ML20071L708

Adequacy of Station Electric Distribution Sys Voltages for Turkey Point Nuclear Generating Plant Units 3 & 4, Technical Evaluation Rept

ML20071L708
Person / Time
Site:	Turkey Point
Issue date:	08/08/1982
From:	Selan J LAWRENCE LIVERMORE NATIONAL LABORATORY
To:	NRC
Shared Package
ML17341B532	List: ML20071L708
References
CON-FIN-A-0250, CON-FIN-A-250 UCID-19148, NUDOCS 8209230424
Download: ML20071L708 (13)

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. TECHNICAL EVALUATION REPORT ON THE ADEQUACY OF STATION ELECTRIC DISTRIBUTION

• SYSTEM VOLTAGES FOR THE

- TURKEY POINT, NUCLEAR GENERATING PLANT '

UNITS 3 AND 4 4

(Docket Nos. 50-250, 50--251)

James C.~Selan

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This is an informal report inte'nded prim'arily fo'r interdal or' limited e$ternal'distNbu' tion. *,. ,.

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The opinions and conclusions stated are those of the author ind may or may'not be thEse'-> , jf3O{f ,,

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1. This work was supported by the United States Nuclear Regulatory Commission under ; . .-i , .

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. . . ..',. l DISCLAIMER .

This document was prepared as se account of work sponsored by se agncy of the United States. Government.Neither -

the United States Government not any agency thereof, nor any of their employees, makes any warranty, empressed or inoplied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any ,

idormation, apparatua, product, or process disclosed. or represents that its use would not infringe privately owned rights. Reference herene to any specific commercial product, process, or service by trade name, trademark, manufac. '

• turer, or otherwise, does not necessarily constitute or imply its endo'esement, recommendation, or favoring by the United .

States Government or any agency thereof. The views and opinions of authors expressed hereia do not neceaanrily state

• or reflect those of the United States Government or any agency thereof. - -

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Available from: Sational Technical ,Information Service .'U.S. Department of, Commerce 5285 Port Royal Road . Springfield, VA 22161. $5.00 per copy . (Microfiche $3.50)

l ABSTRACT l

' ais report documents the technical evaluation of the adequacy of the station electric distribution system voltages for the Turkey Point Nuclear Generating Plant, Units 3 and 4. The evaluation is,to determine if

, the onsite distribution system in conjunction with the offsite power sources has sufficient capacity to automatically start and operate all Class lE loads within the equipment voltage ratings under certain conditions established by the Nuclear Regulatory Commission. The analysis submitted demonstrates that acceptable voltage will be supplied to the Class 1E equipment under the worst case conditions analyzed.

FOREUORD i

This report is supplied as part of the Selected Electrical, Instrumentation, and Control Systems Issues Program being conducted for the U. S. Nuclear Regulatory Commission, Of fice of Nuclear Reactor Regulation, Division of Licensing, by Lawrence Livermore National .

Laboratory.

The U. S. Nuclear Regulatory Commission funded the work under the authorization entitled " Electrical, Instrumentation and Control System Support,"

B&R 20 19 04 031, FIN A-0250.

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, TABLE OF CONTENTS

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1. INTRODUCTION . . . . . . . . . . . . . . . 1

. 2. DESIGN BASIS CRITERIA . . . . . . . . . . . . 2

3. SYSTEM DESCRIPTION . . . . . . . . . . . . . 2

4. ANALYSIS . . . . . . . . . . . . . . . . 4 4.1 Analysis Conditions . . . . . . . . . . 4 4.2 Analysis Results . . . . . . . . . . 5 4.2.1 Overvoltage . . . . . . . . . . . . 5 4.2.2 Undervoltage. . . . . . .. . . . . . 5 4.3 Analysis Verification . . . . . . . . . 5 4

5. EVALUATION . . . . . . . . . . . . . . . 5

6. CONCLUSION . . . . . . . . . . . . . . . 9 I .

REFERENCES . ,. . . . . . . . . . . . . . . 10 ILLUSTRATIONS FIGURE 1 Turkey Point, Units 3 and 4 Electrical One-Line Diagram . . . . . . . . . . 3 TABLE 1 Turkey Point, Unit 3 Class 1E Equipment Voltage Ratings and Analyzed Worst Case Terminal Voltages . . . . . . . 6 TABLE 2 Turkey Point, Unit 4 Class 1E Equipment Voltage Ratings and Analyzed Worst Case Terminal voltages . . . . . . . 7

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TECHNICAL EVALUATION REPORT ON THE ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES FOR THE TURKEY PolNT NUCLEAR GENERATING PLANT (Docket Nos. 50-250, 50-251)

James C. Selan Lawrence Livermere National Laboratory, Nevada

1. INTRODUCTION The Nuclear Regulatory Commission (NRC) by a letter dated August 8, 1979 (Ref. 1] expanded its generic review of the adequacy of the station electric distribution systems for all operating nuclear power facilities. This review is to determine if the onsite distribution system in conjunction with the offsite power sources has sufficient capacity and capability to autonatically start and operate all required safety loads within the equipment voltage ratings. In addition, the NRC requested each licensee to follow suggested guidalines and to meet certain requirements in the analysis. These requirements are detailed in Section 5 of this report.

By letters dated November 9,1979 (Ref. 2], December 18, 1980 (Ref. 3], June 10, 1931 [Ref. 4], February 24, 1982 [Ref. 5], and ltay 20,1982 [Ref. 6], Florida Power and Light Company (FPL), the licensee, submitted their analysis and conclusion regarding the adequacy of the elec-trical distribution system's voltages at the Turkey Point Nuclear Generating i Plant, Units 3 and 4.

The purpose of this report is to evaluate the licensee's submittal with respect to the NRC criteria and present the reviewer's conclusion on the adequacy of the station electric distribution systems to maintain the voltage within the design limits of the required Class lE equipment for the worst case starting and load conditions. -

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2. DESIGN BASIS CRITERIA e

The design basis criteria that were' applied in determining the adequacy of station electric distribution system voltages to start and operate all, required safety loads within their required voltage ratings are as follows: .

(1) General Design Criterion 17 (GDC 17), " Electric Power Systems," of Appendix A, " General Design Criteria for Nuclear Power Plants," in the Code.of Federal Regulations, Title 10, Part 50 (10 CFR 50) [Ref. 7].

(2) General Design Criterion 13 (GDC 13), " Instrumentation and Control," of Appendix A, " General Design Criteria for Nuclear Power Plants," in the Code of Federal Regulations, Title 10, Part 50 (10 CFR 50) [Ref. 7].

g (3) General Design Criterion 5 (GDC 5), " Sharing of Structures, Systems and Components," of Appendix A, " General Design ,

Criteria for Nuclear Power Plants," in the Code ? 7ederal Regulations, Title 10, Part 50 (10 C'rWl50) [ Ret T [].

(4) ANSI C84.1-1977, " Voltage ; Rating,slfor Electric Power Systems. i--

~T and Equipment"'[Ref. 3]. , '

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(5) IEEE Std' 308-19741 "Clas's,1E PhwIr? Systems for ' Nuclear Power i Generating Stations" [Ref. 9].', ,/

(6) " Guidelines for Voltage Drop Calculations," Enclosure 2, to ,

NRC letter dated August 8, 1979 [Ref. 1].

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3. SYSTEMDESCRIFTIpN'

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, I The electrical one-line diagram for Turkey Point, Units 3 and 4 is shown in Figure 1. - Each of the two units has an auxiliary transformer which ,

supplies power to the onsite distribution system during normal operation. The il unit auxiliary transformer is connected to the main generator's isolated phase - 4i )

buses and has two secondary 4160-volt windf ugs each supplying one load group ot* f s Class lE equipnent.

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In addition to the unit auxiliary transfoher, each ig.it has a starbir(

t rans fo rme r. The startup transformers,. withhwo seh.ndary 41(0-"olt windings,- '

are connected to the 240 kV switchyard. The startuti transformers supplies power.

to the onsite distribution system during startup, shutdown, anFTutomatically after a unit trip. The adjacent startup transformer of one unit cav supply one load - i ,

group of the other urit by manually closing the 4160-volt' tit hreaker. 5, t

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k The onsite distribution system can also be supplied by removing the generator links and backfeeding from the 240 kV switchyard via the main trans-former and the unit auxiliary tranformer. The onsite distribution system of each unit consists of two 4160-volt and four 480-volt Class lE buses.

The Class lE equipment is currently protected from voltage degradation by a loss-of-voltage protection scheme. This scheme 9tilizes two undervoltage relays on each 4160-volt Class 1E bus which will actuate at 40%-50% voltage with a time delay of 1 second. A second-level undervoltage protection scheme is presently being designed to add two inverse time delay relays on each 4160-volt Class lE bus and two instantaneous relays at each 480-volt load center. The final voltage setpoints and time relays have not been selected.

4. ANALYSIS 4.1 ANALYSIS CONDITIONS FPL analyzed the need for power to the onsite distribution system through the unit's startup transformer which was initiated by an accident

, condition (largest load demand). For this operating condition, various combi-nations of loading configuarations concurrent with a minimum grid voltage of 235 kV and a maximum grid voltage of 244 kV were analyzed. In addition to the

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various loading configurations, several other assumptions were made and are as follows:

(a) All safety loads start simultaneously with a safety injection signal (SIS).

(b) An SIS initiates an automatic fast transfer from the unit auxiliary transformer to the startup transformer.

(c) Running loads prior to SIS are based on highest recorded load values.

(d) Power factor for running loads of 0.85 (e) Power factor for starting loads of; 0.20 for 4 kV wotors; 0.42 for emergency containment coolers; 0.35 for emergency containment filters; and 0.60 for motor operated values (MOV's).

( f) Starting current of 6 times full load amperage (FLA) for motors and 2.1 times FLA for MOV's.

(g) Running loads assumed as constant kVA.

(h) The steam generator feedwater pumps (SGFP) trip automatically upon a SIS.

d FPL chose to calculate the worst case minimum voltage required at each bus to start the Class lE loads rather than repeatedly calculate Class 1E load terminal voltage for each case analyzed. If the voltage analysis results for each case are above the highest minimum bus voltage required, this would ensure that all Class IE equipment would start within the voltage design rating.

4.2 , ANALYSIS RESULTS

, Using the assumptions defined previously and various running and~ load starting combinations, the worst case voltage analysis results occur under the following conditions and are shown in Tables 1 and 2:

4.2.1 Overvoltage Maximum grid voltage of 244 kV, one-half normal loads on 480-volt buses and minimum motors running on the 4160-volt buses.

4.2.2 Undervoltage Minimum grid voltage of 235 kV, accident condition, the SIS initiates automatic fast transfer from the unit auxiliary transformer to the startup transformer and with the Class lE. equipment starting simul-taneously.

4.3 ANALYSIS VERIFICATION FPL verified their voltage analyses by measuring voltage and current at all Class lE buses. Using the measured loads, a voltage analysis was per-formed and the resulting voltages compared to the measured voltages. The test was conducted when both units were operating at full power. Bus loading was provided at each distribution level. The results indicated that the analysis is conservative in that the measured values were all higher than the calculated values. For unit 3's analysis, the worst case percent errors were -1.5%, -2.7%,

and -3.0% at the 4160-volt bus, 480-volt load center bus, and the motor control center bus respectively. At unit 4, the worst case errors were -1.8%, -2.0%,

and -1.8% at the 4160-volt bus, 480-volt load center, and the 480-volt motor control center bus respectively.

5. EVALUATION The NRC generic letter {Ref.1] stated several requirements that the plant must meet in their voltage analysis. These requirements and an evaluation of the licensee's submittals are as follows:

(1) With the minimum expected grid voltage and maximum load condition, each offsite source and distribution system i

TABLE 1 TURKEY POINT, UNIT 3 CLASS lE EQUIPMENT VOLTAGE RATINGS AND ANALYZED WORST CASE TERMINAL VOLTAGES (in % of Equipment Nominal Voltage Rating)

Maximum Minimum .

Rated Analyzed Rated Analyzed .

Nominal Voltage Rating Steady Steady Equipment (100%) State State Transient Motors 4000 Start 80 93.9 Operate 110 107.8 90 98.2(a) 460 Start 80 85.2 Operate 110 108.7 90 92.8(a)

Starters 120 Pickup (b) , (c)

Dropout (b) (c) '

Operate 110 ---

85 (c)

Other(d)

Equipment (a) Steady state value is with all Class lE loads running in addition to the largest non-Class lE load running (SGFP).

(b) The pickup and dropout voltage ratings (manufacturer's) of the various size starters are: size 1, 88.8 volts and 66.0 volts; size 2 and 3, 85 2 volts and 66.0 volts; size 4, 91.2 volts and 66.0 volts respectively.

(c) Tests were conducted to determine actual pickup voltages taking .into consid-eration cable lengths and control transformer voltage drops. Calculations were then made to determine the minimum 480-volt MCC voltage required to assure starter pickup. These required voltages are listed in Ref. 6, Attachment A. These minimum required voltages are all less than the worst case transient voltages experienced which insure adequate starter operation.

(d) All low voltage AC (less than 480-volts) Class lE buses supplying power to vital instrumentation and control circuits are powered by inverters supplied from the 125-volt DC station batteries.

TABLE 2 TURKEY POINT, UNIT 4 CLASS lE EQUIPMENT VOLTAGE RATINGS AND ANALYZED WORST CASE TERMINAL VOLTAGES (in % of Equipment Nominal Voltage Rating)

Maximum Minimum Rated Analyzed Rated Analyzed Nominal Voltage Rating Steady Steady Equipment (100%) State State Transient Motors 4000 Start 80 94.1 Operate 110 107.9 90 98.4(a) 460 Start 80 87.8 Operate 110 107.2 90 96.3(*)

Starters 120 Pickup , , (1 ()

Dropout (b) ,(c)

Operate llD 85 (c)

Other(d)

Equipment (a) Steady state value is with all Class lE loads running in addition to the largest non-Class lE load running (SGFP).

(b) The pickup and dropout voltage ratings (manufacturer's) of the various size starters are: size 1, 88.8 volts and 66.0 volts; size 2 and 3, 85.2 volts and 66.0 volts; size 4, 91.2 volts and 66.0 volts respectively.

(c) Tests were conducted to determine actual pickup' voltages taking into consid-eration cable lengths and control transformer voltage drops. Calculations were then made to determine the minimum 480-volt MCC voltage required to assure starter pickup. These minimum required voltages are listed in Ref. 6, Attachment A. These minimum required voltage are all less than the worst case transient voltages experienced which insure adequate starter operation.

(d) All low voltage AC (less than 480-volts) Class lE buses supplying power to vital instrumentation and control circuits are powered by inverters supplied from the 125-volt DC station batteries.

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connection must be capable of starting and continuously operating all Class lE equipment within the equipment's voltage ratings.

The voltage analysis submitted by FPL has shown that the offsite source connections to the onsite distribution system have the capacity and capability to start and continuously a operate the Class lE equipment withfu the voltage ratings under worst case conditions. ,

(2) With the maximum expected offsite grid voltage and minimum load condition, each offsite source and distribution system connection must be capable of continuously operating the required Class lE equipment withrat exceeding the equipment's voltage ratings.

The voltage analysis submitted by FPL shows that the Class lE equipment's upper design voltage ratings are not exceeded.

(3) The analysis must show that there will be no spurious separation from the offsite power source to the Class lE buses by the voltage protection relays when th'e grid is within the normal expected limits and the loading conditions established by the NRC are being met.

LLNL will verify in a separate report (TAC Nos.10053 and 10054) that the conditions of this position are met as the proposed undervoltage setpoints and time delays associated with the design changes and modifications for a second-level of under-voltage protection has not been submitted. ,

(4) Test results are required to verify the voltage analyses calculations submitted.

FPL verified the voltage analysis by test. The percentage error differences between the actual measured and the calculated values confirm that the analytical results are acceptable.

(5) Review the plant's electrical power systems to determine if any events or conditions could result in the simultaneous loss of both offsite circuits to the onsite distribution system (compliance of GDC 17).

The licensee has not provided the required review of the plant's electrical system to determine if any event or condition could result in the simultaneous loss of both required offsite circuits to the onsite power distribution system. The licensee is required to submit this review.

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(6) As required by GDC 5, each offsite source shared between units in a multi-unit station must be capable of supplying adequate starting and operating voltage to all required Class lE loads with an accident in one unit and a safe shut-down in the remaining unit (s).

The sharing of an offsite source is via the adjacent unit's startup transformer. This condition only occurs when one unit is shutdown. Manual actiors are required to align this connection. This connection only allows for one train of each unit (the A buses) to be supplied by the adjacent unit's startup transformer. Should a safety injection occur during this connection, the Class lE equipment would automatically be started. Due to the greatly reduced load (i.e. one unit is shutdown) for this condition, the voltages being supplied by the adjacent startup transformer would be more adequate than the worst case analyzed voltages presented in the tables.

Therefore, the shared offsite source (startup transformer) has the capacity and capability of supplying adequate voltage to both unit's Class lE equipment.

6. CONCLUSIONS Based on the information submitted by Florida Power and Light Company for the Turkey Point Nuclear Generating Plant, Units'3 and-4, it is concluded j that: -

(1) Under the worst case conditions analyzed, the Class lE equipment will automatically start and~ continue to operate within their voltage design ratings. -

l (2) The voittge at the Class 1E equipment will not exceed the upper design voltage rating under maximum of fsite voltage and minimum plant loading conditions.

(3) The analysis submitted was verified by test and that the test data indicates the analytical results are acceptable.

(4) Spurious trips will be evaluated in a separate report by LLNL (TAC Nos. 10053 and 10054) entitled " Technical Evaluation Report on the Proposed Design Modifications and Technical Specification changes on Grid Voltage Degradation."

(5) The sharing of offsite sources has the capability and capacity to supply adequate voltage to both unit's Class 1E equipment should an accident occur.

The licensee is required to provide the requested review of the plant's electrical power system to determine if any event or condition exists which could

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I cause the simulcaneous loss of both offsite source circuits to the onsite distribution system.

Accordingly, I recommend that the NRC accept the voltage analysis submitted by the licensee which demonstrates that acceptable voltage will be supplied to the Class lE equipment under the worst case conditions analyzed.

The NRC should continue to pursue the licensee to submit the requested review of the plant's electrical power system for conformance with GDC 17.

REFERENCES

1. NRC letter (W. Cammill) to all Power Reactor Licensees, dated August 8, 1979.

2. FPL letter (R. E. Uhrig) to the NRC (S. A. Varga), dated November 9,1979.

3. FPL letter (R. E. Uhrig) to the NRC (S. A. Varga), dated December 19, 1980.

4. FPL letter (R. E. Uhrig) to the NRC (S. A. Varga), dated Jun'e 10, 1981.

5. FPL letter (R. E. Uhrig) to the NRC (S. A. Varga), dated February 24, 1982.

6. FPL letter (R. E. Uhrig) to the NRC (S. A. Varga), dated May 20, 1982.

7. Code of Federal Regulations, Title 10, Part 50 (10 CFR 50), General Design Criterion' 5,13 and 17 of Appendix A for Nuclear Power Plants.

8. ANSI C84.1-1977, " Voltage Ratings for Electric Power Systems and Equipment."

9. IEEE STD. 308-1971, " Class lE Power Systems for Nuclear Power Generating Stations."

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