ML18101A415

LER 94-014-00:on 941118,number 4 Station Power Transformer Tripped Resulting in Blackout Signal. Caused by Failure of Station Power Transformer or Switcher 125 4T60.Strip Chart Recorder installed.W/941214 Ltr

ML18101A415
Person / Time
Site:	Salem
Issue date:	12/14/1994
From:	HAGAN J J, PASTVA M J Public Service Enterprise Group
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-94-014-02, LER-94-14-2, NUDOCS 9412230051
Download: ML18101A415 (8)

Text

• • e Public Service Electric and Gas Company P.O. Box 236 Hancocks Bridge, New Jersey 08038 Salem Generating Station December 14, 1994 U. S. Nuclear Regulatory Commission Document Control Desk Washington, DC 20555 Attn.: Document Control Desk SALEM GENERATING STATION LICENSE NO: DPR-75 DOCKET NO: 50-311 UNIT NO: 2 LICENSEE EVENT REPORT NO. 94-014-00 This Licensee Event Report is being submitted pursuant to the requirements of Code of Federal Regulation 10CFR50.73(a)

(2) (i) (B). Issuance of this report is required within thirty (30) days of event discovery.

9412230051 941214 ADOCK 05000311 PDR

• MJPJ:vs SORC 94-094 C Distribution LER File The pCM'er is in yDur hands. Sincerely, n nager -at ions ...<: z-z, \ ' ) 95-2189 REV 7-92 NRC FORM 366 (5-92) U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER) APPROVED BY OMB NO. 3150-0104 EXPIRES 5/31/95 (See reverse for required number of digits/characters for each block) ESTIMATED BURDEN PER RESPONSE TO COMPLY WITH THIS INFORMATION COLLECTION REQUEST: 50.0 HRS. FORWARD COMMENTS REGARDING BURDEN ESTIMATE TO THE INFORMATION AND RECORDS MANAGEMENT BRANCH (MNBB n14), U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON, DC 20555-0001, AND TO THE PAPERWORK REDUCTION PROJECT (3150-0104), OFFICE OF MANAGEMENT AND BUDGET, WASHINGTON, DC 20503. FACILITY NAME (1) DOCKET NUMBER (2) Salem Generating Station -Unit 2 05000311 II PAGE (3) 1 OF 6 Engineered Safety Feature (4KV) Vital Buses Blackout Signal Loading of 2B and 2C 4 Kilovolt EVENT DATE (51 LER NUMBER (6 REPORT NUMBER l7l OTHER FACILITIES INVOLVED 18) MONTH DAY 11 18 OPERATING MODE (9) YEAR 94 6 YEAR 94 SEQUENTIAL NUMBER 014 REVISION NUMBER --00 FACILITY NAME DOCKET NUMBER MONTH DAY YEAR 05000 FACILITY NAME DOCKET NUMBER 05000 14 94 12 THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR t: (Check one or more '111 20.402(b) 20.405(c)

IX 50.73(a)(2)(iv) 73.71 (b) I POWER I I 20.405(a)(1)(i) 50.36(c)(1) 50.73(a)(2)(v) 73.71 (c)

(10) O . 20.405(a)(1)(ii) 50.36(c)(2) 50.73(a)(2)(vii)

OTHER 20AOS(a)(1}(iii) 50.73(a)(2)(i) 50.73(a)(2)(viii)(A) (Specify in Abstract 20.405(a)(1)(iv) 50.73(a)(2)(ii) 50.73(a)(2)(viii)(B) below and in Text, NRG

__ -' Form 366A) 20.405(a}(1)(v) 50.73(a)(2)(iii) 50.73(a)(2)(x)

LICENSEE CONTACT FOR THIS LER (12) NAME Michael J. Pastva, Jr., LER Coordinator TELEPHONE NUMBER (Include Area Code) 609 339-5165 CAUSE SYSTEM COMPONENT MANUFACTURER REPORTABLE TO NPRDS SUPPLEMENTAL REPORT EXPECTED f14l I YES (If yes, complete EXPECTED SUBMISSION DATE) NO CAUSE ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines) (16) SYSTEM COMPONENT MANUFACTURER REPORTABLE TO NPRDS EXPECTED MONTH DAY YEAR SUBMISSION DATE (15) At 0103 hours0.00119 days <br />0.0286 hours <br />1.703042e-4 weeks <br />3.91915e-5 months <br /> on 11/18/94, with the reactor core off-loaded and a single off-site power source aligned to Unit 2, No. 4 Station Power Transformer (SPT) tripped resulting in "blackout signal" loading of 2B and 2C 4KV vital buses' Diesel Generators (DGs). Expected loss and transfer of electrical loads occurred.

The vital buses were maintained powered from their DGs until 0458 and 0537 hours0.00622 days <br />0.149 hours <br />8.878968e-4 weeks <br />2.043285e-4 months <br /> (respectively) on 11/19/94.

The most probable root cause of this event is intermittent component failure of either the SPT 4T60 28 VDC manual trip coil open relay, 3X, or the switcher 125 VDC supervisory relay, 890X and both were replaced.

A strip chart recorder has been installed to continually monitor 6 points within the trip circuit, and the 28 VDC and 125 VDC buses. To-date, this device has not shown signals capable of tripping the 4T60 switcher.

The recorder will be maintained until the subsequent restart and return of the Unit to service. This is intended to ensure that most likely combinations of plant operating evolutions, ambient conditions, and work activity evolutions are monitored to obtain further information, regarding this event. NRG FORM 366 (5-92)

BLOCK NUMBER 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 REQUIRED NUMBER OF DIGITS/CHARACTERS FOR EACH BLOCK NUMBER OF DIGITS/CHARACTERS TITLE UP TO 46 FACILITY NAME 8 TOTAL 3 IN ADDITION TO 05000 DOCKET NUMBER VARIES PAGE NUMBER UP TO 76 TITLE 6 TOTAL 2 PER BLOCK EVENT DATE 7 TOTAL 2 FOR YEAR -3 FOR SEQUENTIAL NUMBER LER NUMBER 2 FOR REVISION NUMBER 6 TOTAL 2 PER BLOCK REPORT DATE UP TO 18 FACILITY NAME 8 TOTAL--DOCKET NUMBER OTHER FACILITIES INVOLVED 3 IN ADDITION TO 05000 1 OPERATING MODE 3 POWER LEVEL 1 CHECK BOX THAT APPLIES REQUIREMENTS OF 10 CFR UP TO 50 FOR NAME 14 FOR TELEPHONE LICENSEE CONT ACT CAUSE VARIES 2 FOR SYSTEM 4 FOR COMPONENT EACH COMPONENT FAILURE 4 FOR MANUFACTURER NPRDS VARIES 1 CHECK BOX THAT APPLIES SUPPLEMENTAL REPORT EXPECTED 6 TOTAL 2 PER BLOCK EXPECTED SUBMISSION DATE 1 --

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station Unit 2 Docket Number 50-311 Plant and System Identification:

Westinghouse

-Pressurized Water Reactor LER Number 94-014-00 Page 2 of 6 Energy Industry Identification System (EIIS) codes appear in the text as {xx} Identification of Occurrence:

Engineered Safety Feature Actuation:

Blackout Signal Loading of 2B and 2C 4 Kilovolt (4KV) Vital Buses Event Date: 11/18/94 Report Date: 12/14/94 This report was initiated by Incident Report No.94-422 Conditions Prior to Occurrence:

Mode 6 Refueling/maintenance outage 2R8 in progress, with the reactor core off-loaded.

A single source of off-site power to Unit 2 was aligned from No. 4 Station Power Transformer (SPT) {ED}. No. 2 SPT {ED}, and 2A 4KV vital bus {ED} were cleared and tagged for maintenance.

In addition, No. 4 SPT was supplying 14 SPT {ED} to Unit 1. Description of Occurrence:

At 0103 hours0.00119 days <br />0.0286 hours <br />1.703042e-4 weeks <br />3.91915e-5 months <br /> on November 18, 1994, No. 4 SPT tripped resulting in an undervoltage (UV) signal tripping 2B and 2C 4KV vital buses and engineered safety feature (ESF) automatic starting and signal" loading of the buses' respective Diesel Generators (DGs) {VJ}. Per design, the inservice Unit 2 spent fuel pit (SFP) pump {DB} automatically turned off, and was returned to service, at 0120 hours0.00139 days <br />0.0333 hours <br />1.984127e-4 weeks <br />4.566e-5 months <br /> (same day) . Appropriate Control Room alarms and expected loss and transfer of electrical loads resulted from this event . At 0412 hours0.00477 days <br />0.114 hours <br />6.812169e-4 weeks <br />1.56766e-4 months <br /> (same day), the NRC was notified of this event, in accordance with 10CFR50.72(b)

(2) (ii)

• LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station Unit 2 Docket Number 50-311 Description of Occurrence: (cont'd) LER Number 94-014-00 Page 3 of 6 10CFR50.72(b)

(2) (ii). 2C and 2B vital buses were maintained powered from their DGs until 0458 and 0537 hours0.00622 days <br />0.149 hours <br />8.878968e-4 weeks <br />2.043285e-4 months <br /> (respectively) on November 19, 1994, to permit adequate assessment of the event prior to restoring off-site power to the buses. Analysis of Occurrence:

The 4T60 is the 500 KV input circuit switcher for No. 4 SPT unexpectedly opened deenergizing the transformer and causing 14 and 23 SPTs to deenergize.

This switcher, was installed during Unit 1 Refueling Outage lRll and had been in service approximately 12 months. Unit 2 controls for 4T60 were installed during the ongoing Unit 2 refueling outage and had been in service since November 5. The deenergized 23 SPT resulted in an UV signal tripping the two inservice vital buses and ESF automatic starting and signal" loading of the buses' DGs. In addition, the in-service SFP pump was automatically stopped. However, within approximately 17 minutes it was restarted and returned to service. Spent Fuel Pool (SFP) temperature increased by approximately 1.2 degrees Fahrenheit, at a rate of approximately 4.4 degrees Fahrenheit per hour, during the time the SFP pump was not running. Ongoing maintenance activities, requiring that 2A 4KV vital bus be deenergized, had deenergized the power supply to one of the two diesel fuel oil transfer pumps. Following the automatic starting of 2B and 2C DGs, the remaining fuel oil transfer pump operated per design. On Unit 1, this resulted in automatic transfer of lC 4KV vital bus to 13 SPT and loss of power to operating llB and 13B circulating water (CW) pumps, as per design, (12B CW pump was cleared and tagged for maintenance).

Unit 1 reactor power, which was at 100% prior to the event, was reduced to 85% in response to the reduced CW flow. Following restoration of power to the circulators, reactor power was returned to 100%. Immediate Post-Event Conditions:

-4T60 Control Room green bezel flashing -No ground fault alarms

,

• LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station Unit 2 Docket Number 50-311 Analysis of Occurrence: (cont'd) -No ground fault relay target trips LER Number 94-014-00

-13KV Breakers C-D and D-E remained closed -500 KV Section 1 Breakers remained closed -CW UV flags (as per design) Page 4 of 6 Investigation shows 4T60 opened completely, indicating that the switcher OC latching relay {EB} remained energized for a complete opening cycle. The relay can be considered a separation point, thereby dividing the circuit into two sections:

ahead of the relay towards the 125 volt direct current (VDC) power supply and behind the relay in the direction of the 4T60 drive motor. The OC relay was found in the latched position.

Therefore, it can be assumed the cause of the relay actuation originated from the circuitry supplying the relay. The 4T60 logic was reviewed to determine which components could initiate the sequence leading to the event. Eliminated as suspect to the cause(s) of the 4T60 switcher opening: Depression of the 4T60 push button, which manually opens the switcher, will cause the push button bezel indicator green light to become solidly lit. However, at the time of the event, the light was flashing.

Since the light is not designed to flash when manually operated, the possibility of an inadvertent depression of the push button has been eliminated as a possible cause of the switcher operating.

Broken or otherwise closed contacts on either Ground Fault Protection Regular Relay 86/4GR or Back-up Relay 86/4GB can energize the 4T60 OC opening relay; however, the relays were inspected and no defects were found. Electrical shorting of various cable runs as a possible contributor to the event was eliminated by satisfactory meggering and continuity checks. Inspection of the 4T60 89/bb cam operated contacts, the 4T60 operator hand switch, and the OC latching contacts eliminated

• LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station Unit 2

• Docket Number 50-311 Analysis of Occurrence: (cont'd) LER Number 94-014-00 Page 5 of 6 the possibility that misalignment, vibration, or moisture intrusion, which could have resulted in OC relay latching and 4T60 opening. Apparent Cause of Occurrence:

The most probable root cause of this event is believed to be the result of intermittent component failure of either the 4T60 switcher 28 VDC manual trip coil open relay, 3X, or the switcher 125 VDC supervisory relay 89/0X, which is in electrical series with the switcher OC open contactor.

Testing was unable to duplicate failure of either component.

Testing verified the acceptability of the existing components, wiring, and device configurations.

No activities, involving either modification or operational, were identified as contributory to this occurrence.

Review of pre-operational and in-service testing in progress at the time did not identify a cause(s) of this occurrence.

Prior Similar Occurrence:

Review of documentation did not reveal a prior similar occurrence involving loss of an SPT, due to inadvertent opening of an SPT circuit switcher.

Safety Significance:

This event did not affect the health and safety of the public. It is reportable pursuant to 10CFR50.73(a)

(2) (iv), due to the automatic starting of 2B and 2C DGs. Potential safety significance of this event was minimized on Unit 2 as a result of outage planning, which ensured completion of reactor core off-loading to the SFP, prior to alignment of one source of off-site power to the Unit. Following automatic tripping of the SFP pump, the resulting SFP heatup rate was approximately 4.4 degrees Fahrenheit per hour. This allowed

• .. LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station Unit 2 Docket Number 50-311 Safety Significance: (cont'd) LER Number 94-014-00 Page 6 of 6 sufficient time to restart the pump to normal SFP cooling or to align alternate means of SFP cooling, in accordance with procedure.

In addition, this event resulted in reduction in defense-in-depth of off-site power sources to Unit 1, which placed the Unit in a 72-hour action requirement.

Corrective Action: Relays 890X and 3X were both replaced, based upon the conclusions of the investigation to-date. A strip chart-type recording device has been installed to continually monitor 6 points within the involved trip circuit, as well as both the 28 VDC and 125 VDC buses. To-date, this device has not shown any signals capable of tripping the 4T60 switcher.

This device will be maintained in place until the subsequent restart and return of the Unit to service following completion of the ongoing refueling outage. This is intended to ensure that the most likely combinations of plant operating evolutions, ambient conditions, and work activity evolutions are monitored to obtain further information, regarding this event. MJPJ:vs REF: SORC Mtg ..94-094 nager -Operations