ML18096A827

LER 91-017-01:on 910413,sustained Undervoltage Relay Min Drop Voltage Found Below TS Min Allowable Value & Monthly Surveillance Test of Undervoltage Relay Setpoints Not Performed Since 910109.Procedures enhanced.W/920709 Ltr

ML18096A827
Person / Time
Site:	Salem
Issue date:	07/09/1992
From:	Pollack M, Vondra C Public Service Enterprise Group
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-91-017, LER-91-17, NUDOCS 9207200055
Download: ML18096A827 (6)

Text

PS~G Public Service Electric and Gas Company P.O. Box 236 Hancocks Bridge, New Jersey 08038 Salem Generating Station July 9, 1992

u. s. Nuclear Regulatory Commission Document Control Desk Washington, DC 20555

Dear Sir:

SALEM GENERATING STATION LICENSE NO. DPR-70 DOCKET NO. 50-272 UNIT NO. 1 SUPPLEMENTAL LICENSEE EVENT REPORT 91-017-01 This Licensee Event Report supplement is being submitted pursuant to the requirements of the Code of Federal Regulations 10CFR 50.73. The Apparent Cause of Occurrence and Corrective Action sections have been modified based upon completed Engineering investigations.

Sincerely yours, c/~I t:J~.!/~ffi J,(J_

c. A Vondra General Manager -

Salem Operations MJP:pc Distribution

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NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION 16-89) APPROVED OMB NO. 3150*0104 EXPIRES: 4/30/92 ESTIMATED BURDEN PER RESPONSE TO COMPLY WTH THIS INFORMATION COLLECTION REOUEST: 50.0 HRS. FORWARD LICENSEE EVENT REPORT (LERI COMMENTS REGARDING BURDEN ESTIMATE TO THE RECORDS AND REPORTS MANAGEMENT BRANCH IP*530). U.S. NUCLEAR REGULATORY COMMISSION. WASHINGTON.DC 20555. AND TO THE PAPERWORK REDUCTION PROJECT (31~-0104). OFFICE OF MANAGEMENT AND BUDGET. WASHINGTON. DC 20503.

FACILITY NAME (11 DOCKET NUMBER (2) I *PAGE 131 TITLE (41 -

n,..,; +- i Io I 5 Io Io I O I 21 7 12 1 OF O 15 4~V Vital Bµs UV Relay Setpo~nts Found Below Minimum Tech. Spec. A~lowable V~lu~

EVENT DATE 151 LER NUMBER 16) REPORT DATE (7) OTHER FACILITIES INVOLVED (8)

MONTH DAY YEAR YEAR  !':::::::::: SEQUENTIAL!::;::::::: REVISION MONTH DAY YEAR FACILITY NAMES DOCKET NUMBERISI 1::::::::::: NUMBER  ::;:;:::;:;NUMBER Salem Unit 2 o 1s101010131111 THIS REPORT IS SUBMITTED PURSUANT TO THE R~QUIREMENTS OF 10 CFR §:(Check one or more of the following) (111 OPERATING MODE (91 l 20.402(bl

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LICENSEE CONTACT FOR THIS LER (121 NAME TELEPHONE NUMBER AREA CODE M. J. Pollack - LER Coordinator COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT 113)

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SUPPLEMENTAL REPORT EXPECTED 1141 MONTH DAY YEAR EXPECTED n YES (If yes. complete EXPECTED SUBMISSION DATE!

SUBMISSION DATE 1151

,. I I ABSTRACT (Limir to 1400 sceces, i.e .. accroximsrely fifteen single-scace typewritten lines) (16)

On 4/13/91, the 91.6% sustained undervoltage relay's minimum drop out voltage, for all 3 Vital Busses, ~ere found to be below the Technical Specification minimum allowable value of 91%. This was discovered during Technical Specification Surveillance 4.3.2.1.1 testing which requires monthly testing of undervoltage relay setpoints. New procedures

{Sl. MD-FT. 4KV-0001 (Q) ( 0002 or 0003) , "ESFAS Instrumentation Monthly Functional Test-lA {lB or lC) 4KV Vital Bus Under Voltage") were being used (first use) to support the surveillance testing. The surveillance test was last performed on 1/9/91 using procedure M3T, "Undervoltage and Underfrequency Trip and Time Response Surveillance Test". It had not been performed since 1/9/91 due to ninth refueling outage activities (operability required only in Modes 1, 2, and 3). The causal factors of the setpoint variance are relay design inadequacy and procedure inadequacy. Special relay tests show that the relay circuitry is influenced by the amount/type of harmonics present in the external test signal; the relay trip/reset setpoints change on subsequent checks when the test signal contains a different range of harmonics/noise plus the relay's allowable design setpoint drift. For additional root cause and corrective action details refer to LER 311/91-008-01. *Contributing factors to the cause of this event are test equipment inaccuracies and test methodology. Procedure enhancements have been made to address human factor and test methodology concerns found during System Engineering's investigation.

NRC Form 366 (6-891

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating station DOCKET NUMBER LER NUMBER PAGE Unit 1 5000272 91-017-01 2 of 5 PLANT AND SYSTEM IDENTIFICATION:

Westinghouse - Pressurized Water Reactor Energy Industry Identification System (EIIS) codes are identified in

. the text as {xx}.

IDENTIFICAT.ION OF OCCURRENCE:

The Vital Bus 91.6%*undervoltage relay setpoints (all three busses) were found below the minimum Technical Specification allowable value Event Date: 1/9/91 Discovery Date: 4/13/91 Report Date: 7/9/92 This report was initiated by Incident Report Nos.91-265, 91-266, and 91-267.

CONDITIONS PRIOR TO OCCURRENCE:

M~ge 4 (Hot Standby)

9. Refueling/Maintenance Outage - Plant heat up in progress (outage drawing to a close)

DESCRIPTION OF OCCURRENCE:

On April 13, 1991, at 1430, 1700 and 1950 hours0.0226 days <br />0.542 hours <br />0.00322 weeks <br />7.41975e-4 months <br /> (respectively for each Vital Bus), the 91.6% sustained undervoltage relay's minimum drop out trip setp6int voltage, for all three (3) Vital Busses, was found to be below the Technical Spe.cif ication minimum allowable value of 91%. The average trip setpoint was 107.69 VAC (90.3%) and the average reset setpoint was 108.68 VAC (91.4%). This was discovered during monthly Technical Specification Surveillance 4.3.2.1.1 testing of undervoltage relay setpoints. This testing was not performed during the ninth refueling outage due to system constraints (also, mod~ applicability is modes 1, 2, and 3). New procedures Sl.MD-FT.4KV-OOOl(Q) (0002 or 0003), "ESFAS Instrumentation Monthly Functional Test-lA (lB or lC) 4KV Vital Bus Under Voltage") were being used (first use) for the testing.

The surveillance test was last performed on January 9, 1991, using procedure M3T, "Undervoltage and Underfrequency Trip and Time Response Surveillance Test".

• The as-found condition of the Vit~l Bus relays potentially placed the Unit outside its design basis. To be conservative, the Nuclear Regulatory Commission was notified of this event on April 14, 1991, at 1800 hours0.0208 days <br />0.5 hours <br />0.00298 weeks <br />6.849e-4 months <br /> in accordance with Code of Federal Regulations 10CFR 5 0. 7 2 ( b) ( 1) (ii') ( B) .

LICENSEE EVENT REPORT (LER) .* TEXT CONTINUATION Salem Generating Station DOCKET NUMBER LER NUMBER. PAGE Unit 1 5000272 91-017-01 3 of 5 APPARENT CAUSE OF OCCURRENCE:

The causal factors of the setpoint variance are relay design inadequacy and procedure inadequacy. Special relay tests show that the relay circuitry is influenced by the amount/type of harmonics present in the external test signal; the relay trip/reset setpoints change on subsequent checks when the test signal contains a different amount/type of harmonics/noise plus the relay's allowable design setpoint drift. For additional details refer to LER 311/91-008-01~

Contributing factors, to the cause of this event, include test equipment inaccuracies and test methodology. Procedure M3T did not define the different test equipment setups or specify*the test equipment required to support each type of undervoltage or underfrequency relay test. As explained below, personnel error did not contribute to this.event as.was the case for a similar Unit 2 event (reference LER 311/91-005-01). The Unit 1 calibration (January 9, 1991) had taken place prior to the Unit 2 event.

When the relay's trip/reset setpoints were checked on January 9, 1991, the variable power supply's output voltage was varied using thumb-wheel switches. These switches have increments of 0.1 VAC.

Although the procedure required verification of settings using a DVM (good to 0.01 VAC), the recorded data indicated that the as~found trip/reset setpoints were determined by reading the thumb-wheel switch settings.

When the relay's trip/reset setpoints were checked on April 13, 1991*

in accordance with new procedures, the thumb-wheel switches were set to 115 VAC and relay input voltage was adjusted using a variable resistor network. The variable resistor network provided 0.01 VAC increments instead of the previous thumb-whee*1 method of O. 1 VAC.

Since the trip/reset setpoints indicated. on the DVM were more accurate, this method verified that additional variable power supply calibration and thumb-wheel switch tolerances contributed to the error.

When the as-found setpoint (on January 9, 1991) was not within M3T's administra.tive setpoint span, the relay was recalibrated as follows:

the thumb-wheel switches were set to 108.9 VAC and the relay's "Low Trip" potentiometer was adjusted until the red LED illuminated. Then the thumb-wheel switches were set to 110.0 VAC and the relay's "Low Trip Deadband" potentiometer was adjusted until the red LED extinguished. The thumb-wheel switches were changed between the required trip and reset voltage to verify proper setpoint actuation.

Since M3T's test methodology added the variable power supply's calibration tolerance to the relay's normal monthly setpoint drift, the relay setpoint was set at a lower voltage than M3T's

• administrative setpoint spans of 108.75 VAC - 109.05 VAC and 109.85 VAC - 110.15 VAC, respectively.

. I

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station DOCKET NUMBER LER NUMBER PAGE Unit 1 5000272 91-017-01 4 of 5 APPARENT CAUSE OF OCCURRENCE: (cont'd)

On April 22, 1991, a special test was performed using the January 9,*

1991 variable power supply, the other variable power supply used on April 13, 1991, and a spare 91.6% relay. Test results showed that when the relay trip/reset setpoints were set using the thumb-wheel switches, the as-found setpoints using the DVM and variable resistor network were 0.53 VAC and 0.62 VAC lower respectively. When either va.riable power supply was used to set relay setpoints using the new procedure method, the as-found setpoints were within 0.01 VAC and 0.02 VAC. Based on the worst case.relay drift found during three (3) weekly tests performed on Unit 2 relays (0-.56 VAC), DVM calibration error (0.21), and the special test results above (0.53 VAC), the total trip setpoint drift on April 13, 1991 col,lld have been as much as 1.30 VAC lower compared to the April 13, 1991 average Unit 1 as-found trip setpoint of 1.21 VAC.

ANALYSIS OF OCCURRENCE:

The Vital Bus (lE) 70% Loss of Voltage, 91.6% Sustained Degraded Voltage, and 35% Vital Bus Undervoltage Bus Transfer relays monitor the Vital Bus voltage via 35:1 ratio potential transformers (PTs).

Each Vital Bus contains one 70% IAV relay three 91.6% Rochester Instrument Systems model PR-2035.Pl-Tl-O relays, and one 35% ITE-27H relay. The 70% and 91.6% relays provide input to the Safeguard Equipment Control (SEC) Systems so the SEC can determine Vital Bus emergency loading requirements.

On Aprii 13, 1991, all nine (9) 91.6% relays' as-found trip setpoints were less than the minimum Technical Specification allowable value (91%). The relays were then recalibrated to the 91.6% value specified in the applicable Surveillance Test Procedure Sl. MD-FT. 4KV-0001 (Q) ( 0002 or 0003) . *Recalibration was completed for each relay of each Vital Bus, at the time the out of specification reading was found. All three (3) Vital Busses relays (total of nine relays) were recalibrated on April 13, 1991.

An engineering analysis (conducted in support of Salem Unit 2 LER 311/91-005-00) previously determined the impact low as-found 91.6%

relay setpoints (90%) would have on Vital Bus motors and loads. For all scenarios, the undervoltage relays would perform their design function and provide adequate protection to Vital Bus motors and loads. The analysis consi~ered several .scenarios that could result in.low voltage at the 4KV Vital Busses; however, those situations were highly improbable during this* period since the 500 KV grid voltage was 108% of 500 KV and all step down transformers equipped with load tap changers were operable.

Therefore, based on the above analysis, tnis event did not affect the health or safety of the public. However, since the Technical Specification requirement for the undervoltage relay setpoint was not met, this event is reportable to the commission in accordance with

.

LICENSEE. EVENT REPORT (LER) TEXT CONTINUATION_

Salem Generating Station DOCKET NUMBER LER NUMBER PAGE Unit 1 5000272 91-017-01 _5 of 5 ANALYSIS OF OCCURRENCE: (cont'd)

Code of Federal Regulations 10CFR 50.73(a) (2) (i} (B).

CORRECTIVE ACTION:

For specific details as to the corrective actions taken which address the relay's design inadequacy, refer to LER 311/91-008-01. I As indicated previously, the new relay test procedures are unit and bus specific. The new test procedures: 1} include a test equipmen_t connection diagram for each type of relay test; 2) use a variable resistor network to provide 0.01 VAC input voltage increments; 3}

increase the minimum administrative trip setpoint from 108.75 VAC to 108.90 VAC; and 4) measure relay input voltage at the relay terminals. Additional procedure enhancements have been made to address other human factor and test methodology concerns found during System Engineering's inyestigation.

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- General Manager -

Salem Operations MJP:pc SORC Mtg.92-076