ML19261F330

RO 77-15/3L:on 770529,one of Two Units of 230/4.16 Kv Auxiliary Transformer de-energized,leading to Operation in Degraded Mode Permitted by Tech Spec 3.7.2.b.Caused by Wiring Error on Current Transformers.Sys Repaired.Ler Encl

ML19261F330
Person / Time
Site:	Three Mile Island
Issue date:	06/28/1977
From:	Herbein J METROPOLITAN EDISON CO.
To:
Shared Package
ML19261F331	List: ML19261F330 ML19261F332
References
GQL-0850, GQL-850, NUDOCS 7910250791
Download: ML19261F330 (4)

Text

u.S. NUCLE AR REGULATORY MISSION OCC UMB NRC FORu 195

. , NRC DISTRIBUTION FCs PART 50 DOCKET MATERIAL 'YINEd*

IN REPORT J.P.o"REILLY FROM: METROPOLITAN EDISON CO. DATE OF DOCUMENT TO:

READING, PA 6/28/77 J.G. HERBEIN DATE RECEIVED 7/6/77 TTER O N OTO RIZE D PRCP INPUT FORM NUMBER OF COPIES RECEIVED R GINAL NC LASSIFIE D [

CESCRIPTION EN CLOSU R E REPORTABLE OCCURRENCE # 77-15/3L, ON 5/29/77 CONCERNING ONE AUXILIARY TRANSFORMER BEING DE-ENERGIZED.

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METROPOLITAN EDISON COMPANY . .

POST OFFICE BOX 542 READING, PENNSYLVANI A 19603 TELEPHONE 215 - 929-3601 June 28, 1977 GG 0850

@@ jam " Nb I' e . J. P. O'Reilly, Director

,v l' Office of Inspections and Enforcement, Region 1 _

U. S. Nuclear Regulatory Cctsissicn __'

631 Park Avenue -

King of Prussia, Pa. 19hC6 z

Dear Sir:

~

Dceket No. 50-289 Operating License Uc. DPR - 50 In accordance with the Technical Specificatiens of our Three Mile Island Nuclear Statien Unit 1 (TMI-1), we are reporuing the folleving reportable occurrence.

(1) Report Nu=ber: 77-15/3L (2a) Required Report Date: 06-28-77 (2b) Date of Occurrence: 05-29-77 (3) Facility: Three Mile Island Nuclear Staticn - Unit 1 (h) Identification of Occurrence:

Title:

Cns Auxiliary Transformer was De-energized

?/pe: A reportable occurrence as defined by Technical Specification 6.9 2.3 (2) in that ene (1) of the units two (2) 230/h.16 U auxiliary transformer was de-energized thus leading to operation in a degraded =cde permitted by a limit-ing condition for operatien as defined by Technical Specificatica 3.7.2.b.

(5) Ccnditions Prior to Occurrence:

Pcver: Core: 2521 int Elec: 813 lGe RC Flow: 155 x 106 lb/hr RC Temp: 579 cF RC Pressure: 2160 tsig D

PR:'.R Temp:

6h8 F PR"R Level: 220 inches 1482 061

-- ~ 1 g c , ,;

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J. P. O'Reilly June 28,1977 GQL C850

( 6, Description of Occurrence:

At 02h5 hcurs en May 29,1977, the 230 KV Substatica sus a was de-ener-

.gized by the differential relay 8733-1. The relay operation resulted in a loss of the "13" Auxiliary Transformer since Substaticn Bus b is the only source of pcVer to the "3" Auxiliary Transformer.

(7) Apparent Cause of Cccurrence:

The cause of this occurrence has been deter =ined to be due to a viring error on the current transformers for Unit II Auxiliary Transformer 2A.

The current transformers were wired in accordance with the Unit II drawings . However, there is an errer in the drawing in that the det which represents the polarity, was drawn on the inccrrect connection.

BecLuse of incorrect polarity en the current transformer, the increased load en the Unit II Auxiliary Transformer appeared as a bus fault and caused the relay operation that de-energized the h Bus.

(8) Analysis of Occurrence:

It has been determined that this cccurrence did not constitute a threat to the health and safety of the public in that:

(A) The 1A Diesel Generator aute=atically started and re-energized the "D" h KV ES Bus, thus supplying emergency pcVer.

(3) The "13" Diesel Generator was available in the event the "lA" Auxiliary Transformer was lost.

(9) Corrective action:

DDEDIATE:

The leads frc: the "D" hKV Eus that were required to maintain normal cperation were manually started. In approximately two (2) hours the 230 KV Bus h and the "13" Auxiliary Transformer vere returned to ser-vice. The Unit 1 Electrical System was returned to its ncr:al line-up.

LONG TEEM:

The cause for the relay operation was investigated. The current trans-formers at the Unit II Auxiliary Transformer "2A" were found to be wired inecrrectly. The viring errer was corrected and in-service checks were made en the differential relays to assure that the relays and current transformers were correctly connected. Drawing 207-001 vill be corrected and re-issued by September to show the correct polarity on the current trans formers . The field copy of 207-011 has been red pencil marked appropriately to correct the previously mentioned drawing errors.

The Plant Cperations Review Cen=ittee and Unit Superintendent have re-reviewed and approved the above ccrrective acticn and have taken steps to assure its cc=pletien. .

}kb. b

J. P. C'Reilly June 26, 1977 "4 0650 (10) Failure Data: NA Similar Occurrences: none

• 4ncerely s

J. G. Herbein Vice-President Generation JGH:DGM:bar

Attachment:

LER 1482 063