ML042960385

E-mail from David Loveless to Millard Wohl, Subject: Palo Verde LOOP

ML042960385
Person / Time
Site:	Palo Verde
Issue date:	06/24/2004
From:	David Loveless Division of Reactor Safety IV
To:	Wohl M Office of Nuclear Reactor Regulation
References
FOIA/PA-2004-0307
Download: ML042960385 (1)

Text

David Loveless - He: Palo Verde LUUP M _ Page 1 i From: David Loveless To: Millard Wohl Date: Thu, Jun 24, 2004 1:50 PM

Subject:

Re: Palo Verde LOOP Millard, How are you, bud? Haven't talked in a while.

I'm the lead on the analysis of this. Also, Don Marksberry's group and Pat O'Reilly are helping out.

Please let me know what you are doing, so that we don't overlap or at least can share resources. The answers to your questions are as follows:

1) Root cause (if known) of LOSP Loss of station power was initiated by a fault on the 230 kV portion of the grid about 45 miles from Palo.

A bad relay prevented the fault from bing isolated at the 230 kV side and it was transferred through 3 transformers to the 525 kV grid. The grid survived for 24 seconds until a negative sequence relay isolated Palo switchyard from the rest of the generation on that part of the grid. The Palo switchyard tripped on high impedence (current) and all three units tripped.

2) Number of combustion turbine generators (CTGs) in adjacent yard There are 2 GTGs. I have INEEL designing a fault tree as we speak. Give me a call for the specifics.

3) Number of CTGs that started

--Number of CTGs that were made available to the plant electrical system and by what means (automatic, manual)

Both GTGs were started manually by an onsite crew and were ready to load at about 15 minutes. They were never tied to vital switchgear.

4) Have the CTGs been added to the plant PRA model and, if so, is common cause failure modeled (including CCF w/EDG(s))?

Don't know, but we are modeling them in SPAR.

5) Reason(s) for no voltage/amperage being registered for EDG considered failed The EDG started, tied and was sequencing when a diode in the reference voltage circuitry failed and exciter voltage dropped to zero.

6) Any attempts made to cross-connect EDGs before shutting down all three PVNGS units?

cross-connect EDGs? Always had safety-power, so all efforts were to restore offsite power.

Give me a call, David 817-860-8161 CC: Nancy Salgado