ML18127A662

LER 1978-017-00 for St. Lucie Unit 1, on 05/14/78 Concerning Improper Switching at Pratt & Whitney Substation Combined with Incorrect Wiring of Protective Relays at Midway Substation Led to Deenergization of Midway Substation Resulting in L

ML18127A662
Person / Time
Site:	Saint Lucie
Issue date:	06/13/1978
From:	Schmidt A Florida Power & Light Co
To:	O'Reilly J NRC/RGN-II, NRC/IE
References
PRN-LI-78-154 LER 1978-017-00
Download: ML18127A662 (7)

Text

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SQSTRI80TIQN FOR INCOMING, MATERIAL 50-335 P

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DOCTYPE: LETTER NOTARIZED: NO -'OPIES RECEIVED

SUBJECT:

LTR 1 ENCL LICFNSEE EVENT RE T N78-017 ON 5/14/78 CONCERNING IMPROPER SWITCHING AT THE PRATT L WHITNEY SUBSTATION COMBINED WITH INCORRECT MIRING OF PROTECTIVE RELAY. AT THE MIDWAY SUBSTATIQN LED TO THE DEENERGIZATIOhl OF THE MIDWAY.,

SUBSTATION RESUI TING IN LOSS QF OFFSET-8 Rouen ~ ~8 Sue'er W~efgrgp.

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PLANT NAME: ST LUCIE N1 REVIEWER INITIAL: XRS DISTRIBUTOR 'INITIAL:

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FLORIOA POWER L) LIGHT COMPANY June 13, 1978 PRN-LI-78-154 CD '

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Mr. James P. O'Reilly, Director, Region Office of Inspection and Enforcement II ~ f" C~fh

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CD U. S. Nuclear Regulatory Commission 230 Peachtree Street, N. W., Suite 1217 Al Atlanta, Georgia 30303.

Dear Mr. O'Reilly:

REPORTABLE OCCURRENCE 335-78-17 ST. LUCIE UNIT 1 DATE OF OCCURRENCE: MAY '14, 1978 OFF-SITE POWER The attached Licensee Event Report is being submitted in accordance with Technical Specification 6.9 to provide 30-day notification of the subject occurrence.

Very truly yours, A. D. Schmidt Vice President Power Resources MAS/ms Attachment cc: Harold F. Reis, Esquire Director, Office of Inspection and Enforcement (30)

Director, Office of Management Information and Program Control (3) 78)87P828

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~o 5 incorrect. wirin of rotective rela s at the Midway Substation, led to

~o 4 the deener ization of the Midwa Substation. This resulted in the loss 5 of off-site ower to the St. Lucie Plant for about 8-1/4 minutes. One

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~i I bined with incorrect wirin of both 240/138 kV autotransformer polarizing CT circuits at the Midway Substation. The incorrect wiring has been corrected, and appropriate personnel have been advised of the cause and corrective action for this occurrence.

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1 REPORTABLE OCCURRENCE 33 -17 LICENSEE EVENT REPORT ATTACHMENT PAGE 1 INTRODUCTION Florida Power s Light Co. (FPL) experienced an electrical power system disturbance on .Sunday, IIay 14, 1978, which resulted in the loss of power to an area of the PPL system This blacked .out area included the loss of. off-site power 'to St. Lucie Plant for approximately 8 minutes Fault recorder records, the Hest..Palm Beach computer printout, and logs were used to reconstruct the sequence of events.

PRE-DISTURBANCE CONDITIONS Only conditions in affected area are listed=

.1 St. Lucie Plant unit No 1 off for refueling

.' Pratt s Whitney 240kV 'ring bus open (240G36835 open) prior to switching.' This switch had been previously reported to be arcing.

The Dispatcher believed the switch to still 'be inoperative.

3 Two 240/138kV autotransfoxmers (49-1035 & 49-1168) at Midway Substation vere recently installed to replace smaller capacity units DISTURBANCE On Sunday, May 14,. 1978, at approximately 7:45AM while switching out the Pxatt a Whitney-Ranch 240<V circuit for a routine clearance, a condition vas created on .the Pratt G.Whitney south 240kV bus that caused lightning .

arresters on this bus to fail destructively Hot ionized gas from the lightning arxesters caused a "C" phase to ground fault on the Midvay-Ranch 240kV circuit which passes directly over the-Pratt a Whitney bus.

At Midway Substation improper connection of the relay current polarizing circuit resulted,in incorrect operation of the Directional Carrier Ground Relays (CLPG) on the IIalabax-Midway 240kV No. 1, Malabar-Midway 240kV No. 2 and the Midway-Plumosus 138kV circuits Erroneous current polarizing like-vise resulted in failure to trip by the ground relays of the Midway terminal of the faulted Midway-Ranch 240kV circuit. Failure of this terminal to trip resulted in a back-up operation of the autotransformer tertiary relay at Midway Substation.

The Hartman-Midway and Okeechobee-Midway lines then tripped, interrupting service to St. Lucie and other stations. On-site power was supplied at St. Lucie by automatic diesel generator operation. St. Lucie remained on diesel power until after system conditions stabilized.

REPORTABLE OCCURRENCE 33 -17 LICEQSEF~ EVENT REPORT "ATTACHtfENT PAGE 2 For given phase to ground fault, the north autotransfoxmer tertiaxy relay is

. more sensitive than the south autotransfoxmer tertiary relay.

This accounts for the operation of only the north autotransformer tertiaxy relay The two main contributing factors to the power loss were=

1 Improper switching at. Pratt G whitney Substation 2 Improper connection of both 240/138kV autotransformer polaxizing CT circuits at >Iidway Substation RESTORATION ~

Several attempts were made to energize the north bus at Midway Substation via the Malabar 240kV No 2 circuit. However, the lockout relay previously.trip-ped by the tertiary relay had not been reset. The south bus at Midway Sub-station was energized via.the .Ranch 240kV circuit As switching continued to normalize the system, a breaker at Pratt 6 Hhitney was closed and the original lightning arrester problem was recreated This resulteQ in the deenergizing of Midway Substation..

Pinal reenergization of Midway Substation and St. Lucie Plant was accomplished.

by the closing of the Ranch 240kV circuit at 7:53=30.

This resulted .in the loss of off-site power to St,.Lucie Plant for, approximately eight minutes and ixteen and one-half seconds.'witching, was then carried out until the entire affected area was returned to normal with the exception of Midway Substation's north autotransfoxmer CORRECTIVE ACTIONS The improper polarizing at Midway Substation has been corrected The north and south buses at Pratt 6 IJhitney Substation have been tied together to avoid the bus high voltage problem encountered during switching Drawings jn use at the time were reviewed and an error was detected. As a result of this, System Protection Memorandum No 3 10.1-A titled "The Connection of CT's In An Autotransformer Nhen Used As a Source For Ground

. Polarizing Circuit" was issued May 22, 1978. This memorandum outlines the procedures for checking transfoxmer nameplate data against PPL drawings as well as the electrical tests which axe to be made. This memorandum will be incorporated into the Power. Supply Proceduxes Manual and will prevent a reoccuxence of this event.

4 System Operato s and Dispatchers have been aQviseQ of the hazards of an ungrounded delta