05000341/LER-1989-015, :on 890707,power Lost to Div I Reactor Protection Sys Bus a Due to Motor Generator Overvoltage Condition.Caused by Single Phase Sensing Potentiometer. Component Replaced W/Fixed Resistor

:on 890707,power Lost to Div I Reactor Protection Sys Bus a Due to Motor Generator Overvoltage Condition.Caused by Single Phase Sensing Potentiometer. Component Replaced W/Fixed Resistor

ML20247G801
Person / Time
Site:	Fermi
Issue date:	09/15/1989
From:	Anthony P, Orser W DETROIT EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
CON-NRC-89-0181, CON-NRC-89-181 LER-89-015, LER-89-15, NUDOCS 8909190144
Download: ML20247G801 (6)

LER-1989-015, on 890707,power Lost to Div I Reactor Protection Sys Bus a Due to Motor Generator Overvoltage Condition.Caused by Single Phase Sensing Potentiometer. Component Replaced W/Fixed Resistor

Event date:
Report date:
3411989015R00 - NRC Website

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Nuclear Regulatory Commission Attention:

Document Control Desk Washington, D.C.

20555

Reference:

(1) Fermi 2 NRC Docket No. 50-341 Facility Operating License No. NPF-43 (2) Transmittal of Licensee Event Report No.

89-015-00, dated August 7,

1989, NRC-89-0135

Subject:

Licensee Event Report (LER) No. 89-015-01 Please find enclosed LER No. 89-015-01, dated September 15, 1989, for a reportable event that occurred on July 7, 1989.

This report was revised to reflect the results of further investigation and the corrective actions taken.

A copy of this LER is also being sent to the Regional Administrator, USNRC Region III.

If you have any questions, please contact Patricia Anthony at (313) 586-1617.

Sincerely,

Enclosure:

NRC Forms 366, 366A cc:

A.

B.

Davis J.

R.

Eckert R.

C.

Knop W.

G.

Rogers J.

F.

Stang Wayne County Emergency Management Division fgG l l l

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s NRC Farm 366 U $. NUCL EAR REGULATORY COMMISSION APPROVED OMB NO.2150 0104 LICENSEE EVENT REPORT (LER)

EXPIRES 8/3188 FACILITY NAME (Il DOCKET NUMBER (2)

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on the Motor Generator EVEhiT DATE IS)

LE R NUMBER (6)

REPORT DATE (7)

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NAME TELEPHONE NUMBER

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On July 7, 1939, power was lost to the Division I Reactor Protection System bus A when its motor generator (MG) set experienced an overvoltage condition.

Investigation revealed that voltage meter readings had drifted up from 120 volts to 128 volte following adjustment of the voltage adjustment potentiometer.

A problem with the stability of the installed voltage meter indication was identified.

Both the potentiometer and the voltage meter were replaced prior to placing the MG set back in service.

On July 18, 1989, a similar event occurred and the voltage I

regulator was replaced.

While the MG set was running, a 1

voltage fluctuation occurred on July 19, 1989.

Subsequent I

testing indicates that the most probable cause was the single 11 phase sensing potentiometer.

This component was replaced with I

a fixed resistor.

Following further testing and monitoring I

without discovering any other problems, the motor generator l

set was returned to service on August 16, 1989.

I NRC Foem 366 19 @ 31

_________________________________________L

NRC Form 306A

- U.S NUCLEAR RETULATO'_W COMMISSION LICENSEE EVENT REPORT (LER) TEXT CONTINUATION erROvEo oms NO mo-om EXPlRES: 8/31/88 F ACILITY NAME 0)

DOCKET NUMBER (2)

LER NUMBER (6)

PAGE (3)

YEAR f

T, AL ' !

g N'i o ls lo lo l01314 l 1 8l 9 011l5 0 l1 0 12 or 0 l5 TEXT (# more space is seguned use eaWoon.f NRC Form Jp5WsJ (17)

Initial Plant Conditions

Operationa3 Condition:

1 (Power. Operation)

Reactor Power:

98.4 percent Reactor Pressure:

1000 psig Reactor Temperature:

545 degrees Fahrenheit Description of Occurrence:

On_ July 7, 1989, at approximately 0800 hours0.00926 days <br />0.222 hours <br />0.00132 weeks <br />3.044e-4 months <br />, an operator on rounds found the MG set A voltage meter (MTR) reading 113 volts and adjusted the voltage adjustment potentiometer (FD) so that the meter read 120 volts (v olt a ge adjustment potentiometer setting 8.1).

At 1821 hours0.0211 days <br />0.506 hours <br />0.00301 weeks <br />6.928905e-4 months <br />, the Division I equipment protection assembly (EPA) _ breakers (BKR) tripped on overvoltage which resulted in a loss of power to Division I Reactor Protection System [(RPS)(JC)]

bus A (BU).

A half scram was received.

All the Division I actuations and isolations that should have occurred as a result of this. event did occur.

These included starting of the Standby Gas Trectment System and tripping of the Reactor Building Heating, Ventilating and Air Conditioning System, isolation of the Reactor Water Cleanup System and shifting of the Control Center Heating, Ventilating and Air Conditioning System to recirculation mode.

At 1839 hours0.0213 days <br />0.511 hours <br />0.00304 weeks <br />6.997395e-4 months <br />, the RPS bus A was transferred from its motor generator (MG) cet to its alternate power supply in order to re-energize it.

The half scram was reset and operators restored the actuated systems to their normal condition.

The RPS MG set A was shutdown at 2143 hours0.0248 days <br />0.595 hours <br />0.00354 weeks <br />8.154115e-4 months <br /> and subsequently tagged out for repairs.

At the time of the ov e rv ol t a g e trip, the voltage adjustment potentiometer was still set at 8.1, but the voltage meter read 128 volts.

It was suspected that the voltage adjustment potentiometer was not functioning properly and it was replaced at approximately 2330 hours0.027 days <br />0.647 hours <br />0.00385 weeks <br />8.86565e-4 months <br />.

On July 8, 1989 at approximately 0100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br />. MG set A was started but not loaded.

The voltage was adjusted to 120 volts, which was a voltage adjustment potentiometer setting of 8.3.

At 0157 hours0.00182 days <br />0.0436 hours <br />2.595899e-4 weeks <br />5.97385e-5 months <br />, an operator on rounds reported that the RPS MG set A voltage meter was reading 128 volts.

Investigation of the voltage meter at that point determined that tapping on face of the voltage meter caused the readings to fluctuate between 113 volts and 128 volts.

At the same time, s' volt-ohm meter (VOM) being used to monitor the same output remained steady at 128 volts.

The' voltage adjustment potentiometer was adjusted to 7.1 which translated to 120 volts on both the voltage meter and the VOM at approximately 0230 hours0.00266 days <br />0.0639 hours <br />3.80291e-4 weeks <br />8.7515e-5 months <br />.

At approximately 1400 hours0.0162 days <br />0.389 hours <br />0.00231 weeks <br />5.327e-4 months <br />, a line analyzer was installed on the meter and the MG set was left unloaded.

N2C POEM 3eeA og,g, gro, 1938-120-589r00070

_ _____ b __

NRC Form at6A U.S. NUCLEAQ REGi

. COMMIS$lON LICENSEE EVENT REPORT (LER) TEXT CONTINUATION areaovEo o6. '

io wio4 EXPIRES; 8.'31/O F ACILIW NAME (1)

DOCILET NUMBER (2)

LER NUMBER (6)

PAGE (3)

"=P "MJ:

"^a Fermi 2 o 15 l0 l0 lo l3191 8l 9 0 1115 0l1 0 l3 OF 0 l5 VEKT (2 more spece in requued, une e#0cnet NRC form 366A's} (171 l

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l After a week of unloaded operation without identifying any further problems, the MG set was shutdown and the voltage meter replaced.

The newly installed voltage meter read 113 volts when the voltage adjustment potentiometer was set at 7.1 and the MG set was running unloaded.

The voltage adjustment potentiometer was adjusted to 8.25 which translated to 120 volts on both the voltage meter and the VOM.

There were no other problems found while running the MG set unloaded for the next two days, so the MG set was returned to service at 2112 hours0.0244 days <br />0.587 hours <br />0.00349 weeks <br />8.03616e-4 months <br /> on July 17, 1989.

After loading. the voltage meter reading was 119 volts.

The voltage adjustment potentiometer was adjusted to 8.4 in order to bring voltage on the bus to 120 volts.

The round's readings from the next shift (midnights) indicated the MG set was operating normally at 120 volts.

j At 0748 hours0.00866 days <br />0.208 hours <br />0.00124 weeks <br />2.84614e-4 months <br /> on July 18, 1989, the Division I EPA breakers again I

tripped and the RPS MG set A voltage meter read 130 volts.

At i

0955 hours0.0111 days <br />0.265 hours <br />0.00158 weeks <br />3.633775e-4 months <br />, the voltage adjustment potentiometer was found to be still set at 8.4, but the voltage reading was 129.5 volts on the voltage meter and 129 on the VOM.

The voltage adjustment potentiometer was adjusted to 7.1 which translated to 120.5 volts on the voltage meter and VOM.

A temperature test was performed using a heat gun to see if increasing temperatures caused significant changes in the voltage output.

None of the components appeared to be significantly affected: the voltage increase was l

not greater than that expected due to the temperature increase in any case.

The MG set was shutdown and started again without problem.

Finally, it was shutdown and the voltage regulator replaced.

At 2130 hours0.0247 days <br />0.592 hours <br />0.00352 weeks <br />8.10465e-4 months <br />, the MG set was started unloaded.

The voltage adjustment potentiometer was adjusted to 6.2 in order to obtain an output of 120 volts.

On July 19. 1989, at approximately 0600 hours0.00694 days <br />0.167 hours <br />9.920635e-4 weeks <br />2.283e-4 months <br />, the output voltage was found to be 115 volts with the voltage adjustment potentiometer still set at 6.2.

It was adjusted to 6.8 in order to bring output' voltage to 120 volts.

Testing of the MG set under 1

varying conditions was conducted in an attempt to determine the cause of the intermittent problem.

At 1040 hours0.012 days <br />0.289 hours <br />0.00172 weeks <br />3.9572e-4 months <br />, the MG set was shutdown to install a resistance load bank, a line analyzer and a VOM at the voltage meter.

During the testing no abnormal response was detected.

At 1710 hours0.0198 days <br />0.475 hours <br />0.00283 weeks <br />6.50655e-4 months <br />, the line analyzer recorded voltage cycles between 112 volts and 130 volts in which the minimum and maximum peaks were maintained for a short duration.

The cycling continued for approximately 40 minutes before stabilizing at 120'

]

volts.

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6U S. NUCLEAR REGULATO"4Y COMMIS$10N

' LICENSEE EVENT REPORT (LER) TEXT CONTINUATION AreROvso oms No asso-oio4 EXPIRES.8/31188 FACILtTY NAME til DOCKET NUMBER (2)

LER NUMBER W PMt m "aa

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4*an Fermi'2 o15101olo1314 11 8l 9 0 l1l5 0j1 0 l4 or 0l5 TEXT IM mwe space n reeuwed, u,, nemut NRC Form 366Ksl(17>

On-July 20 through 31, 1989, checks.of the output voltage I

revealed nothing abnormal.

During testing on August 1,

1989, I

it was discovered that small adjustments of the single phase l

sensing (SPS) potentiometer (FD) caused fluctuating voltage 11 output which eventually stabilized at a new output voltage.

l.

None of the other testing produced a similar response in the I

output voltage.

l The SPS potentiometer was replaced with a fixed resistor on I

August 4, 1989.

During the next three days the MG set was l

shutdown once eer day and then restarted.

No abnormalities l

were noted.

The MG set was then run with a resistance load 11 bank and monitoring equipment installed for seven days.

No l

problems with the MG set's performance were found.

RPS MG l

set A was returned to service on August 16, 1989.

I

Cause of Event

Monitoring of the generator output voltage, exciter field l

)

current, voltage regulator temperature, regulator reference 1

voltage, field voltage and the voltage across one of the l

contacts during tests of the MG set at varying amperage l

)

levels was performed in crder to determine the cause of the 11 drifting voltage levels.

A problem with the SPS potentiometer I

appears to be the most probable cause of this event.

None of l

the other testing performed produced the fluctuating cutput l

voltage levels which caused this event.

I

Analysis of Event

The engineered safety features challenged on both July 7 and 18, 1989, responded per their design.

This event did not impair the ability of the Division I RPS EPA safety features to protect the reactor and the health and safety of the public.

Had an event occurred requiring protection of the vessel during either RPS MG 4

set A overvoltage trip, the safety features would have already l

been fulfilling or have been capable of performing their intended I

functions.

Corrective Actions

As described previously, the voltage meter, the voltage l

adjustment potentiometer and the voltage regulator on the MG l

set had been replaced initially.

In addition, based upon the l

results of further testing, the SPS potentiometer was replaced 11 with a fixed resistor.

Testing and monitoring following its replacement showed no abnormalities in the output voltage.*U.S.

GPO, 19pp.$20-599 00070

NMO Form 306A U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER) TEXT CONTINUATION ArraovEo oms No atu-osos l.:

EXPIRES: 8/31/Ril l

FACILITY NAME til DOCKET NUMBER (2)

LER NUMBER (6)

PAGE (3)

YEAR SE Y AL E s p

p Fermi 2 o is j o lo lo l3 l 4l 1 8;9 0l1l5 0;1 0l5 or 0 l5 TEXT (W more space in regsmed, une addreonelNRC Form 3tl5A's)(171

Previous Similar Events

Licensee Event Report 87-040 described another event in which RPS MG set A tripped due to an overvoltage condition.

While a conclusive root cause was not found. it was suspected that the voltage adjustment potentiometer may have had contaminants on it which were " wiped off" by exercising the voltage adjustment potentiometer during troubleshooting.

A preventive maintenance event requiring exercising the voltage adjustment potentiometer was developed to address this event.

Component Data:

SPS potentiometer: model number 1377208 within a General Electric motor generator set model SSJ4326A22Y36 11 l

l l

8-C '* " " " * " ' "

waccomuses.

l 19 83;