ML20084G221

Summarizes Investigation Into 720903 Diesel Generator Malfunction.Caused by Slow Opening Time Delay Relay. Start-failure Circuitry Under Mod

ML20084G221
Person / Time
Site:	Dresden
Issue date:	01/12/1973
From:	Worden W COMMONWEALTH EDISON CO.
To:	Giambusso A US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20084G189	List: ML20084G215 ML20084G221
References
37-73, NUDOCS 8304210535
Download: ML20084G221 (3)

Text

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Commonwealth Edison Company 72 WEST ADAMS STREET

• CHICAGO. ILLINOIS w,. n .,,, ,..

POST OFFICE 80X 767 lir C H I C A O O, ILLlHO45 60490 Dresden Nuclear Power Station 'D R. R. #1 *),\ /g Morris, Illinois 60450 gf .fg.

Wd:Ltr. #37-73 January 12, 1973 J.I'/  %

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fx?e. b, it r p\ ...z Mr. A. Giambusso h , . 7:-g:

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Deputy Director for Roactor Projects 'M -

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Directorato of Licensing k~;bh,\( '

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U. S. At omic Energy Co . mission -

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SUBJECT:

LICENSE DTR-19, DRFSDEN PUCT2AR PO'E3 STATION, liNTT //2, SECTION 6.6.C.1 OF THE TFCi!NIC A_L SPECIFIC ATIC"S, FOLLO / UP 12TTIR.~~

Dear Mr. Giambusso:

This letter su. marizes our investigation into the 2/3 Diesel Generator 1'alfunction incident dated September 3,1972. In a letter sent to your office October 3,1972, it was stated the preliminary investigation indicated the source of the problem to be a slow opening time delav relay. .

Our subsequent studies have verified this.

The TD2 time delay relay on the 2/3 Standby dicul generater was replaced by a dcw relay identical to the TD2 relay in the system at the time of the incident. The 2/3 Staa.dby diesel generator was then subjected to the testing sequence used to recreate the events of the actual incident.

The " Fail to Start" light did not appear and the diesel generator did not trip. An examinatien of the unit 2 diesel c,enerator revealed that it was susceptable to the TD2 relay problem. Replacement of the TD2 relay en the unit 2 dicsol was ecually successful in eliminating the problem.

Strip chart recordings of the pickup and dropout tines for the

.omo two TD2 relays removed frca the system and for the replacement ';D2 relays

$$ - indicated in both cases that the dropout tine after being de-energized was

@@ lenger for the two relays in the system when the " Fail to start" light h.g appeared.

In y The actual trip of the dicsel generator is the result of the oc basic design of the starting circuitry. Thcacortion of the starting 5@ circuitry involved in the 2/3 standby diesel generator trip is shown in L figures 1,2, and 3. The apparent sequence of events that resulted in the g trip is as follows:

a. on auto start signal, TD2 relay is energized closing

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.b. ESR (G-H) opens when diesel reaches 200 rpm (Fig.1)

c. 15 sec. after auto stsrt signal is initiated, TD2 closes (Fig, 1) TDC

d. k' hen the control switch is placed in the stop position, ESR (G-H) closes immediately (Fig. 1) -

e. Due to the finite amount of time required for the slew TD2 relay to open befose the 502/TDC centacts can open the SF relay is energized and the SF (C-D) contacts (Fig. 2) open and must be manually reset at the engine panel.

f. ECR relav is de-energized-starting the tir.o out secuence.

ECR(3-5) closes. TD2 (N-P) opened when the TD2 relay was de-energized.

g. hhen the control switch is returned to the AUTO position, the start sirnal is again initiated, but due to the SF (C-D) contacts being open, the TD2 relay can not be re-energized and censequently the ECR relay shutdown secuence takes precedence.

h. The Diesel generator trips (shuts down with a locked in auto start signal) and cannot be restarted until the SF (C-D) -

contacts are manually reset at the engine control panel.

Placing the nta TD2 relay with the faster drop out time in the system, eliminated step c. Since the start-failure relay is not energized, retu=n-ing the control switch to the " auto" position will re-energizo the TD2 relay and not allow the engine shutdown sequence to take precedence.

The unit 3 diesel generator has not experienced the problem with the TD2 relay.

l At present, a recuest for modificatien of the diesel generator start-failure circuitry is being directed to our station electrical engi-neering department with the intent of decreasing the effect that a slew opening TD2 contact will have on the overall performance of the system.

In the interim, we will continue to operate under the new procedure referenced in our letter of October 3,1972.

Sincerely, U UAw W. P. Worden d

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