ML19209A260

Submits Addl Info Re Degraded Grid Voltage,In Response to NRC 790619 Request

ML19209A260
Person / Time
Site:	Pilgrim
Issue date:	09/27/1979
From:	Andognini G BOSTON EDISON CO.
To:	Ippolito T Office of Nuclear Reactor Regulation
References
79-185, NUDOCS 7910030240
Download: ML19209A260 (4)

Text

9 BOSTON E:DISON COMPANY a Nenac crriers aco sov6stoM sT= cst SosfoM. MassacNustTTs a2199 G. can6 ANOQGNING suPrelNTENOENT NuCLEam OPEWariCNs DEPAATMENT September 27, 1979 BECo. Ltr. #79- 185 Mr. Thomas A. Ippolito, Chief Operating Reactors Branch #3 Division of Operating Reactors Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Comission Washington, D. C. 20555 License No. DPR-35 Docket No. 50-293 Response to Request for Additional Information On Pilgrim Unit #1 Degraded Grid Voltage

References:

(1) Letter to Mr. G. C. Andognini from Mr. D. K. Davis, dated June 3, 1977 (2) Letter to Mr. D. K. Davis from Mr. G. C. Andognini, dated August 8,1979, BECo Letter #77-77 (3) Letter to Mr. D. K. Davis from Mr. J. E. Howard, dated August 24, 1977, BEco Letter #77-85 (4) Letter to Mr. G. C. Andognini from Mr. T. A.

Ippolito, dated June 19, 1979

Dear Sir:

In Reference (1), Boston Edison Company was requested by the NRC to compare the current design of the emergency power systems at Pilgrim Nuclear Power Station with the Staff's positions. Our comparison of the Nuclear Regulatory Commission's Staff positions were delineated in Reference (2). Boston Edison Company comitted, in Reference (2), to install a second level undervoltage relay protection scheme to enhance the electrical protection system at Pilgrim Nuclear Power Station.

In Reference (3), Boston Edison Company proposed changes to the Nuclear Power Station Technical Specifications to incorporate additional electrical power system surveillance requirements. These included trip set points of second level under-voltage relays to be installed during refueling outage which was commenced in /

August, 1977. \

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7910080 .f r

BOSTON EDISON COMPANY Mr. Thomas A. Ippolito, Chief September 27, 1979 Page 2 In Reference (4) you requested Boston Edison Company to provide additional informa-tion in order to review our submittal of August 24, 1977 (Reference (3)). Our response to those questions is given below:

QUESTION #1 Table 3.2.B. Instrumentation that Initiates or Controls the Core and Containment Cooling Systems, Boston Edison Ccepany letter to NRC, dated August 24, 1977, gives a degraded voltage trip point of 3798 volts with 5.2 seconds time delay.

The timo delay appears to be too short and could cause a problem with short duration power disturbances. Provide the analysis and basis for your selection of the 5.2 second time delay.

RESPONSE

In Reference (3), we provided trip set points including voltage and time delay for second level undervoltage relays. Also, we indicated that these trip set points were subject to change af ter installation, testing and monitoring of relay protection scheme.

We have installed a second level undervoltage relay protection scheme, but did not connect the trip circuits of the undervoltage scheme to the 4160V startup transformer supply circuit breakers. Instead, the currents , voltages, and trip contacts of undervoltage relay protection schemes are being monitored by a Gould 3 rush recorder in order to evaluate the trip set points and to satisfy the following:

a) To assure protection of saf ety related electrical equipment and its associated circuitry in the event of degraded voltage conditions at the offsite power source.

b) To avoid spurious separation of safety related buses from of fsite power source.

Presently, we are re-analyzing the degraded voltage trip set points including time delays. An engineering re-analysis will be completed by October 15, 1979.

Any changes on proposed trip set points, including time delay, due to evalua-tion of monitored results and engineering re-analysis will be transmitted under a separate cover letter.

The basis for selection of time delay settings is to override the starting transients of the largest motors (4160V) on one winding of the startup trans-former (which is connected to the safety related buses) with the lowest allow-able voltage at the motor terminals. In su= mary, the voltage time settings for second level undervoltage relays will be selected so as to avoid spurious separation of safety related buses from offsite power during plant startup, normel operation, normal shutdown and shutdown due to anticipated transients.

The trip circuits of the second level undervoltage scheme will be connected to the source side of 4160V startup transformer supply breakers in the 1980 re-fueling outage.

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BOSTON EDISON CO M PANY Mr. Thomas A. Ippolito, Chief September 27, 1979 Page 3 QUESTION //2 State and describe total number of channels per bus in your system for the second level undervoltage protection. State applicable operating modes and action. Refer to Table 3.3-3, Engineered Safety Feature Actuation System Instrumentation, NRC letter dated June 3,1977 (Safety Evaluation and Statement of Staf f Positions Relative to the Emergency Power Systems and Operating.)

RESPONSE

Total number of channels per bus - 4 Total number of channels to trip - 2 per bus As discussed in our response in Reference (2), the following is a description of second level of undervoltage relays:

The additional undervoltage relays will provide 2 out of 4 redundancy technique of applying relay contacts to achieve tripping the startup transformer breakers to the 4160V safety related buses during degraded voltage condition. The com-bination of relay contacts (2 out of 4 logic) will be connected in parallel with the existing undervoltage relay contacts.

QUESTION #3 The voltage monitors shall be designed to satisfy the requirements of IEEE Standard 279-1971, " Criteria for Protection Systems fo r Nuclear Power Gener-ating Stations". State your compliance with this requirement, and include sufficient description for us to verify compliance of your design.

RESPONSE

The following is a description of voltage sensing location and trip logic for the second level of undervoltage relays:

Location Logic a) Source side of startup transformer breaker 504 Trip Breaker 504 b) Source side of startup transformer breaker 604 Trip Breaker 604 The voltage relays applied to the source side of the startup transformer breakers 504 and 604 will have 2 relays monitoring phase AB voltage with their contacts in parallel and then in series with 2 relays monitoring phase BC voltage with their contacts in parallel. This combination of contacts (2 out of 4 logic) will then be connected in parallel with the existing 4160 V emergency undervoltage (loss of voltage) relay contacts.

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BOSTON EDISON COMPANY Mr. Thomas A. Ippolito, Chief September 27, 1979 Page 4 From the above description, it is obvious that the second level undervoltage protection schemes are designed to satisfy the requirements of IEEE Standard 279-1971, " Criteria for Protection Systems for Nucicar Power Generating Stations".

We trust this response addresses your concerns. Should you have any further questions on this matter, please contact us.

Very truly yours, g f. , a /, e m'g' * *lld

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