ML17213A498

Technical Evaluation of Adequacy of Station Electric Distribution Sys Voltages for St Lucie Nuclear Power Plant, Unit 1.

ML17213A498
Person / Time
Site:	Saint Lucie
Issue date:	10/05/1981
From:	SELAN J C LAWRENCE LIVERMORE NATIONAL LABORATORY
To:	Office of Nuclear Reactor Regulation
Shared Package
ML17213A497	List: ML17213A496 ML17213A498
References
CON-FIN-A-0250, CON-FIN-A-250 UCID-19110, NUDOCS 8209280487
Download: ML17213A498 (14)

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• ,'~,*=~l P TECHNICAL EVALUATION OF THE ADEQUACY.OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES: "':..FOR THE ST;LUCIE NUCLEAR POWER PLANT, UNIT l-':.'.'"~'...-'<<'.,'e1ected Issues Program,-,'." Jakes C.Selan'"~"\P J'Docket No.50-335):..'

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ivS~*'a ABSTRACT This report documents the technical evaluation of the adequacy of the station electric'istribution system voltages for the St.Lucie Nuclear Power Plant, Unit.1..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 voltage analysis submirted has adequately demonstrated the capacity and capability of the electrical distribution system to supply adequate voltage to the Class 1E equipment under worst case operating conditions.

FOREWORD 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,'ffice of Nuclear Reactor Regulation, Division of Operating Reactors, by Lawrence Livermore National'aboratory.

The U.S.Nuclear Regulatory Commission funded the work under the authorization entitled"Electrical, Instrumentation and Control System Support", BGR 20 19 04 031, FIN A-0250.-111-TABLE OF CONTENTS~pa e l.INTRODUCTION

..~...o~~..~~~.1 2.DESIGN BASIS CRITERIA o..o~.~~.~~~1 3.SYSTEH DESCRIPTION

......~.~...~2 4 ANALYSIS 4.1 4.2 4'.1 4'.2 4 3 Analysis Conditions

.Analysis Results Overvoltage Undervoltage Analysis Verification

~~~4~4~4~4~4 6 5~EVALUATION 6 6~CONCLUSION 7 REFERENCES

~~~~~~~~~~~~~~~i 8 ILLUSTRATIONS FIGURE 1 St.Lucie-Unit 1 Electrical One-Line Diagram~~~~Pa e~~3 TABLE 1 St.Lucie-Unit 1 Class 1E Equipment Voltage Ratings'and Analyzed Horst Case Terminal Voltages~~.~..~~5 TECHNICAL EVALUATION OF THE ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES FOR THE ST.LUCIE NUCLEAR POWER PLANT UNIT 1 (Docket No.50-335)James C.Selan Lawrence Livermore 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 automatically start and operate all required safety loads within the equipment voltage ratings.In addition, the NRC requested each licensee to follow suggested guidelines 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], September 12, 1980[Ref.3], February 10, 1981[Ref.4], and JuLy 23, 1981[Ref.5], Florida Power&Light Company (FPL), the licensee, submitted their analysis and conclusion regarding the adequacy of the electrical distribution system's voltages at St.Lucie, Unit 1.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 1E equipment for the worst case starting and load conditions'.

DESIGN BASIS CRITERIA 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.6]~(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 Re ulations, Title 10, Part 50 (10 CFR 50)Ref.6 (3)ANSI C84.1-1977,"Voltage Ratings for Electric Power Systems and Equipment"[Ref.7].(4)IEEE Std 308-1974,"Class 1E Power Systems for Nuclear Power Generating Stations"[Ref.8]~(5)"Guidelines for Voltage Drop Calculations," Enclosure 2, to NRC letter dated August 8, 1979[Ref.1].3.SYSTEM DESCRIPTION An electrical one-line diagram of St.Lucie, Unit 1, is shown in Figure 1.The electrical distribution system is designed such that during normal startup and shutdown conditions, the auxiliary loads are supplied by the startup transformer.

When the unit is above 170 MWe power output, the auxiliary loads are supplied by the unit auxiliary transformer.

The two startup transformers are supplied from a 240KV switchyard where the output of the unit generator is connected through a main transformer bank.The two startup transformers have no electrical intertie connections between them with each transformer supplying its own train of auxiliary loads.A unit trip or a safety injection signal (SIS)will initiate automatic transfer of the onsite distributon system from the unit auxiliary transformer to the s'tartup transformer.

Both the startup transformers and unit auxiliary trans-formers have two secondary windings, with one at 6.9KV and the second at 4160 volts.There are three 4160-volt and three 480-volt Class 1E buses.The Class 1E equipment is protected from undervoltage conditions by an undervoltage relay located on each 4160-volt Class'lE bus.The inverse time relay has a voltage setpoint of 88.34X of 4160 volts (3675 volts)with a time dial setting of 1.The relay will actuate at 79.5X of 4160 volts in'pproximately 3 seconds.=The voltage setpoint at the 4160-volt level is equiva-lent to 83%of 480 volts at the Class 1E 480-volt motor control center buses.The licensee states that a design modification is planned to add undervoltage relays on the 480-volt Class 1E buses[Ref.2].The licensee has not provided any further design information on the planned modification.

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4~ANALYSIS 4.1 ANALYSIS CONDITIONS FPL analyzed the onsite distribution system voltages with the startup transformer as the supplying source under minimum and maximum expected grid voltages of 230KV and 244KV, respectively.

In conjunction with the above conditions, three loading cases were analyzed to determine the voltage at the terminals of the Class lE equipment.

In Case 1, the normal running loads were transferred to the startup transformer following a unit trip from full load coincident with a minimum expected grid voltage.The loading conditions of Case 2 are the same as Case 1, but with the addition of loads associated with an accident.Finally in Case 3, the loading conditions were the same as Case 1 except the grid was at the maximum expected value.In addition to the above conditions, the following assumptions were also made: (1)Normal loads used were measured values with the p~ant at full load.(2)Power factor of running loads was assumed as 0.85.(3)Heasured normal running loads included several Class lE loads.(4)Starting power factor for the 4KV motors was assumed as 0.22.Starting current was taken from nameplate data.(5)Starting power factor for the 480-volt motor operated valves was assumed to be 0.60.The starting current was taken from plant startup test data.(6)All currents were assumed to remain constant.4.2 ANALYSIS RESULTS The worst case Class lE equipment terminal voltages from the analyses submitted occur under the following conditions:

Normal running loads being supplied.by the startup transformer (unit trip with load transfer to the startup transformer) and grid at the maximum expected voltage of 244KV.4.2'Undervolta e Unit trip from full load with transfer of the normal running loads to the startup transformer concurrent with an accident condition and the grid at the minimum expected voltage, of 230KV.The above worst case Class 1E equipment terminal voltages are shown in Table l.

TABLE 1 ST.LUCIE-UNIT 1 CLASS lE EQUIPMENT VOLTAGE RATINGS AND ANALYZED WORST CASE TERMINAL VOLTAGES (in X of Equipment Nominal Voltage Rating)Minimum Rated Analyzed Rated Analyzed E uipment Nominal Voltage Rating (100 X)Steady State Steady-State Transient Motors 4000 Start Operate 110 106 5 75 90 99.4 93~5 460(')Start Operate 110 104.3 75 90 92.9 82 Starters(Pickup Dropout Operate 120 62'(c)110 79'(c)81.1 85 89 Other Equipment(d)(a)460-volt motors can operate at 75X terminal voltage for one minute without damage.Also, 460-volt MOV'.s can operate indefinitely at 80X terminal voltage.(b)Motor control center contactors are supplied from 480/120-volt transformers.

Starter sizes 1-2 and 3-4 are supplied by 50VA and 500VA size transformers, respectively.(c)These values obtained from tests performed.(d)Class lE instruments are fed from inverters.

4~3 ANALYSIS VERIFICATION FPL obtained test data by using standard plant test methodologies'his included using voltmeters to measure the secondary voltages of the potential transformers for the 4160-volt switchgear and 480-volt load centers.The bus amperes and the 480-volt MCC voltages were read from the cabinet's panel board meters.The readings taken were on a per phase basis.These readings were then averaged and their respective transformer ratios were used to calculate actual bus voltages and amperes.The verification results shows that the analytical values were within 2X of the actual plant data obtained[Ref.4).5~EVALUATION The NRC generic letter[Ref.1}stated several requirements that the plant must meet in the 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 connection must be capable of starting and continuously operating all Class lE equipment within the equipment's voltage ratings.The voltage analysis results submitted by FPL demonstrate that the offsite sources, in con)unction with the onsite distribution system, have the capacity and capability to automatically start and continuously operate the Class lE equipment with the design ratings for the 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 without exceeding the equip-ment's voltage ratings.The voltage analysis results submitted, by FPL demonstrate that the:Class 1E equipment upper voltage design rating will not be exceeded.(3)The analysis must show that there will be no spurious separa-tion from the offsite power source to the Class 1E buses by the voltage protection relays when the 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 No.10052)that the requirements of this position are met.Final design and Technical Specifications are forthcoming.

FPL did not submit analytical data on starting a large non-Class 1E load after the Class 1E buses Ore fully loaded.The licensee states that starting a large non-Class lE load would actuate the under-voltage protection relay under the worst case condition.

The largest non-Class 1E motor is the condensate.

pump which would be normally operating.

The pump would have to be manually tripped.The licensee states that an analysis of the plant's condition would be made before an attempted restart of the pump.FPL did not submit any written plant procedures addressing the pump restart.(4)Test results are required to verify the voltage analyses calculations submitted.

FPL verified their voltage analysis by test and the percent error difference of 2X confirm 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 with GDC 17.)FPL reviewed the electric power systems and found that no single event or condition could result in the simultaneous or consequential loss of both required circuits to the onsite distribution system, thus no violation of GDC 17 exists.6~CONCLUSIONS Based on the information provided by Florida Power and Light Company on St.Lucie, Unit 1's electrical distribution system, it is concluded that: (1)Voltages within the design ratings of the.Class 1E equipment are supplied from the offsite sources under worst case condi-tions.(2)The verification test performed verifies the analysis results.(3)A separate report will be made by LLNL (TAC No.10052-Degraded Grid)to verify that spurious trips will not occur during voltage transients upon final design and Technical Specification submittal., for the proposed undervoltage protection scheme.

(4), FPL has determined that no potential for either a simul-taneous or consequential loss of the offsite sources exists.(5)Addtional details of the plant procedures for assessing plant conditions prior to the restart of the condensate pump should be submitted.

REFERENCES 1.NRC letter (W.Gammill)to all Power Reactor Licensees, dated August 8, 1979.2.FPL letter (R.E.Uhrig)to NRC (W.Gammill), dated November 9, 1979.3.FPL letter (R.E.Uhrig)to NRC (D.G.Eisenhut), dated September 12, 1980.4.FPL letter (R.E.Uhrig)to NRC (D.G.Eisenhut), dated February 10, 1981.5.FPL letter (R.E.Uhrig)to NRC (D.G.Eisenhut), dated July 23, 1981.6.Code of Federal Re ulations, Title 10, Part 50 (10 CFR 50), General Design Criterion 13 and 17 of Appendix A for Nuclear Power Plants.7.ANSI'C84.1-1977,"Voltage Ratings for Electric Power Systems and Equipment." 8.IEEE STD.308-1971,"Class 1E Power System for Nuclear Power Generating Stations."

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