ML20029C692

LER 94-002-00:on 940324,discovered That Breaker Tripped at Current Below Tolerance.Caused by Design of Breakers. Corrective Action:Circuit Breakers Revised for Further Classification for Testing Instantaneous trip.W/940422 Ltr

ML20029C692
Person / Time
Site:	Monticello
Issue date:	04/22/1994
From:	Richard Anderson, Porter S NORTHERN STATES POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-94-002, LER-94-2, NUDOCS 9404260267
Download: ML20029C692 (6)

Text

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4 Northem States Power Company 414 Nicollet Mall Minneapolis, Minnesota 55401-1927 Telephone (612) 330-5500 April 22, 1994 US Nuclear Regulatory Commission Attn Document Control Desk Washington, DC 205;5 MONTICELLO NUCLEAR GENERATING PLANT Docket No. 50-263 License No. DPR-22 Instantaneous Trip of 480 VAC MCCBs Do Not Meet Acceptance Criteria Due to Manufacturer's Desion The voluntary Licensee Event Report for this occurrence is attached. This letter contains no new NRC commitments, nor does it modify any prior commitments.

Please contact Marv Engen, Sr Licensing Engineer, at (612) 295-1291 if you require further information.

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Roger O Anderson Director Licensing and Management Issues c Regional Administrator - III, NRC NRR Project Manager, NRC Sr Resident Inspector, NRC State of Minnesota Attn: Kris Sanda l

• ) uQ 1 9404260267 940422 ADOCK 05000263 j PDR o eon gg .

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l MRC FORM* 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 3150-0104 r5M)

EXPIRES 5/31/95 EST! MATED BURDEN PER AESPONSE TO COMPLY WITH THis INT OPVATION COLLECTION REQUEST: 50.0 NRS. FOHWARD LICENSEE EVENT REPORT (LER) CCWNS REGMDING BURDEN EMNM TO NE WOHMATM AND RECORDS MANAGEMENT BRANCH (MNBB 77t4L U 5. NUCt'.AR REGULATORY CCMM6S10N. WASHINGTON, DC 2052 000 s, AN ) 10 THE PAFFTTWORK REPUCTION PROJECT {31540104, OF FiCf CF (See reverse for required number of digits / characters for each block) MANAGEMENT AND BUDGET, WASH!NGTON. DC 20503.

ECluTY NAME (t) DOCKET NMtBEH (2) PAGE (3)

MONTICELLO NUCLEAR GENERATING PLANT 05000 - 263 1 OF 5

" " ' Instantaneous Trip of 480 VAC MCCBs Do Not Meet Acceptance criterin Due to Manuhcturer's Desien EVENT DATE (5) LER NUMBER (6i REPORT NUMBER (7) OTHER FACILITIES INVOLVED (8)

SEQUENTIAL REVSON FAOLJYNAML DOCAEI NUMdEH MONTH DH YEAR YEAR "N" " "

P/ UMBER NUMBER 05000 I AQUI( NAME rX)CKET NUMBER

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03 24 94 94 002 00 04 22 94 05000 OPERATING THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR i: (Check one or more) (11)

MODE (9) N 20 402(b) 20 405(c) 50 73(a H2)(iv) 73 71(b)

POWER 20 405(a)(1)(i) 50.36(c)(1) 50 73(a)(2)(v) 73.71(c)

LEVEL (10) 100 20 405(a)(1)(ii) 50.36!c)(2) 50.73(a)(2)(vul D OTHER 20.405(a)(1)(m) 50.73(a)(2)(i) 50.73(a)(2)(viii)(A) M*W 'n Atext 20 405(aM1)(iv) 50 73(a)(2)(ii) 50.73(a)(2)(vhi)(B) r 3 A) 20 405(a)(1)(v) 50.73(a)(2)(m) 50.73(a)(2)(x) Voluntary Rg  :

LICENSEE CONTACT FOR THIS LER (12)

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Steve Porter (612) 295-1497 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)

CAUSE SV57t M COMPCN NT MANUF ACTURE P CAUSE SYS'E M COMF'ONE NT MANUFACTURER O PD SUPPLEMENTAL REPORT EXPECTED (14) EXPECTED MON'" D" *R vEs SUBMISSION P yn, c<ma rwEcTEo susM:ssioN DATo X DATE (15)

ABSTRACT (Um:t to 1400 spaces,i e, approximately 15 single spaced typewritten lines) (16) l During routine plant preventative maintenance testing of a Klockner Moeller 480 VAC 3 phase molded case circuit breakers, it was discovered that the breaker tripped at a current below the lower tolerance for the instantaneous trip. Spare breakers of the same model number produced similar test results.

The tests results were verified by an independent testing laboratory. The cause is believed to be the design of the breakers. In all cases, sufficient

• margin exists above requirements to ensure successful load operation. Motor starting, reduced voltage conditions, and fuse / breaker coordination were all considered. This report is a voluntary report as this issue caused no safety problem at Monticello. An Institute For Nuclear Power Operations - Nuclear Network item was issued on March 28, 1994 to inform the industry of this issue.

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Description:

On March 24, 1994, the plant was operating at 100% power when an anomaly associated with Klockner Moeller molded case circuit breaker (MCCBs)(EIIS Component Function Identifier - 52) was discovered. While performing routine testing of a class lE 480 VAC three phase, Klockner Moeller molded case circuit breaker (Model Number ZM6-33-200. obi-CNA, purchased in 1982), it was i observed that adjustment of the instantaneous trip (magnetic trip) did not result in the expected trip setpoint response.

During subsequent testing of the instantaneous trip, breakers were found to deviate from the trip setpoint at higher settings. The deviation was small for low set points and increased as the setpoint was increased (See attached Figure). The results were consistent for each pole (phase) tested. Spcre breakers of the same model number were tested; all of which produced nearly identical results. Two additional Klockner Moeller molded case circuit breaker models (including a breaker procured in 1993) were tested and exhibited similar characteristics. These other models, however, were not outside of allowed tolerances. The testing was performed by experienced plant electricians in accordance with the requirements of UL (Underwriters Laboratory) Standard 489. The results were confirmed by an independent testing laboratory.

These Klockner Moeller molded case circuit breakers are used in essential 4

motor control centers (EIIS System Code - EC). All essential Klockner Moeller molded case circuit breakers are included in the Monticello preventative maintenance program. This provides assurance that any future problems will also be identified.

Cause:

1 The primary cause of this event is believed to be the design of the molded case circuit breaker. All Klockner Moeller 480 VAC molded case circuit breakers exhibited the trend shown in the attached figure. The trend was consistent between phases, models and manufacturing period. Breakers manufactured by others did not exhibit this trend. The issue identified does not appear to be the result of degrading equipment. Breakers procured in 1993 j exhibited similar characteristics to those procured in 1982. Test data taken j in 1982 appears to correspond to current data. Test results were very consistent from pole to pole and from breaker to breaker. These facts lead to the conclusion that age is not a cause of this characteristic.

I NRC FORM M6A (5 92;

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 3150-0104 pri EXPIRES 5/31/95 ESTIMATED BURDEN PER RESPONSE TO COMPLY Wf7H TH!S INFORMATcN COLLECTcN REQUEST: 60.0 HRS. FORWARD

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YEAR NUMBEA NUMBER 05000 - 263 OF Monticello Nuclear Generating Plant 94 - 002 -

00 3 5 Text g,,no,. ue. w<.e . .ouer cep... or usc *orm asuf o r, A contributing cause was the inadequate acceptance criteria specified during the initial motor control center breaker installation. During installation in 1982, the acceptance band provided was the adjustable range for the instantaneous over current trip, rather than being a function of the established retpoint. This inadequate acceptance criteria prevented the condition f: m being identified during initial motor control center breaker installatior.. Current acceptance testing methods would identify this problem.

The condition could have been identified during the 1991 breaker testing.

However, the testing procedure lacked sufficient detailed guidance to identify the anomaly.

Analysis:

The report is a voluntary report as this issue caused no safety problem at Monticello. It could, however, be of interest to the NRC. An Institute For Nuclear Power Operations - Nuclear Network item was issued on March 28, 1994 to inform the industry of this issue.

The discrepancy identified exists only where the instantaneous setpoint is set above the minimum setting. At settings greater than minimum, the trip would occur at currents below the setting. The primary concern of breakers tripping early (at a lower current than desired) is the resultant loss of equipment when no fault or electrical problem exists, for example, during a pump start.

Therefore, a review was conducted of those Klockner Moeller molded case circuit breakers with the instantaneous trip setpoints greater than minimum. l In all cases, sufficient margin exists al.c n requirements to ensure successful load operation even with the setpoint at minimum. Motor starting, reduced i voltage conditions, and fuse / breaker coordination were all considered. j Load operability has been demonstrated numerous times since the Klockner Moeller molded case circuit breakers were installed. Loads supplied by the molded case circuit breakers have been started many times for surveillance procedures. No problem with these breakers tripping unnecessarily has occurred. Operating history, therefore, provides further assurance of load operability.  !

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NRC FORM 366A (542) j l

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EXPIRES 5/31/95 ESTIMATCD BURDEN PER RESPONSE TO COMPLY wrTH THt$

INFORMATION COLLECTON REQUEST: 60 0 HRS. FORWARD LICENSEE EVENT REPORT (LER) COMvEes REGAc~G BuRoEN ESTiuATE TO inE woRuATON TEXT CONTINUATION AND REC R S MANA EMEW BRANCH ABB MHWS NUCLEAR REGULATORY COMMISSON, WASMrNGTON, DC 70$$50001. AND TO THE PAPERWORK REDUCTON PRCUECT (31504104. OFFICE OF MANAGEMENT AND BVDGET, W ASHINGTON. DC 70503 FACIUTY NAME (1) DOCAET NUMBER (2) LiR NUMBER (s) PAGE (3)

. aON YEAR NUMBER NUMBER 05000 - 263 Or Monticello Nuclear Generating Plant 94 - 002 -

00 4 5 TEXT ta we wace vowee. vue manova; cap.n or Nac rann asui o rp Corrective Action:

1) The industry was informed of this event via Nuclear Network.

2) Klockner.Moeller was informed of this issue and a breaker was shipped to them for testing. ,

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3) An independent laboratory has confirmed our test results on a Model ZM6-33-200. obi-CNA breaker.

4) The preventative maintenance procedure for the 480 VAC molded case circuit breakers was revised for further clarification for testing the instantaneous trip.

Additional Information: 1 Failed Component Identification: NONE Previous Similar Event: NONE j

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