ML19263B618
| ML19263B618 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 01/16/1979 |
| From: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| To: | Goodwin C PORTLAND GENERAL ELECTRIC CO. |
| References | |
| NUDOCS 7901220212 | |
| Download: ML19263B618 (7) | |
Text
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4, UNITED STATES
[y NUCLEAR REGULATORY COMMisslON h.h._ 9> *,
REGION V O
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WALNUT CREEK, CALIFORNI A 94596 JAtt la 879 Docket No. 50-344 Portland General Electric Company 121 S. W. Salmon Street Portland, Oregon 97204 Attention: Mr. Charles Goodwin, Jr.
Assistant Vice President Gentl emen:
The enclosed IE Circular No. 79-02, is forwarded to you for information.
If there a"e any questions related to your understanding of the suggested a,tions, please contact this office.
Sincerely,
/
dNld v$
R. H. Engelken Director
Enclosures:
1.
IE Circular No. 79-02 2.
List of IE Circulars Issued in the last 12 months cc w/encls:
B. Withers, PGE F. C. Gaidos, PGE F. Miller, Director, Dept. of Energy, Salem, Oregon
~
780122CG P
IE Circular No. 79-02 January 16, 1979 Pace 1 of 2 FAILURE OF 120 VOLT VITAL AC POWER SUDPLIES Description of Circumstances:
On September 16, 1978, Arkansas Muclear One - Unit 2, while in hot functional testing precedino initial criticality, suffered a degrada-tion of both of the independent off-site power sources.
This produced an undervoltage condition on the Engineering Safety reatures (ESF) Buses and caused an inadvertent ESF actuation.
The licensee determined that the ESF actuation occurred on a loss of at least two of the uninter-ruptable 120 volt vital AC power sources.
Immediate investigation revealed that all four of the Solidstate Controls, Inc., (SCI) inverter static switches had automatically transferred to the alternate power supply (the 120 volt AC being supplied by transformers directly off the ESF buses rather than from the inverter output.) Figure 1 (attached) shows the functional interconnection of the 120 volt AC power supply system.
A single conclusive cause of the undesired SCI inverter static switch transfer could not be identified.
However, the followina problens were discovered during subsequent investigation.
(a) The SCI inverters have circuitry to nonitor the inccming DC voltage level which, on sensing a low voltage (nominally 104 DC volts for these inverters) will trip both input breakers to the inverter component after an adjustable time delay.
The setting of these time delay relays was not verified during either preoperational testing or subsequent maintenence. The time delay is necessary in order to accommodate transient loading condi-tions which may be encountered.
(b) On one SCI inverter, a DC fuse within the inverter conoonent was found blown. The vendor indicated that this fuse will blow due to an excessive DC voltage to the inverter component caused by a transient on the 480 AC input. The licensee has subsequently reset the taps on the 480V to 120V three-phase AC input transformer to limit the DC voltage to the inverter to less than the nameplate maximum rating in the event of a high AC input voltage transient.
(c) The SCI inverter static switch is designed to transfer to an alternate source on invert Initially, these trips wer 80 percent undervoltage.
DUPLICATE DOCUMENT Entire document previously entered into system under:
ANO No. of pages:
7