ML20043E376

LER 90-007-00:on 900517,discovered That Several Relays Deenergized & Automatic Start & Loading of Diesel Generator D1 Initiated.Caused by Inadequate Design.Mod Initiated to Install Test points.W/900608 Ltr

ML20043E376
Person / Time
Site:	Prairie Island
Issue date:	05/18/1990
From:	Hunstad A, Parker T NORTHERN STATES POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-90-007, LER-90-7, NUDOCS 9006120367
Download: ML20043E376 (4)

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,' Northom States Power Company 414 Nicollet Mall Minneapoks Minnesota 6M011927 Telephone (612) 3345500 June 8, 1990 10 CFR Part 50 Section 50.73 Director of Nuclear Reactor Regulation U S Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 PRAIRIE ISLAND NUCLEAR CENERATING PLANT Docket Nos. 50 282 License Nos. DPR 42 50 306 DPR 60 Auto start of D1 Diesel Cenerator Due to Short Circuit Caused by Test Leads durine a Surveillance Test The Licensee Event Report for this occurrence is at, ached.

This event was reported via the Emergency Notification System in accordance with 10 CFR Part 50, Section 50.72, on May 17,1990. Please contact us if you require additional information related to this event.

(k'k homas M Parker Manager Nuclear Support Services c: Regional Administrator Region III, NRC NRR Project Manager, NRC Senior Resident Inspector, NRC MPCA Attn: Dr J V Ferman Attachment 9006120367 900518 PDR ADOCK 05000282 /

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~~'l v8: ti, m . . avretto sven,wou o res K =0 l l t am uC,,u,,.. ,.,a.. ..--,aa .- - aa,na On May 17, 1990, both units were operating at 100% power. Surveillance test SP1218, the Bus 15 Undervoltage Relay Test, was in progress. At 1020, the technician performing the test noticed several relays deenergize; the control room received annunciation of Bus 15 undervoltage and an automatic start and loading of D1 Diesel Generator. Investigation showed that a fuse in the Bus 15 undervoltage sensing circuitry had blown, causing the undervoltage slave relays to be deenergized. This indicated a loss of voltage to Bus 15 and resulted in actuation of the voltage restoration scheme for Bus 15. Actuation of the scheme causes automatic start of D1 Diesel Generator and causes most loads to be stripped from the bus and reapplied in a timed manner; the scheme operated as designed. No. 11 Component Cooling Water Pump stopped because it was stripped from the bus, and No, 12 Component Cooling Water Pump started automatically on low header pressure. Cause of the blown fuse was shorting of adjacent terminals by the technician's test leads. The leads were removed, the fuse replaced. Bus 15 was transferred back to its original source, and D1 Diesel Generator was shut down at 1112.

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On May 17, 1990, both units were operating at 100% power. Surveillance test Sp1218, the Bus 15 Undervoltage Relay Test, was in progress. At 1020, the technician performing the test noticed several relays (EIIS Component Identifier:

RLY) deenstgize; the control room received annunciation of Bus 15 undervoltage and an automatic start and loading of D1 Diesel Generator (EIIS Component Identifier: DG). Investigation showed that a fuse (EIIS Component Identiflor:

FU) in the Bus 15 undervoltage sensing circuitry had blown, causing the undervoltage slave relays to be deenergized. This indicated a loss of voltage to Bus 15 and resulted in actuation of the voltage restoration scheme for Bus 15.

Actuation of the scheme causes automatic start of D1 Diesel Generator and causes most loads to be stripped from the bus (EIIS Component Identifier: BU) and reapplied in a timed manner; the scheme operated as desi 6ned. No. 11 Component Cooling Water Pump (FIIS Component Identifier: p) stopped because it was stripped from the bus, ane'. No.12 Component Cooling Water pump started automatically on

! low header pressure. Cause of the blown fuse was shorting of adjacent terminals l by the technician's test leads. The leads were removed, the fuse replaced, Bus 15 was transferred back to its original source, and D1 Diesel Generator was shut down at 1112.

CAUSE OF THE EVENT Cause of the event is inadequate design; the system is not designed to be tested.

Exposed terminals were shorted by the technician's test leads during conduct of a surveillance test. The technician's leads terminate in alligator clips, which are applied to wire lugs mounted to a terminal strip. One of the clips rotated after application and contacted an adjacent wire lug, resulting in the blown fuso, ANALYSIS OF THE EVJ,t{I This event is reportable under 10CFR54.73(a)(2)(iv). 11ealth and safety of the public were unaffected since all equip'ent operated as designed.

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0l0l 7 0l0 Oj3 or 0 l3 m ,u . - anac w ma w m CORRECTIVE ACTION Immediate corrective action was to stop the surveillance test and determine the cause of the event. When the cause was determined, the test leads were removed, the blown fuse was replaced, Bus 15 was transferred back to its original source, and D1 Diesel Generator was shut down.

l A modification had been initiated to install test points to decrease the probability of events such as this, but this modification had not been completed, liigher priority will be placed on completion of this modification, with completion expected at the next refueling for each unit.

FAILED COMPONENT IDENTIFICATION None, i

PREVIOUS SIMI'lR EVENTS l

One previous similar event was reported as Unit 1 RO 81 29.

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