ML19274D306

Forwards Results of Study Re Assessment of Degraded Electrical Power Grid Conditions

ML19274D306
Person / Time
Site:	Farley
Issue date:	01/15/1979
From:	Clayton F ALABAMA POWER CO.
To:	Schwencer A Office of Nuclear Reactor Regulation
References
NUDOCS 7901230140
Download: ML19274D306 (7)

Text

A:abama Power Compry

,4 . V' 600 Norn 18'h Street Pow CV1.ce Box 2641 B;rmmnam. Abt>cra 35291 TewprUr:e 205 323-5341 k

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• cen>or lice Pres:dem AlabamaPower the southem e!w!nc system January 15, 1979 Docket Nos. 50-348 50-364 Director of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D.C. 20353 Attn: lir. Albert Schwencer Gentlemen:

JOSEPH M. FARLEY NUCLEAR PLANT-UNITS 1 & 2 DEGRADED ELECTRICAL POWER GRID CONDITIONS Alabama Power Company has performed an assessment of the design pro-posed in our letter of November 7, 1977 for the emergency power system at the Farley Nuclear Plant with the Staff Positions contained in your letter of November 27, 1978. The results of this study are included in the attach-nents of this letter.

Attachment 1 addresses each of the NRC Staff Positions contained in your letter of November 27, 1978. It should be noted that presently the Farley Plant is furnished with loss of voltage protection, using a set of undervoltage relays connected to the Buses IF and 1G (2F and 2G for Unit 2). These relays sense the undervoltage (loss of voltage) at 70% of nominal bus voltage and trip the incoming breaker from the startup trans-former. It is proposed to install an additional set of undervoltage relays for protection from sustained degraded grid voltage conditions at safeguard Buses IF and 1G (2F and 2G for Unit 2). These relays when actuated will trip both incoming breakers from the offsite power sources. The relays will have inverse time characteristic and set at a voltage not less than 87% of nomi nl bus voltage. The time dial will be selected in such a way as to avoid any nuisance tripping during normal operating conditions. This additional protection system will be installed on Unit 1 prior to startup following the second refueling outage. On Unit 2 it will be installed prior to initial fuel loading.

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Mr. Albert Schwencer Page Two January 15, 1979 In accordance with NRC Staff Position 3, we plan to propose changes to the Farley Unit 1 Technical Specifications consistent with the design of the Farley emergency power system in the near future.

Should you have questions, please advise.

Yours truly, j

,J(f1hWdi 4' F. L. Clayton, Jr.

FLCJr/TNE:bhj Attachment cc: Mr. R. A. Thomas Mr. G. F. Trowbridge

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Attachment 1 This attachment addresscs point-by-point the Staff Positions contained in the SRC letter dated November 27, 1978 to Alabama Power Company.

1.a For safeguard Buses IF and 1G (2F and 2G for Unit 2), the acceptable minimum (degraded) sustained voltage has been established as 87% of the nominal bus voleage (4160V). This is based on a plus or minus ten percent of the nameplate rating for motors, or 90% of the nominal 4 KV rating. In our design study, Westinghouse CV2 relays will be employed and will be set at the 105 volt tap, which will cause the relay to drap out at 88.34% of nominal bus voltage. The CV2 relay has an inverse time characteristic, and with a time dial setting of 1.5, a time-trip curve shown in Figure 1 will be obtained. Super-imposed on the curve are the voltage dips due to starting a condensate pump (analyzed as causing greatest dip) or simultaneously starting a group of safeguard motors, indicating that the CV2 relays will not respond to these momentary dips or other spurious short duration dips, thus precluding nuisance tripping. Also, by properly selecting the available taps on the load center transformers, the voltage at the nominal 600 volt buses will be kept at a level to furnish the minimum required voltage to the equipment connected to these buses.

1.b Each of the IF and 1G buses (2F and 2G for Unit 2) will be equipped with undervoltage relays using two out of three logic, as shown in Figure 2. Elementary diagrams implementing this logic are shown in Figures 3 and 4.

l.c.1 The maximum time delay assumed in the SAR is 1.2 seconds with the voltage at 68% of nominal. This time delay remains unaffected with the addition of the new undervoltage relays.

l.c.2 As shown in Figure 1, the inverse time dial setting of 1.5 provides a suitable time delay to minimize the effect of short duration disturbances.

l.c.3 The additional undervoltage relays will be set to trip at 88.34%

on nominal (4160V) bus voltage, above which level all safety systems and components can operate indefinitely. For voltages below S3.34%

the voltage vs. time curve is shown in Figure 1. This figure also demonstrates that the allowable time duration of a degraded voltage condition at all distribution systen levels will not result in the failure of safety systems or components, l.d The voltage sensors will be connected in such a manner that when any two or three of the sensors (relays) are actuated, the associated breakers supplying offsite power will be tripped.

l.e The new undervoltage protection system meets the requirements of IEEE Standard 279-1971.

1.f Proposed technical specifications on this subject will be submitted in the near future-

2. The load shedding action of the Train "A" 4 KV Emergency Buses IF and 2F is initiated by the bus undervoltage relays, and it automatic-ally load strips the bus prior to transferring it, either from the offsite power system to an onsite diasel generator, or from one onsite diesel generator to another onsite diesel generator. This feature of the load shedding action is necessary for the proper operation of the Train "A" swing diesel generators under various postulated events.

The load shedding action of the other 4 KV Emergency Buses (lG, 2G, IJ, 2J, 1H, and 2H) is initiated by the tripping of the offsite power source supply t reakers, and it automatically load strips the bus prior to transfe ring it from the offsite power system to the onsite diesel generator associated with that bus. As soon as the load shedding action is completed, it is not possible to automatically shed the load as long as the bus offsite power source supply breakers are tripped. Once the diesel generator is supplying power to the bus, reclosing of the diesel generator breaker subsequent to its trip is not possible for as long as the automatic closing signal of that breaker is present (which is the case under LOSP condition).

This is due to the breaker anti-pump provision. Therefore, the autonatic load shedding action on interruption of the onsite source is not needed for the subject buses as no power source is available for loading them again. It has to be noted, however, that in dual unit operation load shedding feature of 4 KV Emergency Buses lH and 2H is not disabled while these buses are supplied power from the onsite sources. This is due to the swing feature of the Train "A" diesel generators.

3.a Proposed technical specifications will comply with this testing require-ment.

3.b Proposed technical specifications will comply with this testing require-ment.

3.c Proposed technical specifications will comply with this testing require-nent.

3.d The current Farley Technical Specifications comply with this testing requirement.

3.e The design of the Farley Plant is such that we cannot comply with this testing requirement. For further information, refer to our response to NRC Staff Position 2.

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