ML19256A871

Forwards Response to NRC 781201 Request for Addl Info Re Second Level of Undervoltage Protection Including Logic Diagram & Exerpt from Tech Specs

ML19256A871
Person / Time
Site:	North Anna
Issue date:	01/12/1979
From:	Brown S VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	Harold Denton, Parr O Office of Nuclear Reactor Regulation
References
711-120-78, NUDOCS 7901160258
Download: ML19256A871 (6)

Text

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O VIRGINI A EL ECTRIC AND POWER COMP ANY, RICHMONO. VIRGINI A 23261 January 12, 1979 Mr. Harold R. Denton, Director Serial No. 711/120/78 Office of Nuclear Reactor Regulation PSE&C/CHJ:adw/mc Attn: Mr. O. D. Parr, Chief Light Water Reactors Branch No. 3 Docket No. 50-339 Division of Project Management U. S. Nuclear Regulatory Commission Washington, D. C. 20555

Dear Mr. Denton:

In your letter of December 1,1978 you stated that you required additional information regarding our second level of undervoltage protection.

In our response of December 21, 1978, we informed you that our design of the degraded voltage scheme was not finalized, and we would supply the requested information by January 12, 1978.

Please find attached this information in the form of:

a) Enclosure b) Logic Diagram c) Excerpt from the Technical Specifications.

Verytrul>/yours,

$ $9 Sam C. Brov , Jr.

Senior Vice President Power Station Engineering and Construction 7901160258 A

ENCLOSURE RESPONSE TO STAFF POSITIONS ON DEGRADED ELECTRICAL POWER GRID CONDITIONS NORTH ANNA POWER STATION UNITS 1 AND 2 1.a) Response: A voltage setpoint corresponding to a degraded level of 90%

of the 4160 volt emergency busses was chosen to initiate a trip signal.

This signal subsequently starts the bus's emergency diesel generator and strips the bus. When the diesel generator terminal voltage reaches 95% of rating, the feeder breaker is closed, and load sequencing begins.

The diesel feeder breaker is interlocked so it can only be closed under emergency conditions after one of the two preferred offsite series feeder breakers has opened. This 90% voltage level setpoint represents the minimum voltage at which the safety-related motors can operate with-in their rated nameplate values and offers considerable margin above the approximate 85% potential value at which the loads would operate outside their rated service factor. Time setpoints are discussed later in this respsnse.

1.b) Response: The degraded voltage protection scheme shall be a two-out-of-three coincidence logic. This design will preclude spurious trips of the offsite power source by requiring two out of the three sensors to actuate before generating a trip signal.

l.c) Response: The design of the system provides a 60 second time delay between the actuation of two degraded voltage sensors and the gene-ration of a trip signal under non-accident conditions. This time de-lay is considered system transients. a In suitable buffer to prevent spurious trips during the event a degraded voltage condition occurs with a safety injection actuatior:, the time delay is 10 seconds. This delay does not exceed the maximum delay assumed in the SAR accident analysis but is of enough duration to guard against spurious trios that may safety be caused related loads. by voltage fluctuations during the starting o.

1.d) Response:

+ The voltage sensors are designed to autnmatically initiate

, disconnection of the offsite power source whenever two out of the aree sensors' setpoints are exceeded and after the design time delays.

l.e) (1) Response:

Class IE equipment will be utilized and shall be physi-cally gear.

located at and electrically connected to the emergency switch-l.e) (2) An independent scheme shall be provided for division of offsite power on each of the two emergency busses.

Page 2 1.e) (3) The capability for test and calibration during power operation will be provided.

1.e) (4) Bypasses are incorporated into the design during phases of testing.

These conditions are annunciated in the control room.

1.f An excerpt from the Technical Specifications pertaining to these re-quirements is included in this enclosure.

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,. INFORMATION iROM THE APPL.lCANT t

TABLE 3.3-3 (Continued) 41

_. ENGINEERED SAFETY FEATURE ACTUATION SYSTEM INSTRUMENTATION '!;

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MINIMUM

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$  ; TOTAL NO. CHANNELS CHANNELS APPLICABLE P-S FUNCTIONAL UNIT 0F CHANNELS TO TRIP OPERABLE MODES ACTION i t si 6. AUXILIARY FEEDWATER PUMP p START 2/stm. gen in 2/stm. gen.

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a. Steam Generator 3/stm. gen. 1,2,3,4 18 Water Level Low-Low any operating - .

stm. gen. .

B. SI See #1 above (All SI initiating functions and requirements-) -

c. Station Blackout 2 2 2 1,.2, 3, 4 1B

$ d. Main feed pump trip 2/ pump 1/ pump 1/ pump l, 2 ,

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h 7. LOSS OF POWER

a. 4 kv Bus (3/ Bus) (f. Bus) (2/ Bus) 1, 2, 3 19* .

Loss of Voltage i

b. Grid Degraded Voltage (3/ Bus) (2. Bus) (2./ Bus) 1, 2, 3 19* i N , .

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.a RECElPT1 O TABLE 3.3-4 (Continued) I_ gg 'I b#l i N ! b I E $ P , 1 l C A [j J f

g ENGINEERED SAFETY FEATURE ACTUATION SYSTEM INSTRJMENTATION TRIP SETPOINTS E

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b. S.i. See 1 above (All S.I. Setpoints)

c. Station Blackout > 57.5% Transfer Bus > 52.5% Transfer Bus Vol tage - Voltage .

d. Trip of Main Feed Pump N .A . N.A.

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a 7. LOSS OF POWER k

a. 4.16 kv Emergency Bus Undervoltage (2399+ 60) volts with a (2912+6o) volts with a (Loss of Voltage) (do3) second time delay ( 35o3) second time delay

b. (3619{/.4) volts with a -

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