ML20052C655

Voltage Regulation Study

ML20052C655
Person / Time
Site:	Seabrook
Issue date:	04/30/1982
From:	PUBLIC SERVICE CO. OF NEW HAMPSHIRE
To:
Shared Package
ML20052C654	List: ML20052C653 ML20052C655
References
NUDOCS 8205050339
Download: ML20052C655 (20)

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l TABLES OF CONTENTS SECTION NO.

DESCRIPTION PAGE NO.

.I Purpose 1

II System Model 1

4 III Load Model 9

I IV Methods 10

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V Tabulation of Results 11 1

VI Conclusions 17 2

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PUBLIC SERVICE COMPANY OF NEW HAMPSHIRE SEABROOK STATION VOLTAGE REGULATION STUDY I.

PURPOSE The purpose of this calculation is to determine voltages present at various buses and motors throughout the plant during the following conditions:

A.

Unit at full load (maximum anticipated unit steady state load) with the utility grid at the minimum anticipated voltage.

B.

Unit at full load wit'h the utility grid at the minimum anticipated voltage and simultaneous start of all accident loads or start of other large motor loads.

C.

Unit at Cold Shutdown or Refueling (minimum anticipated load) with the utility grid at the maximum anticipated voltage.

II.

SYSTEM MODEL Thia section contains all assumed and actual data to establish the system being studied.

A.

Utility Grid The utility grid is assumed to be an infinite bus with a resultant zero impedance. The 345 kV bus voltage is ascumed to vary between 105% and 97.5%.

There are two available connections to the offsite power supply (utility grid) one through the Unit Auxiliary Transformer (UAT) and the other through the Reserve Auxiliary Transformer (RAT).

B.

Main Generator and Isolated Phase Bus Duct It is assumed that during running and starting conditions the utility grid voltage dip will be limited to 97.5% of rated.

To compensate for the Generator Step-Up Transformer (GSU) regulation

the generator output voltage must exceed the voltage of 97.5%

of rated on the GSU high voltage terminals. Due to this higher generator (and hence, Unit Auxiliary Transformer primary) voltage, the lowest source voltage can not be obtained with the i

generator connected. Therefore, it is assumed that the main generator is disconnected and that the auxiliary system is being back fed from the utility grid through the GSU. Light load condition is assumed to occur during shutdown with the main generator disconnected and the grid voltage at 105%. The iso-lated ph'ase bus duct connecting the GSU and Unit Auxiliary Transformer has such a small impedance that it is neglected during voltage drop considerations.

C.

Generator Step-Up Transformer The generator step-up transformer (GSU) has an impedance of 10%

on a 1230 MVA base.

This impedance is insignificant compared to other transformer impedances (UAT and unit substation transformers) so that the actual resultant voltage drop is a very small percentage of toe total voltage drop.

In addition, the computer program used to solve for the voltages in this calculation has convergence difficulties when impedances which differ by several orders of magnitude are incorporated into the impedance digram.

For these reasons, the GSU impedance has been neglected in this study.

D.

Unit Auxiliarv Transformer (UAT)

The UAT has the following ratings:

1) Voltages:

24.5-13.8-4.3 kV

2) MVA Ratings of windings (in OA/FA/(Future) FOA) a) Primary:

27/36/45 MVA b) 13.8 kV:

18/24/30 MVA c) 4.3 kV :

12/16/20 MVA

3) Leakage reactances between windings l

a) Primary to 13.8 kV (H-X):

7.5% on 27 MVA base b) Primary to 4.3 kV (H-Y):

12% on 27 MVA base i

c) 13.8 kV to 4.3 kV (X-Y):

18.53% on 27 MVA base The above leakage reactances are subject to a' + 10% manufacturing tolerance.

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Reserve Auxiliary Transformer (RAT)

The RAT has the following ratings:

1) Voltages:

345-13.8-4.3 kV

2) MVA ratings of the windings (in OA/FA/(Future)FOA) a) Primary:

27/36/45 MVA b) 13.8 kV:

18/24/30 MVA c) 4.3 kV:

12/16/20 MVA

3) Leakage reactances between windings:

a) Primary to 13.8 kV (H-X):

8.265% on 27 MVA base b) Primary to 4.3 kV (H-Y):

10.395% on 27 MVA base c) 13.8 kV to 4.3 kV (X-Y):

20.12% on 27 MVA base The abcve leakage reactances are tested values.

F.

Secondary Unit Substation Transformers 1.

All transformers, except that for unit substation (US) #64, have the following ratings:

a) Voltages:

13.8 kV (or 4.16 kV) - 480V b) KVA rating:

1000/1333 KVA, AA/FA c)

Impedance: 8% on 1000 KVA base

) Tested values of all

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Transformer connected to unit substation (US) #64 has the following rating:

a) Voltages: 4.16 kV - 480V b) KVA rating: 1000 KVA, AA c)

Impedance: 5.75% on 1000 KVA base ) Subject to + 7.5%

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Non-Segregated Phase Bus Duct For the purpose of this calculation, there are two types of non-segregated phase bus duct:

1) Type 1 has the following rating:

a) Voltage:

13.8 kV b)

Impedance:

(11.4 + j 56.5)x10-6 ohms / foot

2) Type 2 has the following ratings:

a) Voltage:

4.16 kV b)

Impedances:

(6.1 + j43.1)x10-6 ohms / foot H.

Cables Cables are copper conductor throughout and have lengths and sizes as indicated on Figures 1, 2, 3 and 4 Lengths of all cables have been selected on a worst case basis.

That is, the longest cable run within reason has been used in order to yield conservative results.

I.

Transformer Tap. Settings All transformer taps are on the primary winding.. Therefore, a tap set on the UAT or RAT has an effect on both low voltage windings. A tap set in the minus direction has the effect of raising the secondary voltage. For the assumed utility system voltage variation of 97.5% to 105% of 345 kV, transformer taps are assumed to be set as follows:

1) GSU: +2%

2) RAT: + 5%

3) UAT: Normal tap

4) All US transformers, except for US #64:

-5%

5) US #64 transformer: -2h%

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l 9 III. LOAD MODEL This section contains all assumed and actual data for the loads being studied. A. Starting Motors The motors shown on figures 1, 2, 3 and 4 were chosen because of their large size and/or long feeder length All motors were specified to start successfully with 80% of their voltage at their terminals. B. Running Loads - UAT or RAT Power Supp1v For the purpose of this calculation, the total running loads on the medium voltage buses are assumed to be as follows:

1) Bus #1:

(20.66) + j (11.21) MVA

2) Bus #2:

(18.01) + j ( 9.37) MVA

3) Bus #3 & ES:

(11.662)+ j (5.521) MVA

4) Bus #4 & E6:

(10.473)+ j (5.126) MVA The above bus loading represents worst case loads on these buses during normal and accident conditions. Running load for the equipment shown on Figures 1, 2, 3 & 4 is derived in the following manner: a) Motors - Manufacturer's data (when available) or catalog information is used to determine running MVA and power factor. b) Unit Substations - All 1000/1333 KVA unit substatiens except US #64 are assumed loaded to 1000 KVA at .85 power factor and 0.8 diversity factor in lieu of detailing all their connected loads. i l US #64 is assumed loaded to 600 KVA at 0.85 power factor. l

10 c) Motor Control Centers - The total running loads on the MCC were estimated to be as follows: i MCC # MW MVAR 523 0.338 0.210 612 0.313 0.164 C. Light Loads (Unit at Cold Shutdown) The following loads are assumed to be running simultaneously: 1) R.H. Removal pumps 8A/B (400 hp), service water pumps 41A/B (600 hp) and PCC water pumps 11A/B (700 hp) are running at full load.

2) Each unit substation, except US #64, is loaded to 400 kVA at 0.8 pf,

3) Unit substation No. 64 is loaded to 100 kVA at 0.8 pf.

IV METHODS Computer assisted calculations were made to evaluate the voltage regulation performance of the electrical power system. The computer program employed was the VOLTS Program; a United Engineers and Constructors Inc. computer program. The VOLTS Program is a 25 bus load flow and voltage regulation computer program which utilizes a Causs-Seidel iterative method to obtain l the load flow solution. This calculation is done on a worst case basis. For equipment whose parameters are known, the actual values are used, plus a margin where applicable. For equipment whose parameters are unknown, values were assumed which represent the worst reasonabla case. Consequently, resultant voltages should be the lowest voltages to be expected during the lifetime of the plant.

11 V. TABULATION OF RESULTS The results of the computer calculated voltages are tabulated as follows: TABLE 1 --- Bus and Motor Terminal Voltages when running at full load and utility grid at the minimum anticipated voltage. TABLE 2 --- Bus and Motor Terminal Voltages when starting individual motors and the utility grid at the minimum anticipated voltage. TABLE 3 --- Bus and Mof.or Terminal Voltages when starting all accident loads simultaneously and the utility grid at the minimum anticipated voltage. TABLE 4 --- Bus Voltages when running at light load and the utility grid at the maximum anticipated voltage. TABLE 5 --- 120 V ac System Voltages. 3

_12_ TABLE 1 BUS AND MOTOR TERMINAL VOLTAGES WHEN RUNNING AT FULL LOAD UTILITY GRID AT MINIMUM ANTICIPATED VOLTAGE (ALL VOLTAGES ARE ON MOTOR VOLTAGE BASE) NOMINAL SOURCE: BUS OR MOTOR TAG # HP VOLTAGE, V FROM UAT. pu FROM RAT. pu P 4160 0.9500 0.9458 4.16 kV Bus E5 4160 0.9595 0.9545 4.16 kV Bus E6

• Co-P-30A 3500 4000 0.9482 0.9440 480 0.9586 0.9537 480V Bus ES2 480' O.9551 0.9504 480V Bus ES3 480 0.9656 0.9601 480V Bus E61 480 0.9557 0.9504 480V Bus E64 460 0.9407 0.9357

.MCC 523 460 0.9627 0.9571 MCC 612 C* CAH-FN-1C 200 460 0.9345 0.9297 EAH-FN-5A 125 460 0.9446 0.9396 FAH-FN-11B 60 460 0.9530 0.9474 2SW-FN-51B 250 460 0.9434 0.9380 SF-P-10B 20 460 0.9481 0.9425 t NOTES:

• CO-P-30A -- CONDENSATE PUMP IS A 3500 HP NON SAFETY LOAD. THIS REPRESENTS THE WORST VOLTAGE DROP ON THE 4160 VOLT SYSTEM.

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• • NON SAFETY RELATED.

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TABLE 2 l BUS AND MOTOR TERMINAL VOLTAGES WHEN STARTING INDIVIDUAL MOTORS _ UTILITY GRID AT MINIMUM ANTICIPATED VOLTAGE (ALL VOLTAGES ARE ON MOUR VOLTAGE BASE) BUS OR NOMINAL SOURCE: MOTOR TAG # E VOLTAGE, V FROM UAT, pu FROM RAT pu 4160 .8412 .8517 4.16 kV Bus E5 4160 .8537 .8607 4.16 kV Bus E6

• CO-P-30A 3500 4000

.8339 .8445 480 .8318 .8433 480V Bus ES2 480 .8325 .8445 480V Bus E53 480 .8431 .8547 480V Bus E61 480 .8391 .8500 480 Bus E64 460 .8097 .8217 MCC 523 460 .8398 .8515 MCC 612

• CAH-FN-1C 200 460

.7622 .7628 EAH-FN-5A 125 460 .8660 .8663 FAH-FN-11B 60 460 .8430 .8392 ~ 2SW-FN-51B 250 460 .8282 .8247 SF-P-10B 20 460 .9229 .9177 NOTEEs 1) FOR BUS VOLTAGES, THIS TABLE REPRESENTS MINIMUM VOLTAGE AT THE BUS WHEN STARTING ANY ONE MOTOR FED FROM ANY BUS IN THE PLANT. 2) THIS TABLE SUMMARIZES THE RESULTS OF MANY COMPUTER RUNS. THE BUS VOLTAGES LISTED REPRESENT THE LOWEST VOLTAGES EXPERIENCED AT THAT BUS WHEN STARTING ANY INDIVIDUAL MOTOR, CLASS lE OR NON-CLASS 'lE, IN THE PLANT. THE MOTOR VOLTAGES LISTED ARE THE LOWEST REPRESENTATIVE MOTOR TERMINAL VOLTAGES UPON MOTOR START. CO-P-30A, A NON SAFETY II)AD, REPRESENTS THE WORST VOLTAGE DROP ON THE 4160 VOLT SYSTEM, INCLUDING THE SAFETY BUSES.

• • THIS IS A NON SAFETY RELATED MOTOR. HOWEVER, ITS CAPABILITY TO SUCCESSFULLY START AND ACCELERATE AT THE AVAILABLE VOLTAGE HAS BEEN VERIFIED BY CALCULATION.

. TABLE 3 BUS AND MOTOR TERMINAL VOLTAGES WHEN STARTING ALL ACCIDENT LOADS SIMULTANEOUSLY UTILITY GRID AT MINIMUM ANTICIPATED VOLTAGE (ALL VOLTAGES ARE ON MOTOR VOLTAGE BASE) SOURCE: NOMINAL EUS OR. MOTOR TAG # E VOLTAGE, V FROM UAT pu FROM RAT pu .8856 .8944 4160 4.16 kV Bus E5 .8749 4160 .8661 4.16 kV Bus E6 '* SI-P-6B 450 4000 .8640 .8727

• RH-P-BB 400 4000

.8646 .8733

• CS-P-2B 600 4000

.8626 .8713

• FW-P-37B 900 4000

.8592 .8679 480 .8811 .8911 480V Bus E51 480 .8797 .8897 480V Bus E52 480 .8832 .8932 480V Bus E53 480 .8597 .8696 480V Bus E61 480 .8631 .8724 480V Bus E64 460 .8786 .8886 MCC 512 460 ,8564 .8663 MCC 612 CAH-FN-3B 30 460 .8313 .8416 CBA-FN-32 40 460 .8499 .8599 2-SW-FN-51B .250 460 .8494 .8589

• STARTING IDAD NOTES:

1) OTHER SAFETY LOADS SUCH AS SFRVICE WATER PUMPS, ETC., ARE RUNNING.

2) TABLE LISTS TRAIN B ACCIDENT LOADS, WHICH IS WORST CASE.

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. l TM2 4 BUS TERMINAL VOLTAGES WHEN RUNNING AT LIGHT LOAD UTILITY GRID AT MAXIMUM ANTICIPATED VOLTAGE (ALL VOLTAGES ARE ON MOTOR VOLTAGE BASE) BUS OR NOMINAL SOURCE: MOTOR TAG # H_P VOLTAGE, V FROM UAT, pu FROM RAT. ou P 4160 1.0920 1.0639 4.16 KV Bus E5 4160 1.0910 1.0627 4.16 kV Bus E6 480 1.1293 1.1009 480V Bus ES2 480 1.1294 1.1010 480V Bus E53 480V Bus E61 480 1.1293 1.0988 480 1.1176 1.0884 480V Bus E64 460 1.1241 1.0956 MCC 523 460 1.1283 1.0978 MCC 612 i 4

TABLE 5 e 120 V ac System Voltages 1. Most of the control and instrumentation circuits for safety related systems at Seabrook Station are power from Vital AC Distribution panels supplied by 118 V ac regulated Uninterruptible Power supply units. For the remaining safety related circuits which are powered from non regulated Class lE 120 V ac power distribution panels (powered from motor control centers), our analysis is as follows: 1 (LATER) r / e e l i l f e t e 1 i t

. 4 VI. CONCLUSIONS A. Full and Light Load Conditivas All motors will receive more than the minimum 90% of their rated voltage during normal plant operating conditions. During light load conditions, all buses and motors will receive less than 110% of their rated voltage except that some 480 V buses', when fed via the UAT, may exceed the allowable, maximum motor voltage by up to 2.9%. However, assuming a nominal motor feeder drop of 2 to 3%, 480 V motor terminal voltage should not exceed the allowable maximum voltage when supplied by the UAT. There is no overvoltage problem when the system is fed via the RAT. B. Motor Starting Conditions All safety-related motor receive more than 80% of their rated voltage and will accelerate without any problems. C. Transformer Tap Settings The assumed transformer tap settings are acceptable for the assumed utility system voltage variation of 97.5 to 105 percent of 345 kV.

f o REVISED RESPONSE TO RAI 430.5 RAI 430.5 The voltage levels at the safety-related buses should be optimized for the full load and minimum load conditions that are expected throughout the anticipated range of voltage variations of the offsite power source by appropriate adjust-ment of the voltage tan settings of the intervening transformers. Submit the planned range of normal operating voltages for each safety-related bus. RESPONSE (Revised 4/30/82) Enclosed is the Voltage Regulation Study for the Seabrook Station. This study provides the voltage analysis required by BTP PSB-1 (See RAI 430.14). Additional data for 120 volt ac level will be submitted to the NRC by 6/1/82. t l l .}}