ML20126D709

Responds to NRC Requests Re Adequacy of Station Electrical Distribution Sys Voltages.Computer Analysis for Cases 11 & 13 Encl.Evaluation Is Underway to Determine Necessity of Addl Testing to Further Verify Accuracy of Analysis

ML20126D709
Person / Time
Site:	Farley
Issue date:	05/01/1980
From:	Clayton F ALABAMA POWER CO.
To:	Gammil W Office of Nuclear Reactor Regulation
References
NUDOCS 8005060196
Download: ML20126D709 (10)

Text

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5 Alibima Pow:r Company

' 600 North 18th Street Post Offics Box 2641 80050 Birmingham, Anama 35291 Telephone 205 323-5341 60 (/ fO [ {

h k LLiWW,5fe"en, Maba m m m May 1, 1980 the southern esecinc system Docket No. 50-348 and 50-364 Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D.C. 20555 Attn: Mr. William Gammill

Dear Mr. Gammill:

ADEQUACY OF STATION ELECTRICAL DISTRIBUTION SYSTEMS VOLTAGES Alabama Power Company responded on December 11, 1979, to your letter dated August 8, 1979, on this subject. After reviewing our response, members of your staff requested, by telephone, information on additional studies. A computer analysis was performed as requested for Case #11 and Case #13 presented in the enclosure to this letter.

Members of the NRC staff also requested that additional testing be conducted to verify the accuracy of the analysis. In the enclosure to Alabama Power Company's December 11, 1979 letter on this subject, the following was stated:

"A test was performed at Farley Nuclear Plant Unit 1 to verify that the analytical method used for calculating the voltage cases described above is valid. A 7,000 hp Circulating Water Pump Motor connected to 4.16 KV Bus 1B was started, and the voltage on the high voltage side of Startup Auxiliary Transformer 1B and the voltage on 4.16 KV Bus 1B were recorded for the motor starting condition. The transformer low voltage winding which supplies the 7,000 hp motor was unloaded prior to the motor starting test. This test case was modeled on the voltage drop computer program, and the calculated voltage on 4.16 KV Bus 1B at the instant of motor starting was within 0.3% of the measured bus voltage for this condition. Therefore, the computer program provides satisfactory ressults."

While it is Alabama Power Company's position that the above is adequate to verify the accuracy of the analysis method used, an evaluation is being conducted to deterrdne if additional testing to further verify i

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accuracy is feasible and warranted. Results of this evaluation will be transmitted to you when complete.

Yours very t.t1lly, (J D F. L. Clayton, Jr.

FLCJr/TNE:aw Enclosure cc: Mr. R. A. Thomas Mr. G. F. Trowbridge 2

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EWCLOSURE A computer analysis was performed for Case #11 and Case #13. The postulated i conditions for these cases are as follows:

1. One Unit 1 Startup Auxiliary Transformer is out of service and "

Unit 1 is operating at full power with all emergency buses train A and train B connected to the operating Startup Auxiliary Trans-former. The normal buses are energized from the Unit Auxiliary Transformers.

(In Case #11 Startup Auxiliary Transformer 1A is out of service; l in Case #13 Startup Auxiliary Transformer 1B is out of service.)

2. The transient condition which subsequently occurs consists of:

A. LOCA - resulting in simultaneous start of all required LOCA loads.

B. The running loads on emergency buses remain on buses.

C. The 4.16KV normal buses 1B and 1C are Lutomatically trans-ferred to the Startup Auxiliary Transformer 1B, in Case #11; the normal bus lA is automatically transferred to the Startup Auxiliary Transformer 1A, in Case #13. These buses remain connected to the respective Startup Auxiliary Transformer after the transient.

D. Unit 2 is in the Emergency Shutdown condition.

3. The 230KV switchyard is at the minimum expected voltage based on grid stability analysis before, during and after the transient.

The analysis consisted of the following:

1. Calculation of the steady state voltages prior to the transient.

2. Calculation of the voltage conditions during the transient.

3. Calculation of the steady state voltage af ter the transient.

i The voltage results of the computer analysis performed for Case #11 and Case

1. 13 are shown on the attached voltage profiles for the steady state condition

( prior to the transient, for the transient condition, and for the steady state condition after the transient. For the 600V and 208V systems, the voltage drops were computed for the worst Load Center and Motor Control Center distri-bution network based on loading and distance of cable routing. 1 The results of the computer analysis depicting the voltages at the instant of simultaneous motor starting indicate that all motor terminal voltages are above the minimum momentary motor starting voltage and running voltage of 75%

and the motor contactor pickup' voltage of 71% for safeguard motors. The voltage-time setting for the 4.16KV Emergency Bus Undervoltage (loss of voltage) relays have been selected to avoid separation of the safety buses from offsite power during the transient conditions postulated.

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The results of our analysis for the steady state conditions prior to the transient and after the transient indicate that the steady state motor terminal voltages before and after the motor starting transient are above 90% of the continuous voltage rating of the safeguard motors. For the steady state conditions, the voltage-time settings of the 4.16KV Emergency Bus Undervoltage (Degraded Voltage) relays have been selected to avoid separation of the safety buser from offsite power.

Based on the results of the analysis described above, it can be concluded that the Farley station electric distribution system is of sufficient capacity and capability to automatically start and operate all required safety loads within their required voltage ratings for the anticipated transient and steady state. conditions assuming one of the two offsite electric power circuits and all onsite sources of AC power are not available.

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