View source for PNO-V-90-001, on 891230,while at 12% Reactor Power W/Main Generator Sypplying Power to Grid Plants Unit 3 Phase a Main Transformer Experienced Internal Fault,Which Caused Immediate Trip of Main Generator Output Breakers

{{Adams
| number = ML20198K273
| issue date = 01/02/1990
| title = PNO-V-90-001:on 891230,while at 12% Reactor Power W/Main Generator Sypplying Power to Grid Plants Unit 3 Phase a Main Transformer Experienced Internal Fault,Which Caused Immediate Trip of Main Generator Output Breakers
| author name = Coe D, Wong H
| author affiliation = NRC OFFICE OF INSPECTION &amp; ENFORCEMENT (IE REGION V)
| addressee name = 
| addressee affiliation = 
| docket = 05000530
| license number = 
| contact person = 
| document report number = PNO-V-90-001, PNO-V-90-1, NUDOCS 9710230252
| document type = PRELIMINARY NOTIFICATION OF EVENT OR OCCURRENCE (PNO,, TEXT-INSPECTION &amp; AUDIT &amp; I&amp;E CIRCULARS
| page count = 2
}}
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                                           /&VWL OF EVENT OR UNUSUAL OCCURRENCE--PNO-V-90-01                  Date 01/02/90 This preliminary notification constitutes EARLY notice of events of POSSIBLE safety or public interest 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: ARIZONA NUCLEAR POWER PROJECT                      Emergency Classification PALO VERDE UNIT 3                                        Notification of Unusual Event DOCKET NO. 50-530                                        Alert hf WINTERSBURG, AZ.                                         Site Area Emergency General Emergency                      g T ~Not Applicable                               (F-     p '(O '

==SUBJECT:==
MAIN TRANSFORMER FAULT l
On D: comber 30, 1989 While at 12% reector power with the main generator supplying power to tha grid, the Palo Verde Unit 3 phase "A" main transformer experienced what appears to be an internal fault at 4:30 pm (MST). Unit 3 was being returned to power operation j follawing its first refur"ng (extended) outage. The internal fault apparently caused excessive internal pressure within the phase "A" transformer, splitting several seams l   in the housing and draining or spraying out all of the internal oil causing smoke to i   come from the trsnsformer. One of two main transformer ceramic insulator bushings i crack:d, and a surge capacitor bank inside the turbine building was damaged.
TQuit caused an immediate trip of the main generator output breakers and the j   t,    je was stabilized at approximately 105 power. Site fire protection personnel Qnded and activated the transfomer deluge system in addition to forcio, water and foaa into an opening in the upper section of the trentfonner houing. Smoke and an eccasional flame were seen emanating from the transfonner. The licensee declared the fire out within 10 minutes and therefore did not declare an Unusal Event.
Although at Units 1 and 2 some non-safety-related alarms came in and some non-safety-related equipment tripped due to a momentary undervoltage condition caused by the grid disturbance, there was no impact to any safety-related electrical busses or squipment. Unit 3wasyaturnedtoMode3at1:20am(MST)onDecember 31, 1989.
The licensee intends to move the phase "A" transformer to a location ensite where it can be disassembled and inspected to detennine the causes for failure. In parallel, the licensee is replacing the damaged transformer with a spare locai:ed onsite.
A siallar event occurred at Unit 1 in July,1988, when the auxiliary transformer which supplies 13.8KV power from the main generator to plant non-safety-related busses exploded while Unit I was at 100% power. This auxiliary transferrer was of a different d: sign and manufacturer than that of the main transformer involved in the event of December 30, 1989. The cause of that event was an internal fault in the transfomer.
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The licensee has issued a press release.
This information is cu: rent as of 10:00 am. January 2,1990 CONTACT:       H. Wong                                             D. Coe FTS 463-3733                                        (602)_386-3650 OV DISTRIBUTION BY 5520:                                                    FAX TO:
Date. ..            Time.                                                Date Time.
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    -Comm. Remick                 RES HQS. OPERATIONS OFFICER OCA                          NRR OGC PDR(202)634-3343
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