ML19210D629

Responds to 791023 Telcon in Response to 791009 Ltr Re Electrical Power Sys.Explains That No Relays Removed to Allow Reactor Coolant Pumps to Restart & Clarifies Proposed 13.8 Kv Bus Fast Dead Transfer W/Synchrocheck

ML19210D629
Person / Time
Site:	Davis Besse
Issue date:	11/16/1979
From:	Roe L TOLEDO EDISON CO.
To:	Reid R Office of Nuclear Reactor Regulation
References
NUDOCS 7911270410
Download: ML19210D629 (6)

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M)LEDO Docket No. 50-346 License No. NPF-3 LOWELL E. ROE Serial No. 555 Tl'gll$",',,,,,

November 16, 1979 Director of Nuclear Reactor Regulation Attention: Mr. Robert N. Reid, Chief Operating Reactors Branch No. 4 Division of Operating Reactors United States Nuclear Regulatory Commission Washington, D. C. 20555

Dear Mr. Reid:

This letter is in reply to a telephone inquiry from your staf f on October 23, 1979 concerning our response dated October 9,1979, Serial No. 543, to your letter dated August 8,1979 on electrical power systems at Davis-Besse Unit No. 1.

Question 1: What relay was removed to allow reactor coolant pumps to be started on October 15, 19797 Presently, no relay is removed. Section II.E.3 of our October 9,1979 response refers to momentary pushbutton defeat of undervoltage relays on 4.16 KV essential buses. These relays are ITE Model 27D static relays in a drawout case. Use of a pushbutton defeat is necessary for a reactor coolant pump motor start, because the undervoltage relays would otherwise see depressed bus voltage and would initiate bus transfer to a diesel generator. Installation of these pushbuttons is covered by a f acility change which is not complete at this time and cannot be made until NRC approves a Technical Specification change. Until the change is made, Operating personnel at the Station avoid this type of undervoltage condition by temporarily powering both essential 4.16 KV buses from the 13.8 KV bus which is not having a motor start. This procedure is explained in Temporary Modification T-3444, dated January 3,1979 to the Reactor Coolant Pump Operating Procedure SP 1103.06.

On October 15, 1979, only one startup transformer was available, sad the method of starting a reactor coolant pump motor in T-3444 was not viable. Temporary Modifica-tion T-4125 was written to allow removal of the ITE undervoltage relays for those motor starts on that day.

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THE TOLEDO EDISON COMPANY EDISON PLAZA 300 MADISON AVENUE TOLEDO, OHIO 43852 7 9112 7 0 4- t r>

Question 2: How does the proposed 13.8 KV bus. fast dead transfer with synchrocheck work?

Section II.E.2 of our October 9, 1979 response briefly explains the scheme. What follows is a more detailed explanation.

The fast bus transfer is a six cycle fast dead bus transfer whereby the time span of power interruption to the bus does not exceed six cycles.

The time span is defined as beginning with completion of arc interruption in the breaker tripping and ending with the contact closure in the breaker closing.

The 13.8 KV fast bus transfer scheme uses a "b" contact of the breaker tripping as a closure signal to the alternate source of power. For example, on the 13.8 KV bus A (figure #2 of the report), a "b" contact of breaker HX11A would give a closure signal to breakers HX01A and HX02A. Depending upon the position of the reserve source selection switch, either breaker HX01A or HX02A would close as discussed in Section II.E.2 of the report. The fast bus transfer of the 13.8 KV buses A and B from the unit auxiliary transformer 11 to the startup transformers 01 and/or 02 is initiated by either abnormal conditions originating in the main generation system or operation of the turbine protection system as described in Section II.E.1 of the report.

For abnormal conditions originating in the main generation system, the fast bus transfer of the 13.8 KV buses A and B occurs immediately upon detection of the abnormal condition. For operation of the turbine protection system, the fast bus transfer of the 13.8 KV buses A and B occurs 30 seconds after initiation,of the turbine protection system.

The fast bus transfer of the 13.8 KV buses A and B does not occur for abnormal conditions originating in the grid system. In addition, without the fast acting synchrocheck relays, the fast bus transfer would not occur for the following two conditions:

1) Inadvertent opening of breakers 34560 and 34561 during normal operation (figure #1 of the report). , ,

2) Inadvertent opening of breakers 34560 and 34561 during the 30 second delayed transfer associated wich the turbine protection system.

The fast bus transfer was not initiated under these conditions because the opening of breakers 34560 and 34561 immediately isolated the plant's electrical auxiliary system from the 345 KV grid system. Once the plant's electrical auxiliary system was isolated, synchronism could not be guaranteed at the 13.8 KV buses A and B between the unit auxiliary transformer 11 source of power and the startup transformers 01 and/or 02 sources of power. Therefore, the 13.8 KV buses were not automatically transferred under these conditions.

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3-Since an automatic transfer was not performed under the aforementicaed conditions, it has been interpreted by NRC that this constitutes a violation of FSAR Chapter 3D, Section 1.13 and Chapter 8, Section 8.2.1. Therefore, the fast acting synchrocheck relays are to be added under facility change 78-454 during the first refueling outage La early 1980 to correct this deficiency. At present, the plant's electrical auxiliary system is supplied from the startup transformer 01 and/or 02.

The f ast acting synchrocheck relays are General Electric solid state relays type SLJ12A.

The relays are actuated by "b" contacts fron breakers 34560 and 34561. The relays continuously monitor synchronism between the secundary of the wait auxiliary trans-former 11 and the startup transformer 01 or 02 which has been preselected as the reserve source.

As indicated in the report, the relays are set at 350 This setpoint is based on a criterion that the transfer will be blocked for a phase angle difference of greater than 600 in order to avoid equipment damage. An analysis was performed to determine the time rate of change of the 13.8 KV bus A and B voltage and its associated phase angle whenever breakers 34560 and 34561 were opened with the plant's electrical auxiliary system being supplied through the unit auxiliary transformer 11. Based on this analysis, the 35 setpoint assures the actual transfer of the 13.8 KV buses A and B will occur at less than 60 out 0 of phase whenever the bus transfer is initiated with a phase angle difference of less than 350 In addition, a voltage signal is inputted to the fast bus transfer scheme to assure that the voltage on the secondary of the startup transformers 01 and 02 is not being supported by the main turbine generator during the case that the Davis-Besse 345 KV switchyard was isolated from the grid system. The voltage signal is produced from Gould-Brown Boveri solid state undervoltage relays.

Each 13.8 KV bus is provided with a fast acting synchrocheck relay. As indicated, the specific operation of the relay in the fast bus transfer scheme is initiated by breakers 34560 and 34561 opening due to inadvertent action other than system trouble trips. Once the breakers 34560 and 34561 open, the synchrocheck relay compares the phase angle difference between the secondary voltages of the unit auxiliary transformer 11 and the startup transformers 01 and 02. If the phase angle difference is less than 350 and the voltage of the secondary of the startup transformers 01 and 02 has not degraded, the relays send trip signals to the respective breakers EX11A and HX11B (figure #2 of the report) and permissive signals to breakers EX01A, HX0,1B, HX02A, and HX02B. Breakers HX11A and HX11B trip which sends a close signal to the preselected reserve source breaker on the respective 13.8 KV buses A and B, which completes the bus transfer. If either the phase angle is greater than 35 or the voltage of the secondary of the startup transformers 01 and 02 degrades, the relays do not send trip signals to breakers EX11A and HX11B. Thus, the plant's electrical auxiliary system remains connected to the main turbine generator.

With the addition of the fast acting synchrocheck relays, an automatic transfer of the 13.8 KV buses A and B to the off-site sources of power will be performed under acceptable conditions for an inadvertent opening of the switchyard breakers 34560 and 34561. The addition of these relays is to bring the Davis-Besse electrical auxiliary system design into full compliance with FSAR Chapter 3D, Section 1.13 and Chapter 8, Section 8.2.1.

Question 3: Did implementation of the 13.8 KV fast dead transfer with synchrocheck occur prior to the October 9 response?

No, the new fast transfer scheme has not yet been implemented.

Yours very truly, Attachment db b/9-12 cc:

Mr. William Gammill Acting Assistant Director for Operating Reactors Projects Division of Operating Reactors United States Nuclear Regulatory Commission Washington, D.C. 20555 e

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