PNO-V-86-045, on 860717,reactor Trip Occurred from 3% Power. Caused by Momentary Drop in Voltage Through break-before- Make Switch.Momentary Drop Allowed Permissive P7 to Unblock & Trip Signal Went to Reactor Protection Sys

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PNO-V-86-045:on 860717,reactor Trip Occurred from 3% Power. Caused by Momentary Drop in Voltage Through break-before- Make Switch.Momentary Drop Allowed Permissive P7 to Unblock & Trip Signal Went to Reactor Protection Sys
ML20207F350
Person / Time
Site: San Onofre Southern California Edison icon.png
Issue date: 07/17/1986
From: Huey R, Norbut P
NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V)
To:
References
PNO-V-86-045, PNO-V-86-45, NUDOCS 8607220521
Download: ML20207F350 (1)


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' PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE--PNO-V-86-45 Date:07/17/86 This preliminary notification constitutes EARLY notice of events of POSSIBLE safety or public intsrest significance. .The information presented is as initially received without verification or evaluation and is basically all that is known by Region V staff on this date.

FACILITY: Southtrn California Edison Company Licensee Emergency Classification San Onofre Unit 1 Notification of Unusual Event DOCKET NO. 50-206 Alert Site Area Emergency General Emergency XX Not Applicable

SUBJECT:

REACTOR TRIP FROM LOW POWER At 8:40 am PDT on July 17, 1986, the reactor tripped from 3% power. At the time of the trip the licansee was switching 120 VAC vital power from an alternate to the normal power supply. The powar supply switching is done through a break-before-make switch. Therefore, the switch allowed a momntary (about 120 milliseconds) drop in voltage. The turbine was not running at the time.

Tha turbine trip / reactor trip signal is normally blocked however (at less than 10% power) by Parmissive P7. The momentary drop in voltage is believed to have allowed the Permissive P7 to unblock and the reactor tripped due to the turbine trip signal coming in to the reactor protection system.

This information is current as of 3:00 pm PDT, 07/17/86.

CONTACT: P. Narbut R. Huey FTS 463-3720 714-492-2641 DISTRIBUTION H St. 7.'/ 2 - MNBB II/Y Phillips8'O/ E/W 7#Il Willste 7#5JAir Rights 7/J'/ Mail:

Chairman Zech EDO NRR IE NMSS ADM:DMB Comm. PA OIA RES DOT:Trans Only Comm. Bernthal MPA AEOD Comm. Roberts ELD Comm. Asselstine Regions: /r- 7/ 9'%/E- 8'o2f #2Zr fly #s-//og SECY INP08?/ 7 NSAC fle9 ACRS Licensee: F:o/

CA (Reactor Licensees) REGION V: FORM 211 PDR Resident Inspector _ffR I (Revised 3/14/83) 8607220521 860717 PDR I&E -]

PNO-V-86-045 PDR

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