ML19250B957

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Station Electric Distribution Sys Voltage Analysis.
ML19250B957
Person / Time
Site: Oyster Creek
Issue date: 10/31/1979
From:
JERSEY CENTRAL POWER & LIGHT CO.
To:
Shared Package
ML19250B956 List:
References
NUDOCS 7911060304
Download: ML19250B957 (12)
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STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGE ANALYSIS OYSTER CREEK NUCLEAR GENERATING STATION 1276 138 i 791106 0 3Oy October, 1979

I. PURPOSE The purpose of this study was to determine analytically if the oi .,ite power system and the onsite distribution system for Oyster Creek Nuclear Generating Station is of sufficient capacity and capability to automa-tically start as well as operate all required safety loads within their required voltage ratings in the event of: 1) an anticipated transient (such as a unit trip); or 2) e.n accident (such as a LOCA). This must be assured regardless of other actions the electric power system is designed to automatically initiate and without the need for manual shedding of any electric loads. The impetus for this study was the Arkansas Nuclear One event of September 16, 1978, which was described in NRC IE Information Notice No. 79-04, and the NRC letter of August 8, 1979, to all Power Reactor Licensees which contained specific actions required to be taken as a result of the Arkansas event.

II. EXISTING CONDITIONS AT OYSTER CREEK Undervoltage relays are presently provided for the 4160V buses l A,18, 1C, and 1D, and for the Start-up Transformers SA and SB, and are fed from 4200-120V potential transformers. These relays are all General Electric type IAV53K, under/overvoltage induction relays. The under-voltage trip point for these relays is presently set at 88% of the 93V overvoltage trip set point or 2864V on the 4160V buses. With this set point, they will trip in 3 seconds on total loss of voltage.

In addition to these undervoltage relays, some 460V loads are provided with undervoltage trip devices which are integrally mounted in individual circuit breakers. These undervoltage devices trip their individual loads after 5 seconds of less than 50% voltage 1276 139

The grid voltage is limited to V:,ltages between 212.75 KV and 238 KV per Attachment #1. The Auxiliary Transformer is set on tap number 5; and, the Start-up Transformers are set on tap number 4. Unit Substation Transformers iA1, 1B1, lA3, and 1B3 are set on tap number 1; and Unit Substation Transformers lA2 and 1B2 are set on tap number 3.

III. ANALYTICAL RESULTS A. General The voltage drop study for all safety-related buses and pumps was done using an approved Burns and Roe, Inc. computer program, EL0110E.

This program has been used for a number of other plant studies, including Three Mile Island, Unit No. 2. In addition, per an NRC request, this program was field verified on Three Mile Island Unit No. 2 to assure its accuracy. The results of the program were within 2% of the field measured values as shown on Attachment #2. This testing provides confidence that the analysis performed accurately predicts the performance of the Oyster Creek systems since testing at Three Mile Island Unit No. 2 verified the capabilities of the program.

The voltage drop calculations for all safety-related valve feeder cables were performed using an iterative approach based on the formula:

VD= KVA (R cos 0 + X sin 0)

VA V3 where VD =Line to Line Voltage Drop; V = AAssumed Motor Terminal Voltage; KVA= Load KVA; 0= Load Power Factor Angle; R= cable resistance; and X= cable reactance.

The assumptions made for the purposes of this program are listed on Attachment #1. Although these are assumptions, they are all firmly based on experience, testing, specification requirements, industry standards, or manufacturer's guarantees. In addition, all assumpt ~ ;ns were made in line with the intent of making this a worst case analysis.

1276 140 2

B. Undervoltacee The results of the analysis for Oyster Creek are shown on Tables I, II, III, and IV. As shown on Attachment #1, the minimum allowable voltages for 440 V motors are: 347 V running, and 330 V starting.-

For 4000 V motors the minimum voltages are: 3400 V running, and 3000 V starting.

Thus, with the grid at its minimum of 212.75 KV as stated in Attachment #1, all safety-related motors will have sufficient voltage at their terminals to stcrt and operate within their ratings.

Also, since the minimum Motor Control Center voltage at which all starters can be guaranteed to pick up is 403V, as shown on Attachment

  1. 1, all safety-related starters can be shown to pick up under worst case loading and minimum grid voltage.

As stated in Attachment #1, the drop out voltage for the starters at Oyster Creek is 276 V at the Motor Control Center, allowing for voltage drop in the control wiring. This study shows that the lowest voltage a safety-related Motor Control Center will momentarily drop to, when starting the largest non-safety related load, is 326 V.

Therefore, at minimun orid voltane, full load, and starting the largest non-safety related load, the starters will not drop out.

C. Overvoltage As mentioned above, the transformer taps for U.S.S. lA2 and 182 are set on tap #3. The study indicates that with the grid voltage of 238 KV, a minimum load of 2.5 MW randomly distributed among the buses on each Start-up Transformer, and the U.S.S.'s on tap #3 the maximum MCC voltage is 498 V. Per Attachment #1, the maximum voltage for which the 440V motors at Oyster Creek are rated is 484V.

Thus, even taking credit for voltage drop in the motor feeders will not guarantee that the motors' maximum voltage limit is not exceeded.

1276 141 However, exceeding the motors' maximun voltage limit, is only a potential problem when the plant is not in operation, with a minimal auxiliary load and a grid voltage higher than approximately 233 KV.

In addition, this value of overvoltage is not deemed to be a problem in that there will be less current draw at these higher voltages. This means that the motor winding temperature will be decreased; the amount of wear will be decreased; and the amount of insulation breakdown will be decreased. Therefore, operation of the motors at these higher levels of voltage will not have an adverse effect on the life of the motors.

In conclusion, the possibility of this overvoltage is deemed to be fairly remote. The value of 498 volts (+ 13.2%) is insignificantly above the specified value of 484 volts (+10%) and does not take into account the voltage drop in the feeder cables. Also, during a LOCA, as more loads are stm ted, the voltage level drops such that this

" worst case" overvoltage condition will be maintained for no more than three (3) minutes.

1276.142 TA3IS I - COMPUTER FISULTS 4160V LEVEL 4160V LEVEL:

GRID START-UP XFMR'S TAP # 4 AUX. XFMR TAP # 5 VOLTAGE & USS XFMRS' TAP #: USS XFMRS' TAP # :

LCAD 1 2 3 1 2 3 230 KV:

1:0 LCAD 4266 4266 4266 4379 4379 4379 238 KV:

MIN. LCAD 4378 4376 LOCA 4083 4081 4079 PCST LOCA 4139 4137 4136 LMS 3394 3392 POST LMS 4138 4136 230 KV:

MIN. LCAD 4228 4226 LOCA 3929 3926 3925 POST LOCA 3983 3981 3979 LMS 3263 3261 3259 POST LMS 3975 3972 3970 218.5 KV:

LOCA 3707 3704 3703 POST LOCA 3757 3755 3753 LMS 3070 3068 3066 POST LMS 3734 3731 3729 216 KV:

LOCA 3656 PCST LOCA 3706 IIG 3025 PCST LMS 3678 212.75 KV:

LOCA 3595 3593 3591 POST LOCA 3644 3642 3640 LMS 2972 2970 2968 POST LMS 3612 3609 3606 Notes:

Min Load is 2.5MW on each Start-Up transformer.

LOCA - values shown are for last pumps to start during a LOCA, which are the second Emergency Service Water Pumps on each bus.

LMS - Largest Motor Starting: the Reactor Feed Pumps were used for this study.

1][76 143

TABLE II - COMPUTER RESULTS 480V LEVEL 480V LEVEL:

START-UP XFMR'S TAP # 4 AUX. XFMR TAP # 5 VOLTAGE & USS XFMRS' TAP #: USS XFMRS' TAP #:

LCAD 1 2 3 1 1 2 3 230 KV:

1:0 LOAD 470 481 492 482 493 505 238 KV:

MIN. LCAD 487 498 LOCA 433 443 452 POST LOCA 439 449 459 LMS 384 393

, PCST LMS 455 466 230 KV:

MIN. LCAD 460 481 LOCA 417 426 435 PCST LOCA 423 432 441 LMS 359 368 377 PCST LMS 428 437 447 218.5 KV:

LOCA 393 402 411 POST LOCA 399 407 416 LMS 338 347 355 POST LMS 402 410 420 216 KV:

LOCA 397 PCST LOCA 402 LMS 342 POST IRS 405 212.75 KV:

LOCA 382 390 398 POST LOCA 387 395 404 LMS 326 334 343 POST LMS 389 397 406 Notes:

Min Load is 2.5MW on each Start-Up transformer.

LOCA - values shown are for last pumps to start during a LOCA, which are the second Emergency Service Water Pumps on each bus.

LMS - Largest Motor Starting: the Reactor Feed Pumps were used for this study.

1

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TABLE III Grid Voltage = 212.75 KV BUS START-UP XFMRS. (TAP #4) i AUXILIARY XFMR. (TAP #5)

LOAD RUNNING V STARTING V RUNNING V STARTING V SWGR. 1C 3735 3661

  • 3757 3675

Core Spray 1C 3726 3626 - -

Emerg. S.W.1-1 3730 3655 3652 3654 Emerg. S.W.1-2 3730 3655 3652 3654 SWGR. 1D 3673 3600

  • 3663 3582

Core Spray 1D 3669 3584 - -

Emerg. S.W.1-3 3668 3594 3658 3561 Emerg. S.W.1-4 3668 3594 3658 3561 U. S . S . lA2 ( TAP-3) 411 . 382

  • 419 390
  • Cont. Spray 1-1 408 361 - -

Cont. Spray 1-2 408 361 - -

CRD Feed 8A 410 378 417 382 C.S. BSTR. 3A 408 358 - -

C.S. BSTR. 3C 408 358 - -

R. B . CLS D. CLG .1- 1 410 380 417 384 U.S.S. 1B 2 ( TAP-3) 403 375

  • 407 379
  • Cont. Spray 1-3 396 336 - -

Cont. Spray 1-4 396 336 - -

CRD Feed 8B 401 370 405 370 C.S. BSTR. 3B 398 346 - -

C.S. BSTR. 3D 398 346 - -

R.B.CLSD.CLG.1-2 400 366 404 367 U.S.S. lA3(TAP-1) 406 357

  • 406 354 Service Wtr. 1-1 405 353 405 350 U.S.S. 1B3(TAP-1) 398 350
  • 395 344
  • Service Wtr. 1-2 397 345 394 340
  • LOWEST BUS VOLTAGE DUE TO ANY MOTOR STARTING WHEN BUS IS AT FULL LOAD 1276 145

, TABLE IV Grid Voltage = P12.75 KV BUS START-UP XFMRS. (TAP #4) AUXILIARY XFMR. (TAP #5)

LOAD RUNNING V STARTING V RUNNING V STARTING V MCC 1A21 Liq. Pols.PP. 402 379 410 385 Fuel Pool Fltr. 407 388 414 393 V-20-21 408 404 415 411 V-20-3 411 410 418 418 V-20-33 411 410 418 418 V-20-12 408 404 415 411 V-21-7 411 410 418 417 V-21-9 411 410 418 417 V-21-ll 411 410 418 418 V-21-17 411 411 418 418 V-21-18 411 411 418 418 V-3-88 411 410 418 418 V-20-27 410 409 417 416 MCC 1B21 Liq.Pois.PP. 394 371 398 374 Fuel Pool Fltr. 398 379 402 382 V-5-106 403 403 406 406 V-20-4 402 402 406 406 V-20-18 & 40 399 395 403 399 V-20-26 402 401 405 404 V-5-147 & 148 403 402 406 406 V-20-32 402 402 406 405 CoreSprayFillPP. 401 i 397 404 400 V-21-1 402 401 405 404 V-21-3 402 401 405 404 V-21-5 402 402 406 406 V-21-13 402 402 406 406 V-21-15 403 403 406 406 V-3-87 402 402 406 405 V-5-166 & 167 403 402 406 406 MCC 1A32 V-20-41 39.9 315 403 399 V-14-30 397 391 -401 395 V-14-32 397 391 401 395 V-14-36 396 389 400 393 V-14-37 396 389 400 393 1276 146

Sh. 1 of 2 Attachment #1 - Assumptions

1. According to General Electric technical publication No. GET-3101C, which was in effect at the time of MCC fabrication, the following starter voltage criteria apply:

Normal Voltage 460 VAC Drop Out Voltage 60% of normal (276 V)

Pick Up Voltage 85% of normal (391 V)

Testing of safety related starters at-Oyster Creek showed that Size 1 and Size 2 starters.will pick up below this value, but 85% was used for this study since this is the value guaranteed by General Electric.

2. The maximum voltage drop in control wir.ing for any safety-related starter circuit is 3 V. Since the motor starters' control transformers have a 4:1 ratio, 12 V on the primary of these transformers is re-quired to account for this control wiring voltage drop.

Thus the minimum voltage on the primary side of the control transformers which will guarantee cl1 starters pick up is 403 V (391'V (from #1 above) +12 V) .

3. Per random specifications which were checked, safety-related motors furnished for Oyster Creek were required to be capable of starting satisfactorily at a minimum voltage of 75% nominal. In addition, they were required to be capable of continuous operation at any voltage between +10% and -15% of nominal. Thus the guaranteed running voltage for motors rated at 440 V is from 374 V to 484 V with a minimum of 330 V required for starting.

For motors rated at 4000 V, the operating range is from 3400 V to 4400 V with 3000 V required for starting.

4. The longest time required for any large motor at Oyster Creek to accelerate to running speed. wi.th rat.ed_ volt _ age..a_tc,.i,ts termina-1scis.5.= seconds .
5. Per General Electric, the starting inrush for their starters at rated voltage is as follows:

Size 1 145 VA Size 2 528 VA 1276 147

Attachment #1 sh. 2 of 2

6. The minimum load on the Start-Up Transformers is 2.5 MW each. The basis for this valve is plant operating experience.
7. Where vendor information for motors was not available, the following values were used:

Efficiency .9 Running pf .85 Starting pf .2 Lock Rotor / Full Load Current 6.5 Brake HP Nameplate HP

8. ES signals trip the Reactor Recirculation Pumps.
9. The grid voltage range is from 212.75 KV to 238 KV.

These valves were predicted by grid stability analysis.

10. Control relays are rated at 120 V and can withstand +10%

overvoltage. This is equivalent to 528 V @ the 480 V level.

/

1276 148

ATTACHMENT #2 PREDICTED VOLTAGE VS. MEASURED VOLTAGE Bus Predicted Value Measured Value Percent Deviation 2-1 6.991 KV 7 002 KV -0.2%

2-3 4.209 KV 4.134 KV ^1.8%

2-5 4.207 KV 4.159 KV +1.2%

2-lE 4.209 KV 4.151 KV +1.4%

2-3E 4.207 KV 4.153 KV +1 3%

USS2-IlE 0.487 KV 0.478 KV +1.9%

USS2-12E 0.492 KV 0.482 KV +2.1%

USS2-31E 0.497 KV 0.492 KV +1.0%

2-2 7 056 KV 7 092 KV -0 5%

2-4 4.244 KV 4.198 KV +1.1%

2-6 4.241 KV 4.213 KV +0.7%

2-4E 4.243 KV 4.219 KV +0.6%

USS2-21E 0.491 KV 0.484 KV +1.4%

USS2-22E 0.497 KV 0.490 KV +1.4%

USS2-41E 0 501 KV 0.497 KV +0.8%

2-2E 4.244 KV 4.218 KV +0.6%

1276 149

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