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{{#Wiki_filter:REGULA, Y INFORMATION DISTR I BUT I YSTEM (R IDS)ACCESSION NBR: 8802020148 DOC.DATE: 88/01/29 NOTARIZED:
{{#Wiki_filter:REGULA,Y       INFORMATION DISTR I BUT I     YSTEM ( R IDS )
NO FACIL: 50-389 St.Lucie Plant>Unit 2>Florida Poeer 5 Light Co.AUTH.NAME AUTHOR AFFILlATION JOHNSON'.B.Fl or i da Poeer 5 Light Co.WOODY.C.O.Florida Power 5 Light Co.REC IP.NAME RECIPIENT AFFILIATION DOCKET¹05000389 ,
ACCESSION NBR: 8802020148           DOC. DATE: 88/01/29     NOTARIZED: NO         DOCKET  ¹ FACIL: 50-389 St. Lucie Plant> Unit     2> Florida Poeer   5 Light Co.       05000389 AUTH. NAME             AUTHOR   AFFILlATION JOHNSON'. B.         Fl or i da Poeer 5 Light   Co.
WOODY. C. O.         Florida   Power 5 Light Co.
REC IP. NAME           RECIPIENT AFFILIATION


==SUBJECT:==
==SUBJECT:==
LER 87-007-01:
LER 87-007-01: on 871125. reactor tripped on loss of load due to turbine trip. Caused bg personnel error. Permanent magnet generator 5 exciter bearing replaced Zc exciter bearing thermocouple removed. W/880129       ltr.
on 871125.reactor tripped on loss of load due to turbine trip.Caused bg personnel error.Permanent magnet generator 5 exciter bearing replaced Zc exciter bearing thermocouple removed.W/880129 ltr.DISTRIBUTION CODE: IE22D COPIES RECEIVED: LTR ENCL SIZE: TITLE: 50.73 Licensee Event Report (LER)i Incident Rpti etc.NOTES: REC IP IENT ID CODE/NAME PD2-2 LA TOURIGNYi E COPIES LTTR ENCL 1 1 1 1 REC IP IENT ID CODE/NAME PD2-2 PD COPIES LTTR ENCL 1 1 INTERNAL: ACRS MICHELSON AEOD/DOA AEOD/DSP/ROAB ARM/DCTS/DAB NRR/DEST/ADS NRR/DEST/ELB NRR/DEST/MEB NRR/DEST/PSB NRR/DEST/SGB NRR/DLPG/GAB NRR/DREP/RAB A)R/SIB REG FILE 02 IB RGN2 FILE 01 EXTERNAL: EG5G GROHi M H ST LOBBY WARD NRC PDR NSIC MAYST G 1 1 1 1 2 2 1 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 5 5 1 1 1 1 1 1 ACRS MOELLER AEOD/DSP/NAS AEOD/DSP/TPAB DEDRO NRR/DEST/CEB NRR/DEST/ICSB NRR/DEST/MTB NRR/DEST/RSB NRR/DLPG/HFB NRR/DOEA/E*B NRR/DREP/RPB NRR/PMAS/ILRB RES TELFORDi J RES/DRPS DIR FORD BLDG HOY>A LPDR" NSIC HARRIS>J 2 2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 1 1 1 1 1 1 1 1 1 1 1 TOTAL NUMBER OF COPIES REQUIRED: LTTR 46 ENCL 45  
DISTRIBUTION CODE: IE22D COPIES RECEIVED: LTR                 ENCL     SIZE:
TITLE: 50. 73 Licensee Event Report (LER) i Incident Rpti etc.
NOTES:
REC IP IENT         COPIES            REC IP IENT        COPIES ID CODE/NAME          LTTR ENCL        ID CODE/NAME       LTTR ENCL PD2-2 LA                 1     1     PD2-2 PD               1      1 TOURIGNYi E              1     1 INTERNAL: ACRS MICHELSON               1    1      ACRS MOELLER            2      2 AEOD/DOA                 1    1      AEOD/DSP/NAS            1      1 AEOD/DSP/ROAB             2    2      AEOD/DSP/TPAB          1      1 ARM/DCTS/DAB             1            DEDRO                  1      1 NRR/DEST/ADS             1    0      NRR/DEST/CEB            1      1 NRR/DEST/ELB                    1      NRR/DEST/ICSB          1      1 NRR/DEST/MEB              1    1      NRR/DEST/MTB            1       1 NRR/DEST/PSB              1    1      NRR/DEST/RSB            1      1 NRR/DEST/SGB                    1      NRR/DLPG/HFB            1 NRR/DLPG/GAB              1    1      NRR/DOEA/E*B           1      1 NRR/DREP/RAB              1    1      NRR/DREP/RPB           2 A)R    /SIB          1    1      NRR/PMAS/ILRB           1      1 REG  FILE        02      1    1      RES TELFORDi J         1      1 IB            1    1      RES/DRPS DIR           1      1 RGN2    FILE    01      1    1 EXTERNAL: EG5G GROHi M                5    5      FORD BLDG HOY> A       1 H ST LOBBY WARD          1     1     LPDR"                  1       1 NRC PDR                  1     1     NSIC HARRIS> J          1       1 NSIC MAYST G              1     1 TOTAL NUMBER OF COPIES REQUIRED: LTTR             46   ENCL     45


NRC Form 3SSA 19413 l LICENSEE ENT REPORT (LER)TEXT CONTINUA ION U.S, NUCLEAR REGULATORY COMMISSION APPROVED OMB NO.3150&104 EXPIRES: 9/31/BB FACILITY NAME III St.Lucie, Unit 2 OOCKET NUMBER Ill YEAR LER NUMBER IBI@~a.SFOVENT/AL NvM Err xo,: REvrsroN iM NVM Ell PAGE 0)TEXT/if moro s/rsco is rsr/rr/rsd, rrso sddio'orrs/
NRC Form 3SSA                                                                                                               U.S, NUCLEAR REGULATORY COMMISSION 19413 l LICENSEE                   ENT REPORT (LER) TEXT CONTINUA ION                       APPROVED OMB NO. 3150&104 EXPIRES: 9/31/BB FACILITY NAME III                                                                   OOCKET NUMBER Ill            LER NUMBER IBI                    PAGE 0)
H/IC Fonrr 3////A'/(IT)o s o o o 3 89'87 007 0 1 0 2 OF 0 4 DESCRIPTION OF ENTENTE On 25 November, 1987, St.Lucie Unit Two was operating at 50 percent power steady state in Mode 1.The unit was returned to service on 23 November following a refueling outage and was holding at 50 percent power while repairs were in progress on the 2A Steam Generator Feed Pump (SGFP)(EIIS:SJ)due to a small water leak that developed on the vent line at the pump casing.The reactor was being maintained in a steady state condition with all automatic controllers placed in automatic with the exception of the Control Rod Drive System (EIZS:JD)which was in OFF.At 2331 hours, the Reactor Protective System (EIZS:JC)initiated a reactor trip on loss of load due to a turbine trip.The turbine tripped on a main generator (EIIS:TB)lockout.The control room was alerted with information that smoke was seen coming out of the Main Generator Exciter (EZIS:TL).
St. Lucie, Unit                       2                                                           YEAR @~a.
The Assistant Nuclear Plant Supervisor (ANPS)instructed the Turbine Operator (TO)to check for rubs on the rotating components of the turbine-generator.
NvM Err xo,: REvrsroN SFOVENT/AL iM NVM Ell o  s   o  o  o  3 89 '87        007              0 1 0      2 OF 0 4 TEXT /ifmoro s/rsco is rsr/rr/rsd, rrso sddio'orrs/ H/IC Fonrr 3////A'/ (IT)
The TO reported evidence of turbine-generator rubs to the control room and the ANPS instructed the Reactor Control Room Operators (RCOs)to open the vacuum breakers on the main condenser (EIZS:SG)to aid in slowing down the turbine.A fire team was assembled and stationed with fire fighting equipment at the vicinity of the main generator exciter.There were no reports of an actual fire.The trip was an uncomplicated trip and all systems functioned normally.The Steam Bypass Control System (SBCS)(EIIS:JI)operated to reduce primary average temperature (T-avg)to the zero percent power setpoint of 532 degrees F.Auxiliary feedwater (EIZS:BA)was initiated manually to control the steam generator (S/G)level for Reactor Coolant System (RCS)(EIZSEAB)heat removal.The standard post trip actions were completed and the unit was immediately stabilized in Hot Standby, Mode 3.NRC FORM 316A 19831 NRC Form 3ddA (983)LICENSE ENT REPORT (LER)TEXT CONTINU ON V.S.NUCLEAR REGULATORY COMMISSION APPROVEO OMS NO.3150MI(H EXP!RES: 8/3(188 FACILITY NAME (I)DOCKET NUMBER (3)LER NVMSER (8)PACE (3)St.Lucie, Unit 2 TERT (Il moro<<>>oo b ror)rrr'rod, Ir>>odds'onel NRC Farm 3ddl3 I ()T)o s o o o YEAR@g SEQUENTIAL NUM tR 0 0 7 REVISION NUM ER 0 1 0 3 OF 0 4 CAUSE OF TBB EVENTS The immediate cause of the main generator lockout was loss of the generator field.The loss of field was caused by destruction of the exciter Permanent Magnet Generator (PMG)that occurred when the exciter bearing failed allowing the PMG armature to rub on the PMG stator.Further investigation into the failure of the exciter bearing indicated that a ground was caused by a completed electrical circuit between the exciter bearing and the exciter base.This completed electrical circuit bypassed the insulation between the bearing pedestal and the exciter base.The ground was caused by an improper installation of an instrument cable (EIIS:IT).
DESCRIPTION OF                          ENTENTE On 25          November, 1987, St. Lucie Unit Two was operating at 50 percent power steady state in Mode 1. The unit was returned to service on 23 November following a refueling outage and was holding at 50 percent power while repairs were in progress on the 2A Steam Generator Feed Pump (SGFP) (EIIS:SJ) due to a small water leak that developed on the vent line at the pump casing. The reactor was being maintained in a steady state condition with all automatic controllers placed in automatic with the exception of the Control Rod Drive System (EIZS:JD) which was in OFF.
The instrument cable provides the terminal connection from the thermocouple of the N9 exciter bearing housing to its terminal box, which provides remote temperature indication in the control room.The as-found condition of the instrument cable indicated that the braided wire cable shield was not properly positioned in the clamp;therefore, a ground developed at the exciter bearing.Examination of the exciter bearing revealed pitting marks on the bearing surface, characteristic of current flowing across the bearing journal to the bearing pad, which resulted in the bearing failure.The improper arrangement of the instrument cable cannot be conclusively identified as a wiring error during the installation of the new main generator exciter.The PMG and the instrument cable were meggered to detect for possible grounds and the results were acceptable.
At 2331 hours, the Reactor Protective System (EIZS:JC) initiated a reactor trip on loss of load due to a turbine trip. The turbine tripped on a main generator (EIIS:TB) lockout. The control room was alerted with information that smoke was seen coming out of the Main Generator Exciter (EZIS:TL). The Assistant Nuclear Plant Supervisor (ANPS) instructed the Turbine Operator (TO) to check for rubs on the rotating components of the turbine-generator. The TO reported evidence of turbine-generator rubs to the control room and the ANPS instructed the Reactor Control Room Operators (RCOs) to open the vacuum breakers on the main condenser (EIZS:SG) to aid in slowing down the turbine.
It has been postulated that one of two circumstances may have occurred: 1)the instrument cable was installed correctly with the braided wire shield in the clamp when it was meggered;then at some later date, the instrument cable was accidently stepped on causing the cable shield to become separated from the clamp;or 2)the instrument cable, being clamped incorrectly to the pedestal, had not yet been connected to the terminal box when the megger test was performed.
A fire team was assembled and stationed with fire fighting equipment at the vicinity of the main generator exciter. There were no reports of an actual fire.
After placing the main generator back in service, the ground should have been detected during the performance of the weekly generator exciter ground check.The preventative maintenance Plant Work Order (PWO)requires voltages to be read across the N9 bearing shaft to ground and across the 59 bearing pedestal to ground.The data is to be evaluated to ensure no grounds have developed in the main generator exciter.Early recognition of the ground would have prompted immediate action to remove the main generator from service for the necessary repairs.The root cause of the event was a cognitive personnel error by a utility main-tenance supervisor in misinterpretation of the main generator exciter ground voltage readings.The appropriate procedure was properly followed.However, lack of understanding of the significance of the generator exciter ground check and inadequate acceptance criteria in the PWO were contributing factors in the personnel error.There were no unusual characteristics of the work location that directly contributed to the personnel error.NRC fORM 3ddA (983)
The trip               was an uncomplicated                       trip and   all   systems functioned normally. The Steam Bypass Control System (SBCS) (EIIS:JI) operated to reduce primary average temperature (T-avg) to the zero percent power setpoint of 532 degrees F. Auxiliary feedwater (EIZS:BA) was initiated manually to control the steam generator (S/G) level for Reactor Coolant System (RCS) (EIZSEAB) heat removal. The standard post         trip         actions were completed and the unit was immediately stabilized in Hot Standby, Mode 3.
URC Form 366A (983)LICENSEE NT REPORT (LER)TEXT CONTINUA ON U.S.NVCLEAR RECULATORY COMMISSION APPROVED OMB NO.3150WIOi EXPIRES: 8/31/88 FACILITY NAME (11 St.Lucie, Unit 2 DOCKET NUMBER (2)YEAR LER NUMBER (6)SEOUENTIAL NUMBER REVISION NUM Ell PACE (3)TEXT/I/mort t/Mcoit ror)rr/rtd.
NRC FORM 316A 19831
Ihto tdChr/ont/HRC Forrrr 36(L('ti (17)p 5 p p p 3 8 9 8 7 0 0 7 0 1 0 4 OF 0 4 ANALYSIS OF THE EVENT: The event is reportable under 10 CFR 50.73 (a)(2)(iv),"any event or condition that resulted in manual or automatic actuation of any Engineered Safety Feature, including the Reactor Protection System." This event was observed to be a routine reactor trip on loss of load.The resulting transient was well enveloped by the St.Lucie Unit II2 Final Updated Safety Analysis Report section 15.2.1.2"Limiting Reactor Coolant System Pressure Event-Isolation of Turbine (100%power)." All Plant Safety Functions were met and there were no additional complications.
 
Consequently, the health and safety of the public were not affected by this event.CORRECTIVE ACTIONS.1.The Permanent Magnet Generator was replaced.2.The Exciter Bearing was replaced.3.An evaluation was made and'the Exciter Bearing thermocouple was determined to be unnecessary and it was removed to prevent future incidents of this type.4.The preventative maintenance plant work order was revised to adequately define the acceptance criteria and the proper actions when the acceptance criteria are not met.5.Training was given to all Electrical Maintenance personnel to elaborate on the importance of properly evaluating the data during performance of the weekly generator exciter ground check.h 6.The plant training group will evaluate this item to determine appropriate training requirements and methods.ADDITIONAL INFORMATION:
NRC Form 3ddA                                                                                                       V.S. NUCLEAR REGULATORY COMMISSION (983)
LICENSE                 ENT REPORT (LER) TEXT CONTINU         ON               APPROVEO OMS NO. 3150MI(H EXP!RES: 8/3(188 FACILITY NAME (I)                                                           DOCKET NUMBER (3)             LER NVMSER (8)                 PACE (3)
SEQUENTIAL      REVISION YEAR @g NUM tR          NUM ER St. Lucie, Unit                     2 o  s  o  o    o                  0 0 7          0    1 0 3    OF    0 4 TERT  (Ilmoro <<>>oo b ror)rrr'rod, Ir>> odds'onel NRC Farm 3ddl3 I ()T)
CAUSE OF TBB EVENTS The immediate cause                         of the main generator lockout was loss of the generator field. The loss of                         field was caused by destruction of the exciter Permanent Magnet Generator (PMG) that occurred when the exciter bearing failed allowing the PMG armature to rub on the PMG stator.
Further investigation into the failure of the exciter bearing indicated that a ground was caused                         by a completed electrical circuit between the exciter bearing and the exciter base.                             This completed electrical circuit bypassed the insulation between the bearing pedestal and the exciter base.                                   The ground was caused by an improper installation of an instrument cable (EIIS:IT). The instrument cable provides the terminal connection from the thermocouple of the N9 exciter bearing housing to its terminal box, which provides remote temperature indication in the control room. The as-found condition of the instrument cable indicated that the braided wire cable shield was not properly positioned in the clamp; therefore, a ground developed at the exciter bearing. Examination of the exciter bearing revealed pitting marks on the bearing surface, characteristic of current flowing across the bearing journal to the bearing pad, which resulted in the bearing failure.
The improper arrangement of the instrument cable cannot be conclusively identified as a wiring error during the installation of the new main generator exciter.
The PMG and the instrument cable were meggered to detect for possible grounds and the results were acceptable.                               It has been postulated that one of two circumstances may have occurred: 1) the instrument cable was installed correctly with the braided wire shield in the clamp when                               it was meggered; then at some later date, the instrument cable was accidently stepped on causing the cable shield to become separated from the clamp; or 2) the instrument cable, being clamped incorrectly to the pedestal, had not yet been connected to the terminal box when the megger test was performed.
After placing the                       main generator back in service, the ground should have been detected during the performance of the weekly generator exciter ground check.
The preventative maintenance Plant Work Order (PWO) requires voltages to be read across the N9 bearing shaft to ground and across the 59 bearing pedestal to ground. The data is to be evaluated to ensure no grounds have developed in the main generator exciter. Early recognition of the ground would have prompted immediate action to remove the main generator from service for the necessary               repairs.
The   root cause of the event was a cognitive personnel error by a utility main-tenance supervisor in misinterpretation of the main generator exciter ground voltage readings. The appropriate procedure was properly followed. However, lack of understanding of the significance of the generator exciter ground check and inadequate acceptance criteria in the PWO were contributing factors in the personnel error. There were no unusual characteristics of the work location that directly contributed to the personnel error.
NRC fORM 3ddA (983)
 
URC Form 366A                                                                                                                 U.S. NVCLEAR RECULATORY COMMISSION (983)
LICENSEE                     NT REPORT (LER) TEXT CONTINUA ON                           APPROVED OMB NO. 3150WIOi EXPIRES: 8/31/88 FACILITY NAME   (11                                                               DOCKET NUMBER (2)               LER NUMBER (6)                   PACE (3)
YEAR    SEOUENTIAL       REVISION NUMBER       NUM Ell St. Lucie, Unit                      2 p   5   p p   p 3 8 9 8   7     0 0 7           0     1 0   4 OF     0 4 TEXT /I/mort t/Mcoit ror)rr/rtd. Ihto tdChr/ont/HRC Forrrr 36(L('ti (17)
ANALYSIS OF THE EVENT:
The event                 is reportable                   under 10   CFR 50.73 (a)(2)(iv), "any event or condition that resulted in                       manual or automatic               actuation of any Engineered Safety Feature, including the Reactor Protection System."
This event                 was observed                 to be a routine reactor trip on loss of load. The resulting transient                           was       well enveloped by the St. Lucie Unit II2 Final Updated Safety Analysis Report section 15.2.1.2 "Limiting Reactor Coolant System Pressure Event-Isolation of Turbine (100% power)." All Plant Safety Functions were met and there were no additional complications.                                             Consequently, the health and safety of the public were not affected by this event.
CORRECTIVE ACTIONS.
: 1.       The Permanent                   Magnet Generator was replaced.
: 2.       The       Exciter Bearing                       was   replaced.
: 3.       An     evaluation was                     made       and'the Exciter Bearing thermocouple was determined to be unnecessary type.
and       it was removed to prevent future incidents of this
: 4.       The       preventative maintenance plant work order was revised to adequately define the acceptance criteria and the proper actions when the acceptance criteria are not met.
: 5.       Training               was given to                 all Electrical Maintenance personnel to elaborate on the importance of properly evaluating the data during performance of the weekly generator exciter ground check.                                                   h
: 6.       The       plant training group will evaluate this item to determine appropriate training requirements and methods.
ADDITIONAL INFORMATION:
FAILED COMPONENT INFORMATION:
FAILED COMPONENT INFORMATION:
Westinghouse Exciter Bearing (89 bearing)Part I)613F432 GOl PREVIOUS SIMILAR EVENTS: See LER 5389-84-011 for a previous reactor trip due to exciter bearing failure.NRC FORM 366*(983)
Westinghouse Exciter Bearing (89 bearing)
P.O.14000, JUNO BEACH, FL 33408.0420 SKNLI5 2 9 1988 L-88-41 10 CFR 50,73 U.S.Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C.20555 , Gentlemen:
Part I)613F432                 GOl PREVIOUS SIMILAR EVENTS:
Re: St.Lucie Unit 2 Docket No.50-389 Reportable Event: 87-07 Revision 1 Date of Event: November 25, 1987 Reactor Trip on Loss of Load Caused by Main Generator Exciter Bearin Failure Due to Personnel Error The attached Licensee Event Report (LER)is being submitted pursuant to the requirements of 10 CFR 50.73 to provide an update on the subject event.Very truly yours, C.0.ody Executive Vice President COW/GRM/gp Attachment cc: Dr.J.Nelson Grace, Regional Administrator, Region ZI, USNRC Senior Resident Inspector, USNRC, St.Lucie Plant GRM/022.LER an FPL Group company}}
See LER 5389-84-011                       for a previous reactor     trip due to exciter bearing         failure.
NRC FORM 366*
(983)
 
P. O. 14000, JUNO BEACH, FL 33408.0420 SKNLI5 2 9 1988 L-88-41 10 CFR 50,73 U. S. Nuclear Regulatory Commission Attn:   Document Control Desk Washington, D. C. 20555
, Gentlemen:
Re:   St. Lucie Unit 2 Docket No. 50-389 Reportable Event: 87-07 Revision 1 Date of Event: November 25, 1987 Reactor Trip on Loss of Load Caused by Main Generator Exciter Bearin Failure Due to Personnel Error The attached Licensee Event Report (LER) is being submitted pursuant to the requirements of 10 CFR 50.73 to provide an update on the subject event.
Very truly   yours, C. 0. ody Executive Vice President COW/GRM/gp Attachment cc:   Dr. J. Nelson Grace, Regional Administrator, Region ZI, USNRC Senior Resident Inspector, USNRC, St. Lucie Plant GRM/022.LER an FPL Group company}}

Latest revision as of 14:28, 4 February 2020

LER 87-007-01:on 871125,reactor Tripped on Loss of Load Due to Turbine Trip.Caused by Personnel Error.Permanent Magnet Generator & Exciter Bearing Replaced & Exciter Bearing Thermocouple removed.W/880129 Ltr
ML17221A601
Person / Time
Site: Saint Lucie NextEra Energy icon.png
Issue date: 01/29/1988
From: Andrea Johnson, Woody C
FLORIDA POWER & LIGHT CO.
To:
NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
L-88-41, LER-87-007, LER-87-7, NUDOCS 8802020148
Download: ML17221A601 (6)
v • d • e


Text

REGULA,Y INFORMATION DISTR I BUT I YSTEM ( R IDS )

ACCESSION NBR: 8802020148 DOC. DATE: 88/01/29 NOTARIZED: NO DOCKET ¹ FACIL: 50-389 St. Lucie Plant> Unit 2> Florida Poeer 5 Light Co. 05000389 AUTH. NAME AUTHOR AFFILlATION JOHNSON'. B. Fl or i da Poeer 5 Light Co.

WOODY. C. O. Florida Power 5 Light Co.

REC IP. NAME RECIPIENT AFFILIATION

SUBJECT:

LER 87-007-01: on 871125. reactor tripped on loss of load due to turbine trip. Caused bg personnel error. Permanent magnet generator 5 exciter bearing replaced Zc exciter bearing thermocouple removed. W/880129 ltr.

DISTRIBUTION CODE: IE22D COPIES RECEIVED: LTR ENCL SIZE:

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

NOTES:

REC IP IENT COPIES REC IP IENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD2-2 LA 1 1 PD2-2 PD 1 1 TOURIGNYi E 1 1 INTERNAL: ACRS MICHELSON 1 1 ACRS MOELLER 2 2 AEOD/DOA 1 1 AEOD/DSP/NAS 1 1 AEOD/DSP/ROAB 2 2 AEOD/DSP/TPAB 1 1 ARM/DCTS/DAB 1 DEDRO 1 1 NRR/DEST/ADS 1 0 NRR/DEST/CEB 1 1 NRR/DEST/ELB 1 NRR/DEST/ICSB 1 1 NRR/DEST/MEB 1 1 NRR/DEST/MTB 1 1 NRR/DEST/PSB 1 1 NRR/DEST/RSB 1 1 NRR/DEST/SGB 1 NRR/DLPG/HFB 1 NRR/DLPG/GAB 1 1 NRR/DOEA/E*B 1 1 NRR/DREP/RAB 1 1 NRR/DREP/RPB 2 A)R /SIB 1 1 NRR/PMAS/ILRB 1 1 REG FILE 02 1 1 RES TELFORDi J 1 1 IB 1 1 RES/DRPS DIR 1 1 RGN2 FILE 01 1 1 EXTERNAL: EG5G GROHi M 5 5 FORD BLDG HOY> A 1 H ST LOBBY WARD 1 1 LPDR" 1 1 NRC PDR 1 1 NSIC HARRIS> J 1 1 NSIC MAYST G 1 1 TOTAL NUMBER OF COPIES REQUIRED: LTTR 46 ENCL 45

NRC Form 3SSA U.S, NUCLEAR REGULATORY COMMISSION 19413 l LICENSEE ENT REPORT (LER) TEXT CONTINUA ION APPROVED OMB NO. 3150&104 EXPIRES: 9/31/BB FACILITY NAME III OOCKET NUMBER Ill LER NUMBER IBI PAGE 0)

St. Lucie, Unit 2 YEAR @~a.

NvM Err xo,: REvrsroN SFOVENT/AL iM NVM Ell o s o o o 3 89 '87 007 0 1 0 2 OF 0 4 TEXT /ifmoro s/rsco is rsr/rr/rsd, rrso sddio'orrs/ H/IC Fonrr 3////A'/ (IT)

DESCRIPTION OF ENTENTE On 25 November, 1987, St. Lucie Unit Two was operating at 50 percent power steady state in Mode 1. The unit was returned to service on 23 November following a refueling outage and was holding at 50 percent power while repairs were in progress on the 2A Steam Generator Feed Pump (SGFP) (EIIS:SJ) due to a small water leak that developed on the vent line at the pump casing. The reactor was being maintained in a steady state condition with all automatic controllers placed in automatic with the exception of the Control Rod Drive System (EIZS:JD) which was in OFF.

At 2331 hours0.027 days <br />0.648 hours <br />0.00385 weeks <br />8.869455e-4 months <br />, the Reactor Protective System (EIZS:JC) initiated a reactor trip on loss of load due to a turbine trip. The turbine tripped on a main generator (EIIS:TB) lockout. The control room was alerted with information that smoke was seen coming out of the Main Generator Exciter (EZIS:TL). The Assistant Nuclear Plant Supervisor (ANPS) instructed the Turbine Operator (TO) to check for rubs on the rotating components of the turbine-generator. The TO reported evidence of turbine-generator rubs to the control room and the ANPS instructed the Reactor Control Room Operators (RCOs) to open the vacuum breakers on the main condenser (EIZS:SG) to aid in slowing down the turbine.

A fire team was assembled and stationed with fire fighting equipment at the vicinity of the main generator exciter. There were no reports of an actual fire.

The trip was an uncomplicated trip and all systems functioned normally. The Steam Bypass Control System (SBCS) (EIIS:JI) operated to reduce primary average temperature (T-avg) to the zero percent power setpoint of 532 degrees F. Auxiliary feedwater (EIZS:BA) was initiated manually to control the steam generator (S/G) level for Reactor Coolant System (RCS) (EIZSEAB) heat removal. The standard post trip actions were completed and the unit was immediately stabilized in Hot Standby, Mode 3.

NRC FORM 316A 19831

NRC Form 3ddA V.S. NUCLEAR REGULATORY COMMISSION (983)

LICENSE ENT REPORT (LER) TEXT CONTINU ON APPROVEO OMS NO. 3150MI(H EXP!RES: 8/3(188 FACILITY NAME (I) DOCKET NUMBER (3) LER NVMSER (8) PACE (3)

SEQUENTIAL REVISION YEAR @g NUM tR NUM ER St. Lucie, Unit 2 o s o o o 0 0 7 0 1 0 3 OF 0 4 TERT (Ilmoro <<>>oo b ror)rrr'rod, Ir>> odds'onel NRC Farm 3ddl3 I ()T)

CAUSE OF TBB EVENTS The immediate cause of the main generator lockout was loss of the generator field. The loss of field was caused by destruction of the exciter Permanent Magnet Generator (PMG) that occurred when the exciter bearing failed allowing the PMG armature to rub on the PMG stator.

Further investigation into the failure of the exciter bearing indicated that a ground was caused by a completed electrical circuit between the exciter bearing and the exciter base. This completed electrical circuit bypassed the insulation between the bearing pedestal and the exciter base. The ground was caused by an improper installation of an instrument cable (EIIS:IT). The instrument cable provides the terminal connection from the thermocouple of the N9 exciter bearing housing to its terminal box, which provides remote temperature indication in the control room. The as-found condition of the instrument cable indicated that the braided wire cable shield was not properly positioned in the clamp; therefore, a ground developed at the exciter bearing. Examination of the exciter bearing revealed pitting marks on the bearing surface, characteristic of current flowing across the bearing journal to the bearing pad, which resulted in the bearing failure.

The improper arrangement of the instrument cable cannot be conclusively identified as a wiring error during the installation of the new main generator exciter.

The PMG and the instrument cable were meggered to detect for possible grounds and the results were acceptable. It has been postulated that one of two circumstances may have occurred: 1) the instrument cable was installed correctly with the braided wire shield in the clamp when it was meggered; then at some later date, the instrument cable was accidently stepped on causing the cable shield to become separated from the clamp; or 2) the instrument cable, being clamped incorrectly to the pedestal, had not yet been connected to the terminal box when the megger test was performed.

After placing the main generator back in service, the ground should have been detected during the performance of the weekly generator exciter ground check.

The preventative maintenance Plant Work Order (PWO) requires voltages to be read across the N9 bearing shaft to ground and across the 59 bearing pedestal to ground. The data is to be evaluated to ensure no grounds have developed in the main generator exciter. Early recognition of the ground would have prompted immediate action to remove the main generator from service for the necessary repairs.

The root cause of the event was a cognitive personnel error by a utility main-tenance supervisor in misinterpretation of the main generator exciter ground voltage readings. The appropriate procedure was properly followed. However, lack of understanding of the significance of the generator exciter ground check and inadequate acceptance criteria in the PWO were contributing factors in the personnel error. There were no unusual characteristics of the work location that directly contributed to the personnel error.

NRC fORM 3ddA (983)

URC Form 366A U.S. NVCLEAR RECULATORY COMMISSION (983)

LICENSEE NT REPORT (LER) TEXT CONTINUA ON APPROVED OMB NO. 3150WIOi EXPIRES: 8/31/88 FACILITY NAME (11 DOCKET NUMBER (2) LER NUMBER (6) PACE (3)

YEAR SEOUENTIAL REVISION NUMBER NUM Ell St. Lucie, Unit 2 p 5 p p p 3 8 9 8 7 0 0 7 0 1 0 4 OF 0 4 TEXT /I/mort t/Mcoit ror)rr/rtd. Ihto tdChr/ont/HRC Forrrr 36(L('ti (17)

ANALYSIS OF THE EVENT:

The event is reportable under 10 CFR 50.73 (a)(2)(iv), "any event or condition that resulted in manual or automatic actuation of any Engineered Safety Feature, including the Reactor Protection System."

This event was observed to be a routine reactor trip on loss of load. The resulting transient was well enveloped by the St. Lucie Unit II2 Final Updated Safety Analysis Report section 15.2.1.2 "Limiting Reactor Coolant System Pressure Event-Isolation of Turbine (100% power)." All Plant Safety Functions were met and there were no additional complications. Consequently, the health and safety of the public were not affected by this event.

CORRECTIVE ACTIONS.

1. The Permanent Magnet Generator was replaced.
2. The Exciter Bearing was replaced.
3. An evaluation was made and'the Exciter Bearing thermocouple was determined to be unnecessary type.

and it was removed to prevent future incidents of this

4. The preventative maintenance plant work order was revised to adequately define the acceptance criteria and the proper actions when the acceptance criteria are not met.
5. Training was given to all Electrical Maintenance personnel to elaborate on the importance of properly evaluating the data during performance of the weekly generator exciter ground check. h
6. The plant training group will evaluate this item to determine appropriate training requirements and methods.

ADDITIONAL INFORMATION:

FAILED COMPONENT INFORMATION:

Westinghouse Exciter Bearing (89 bearing)

Part I)613F432 GOl PREVIOUS SIMILAR EVENTS:

See LER 5389-84-011 for a previous reactor trip due to exciter bearing failure.

NRC FORM 366*

(983)

P. O. 14000, JUNO BEACH, FL 33408.0420 SKNLI5 2 9 1988 L-88-41 10 CFR 50,73 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555

, Gentlemen:

Re: St. Lucie Unit 2 Docket No. 50-389 Reportable Event: 87-07 Revision 1 Date of Event: November 25, 1987 Reactor Trip on Loss of Load Caused by Main Generator Exciter Bearin Failure Due to Personnel Error The attached Licensee Event Report (LER) is being submitted pursuant to the requirements of 10 CFR 50.73 to provide an update on the subject event.

Very truly yours, C. 0. ody Executive Vice President COW/GRM/gp Attachment cc: Dr. J. Nelson Grace, Regional Administrator, Region ZI, USNRC Senior Resident Inspector, USNRC, St. Lucie Plant GRM/022.LER an FPL Group company

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