ML20086B222

Ro:On 700908,series of Events Associated W/Emergency Diesels & 480 & 4160 Volt Buses & Breakers Resulted in Temporary Loss of Power.Caused by Sticking Fuel Injector.Investigation Underway by Fairbanks-Morse Co

ML20086B222
Person / Time
Site:	Robinson
Issue date:	10/30/1970
From:	Utley E CAROLINA POWER & LIGHT CO.
To:	Morris P US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20086B227	List: ML20086B222
References
NUDOCS 8311170103
Download: ML20086B222 (5)

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. 50 201 Carolina Power & Light Company ,/ n' y; S~ - . ..

Ralei;;h, North Carol.'na 27c02 r .."

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October 30, 1970 H; ffgfp>

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Dr. Peter A. Morris, Director Division of Reactor Licensing U. S. Atomic Energy Commission Washington 25, D. C. 20545

Dear Dr. Morris:

On September 8, 1970, a series of events associated with the emergency diescis and the 480 and 4160 volt buses and breakers resulted

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in a temporary loss of power at the H. B. Robinson Steam Electric Plant, 7 g fk.;. .J. .-

Unit No. 2. Though not considered an abnormal occurrence as defined by c g..

the Technien1 Specifications, the following report is submitted as an 't [14l item of interest to the AEC. These events uere of considerabic concern ?h?

to Carolina Power & Light Company and resulted in a thorough review of T%(~

design, equipment, and operating procedures to assure the Company that 7T;W" a reliable cicctrical system has been installed. Of primary concern $\j-) L ;

was the inability to understand completely what caused the upset and to f 11~ 9 reconstruct logically and precisely the sequence of events. Subsequent T2. .

to the upset, a careful investigation of all systems was made including:

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1. Complete check of emergency diesels by a representative of the Fairbanks-Morse Company C

2. Complete wire check of diesel control circuits.

3. Complete check of individual breakers and all control ,__

circuits. T R p;t 2

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4. Complete operational check of 480-volt breaker train 5. .[. ; ?

interlock system including re-running of the pre- _ g p,j . .-

) operational test of the system.

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[ 5 Attempt to reproduce, as far as possibic, the series of events that led to the power failure.

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The results of this inspection and additional testing indicate j '. VV.

th g c:. system is now functioning as designed. ^ *

• 8311170103 701030

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gDRADOCK 05000261 PDR COPY SENT REGION , _ NOV 4 1970

l Dirce or, O O \!

,t Divis on of Reactor Licensing October 30, 1970 f i.

i Initial Conditions At the time of the upset, the core had been loaded aua pre-operational testing was in progress prior to initial criticality. The reactor was shug down with a 107 margin with the reactor coolant system I at 500 psig 345 with a stcan void in the pressurizer. The reactor coolant pumps were not operating.

The initial conditions of the electrical system were: t (Refer to rigure 8.2-3 of the FSAR fo;r breaker locations). .

1. 4160 volt buses 1 and 2 were isolated while response b time checks of the reactor protection features Under i Frequency and Under Voltage trips were being performed *:

in accordance with an approved test procedure. -

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2. 4160 volt buses 3 and 4 were energized from the Unit l No. 2 Start-up Transformer, but isolated from the 480 volt system. ['

3. 480 volt buses 1, 2A, and E-1 were energized by "A" Emergency Diesel Generator with a load of 700 137, 1000 ampercs at 480 volts.

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4. 480 volt buses 2B, 3, and E-2 were energized by "B" f l Emergency Diesel Generator with a load of 1250 IG1, ,!

2000 amperes at 480 volts, i Description of Events s

The plant had been operating in this mode since 5:55 p.m. when at 8: 35 p.m. a change in the sound of "A" Emergency Diesel caused the Auxiliary Operator to inspect the engine. Indications were that frequency ha51 dropped off scale and was below 55 cycles /second. The indicated load, as best remembered by the Auxiliary Operator, had increased to 750131 at 1000 amperes. As the Auxiliary Operator attempted to increase engine speed, the generator breakcr 52/17B tripped, de-energizing 480 volt buscs E-1, 1 and 2A. The engine then tripped to overspeed. An attempt was made to restart the engine, but it could not be restarted. Subsequent investigation indicatesy. A;f that the Auxiliary Operator may have failed to reset the mechanical overspeed 4'% i trip before attempting to start the engine, d #b At 8:50 p.m. the personnel running the underfrequency and under- j voltage tests on the 4160 volt buses 1 and 2 removed their equipment. The y potential resto' red tofuses theseon 4160 volt buses 1 and 2 were replaced and power was jg;e/

buses. ,

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I Director, 0 0 Division of Reactor Licensing October 30, 1970 An attempt was made to restore 480 volt power to buses 1, 2A, and E-1 through the 4KV/480V Station Service Transformers 2A and 2B concurrently with restoring off-s'tc power to buses 2B, 3, and E-2 through Station Service Transformers 2B and 2C. Since there is no way ,

to synchronize an operating dicsc1 with incoming off-site power, the  !

Operator mt.nually tripped "B" Emergency Diesel Generator with the

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intention of inmediately closing breaker 52/16B. This operator error i resulted in the loss of all 480V power.

The Control Operator attempted to close breakers 52/1B and 4 I 52/16B; however, they would not close due to a safety ~ injection l sign Breakers 52/8B and(52/5B Vc E closed /b f**j l

and undervoltage on E-1 and E-2. -

f restoring power to buses 1 and 2A. Similarly, breakers 52/9B and 52/12B f

were closed energizing buses 2B and 3. The safety injection was reset {

and breakers 52/1B and 52/16B were closed. However, breakers 52/18B and 'q d 52/28B could not be closed to energize buses E-1 and E-2. The fuses whi h f supply undervoltage auxiliary relay power were removed from E-1 and breaker -

52/183 was closed from the control board, successfully energizing the l M g y [i E-1 bus. When the fuses were replaced, breakers 52/18B and 52/1B tripped; g I 52/18B to undervoltage and 52/1B to undervoltage and a safety injection signal. The safety injection signal was again reset and 52/1B was closed.

Breaker 52/18B was then successfully closed restoring power to E-1; however,

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52/28B would not close and the bus tic breakers 52/22B and 52/29B were , a closed energizing the E-2 emergency bus. All power was restored at 9:37 p.m. I l

The simultancous loss of power to both E-1 and E-2 caused a loss i j

of lighting and various instrument buses. High voltage was lost to the i source range nucicar instrumentation for approximately 15 minutes when instrument bus 4 was de-energized. This bus feeds a portion of the power range instrumentation. When power was lost, the P-10 interlock functioned s

as designed removing high voltage from the source range nuclear instruments.

Prior to the restoration of 480V power, "A" Emergency Diesel '

Generator was started successfully, but difficulty was experienced in closing generator output breaker 52/17B.

Following the upset, the pressurizer icvel had 1nereased 87.

due to the starting of the safety injection pumps. Reactor coolant pressure was 500 psig at 325 F.

Re'sults of the Investigation (1) 'The "A" Emergency Diesel Generator malfunction, as reported by the Fairbanks-Morse representative, was caused by a sticking fuel inje . tor. There are indications that dirty fuel may have contributed to the sticking fuel injector.

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Director, o o ,

Division of Reactor Licensing October 30, 1970 (2) The cause for the malfunction of, breakers 52/18B, 52/283, and 52/17B has not been deterndned with w

certainty. The reason for breaker 52/18B mal-function could have been a sticking undervoltage, @ pc jv relay since. the breaker closed when the fuses which supply auxiliary relay power were pulled - 'ge ^

and then opened again when the fuses were replaced.

Follow-Up Actions (1) A representative from the Fairbanks-Morse Company was brought to the site to determine the cause and make l the necessary repairs to "A" Emergency Diesel Cencrator.  !

The injector on Number 2 cylinder was replaced and the i Emergency Diesel Cencrator was test operated for 1 I hours with a 750 KR load while connected to bus E-1 I only. It was then operated for 20 minutes connected  !

to the Start-up Transformer via E-1, carrying a 2500 1 KW load. The "A" Emergency Diesel Generator performed without problems and appears to be in excellent condition.

(2) The 480 volt breaker operation has been checked using an approved pre-operational test procedure. All breakers i worked satisfactorily. i 0

(3) The undervoltage relays ucre removed from E-1 and E-2 [1:

and were checked for cicanliness and operation. The j undervoltage relays were in satisfactory condition (

and were re-installed. Each of the three breakers that ll l s operated erratically, 52/18B, 52/28B, and 52/17B, has ll l been operated at 1 cast two dozen times without a mal- 1 l function. On two occasions the plant conditions, breaker t I line-up, and sequence of events during the incident have i been repeated as closely as possible. All equipment has I L

operated properly during all testing subsequent to the upset.

(4) Action has been taken to provide for manual synchronization of the emergency buses with off-site power across breakers 52/18B and 52/28B.

(5) The diesel fuel oil system has been checked for cleanliness to ensure that cican oil of the appropriate specification is delivered to the engine. Administrative procedures have been reviewed to ensure that fuel delivered to the plant is inspected, that fuel oil contamination does not occur, and that fuel oil filters are inspected regularly.

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O O Diract'or,

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Division of Reactor Licensing October 30, 1970 l

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In addition to carefully checking out all equipment by retesting and conducting various circuit checks, all operating per- l sonnel have reviewed the sequence of events in detail. All operating l personnel, including contractor representatives, have been reminded  ;

of the necessity to collect precise data concerning each unusual f event. The necessity for careful deliberate plant operation, including maintenance procedures, has been re-emphasized.

Yours very truly,  ;

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E. E.'Uticy / l Manager {

Generation & System Operations l

EEU/bbw cc: Mr. G. P. Beatty Mr. N. B. Bessac Mr. P. S. Colby Mr. J. A. Jones Mr. J. J. LeB1cng '

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