22 KV subsystem.

The root cause of the event was identified as inadequate design implementation. The most probable cause of the turbine trip was due to vibration-induced wear on the 22 KV potential transformer primary contacts.

This event was reported pursuant to the requirements of 10CFR50.72(b)(2)(ii) on January 6,1997. This report is being made pursuant to the requirements of 10CFR50.73(a)(2)(iv) as "Any event or condition that resulted in a manual or automatic actuation of any Engineered Safety Feature (ESF), including the Reactor Protection System (RPS).. "

Secondary plant-related component problems observed prior to the event and during the post-trip recovery were evaluated by the Event Review Team (ERT) and it was concluded they were urirelated to the cause of the trip. It was also concluded by the ERT that these secondary plant problems did not significantly impact post-trip recovery or plant stabilization efforts.

Evahiation has shown that there was no actual ground on the 22 KV subsystem. Post-trip control and protection systems functioned correctly in response to the turbine and reactor trip. Plant parameters were established within their normal control bands shortly after the turbine trip and the plant was placed in a safe, shutdown condition in accordance with procedures. There were no implications to the health and safety of the public as a result of this event.

NRC FORM 3no(4 951

._U.S. NUCLEAR REOULATORY COMMISSION (4-95)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACilJrY N AME (1)

IXX'KET NUMilER (2)

LER NUMBER (6) l PAGE (3)

SEQUENTIAL REvlSION Beaver Valley Power Station Unit 2 05000412 YEAR NUMBER NUMBER j

97 001 00 2 OF 5 nxiora=..pm.

g=.d.m. anon.i.op orwac rann wa)(17)

PLANT AND SYSTEM IDENTIFICATION

I Westinghouse Pressurized Water Reactor (PWR)

Main Transformer Ground Protection Relay 59-202G {EU59/G182}*

Main Generator Backup Ground Protection Relay.50-20lG {EU50/W120}*

Main Generator Primary Ground Protection Relay 59-201G (EU59/G182}*

Main Generator Backup Ground Protection Relay 51-201G {EU51/G182}*

Main Transformer Auxiliary Relay 87-202XI (EU87/G080}*

Main Generator Potential Transformer 2 GEN-PT-CUB {EUXPT/G080}*

Energy Industry identification System (Ells) Plant System, Component, and Manufacturer Codes are identified in the text as (Ells:SS/CC/MMMM).

j CONDITIONS PRIOR TO OCCURRENCE Unit 1: Mode 1,99% Reactor Power Unit 2: Mode 2,98% Reactor Power i

DESCRIPTION OF EVENT

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l On January 6,1997, at 0556 hours0.00644 days <br />0.154 hours <br />9.193122e-4 weeks <br />2.11558e-4 months <br />, while in Mode 1 at 98% power, Beaver Valley Power Station Unit 2 experienced a reactor trip caused by turbine trip. The turbine trip was caused by the operation of Main Transformer Ground Protec'wn Relay 59-202G

{ Ells:EU59/G182} which actuated Main Transformer Auxiliary Relay 87-202XI { Ells:EU87/G080}. According to the specification sheet for relay 59-202G, an ASEA Brown-Boveri Type ITE-59G, the relay should only be in senice to proside ground protection u hen backfeed is established to the Main Transformer from the 345 KV system and the main generator links are open. However, the Unit 2 Operating Manual normal system arrangement and plant electrical drawings indicate that this i

relay has been in senice during plant operation since initial startup. The relay is not addressed in the backfeed procedure.

t i

Relay 59-202G was functionally tested and found acceptable. Inspection of the potential transformer wiring and contacts revealed some vibration-induced wear on the 22 KV potential transformer {EIIS:EUXPT/G080} primary contacts. It is believed t

that this condition resulted in a small voltage drop across these contacts which resulted in an increased voltage to the 59-202G relay, causing it to actuate. Main Generator Backup Ground Protection Relay 50-201G { Ells:EU50/W120}, Main Generator Primary Ground Protection Relay 59-201G (Ells:EU59/G182 }, and Main Generator Backup Ground Protection Relay 51-201G

{EU51/G182}, which should have responded had there been an actual 22 KV ground fault, were tested with no anomalies noted.

In addition, the results of post-trip startup testing, information from the switchyard fault recorder, the absence of other obsen*cd electrical protective circuit actuations, and the results of transformer oil samples from the Main, 2C and 2D transformers, support that there was no actual ground on the 22 KV subsystem.

Secondary plant-related component problems observed prior to the event and during the post-trip recovery were evaluated by the Event Review Team (ERT) and it was concluded they were unrelated to the cause of the trip. It was also concluded by the ERT that these secondary plant problems did not significantly impact post-trip recovery or plant stabilization efforts.

i hRC FORM 306A(4-95)

NRC IORM 366A

~ N.s. NUCLEAR REGULA1ORY COMMISSION (4-95)

LICENSEE EVENT REPORT (LER)

TEXT CONTINt'ATION l' AC11JTY N AME (1)

IX)CKET NUMBER (2) 1.ER NUMBER (6) h PAGE (3)

SEQUENTIAL REvlSION Beaver Valley Power Station Unit 2 05000412 YEAR NUMBER NUMBER 97 001 00 3 OF 5 TITT(If more space a requued, uns addenal copus of NRC Form 306A)(17)

CAUSE OF EVENT

i The root cause of the event was identified as inadequate design implementation. Relay setting sheet BVT-TM-It, normal system aligmnent (NSA) information for relay 59-202G was not reflected in the resised Elementary Diagram 12241-E-8BE, and consequently was not used in the development of the associated Operating Manual procedures. The most probable cause of the turbine trip was due to vibration-induced wear on the 22 KV potential transformer primary contacts.

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ANALYSIS OF EVENT

An Event Resiew Team (ERT) was formed on January 6,1997, to conduct a resicw of this event in aardance with plant i

procedures. The following information was provided in the ERT Report.

Main Transformer Ground Protection Relay 59-202G is an ABB type ITE-590 model 211 Ell 75 provided for ground fault protection on the 22 KV side (delta side) of the Main Transformer, when the transformer is being energized from the 345 KV system (backfeed). The type ITE-59G is a low pickup overvoltage relay which responds to 50 or 60 Hz voltages. The relay has a third harmonic bbcking circuit uhich renders it insensitive to 180 Hz voltages.

Under backfeed conditions, the 22 KV system changes from a " grounded" system to an " ungrounded" system. Under ungrounded (backfeed) conditions, the phase to ground voltages are balanced. However, the third-harmonic voltages will appear in phase with each other and the relay will see three times the third-harmonic component of the phase to neutral voltages. The relay is a low-pickup overvoltage relay, but is designed to ignore third-harmonic voltages. During normal system operation (reactive grounded system) the normal zero sequence voltage swings will be amplified. The 59-202G relay is installed to monitor these nro sequence voltages on an ungrounded system. Since these voltages will be amplified in a grounded system, the relay may inadvertently actuate.

Resiew of this protection scheme identified that it was not intended to be in service during normal plant operation. This was indicated ra alay 59-202G's setting sheet (BVT-TM-16); however, it was not identified on Elementary Diagram 12241-E-8BE or in Opet.uons Manual 20M-35.4C, " Power Supply Control Switch List," or 2OM-35.4L, "Backfeed No. 2 Main Transformer" to be " cut-out" during normal plant operation. Relay 59-202G has the lowest effective setpoint and was not intended to coordinate with generator ground protection, which is designed to protect the generator during operation for ground faults.

)

j Initial troubleshooting tested relay 59-202G and the relay's "as found" condition was satisfactory. It was identified that the relay was operating on the low side ofits setpoint tolerance. It was also identified that the target took a few seconds to operate. It is suspected that since the trip was immediate, the trip conditic t, pparently cleared prior to the relay target operating.

The original 59-202G relay which initiated the event was sent to the Duquesne Light Company (DLC) Standards Laboratory for special testing. Tests included a Surge Withstand Capability (SWC), harmonic and a thermal stress test. This special testing did not identify any problems with the relay.

I Resiew of the Beaver Valley Substation famt recorder did not identify any system disturbance prior to the trip. System j

Operations also confirmed that there were no grid anomatics on the 345 KV power grid at the time of the event. Note that a ground fault on the Main Transformer de19 side would not be seen on the 3r ;V symm.

Main Generator Ground Protection Relays (50-201G,59-20lG and 51-2010) which would be expected ;s opcrate for an actual 22 KV ground fault were tested and found to be functionally satisfactory.

< check of the relay 59-202G input circuit was performed. The circuit was checked for continmty, grounds and tight connections l

with satisfactcry results. It was noted that thcre was esidence of wear on the primary contacts of the 22 KV potential l

transformers from vibratien.

l ac sua mm l

I

NRC IORM 366A U.s. NUCLEAR REGULA'IORY COMMISslON (4-95)

LICENSEE EVENT REPORT (LER)

TEXT CONTINt'ATION 1 ACI!JTY NAME(1)

DOCKFT NUMBE R (2)

LER NUMBER (6)

PAGE (3)

SEQUENTIAL REvlSION Beaver Valle) Power Station Unit 2 05000412 YEAR NUMBER NUMBER 97 001 00 40F5 TEXT Uf muse space in scquued, une ad&tumal cope of NRC Form 306A)(17)

Also, oil samples were obtained and analyzed from the Main,2C and 2D transformers with normal results, supporting that a fault had not oc:urred in the transformers.

The ERT concluded that the most probable cause of the turbine trip was due to vibration-induced wear on the 22 KV potential transformer primary contacts This condition resulted in a small voltage drop across these contacts that resulted in an increased voltage to the 59-202G relay. The "as-found" trip setpoint of the 59-202G relay was 17.1 VAC and the measured voltage at full power was found at t1.5 VAC. Therefore, the increased contact resistance would have only had to produce a 5.6 VAC increase for it to actur,. Actuation of 59-202G actuated relay 87-202XI which, in turn, closed the trM mutacts associated with the Main Generator exciter field breaker, mrbine, main generator output breakers and Bus 2A,2B, id2D semly air circuit breakers (ACBs).

The ERT performed an evaluation of secondary plant-related component problems observed prior to the event and during the post-trip recovery and concluded they were unrelated to the cause of the trip. It was also concluded by the ERT that these secondary plant problems did not significantly impact post-trip recovery or plant stabilization efforts.

CORR 1 CTIVE ACTIONS

1. Procedures 20M-35.3C and 20M-35.4L were revised by January 10,1997 such that relay 59-202G will only be in service during main transformer backfeed operations. The output of this relay was cut-out (disconnect switches open)

January 10,1997.

2. Elementary diagram 12241-E-8BE was resised January 7,1997.

3. The relay setting sheet far relay 59-202G (BVT-TM-16) will be revised by March 15,1997 to provide additional clarification that relay 59-202G protection is cut-out except during backfeed.

4. Selected parameters were monitored during plant startup on January 15,1997 during field flashing of the generator and the power ascension to confirm that there was no 22 KV ground path. This monitoring determined that there is not a l

ground on the 22 KV system.

5. The Main Generator exciter diodes were checked during plant startup on January 15,1997 and found to be satisfactory.

6. The contacts on the Unit 2 22 KV Regulator potential transformers and the 22 KV Met +e and Relay potential transformers were cleaned and lubricated and assessed to be fully functional. These cone will be repla':cd during the next refueling outage (2R7).

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7. A Preventive Maintenance Procedure will be written and implemented by the next refueling outage for each respective Unit (Unit 1 - IR12, Umt 2 - 2R7) to periodically inspect the contacts of the 22 KV Regulator potential transformers and the 22 KV Metering and Relay potential transformers.

8. An extent of condition resiew will be performed for both Units by March 15,1997 to determine if there are other relsy setting sheet conditions that are different than those specified by the controlled drawings.

9. The relay setting shect, procedures, and drawings for the Unit I ground protection relay comparable to Unit 2 relay 59-202G were resiewed by January 9,1997 and determined to be correct.

10. The Nuclea ' ngineering Department will evaluate a setpoint change, to reduce the potential for inadvertent actuEtion on the Unit 2 Main Generator Ground Protection Relays by April 30,1997. Setpoint changes, if required, uir e implemented by the completion of refueling outage 2R7.

hRC M>U' '

• A (44h

. ~.. _ _ _

l NRC tORM 366A U.S. NUCLEAR REOUEATORY COMMISSION j

(4-M)

)

LICERSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILJTY NAME(1)

IXX'KET NUMBER (2) 11R NUMBER (6)

PAGE(3) i SEQUENTIAL REVislON l.

Beaver Valley Power Station Unit 2 05000412 YEAR NUMBER NUMBER 97 001 00 5 OF 5 TEXT Of more space a regiared. une additumal sups of MC Form h6A)(l 7)

REPORTABILITY

This event was reported pursuant to the requirements of 10CFR50.72(b)(2)(ii) on January 6,1997. This report is being made pursuant to the reqrirements of 10CFR50.73(a)(2)(iv) as "Any event or condition tnat resulted in a manual or automatic actuation of any Er_gineered Safety Feature (ESF), including the Reactor Protection System (RPS).. "

i i

Sj.FETY IMPLICATIONS f

l Evaluation has shown that there was no actual ground on the 22 KV subsystem. Post-trip control and protectir,n systems functiened correctly in response to the turbine and reactor trip. Plant parameters were established within their nortc.al control 5

bands shortly after the turbine trip and the plant was placed in a safe, shutdown condition in accordance with procedures. There j

wcre no implications to the health and safety of the public as a result of this event.

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SIMILAR EVENTS

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l A review of Licensee Event Reports for the past two years identified no similar events.

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