ML17219A654

LER 87-011-00:on 870521,turbine Generator Lockout Relay Trip Occurred Resulting in Automatic Turbine Trip.Caused by Increase in Exciter Field Current Due to Failed Transducer. Faulty Wires Repaired & Transducer replaced.W/870622 Ltr

ML17219A654
Person / Time
Site:	Saint Lucie
Issue date:	06/20/1987
From:	Mendoza V, Woody C FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
L-87-260, LER-87-011-01, LER-87-11-1, NUDOCS 8706300862
Download: ML17219A654 (6)

Text

REGULA INFORMATION DISTRIBUTIQ YSTEM (RIDS)

ACCESSION NBR: 870b3008b2 DOC. DATE: 87/Ob/20 NOTARIZED: NO DOCKET 0 FACIL: 50-335 St. Lucie Plant/ Unit iI Florida Poeer 5 Light Co. 05000335 A'UTH. NAME AUTHOR AFFILIATION MENDOZA. V. N. Florida Power h Light Co.

WOODYI C. O. Florida Poeer. 8c Light Co.

REC IP. NAME REC IP IENT *FF ILI AT ION

SUBJECT:

LER 87-011-00: on 870521/ turbine generator lockout relay trip occurred resulting in automatic turbine trip. Caused bg increase in exciter field current due to failed transducer.

Faulty eires repaired 8c transducer replaced. W/870b22 ltr.

DISTRIBIJTION CODE: IE22D COPIES RECEIVED:LTR g ENCL / SIZE:

TITLE: 50. 73 Licensee Event Report HLER)i Incident Rpti etc.

NOTES:

RECIPIENT CQP IES REC IP IENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD2-2 LA 1 PD2-2 PD 1 TOURIGNYI E 1 1 INTERNAL: ACRS NI CHELSON 1 1 *CRS MOELLER 2 2 AEOD/DOA 1 1 AEOD/DSP/ROAB 2 2 AEOD/DSP/TPAB 1 1 DEDRO 1 NRR/DEST/ADE 0 NRR/DEST/ADS 1 0 NRR/DEST/CEB 1 1 NRR/DEST/ELB 1 NRR/DEST/ICSB 1 NRR/DEST/MEB 1 NRR/DEBT/NTB 1 NRR/DEST/PSB 1 1 NRR/DEST/RSB 1 1 NRR/DEBT/SGB NRR/DLPG/HFB 1 NRR/DLPG/G*B 1 1 NRR/DOEA/E*B 1 1 NRR/DREP/RAB 1 1 NRR/DREP/RPB 2 2 NRR/PNAS/ILRB 1 1 NRR/PNAS/PTSB 1 1 G IL 02 1 RES DEPY GI 1 1 RGN2 FILE 01 1 1 EXTERNAL: EGSG GRQHI M- 5 5 H ST LOBBY WARD 1 1 LP DR. 1 NRC PDR 1 NSIC HARRISI J 1 1 NSIC MAYSI G 1 1 TOTAL NUMBER OF COP IES REQUIRED: LTTR 42 ENCL 40

NRC Form 344 U.S. NUCLEAR REOULATORY COMMISSION (943)

APPROVED OMB NO. 31500)BI LICENSEE EVENT REPORT ILER) EXPIRES.'/31/88 FACILITY NAME (1) DOCKET NUMBER (2) PA E 3 St. Lucie Unit 1 0 5 0 0 03 5 1 OF o 4 REACTOR TRIP RESULTING FROM A TURBINE GENERATOR LOCKOUT TRIP CAUSED BY EQUIPMENT FAILURE EVENT DATE IS) LER NUMBER (4) REPORT DATE (7) OTHER FACILITIES INVOLVED IB)

MONTH DAY YEAR &or SEQUENT/AL sr E YrcloN DAY YEAR FACILITYNAMES DOCKET NUMBER(SI YEAR NUMBER:~N NUMBER MONTH N/A 0 5 0 0 0 05 21 8787 0 1 0 0 0 6 8 7 0 5 0 0 0 THIS REPORT IS 4UBMITTEO PURSUANT T 0 THE REQUIREMENTS OF 10 C FR (): /Checsr Onr Ol mOrr O/ tne /Ollrwino/ (11 OPERATINO MODE (Sl 20A02(B) 20AOS(c) 50.73(e) (2)(lr) 73.71 (rs)

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LICENSEE CONTACT FOR THIS LER (12)

NAME TELEPHONE NUMBER AREA CODE Victor N. Mendoza, Shift Technical Advisor 30 46 5-35 50 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)

CAUSE SYSTEM COMPONENT MANUFAC. EPORTABLE SYSTEM COMPONENT MANUFAC. EPORTAB(.E TURER TO NPRDS TURER TO NPRDS TL TD Wl 20 N jj+ittwj jb~@'4Q~

eF'i'var Pew@ax SUPPLEMENTAL REPO/lT EXPECTED IICI MONTH DAY YEAR EXPECTED SU 8 MISSION DATE (15)

YES /I/ yrs, comp/rtr EXPECTED St/SM/$ 3/D// DATE/ X ABBTRAGT /Limit ro /r00 sneer/, /r., epproelmerrly /i/rem slnolr ewer ryprwrirrrn linn/ (14)

ABSTRACT While St. Lucie Unit 1 was in Mode 1 and at steady state conditions, the reactor tripped by virtue of the loss of turbine load trip. A turbine lockout trip was initiated by the tripping of the generator lockout relay by the overexcitation protection limiter. The cause of the event was due to an increase in exciter field current which exceeded the setting of Instantaneous Current Limiter I3 which directly gives a generator lockout. The root cause of .the exciter field current increase was a failed transducer. Immediate actions were performed to bring the reactor to a stable condition. Two defective wires were repaired, the failed transducer was replaced, and the current limiter was re-set to its specified setting.

87063008h2 870620 PDR ADQCI(I 05000335 S PDR NRC form 344 (9 83 I

NRC FoIm 366A US. NUCLEAR REGULATORY COMMISSION (94)3)

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION APPROVEO OM8 NO. 3160M(04 EXPIRES: 8/31/88 FACILITY NAME (1) DOCKET NUMBER (2) LER NUMSER (6) PAGE (3)

SEOUENTIAL >VFr. REVISION YEAR gg NUMBER "IP/Y NUMEER St. Lucie Unit 1 0 5 0 0 0 3 3 8 7 011 0 0 0 2 OF 0 4 TEXT ///mevF FPFc>> /I IFEIIPFd, IIFF afdiceI>>/NRC FdmI 3664'F/ (12)

DESCRIPTION OF THE EVENT On May 21, 1987, St. Lucie Unit I was in Mode 1 and steady state conditions.

All systems were functioning normally. All major control stations were in automatic mode with the exception of the turbine controls and the atmospheric steam dumps which were in manual mode. At approximately 1504 hours0.0174 days <br />0.418 hours <br />0.00249 weeks <br />5.72272e-4 months <br />, a turbine generator (EIISETB) lockout relay trip occurred and resulted in an automatic turbine trip.

The Reactor Protection System (RPS) functioned as designed providing an automatic reactor trip signal on loss of load. Operations personnel performed all the required immediate actions necessary to bring the plant to a stable condition.

All safety functions were met. Auxiliary Feed Water Pumps lA, 1B, and 1C were manually started to ensure that steam generator levels were maintained. This event was observed to be an uncomplicated reactor trip.

CAUSE OF THE EVENT The cause of the event was due to an increase in exciter (EIIS:TL) field current reaching the Instantaneous Current Limiter N3 setting resulting in a turbine generator lockout trip. The Instantaneous Current Limiters ILN1, ILN2 and ILI3 are part of the newly installed high initial response exciter system'.

During the initial investigation by plant electrical maintenance, plant operations, and site Westinghouse personnel, a potential cause was found in that the cover of a current transformer had pinched one wire lead and that another wire lead was worn to a bare wire condition. The pinched and the bare wires could have caused the signal to the current transformer to be degraded giving a false indication of low current or no current. The Minimum Excitation Limiter (MEL) would respond by providing an increase in field current thus resulting in the transient.

It was also found that the setting of the Instantaneous Current Limiter N2 was incorrectly set at a higher setting than Instantaneous Current Limiter N3.

As designed, the setting for ILN2 should be at a setting lower than ILI3 to provide a limiting action before ILI3 trips the generator. The wiring deficiencies were the result of cognitive personnel error by contractor technicians and the incorrectly set current limiter was the result of cognitive personnel error by generator vendor technicians. There were no procedure deficiencies or unusual characteristics of the work location that directly contributed to the errors.

NRC FORM 3ddA (943)

(.

,' NRC Form 3SSA UA, NUCLEAR REOULATORY COMMISSION (943)

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION APPROVED OMB NO. 3160&104 EXPIRES: 8/31/88 FACILITY NAME (1) OOCKET NUMBER (3) LER NUMBER (6) PACE (3)

YEAR SEOUENTIAL REVISION NUMBER NUMSER St. Lucie Unit 1 o s o o o 8 7 0 1 1 0 0 3 OF 0 4 TEXT ///mare e/reee ie ee/vlrerL vee er/I//1/one/NRC Form 3SSA'e/ (17)

The wiring deficiencies were corrected and the current limiter was readjusted.

After the corrective actions were performed, it was.concluded that it would be necessary to return to power to perform additional testing to further confirm the root cause of the event. The unit was then returned to full power operation on May 23, 1987. After the unit was at full power, at approximately 1131 on May 24, 1987, oscillations on megawatt, megavar, and kilovolt recorders and indicators were observed. Further troubleshooting was then performed. The voltage regulator was placed in manual to minimize the potential of further transients. An on-line recorder was connected to various signals inside the voltage regulator. This monitoring effort revealed the actual root cause to be an intermittent equipment failure of an exciter current isolation transducer.

A new transducer was obtained from plant stores and was calibrated prior to replacement. On May 30, 1987, the defective transducer was replaced.

ANALYSIS OF THE EVENT The event is reportable under 10 CFR 50.73 (a) (2) (iv), "Any event or condition that results in manual or automatic actuation of any engineered safety feature (ESF), including the Reactor Protection System (RPS)". This event was a classic loss of load reactor trip and as such is conservatively bounded by the analysis of Updated Final Safety Analysis Report chapter 15.2.7, "Loss of external electrical load and/or turbine stop valve closure."

The trip was observed to be uncomplicated and all safety functions were met.

At no time during the event was the health and safety of the public endangered.

CORRECTIVE ACTIONS

1. The defective wire leads on the current transformer were repaired.

2. Instantaneous Current Limiter ILN2 was readjusted to the correct setting.

3. The defective transducer was replaced.

NRC FORM ESSA (9431

NI)C Form 3ESA U.S. NUCLEAR REGULATORY COMMISSION (943)

LICENSEE EVENT REPORT ILER) TEXT CONTINUATION APPROVED OMB NO. 3150-0104 EXPIRES: B/31/EB FACILITY NAME (11 DOCKET NUMBER (2) LER NUMBER (6I PAGE (3)

YEAR S~P SEGUENTIAL ÃQ REVISION NUMBER NUMSER St. Lucie Unit 1 o 5 o o o 8 7 011 00 04 OF 0 4 TEXT ///more e/rece /1 /er/Irrled, Iree eddio'orre/NRC Fomr 3654'e/()7)

ADDITIONAL INFORMATION Failed Component Identification:

Isolation Transducer:

Style No. 688C563G01 Manufacturer: Westinghouse Electric Corporation PREVIOUS SIMILAR EVENT This is the first time a failure of this type of transducer has occurred in St. Lucie Plant.

NRC FORM SSSA (943)

P. O. 4000, JUNO BEACH, FL 33408-0420 33 1981 JUNE L7-260 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555 Gent I em en:

Re: St. Lucie Unit No. I Docket No. 50-335 Reportable Event: 87-I I Date of Event: May 2I, l987 Reactor Trip Resulting From a Turbine Generator Lockout Tri Caused b E ui ment Failure The attached Licensee Event Report is being submitted pursuant to the requirements of IO CFR 50.73 to provide notification of the subject event.

Very truly yours, roup Vice President Nuclear Energy COW/GRM/gp cc: Dr. J. Nelson Grace, Regional Administrator, Region II, USNRC Senior Resident Inspector, USNRC, St. Lucie Plant an FPL Group company GR M3/029/ I