ML19330B670

Forwards Revised Response to Inquiry on Adequacy of Facility Safety Grade Electrical Distribution Sys Voltage Since Condition Discovered at Millstone Unit 2.Util Is Planning to Implement Mod to Sys During 810601 Refueling Outage

ML19330B670
Person / Time
Site:	Rancho Seco
Issue date:	08/01/1980
From:	Mattimoe J SACRAMENTO MUNICIPAL UTILITY DISTRICT
To:	Reid R Office of Nuclear Reactor Regulation
References
TAC-10968, TAC-12746, NUDOCS 8008050353
Download: ML19330B670 (53)

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$"' SACRAMENTO MUNICl PAL UT:LITY oisTRI SMUD 6201 s street, Box 15830, sacramento, California 95813; (91f) 452-3211 August 1,1980 Director of Nuclear Reactor Regulation Attention: Mr. Robert W. Reid, Chief Operating Reactors, Branch 4 U.S. Nuclear Regulatory Commission Washington, D.C.

20555 Docket No. 50-312 Rancho Seco Nuclear Generating Station, Unit 1 Adequacy of Station Electrical Distribution System Voltage

Dear Mr. Reid:

There have been a number of letters and telephone conversations betwe3n the District and the NRC concerning the adequacy of the Rancho Seco Safet/ Grade Electrical Distribution System since the off site degraded voltage cotidition at Millstone Unit No. 2 during July,1976.

In the various letters and telephone conversations, the District has reported the results of analyses and made design commitments. Over the past four years, the NRC has clari-fied their position on certain items which have required the District to perform additional analyses and make new design commitments. Also, the District has made major modifications and is planning future modifications to the electrical distribution system that has required additional analyses and new design commitments.

The number of letters and telephone conversations that describe the District's proposed modifications have become so numerous that the staff and the District are not communicating effectively. To resolve this problem, the District is resubmitting in their entirety, our responses to your letters of June 3,1977 and August 8, 1979.

These responses have been revised to indicate:

(a) All commitments made to the NRC.

(b) All modifications that have been performed.

(c) All proposed modifications.

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(d) All proposed technical specifications and operating procedure changes.

Enclosures I and II of this letter contain all the information required for an evaluation of the District's existing and proposed distribution system. -

They supersede all other transmittals on this item.

Revisions from our previous response are indicated by a line in the margin with a revision num-ber next to it.

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tir. Robert' W. Reid August 1,1980 The District is planning to implement all the proposed modifications during the 1981 refueling outage, scheduled for June 1,1981.

-It will require nine months of engineering to complete the design. The material required to implement the task have lead times as'long as 9 - 12 months. 'Therefore, to be able to implement the modification during the

' June,1981 refueling outage, the District must have all NRC comments resolved and the design approved by September. 30,1980.

If you have any questions on this item, please do not hesitate to. contact

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Sincerely, b

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attimoe Assistant General Manager and Chief Engineer Enclosure i

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Enclosure I i

i SACRAMENTO MUNICIPAL ITTILITY DISTRICT RANCHO SECO NUCLEAR GENERATING STATION, UNIT No. 1 RESPONSE TO:

NUCLEAR REGULATORY COMMISSION REQUEST TO REVIEW THE ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES (LETTER FROM WILLIAM GAMMILL TO POWER REACTOR LICENSEES DATED AUGUST 8, 1979)

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Issued: October 17, 1979 Revision 1: August 1, 1980 i

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ENCLOSURE I PART A GENERAL RESPONSE TO k'ILLIAM GAMMILL TO PohT.R REACTOR LICENSEES' LETTER DATED AUGUST 8, 1979

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The following is the revised text of the October 17, 1979 letter to l

William Gammill, NRC's Acting Assistant Director for Operating Reactors Projects, from John J. Mattimoe, SMUD's Assistant General Manager and Chief Engineer.

The August 8, 1979, letter from the NRC to all Power Reactor Licensees,(except Humbolt Bay) requested:

1.

A verification by analysis of the capacity and capability of Rancho Seco's offsite power system and the onsite electrical distribution system.

2.

A verification, by test, of the adequacy of Ra.ncho Seco's offsite power system and the onsite electrical distribution system.

3.

A review of Rancho Seco's electrical power supply system to determine if there are any conditions which could result in the simultaneous or consequential loss of both required cir-cuits to the offsite network to determine if any potential exists for violation of GDC-17 in this regard.

4.

Immediate remedial action and prompt notification of the Commission with written followup in the event of a violation or potential violation of GDC-17 or voltage requirements of safety loads.

The responses to these requests are listed below:

1.

The analysis of Rancho Seco's offsite power system and the onsite electrical distribution system demonstrates that the District's existing systems are adequate. To achieve this adequacy, it was necessary to change the loading sequence of the diesel generator room supply and exhaust fans from Block Two to Block Three. The setpoint on the inverse-time undervoltage relays was raised to 3744V (90 percent of 4160V) to assure equipment protection. Special orders have been issued to the plant operators to describe operator actions at degraded voltage conditions (Reference SO 5-79).

Subsequent analysis, taking into account proposed relay type changes and accuracy considerations discussed in Enclosure II, have determined that the 1

modifications listed below should be implemented.

Set undervoltage relay dropout at 3771V (91 percent of 4160V).

a.

b.

Set overvoltage relay pickup at 4580V.

Limit plant operation if the switchyard voltage is less than 218kV.

c.

d.

Block' automatic condensate pump starting-on a turbine trip to assure that safety equipment terminal voltage does not dip below the minimum required.

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.c Since the normal switchyard voltage range is 221kV to 239kV, neither the setpoints nor operational limits will be affected by normal voltage variations. The voltage dip during condensate pump starting, although 1

undesired, does not prevent the safety equipment from perfonning their required functions since the dip is of a short duration.

.A discussion of each modification is included in the response to guidelines contained in Enclosure I, Part B.

The applicable guideline for each modification is listed below:

Modification Reference Guideline a

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b 11 c

6, 9 and 10 d

9 The above modifications insure the adequacy of the Rancho Seco offsite power system and the onsite electrical distribution system to supply safety-related loads under the conditions described in Enclosure I, Part B.

The capacity of the transformers to continuously carry the expected i

load demand is illustrated in Sketches 2-7 of Enclosure I, Part B.

2.

The District's method of determining the adequacy of the offsite power system and onsite electrical system is based on a combination of test data and analysis.

The load data for the Class IE 4.16-kV system and safety motors greater than 60 hp was based on actual field measurements (under s0mulated accident conditions, if applicable). The impedance data for transformers was based on factory test results.

If test data was not available, the data used in the analysis was based on conservative engineering assumptions. Refer to Enclosure I, Part B l1 Response to Guideline 13 for a discussion of the assumptions made in the analysis. The analytical results were obtained using a computer load flow program. The program has been checked to verify its accuracy. It solves nodal admittance network equations by the accelerated Gauss-Seidel method.

A single full scale system test will not provide sufficient data to justify or verify the analytical methods and assumptions used in the analysis.

It is not practical and in some cases not possible to simul-taneously produce, in a test, all the conservative assumptions made in the analysis. Listed below are three examples of assumptions made in the analysis that are impractical to implement in a test:

The analysis assumes 214kV in the Rancho Seco switchyard.

a.

The normal operating voltage range for the switchyard is 1

221kV to 239kV. The District cannot lower the switchyard I.A-2 l

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voltage to 214kV without seriously affecting the grid.

Simulation of a degraded switchyard voltage condition by raising the startup transformer taps is not feasible since i

the transformers are already operating at the maximum tap setting.

b.

The analysis assumes full operating load on the non-Class IE buses. The test would have to be run with the unit shut down. In this condition it is not possible to obtain full load on the non-safety related equipment. For example, the condensate pumps would be operating at miniflow conditions instead of rated flow and load assumed in the analysis.

The analysis assumes all safety related loads are operating c.

at maximum design conditions encountered during a loss of coolant accident (LOCA). The upper dome air circulators and the reactor building emergency air coolers would be operating during a test at loads less than the load assumed in the analysis since the reactor building atmosphere would not be at a LOCA condition.

Therefore, it is not practical to perform a test at the conditions assumed in the analysis. The use of a proven computer program with actual measured test data combined with conservative assumptions provide the District with assurance that the offsite power system and onsite distribu-tion systems are adequate.

3.

The District has completed a review of Rancho Seco's Il electrical po,wer supply for compliance to GDC-17. The cases analyzed indicated that the District's electrical power supply system is in compli-ance with GDC-17.

Il For information on the analysis performed for compliance to GDC-17 refer to Enclosure I, Part C.

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The District has implemented loading sequence changes, relay setpoint changes and issued special orders.

The modifications proposed (a thru d) will be implemented after 1

the District receives NRC approval and the new relay types are installed.

Enclosure I, Part B is the District's response to the Guidelines contained in Enclosure 2 of William Gammill to Power Leactor Licensee's letter dated August 8, 1979.

Enclosure I, Part C is an evaluation of the District's offsite Il power supply system for compliance to GDC-17.

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ENCLOSURE I PART B RESPONSE TO GUIDELINES LISTED IN ENCLOSURE 2 NRC'S WILLIAM GA.'C!ILL TO PC'aT.R REACTOR LICENSEES, LETTER DATED AUGUST 8, 1979 e

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Listed below is a response to each guidel'ine listed in Enclosure 2

" Guidelines for Voltage Drop Calculations" of NRC's, William Gammill to Power Reactor Licensees, letter dated August 8, 1979.

GUIDELINE #1

, Separate analyses should be performed assuming the power source to safety buses is (a) the unit auxiliary transformer; (b) the start-up transformer; and (c) other available connections to the offsite network one by one assuming the need for electric power is initiated by (1) an antici-pated transient (e.g., unit trip) or (2) an accident, whichever presents the largest load demand situation.

RESPONSE TO GUIDELINE #1 The Rancho Seco electrical power system is described by the attached single line diagram (Sketch 1).

The District's analysis was performed assuming the power source for the safety buses was obtained with the following olant configurations.

(Case 1 is the normal operating configuration).

Case Description Reference Sketches lA Bus 4A on start-up transformer #1 2

1B Bus 4B on start-up transformer #2 3

2 Buses 4A and 4B on start-up transformer #1 4

3 Buses 4A and 4B on start-ur transformet #2 5 & 8-14 l1 4A Bus 4A on start-up transformer #2 6

4B Bus 4B on start-up transformer #1 7

Sketches 2-7 illustrate the steady-state condition immediately following completion of automatic load sequencing due to safety features actuation. Starting conditions are illustrated for' Case 3 only which, due to the heavy loading on start-up transformer #2, represents the limiting i

Sketches 8-13 illustrate the minimum system voltages occurring case.

during automatic load sequencing and Sketch 14 illustrates the minimum system voltages that could occur should the largest 4.16-kV load, a conden-sate pump, be manually started after completion of automatic load sequencing.

The unit auxiliary transformers are not an available source for the safety busas as indicated by Sketch 1; the above cases are all the l1 connections available to the safety buses from the offsite network.

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O The transient assumed in the analysis is a loss of coolant accident (LOCA) with the reactor at 100 percent power coincident with a turbine generator trip and a safety features actuation signal (SFAS) to both redundant safety systems. This transient produces the maximum load on the start-up transformers.

A *.urbine generator trip will place non-safety buses 6A and 6B on start-up transformer #1 and non-safety buses 4C, 4D,'4E1 and 4E2 on start-up transformer #2.

GUIDELINE #2 For multi-unit stations a separate analysis should be performed for each unit assuming (1) an accident in the unit being analyzed and simultaneous shutdown of all other units et that station; or (2) an anti-cipated transient in the unit being analyzed (e.g., unit trip) and si=ul-taneous shutdown of all other units at that station, whichever presents the largest load demand situation.

RESPONSE TO GUIDELINE #2 This guideline is not applicable to Rancho Seco. Rancho Seco is a single unit station.

GUIDELINE #3 All actions the electric power system is designed to automatically initiate should be assumed to occur as designed (e.g., automatic bulk or sequential loading or automatic transfers of bulk loads from one transformer to another).

Included should be consideration of starting of large non-safety loads (e.g., condensate pumps).

RESPONSE TO GUIDELINE #3 The District's analysis assumed the following automatic actions occur coincident with the LOCA/ turbine generator trip:

(a) Buses 6A and 6B transfer from unit auxiliary transformer #1 to start-up transformer #1.

Il (b) Buses 4C, 4D, 4El and 4E2 transfer from unit auxiliary transformer #2 to start-up transformer #2.

(c) Heater drain p2mps trip due to loss of net positive suction head.

(d) The safety buses are sequentially loaded. The loading sequence is indicated in Table 1.

Time zero is when the SFAS signal is received.

Large non-safety loads are not started coincident with the event.

Automatic starting of the condensate pump, for example, is blocked on a 1

turbine trip.

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GUIDELINE #4 Manual load shedding should not be assumed.

RESPONSE TO GUIDELINE #4

, Manual load shedding was not assumed in the District's analysis.

GUIDELINE #5 For each event analyzed, the maximum load necessitated by the event and the mode of operation of plant at the time of event should be assumed in addition to all loads caused by expected automatic actions and manual actions permitted by administrative procedures.

RESPONSE TO GUIDELINE #5 The event the District analyzed provided the maximum load on the start-up transformers.

The analysis assumed automatic starting of safety equipment due l1 to an STAS signal. The safety equipment automatic loading sequence is indicated in Table 1.

It was assumed that the train B auxiliary feedwater pump was manually started simultaneously with the automatically started Train A 1

auxiliary feedwater pump during the fourth automatic sequential loading block. Manual starting is an action permitted by operating procedures.

GUIDELINE #6 The voltage at the terminals of each safety load should be calculated based on the above listed considerations and assumptiens and 1

based on the assumption that the grid voltage is at the " minimum expected value". The " minimum expected value" should be selected based on the least of the following:

l The minimum steady-state voltage experienced at the connec-a.

tion to the offsite circuit.

b.

The minimum voltage expected at the connection to the off-site circuit due to the contingency plans which may result in reduced voltage from this grid.

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The minimum predicted grid voltage from grid stability analysis (e.g., load flow studies).

In ths report to NRC on this matter the licensee should state planned actions, including any proposed " Limiting Conditions for Operation" l

for Technical Specifications, in response to experiencing voltage at the l

connection to the offsite circuit which is less than the " minimum expected l

value". A copy of the plant procedure in this regard should be provided.

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RESPONSE TO GI'IDELINE #6 The " minimum expected value" of the grid voltage is 214kV and is based on the minimum steady-state voltage experienced at the connection to the offsite circuit. The value of the voltages at the safety buses and at the most distant (electrically) load during this condition is shown on Sketches 2 through 14 for the cases the District analyzed.

Refer to Attachment 1 of Enclosure II for a description of

" Limiting Conditions for Operation" being considered for inclusion in the Technical Specifications.

The District will modify operating procedures to incorporate the operating constraints described in Attachment 1 of Enclosure II when 1

the proposed design, and proposed technical specifications are approved by the NRC and the relays described in Enclosure II are installed.

Special orders have been issued to the plant operators to described operator action at degraded voltage conditions when the switch-yard voltage is less than 216kV. The special order is available for review at Rancho Seco.

GUIDELINE #7 The voltage analysis should include documentation for each condition analyzed of the voltage at the input and output of each trans-former and at each intermeciate bus between the connection to the offsite circuit and the terminals of each safety load.

RESPONSE TO GUIDELINE #7 Sketches 2-14 indicate the voltages at each intermediate bus l1 between the connection to the offsite circuit and the terminals of the safety loads with the lowest steady-state voltage.

GUIDELINE #8 The analysis should document the voltage setpoint and any

' Laherent or adjustable (with nominal setting) time delay for relays which (1) initiate or execute automatic transfer of loads from one source.to another; (2) initiate or execute automatic load shedding; or (3) initiate l

or execute automatic load sequencing.

RESPONSE TO GUIDELINE #8 The District has overvoltage and undervoltage trip relays which will (1) initiate an automatic' transfer of the safety buses from the offsite power source to the diesels and (2) initiate automatic load shedding.

Automatic load sequencing is initiated by an SFAS signal and not by the voltage relaying.

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I The setpoint for the undervol' age relay is documented in the response to Guideline #10.

The setpoint for the overvoltage relay is documented in the response t: _aideline #11.

GUIDELINE #9 The calculated voltages at the terminals of each safety load should be compared with the required voltage range for normal operation and starting of that load. Any identified inadequacies of calculated voltage require immediate remedial action and notification of NRC.

RESPONSE T,0 GUIDEI,INE 49 The District compared the calculated terminal voltages to that required for cormal operation and starting of each safety load. The analysis identified inadequacies. To correct the inadequacies, the follow-ing modifications were implemented.

1.

Automatic sequential loading of the diesel-generator supply and exhaust fans was changed from Block 2 to Block 3

(!able 1).

This change assured that an acceptable level of terminal voltage would be available for all safety motors being started.

2.

Special order 5-79 was issued to describe operator actions when the switchyard voltage is less than 216kV.

The analysis demonstrated that for this voltage level, or 1

higher, the terminal voltage at any safety motor would never be less than its minimum required starting voltage.

Subsequent analyses, taking into relay accuracy considerations discussed in Enclosure II, demonstrate that reactor operation can only be permitted down to 218kV. These analyses also assumed that automatic condensate pump starting is blocked on a turbine trip.

Only automatic starting is blocked, the pumps continue to operate if they have been running prior to the event; all studies conservatively assumed that the condensate pumps were running at normal operating load. Condensate pump starting concurrent with auto-matic starting of safety equipment could cause the safety equipment termi-nal voltage to dip below the minimum required voltage during the condensate pump starting interval.

The justification for each type of load to operate at O.e calcu-lated voltages indicated on sketches 2 through 14 is given below. This analysis assumes that the modification blocking auto starting of the conden-1 s4te pumps has been implemented,.

Motors - The voltage data shown on sketches 2-7 show that some safety-related motors could be operating below the nominal 90-percent minimum steady-state voltage stipulated by NEMA MG 1.

Generally, the l

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motors operating below this voltage are driving 11 ads that are less than their nameplate horsepower. The District has performed an analysis that indicates continuous operation at the voltage indicated is practical with no net loss in motor life since the increased heating effects due to the reduced voltage are offset by the lighter than nameplate load. For excep-tions, where the motors are operating at a high load demand factor, motor life will be expended at a greater rate. However, this increased rate is acceptable since the total life expended is negligible due to the limited time of operation anticipated at the reduced voltage level.

(E.g.: For a fully loaded motor with Class B insulation, the life expended during y

4-hours of operation - actual duration of the degraded voltage condition experienced - at 85 percent voltage is equivalent to 9 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br /> of operation at 90 percent voltage *.)

The District's safety-related motors were qualified to start at 75 percent of rated voltage. Sketches 8-14 show that voltage above this l1 value will be available during starting periods and the motors will start.

Motor-Operated Valves - Motor-operated valves are capable of operating properly down to at least 368V (.80 of 460V) which is below the 1

minimum voltage calculated for the valve motors.

Battery Chargers - The battery chargers were factory tested at rated load, at 140VDC, with an input voltage of 432 volts (.94 of 460V).

The District has performed additional tests to verify that the battery chargers can operate at the minimum calculated voltage of 387 volts (.84 of 1

460V).

Heat Tracing System - The heat tracing system for the safety-related pipes, tanks and valves containing boric acid consists of strip-type resistance heating tape, transformers, and thermostats. At the calculated minimum voltage (394V) the heat tracing system is capable of providing sufficient heat to maintain the temperature above crystallization,

t for the expected (4 hr.) duration.

MCC Control Circuits - The District has verified by field test that the components in the control circuits of the MCC's can ba operated at the minimum calculated voltage.

Overcurrent Protection - The switchgear overcurrent protective 1

devices have been analyzed to verify that tripping of safety-related loads will not occur. Analysis of MCC overload protection is still being performed.

GUIDELINE #10 For each case evaluated the calculated voltages on each safety bus should be compared with the voltage-time settings for the undervoltage relays on these safety buses. Any identified inadequacies in undervoltage relay settings require Lamediate remedial action and notification of NRC.

• This analysis assumes that for each 10*C temperature rise, life ia 1

expended at twice the rate.

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i RESPONSE TO GUIDELINE //10 In the October 17, 1979 analysis report, the District compared the voltage-time settings of the undervoltage relays with the voltage requirements of the safety equipment. This comparison identified a poten-tial inadequacy. The District changed the undervoltage relay setpoint from 1

85 to 90 percent of 4160V to correct the inadequacy.

Subsequent analyses, taking into account proposed undervoltage relay type changes and accuracy considerations to implement NRC's position 1 (see Enclosure II), ongoing power system modifications and proposed modi-fications, indicate that an increase in the undervoltage relay setting to 3771V (0.91 of 4160V), which is equivalent to a switchyard voltage of 216 kV, is desirable.

With this setting and the switchyard at 214 kV the steady state voltages on the 4160 volt buses 4A and 4B will be less than the relay setpoint.

(Refer to Sketches 2 through 7 for steady state voltages). The analysis indicates that 214 kV is the minimum experienced voltage and the minimum voltage that the offsite power system is capable of supplying the onsite distribution system. However, the proposed relay setting is justifi-able when the +1 percent relay tolerance is considered. The table below indicates the relay setpoint, dropout voltage limits based on the relay tolerance and the equivalent switchyard voltage.

4160 Volt Bus Switchyard 3'

Voltage Voltage Maximum' Dropout Voltage 3827 (.92 of 4160) 218 kV Setpoint 3771 (.91 of 4160) 216 kV Minimum Dropout Voltage 3731 (.90 of 4160) 214 kV The proposed relay setpoint provides adequate prot.ection for safety equipment since the minimum dropout voltage is equal ~to the m.uimum voltage the equipment is qualified to operate at.

The setpoint will uet cause spurious inadvertent operation since the maximum dropout voltage is below the normal operating voltage range.

GUIDELINE (111 To provide assurance that actions taken to assure adequate voltage levels for safety loads do not result in excessive voltage, assuming the maximum expected value of voltage at the connection to the offsite circuit, a determination should be made of the maximum voltage expected at the terminals of each safety load and its starting circuit. If this voltage exceeds the maximum voltage rating of any item of safety equipment immediate remedial action is required and NRC shall be notified.

I.B RESPONSE TO GUIDELINE #11 1

The District has performed a review of data on voltage in the Rancho Seco switchyard. Based on this review, the maximum expected switch-yard voltage is 239kV. For the existing transformation ratios (Sketches 2-7) and assuming a no load condition, the maximum voltage is on the 4.16-kV system and on the 480-V system. This voltage is equal to or less than the maximum voltage rating of any safety equipment except the 460-V motors and motor-operated valves (MOV's).

An analysis for each type of safety-related equipment is listed below.

1 This analysis was based on the maximum steady-state vc1tage allowed (4626V) by the overvoltage protection relays since this voltar: is higher than the maximum expected voltage and represents the permi sible extreme.

Motors & Motor-Operated Valves - The 4160-volt motors are designed to operate at a maximum voltage of volts which is less than the maximum calculated voltage of 4626 volts (111 percent of 4160V). The 460-volt motors and motor-operated valves have a maximum voltage rating which is less than maximum calculated voltage of 521 volts (113 percent of 460V).

Operation of the motors and motor-operated valves at these voltages is acceptable for the following reasons:

a.

Operation at the maximum expected switchyard voltage is an extreme condition that is only expected to occur on rare occasions and for short durations.

(Note - Operating time of MOV's during this condition is further limited by their inherent short-time operating duty.)

b.

The maxinum calculated voltage condition conservatively assumes that there is absolutely no auxiliary load operating (i.e:

,o voltage drep) when the maximum expected switchyard voltage occurs.

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The maximum calculated voltage condition conservatively assumes operation at two-percent above the maximum expected voltage (i.e., it allows for relay inaccuracy).

d.

The motors and motor-operated valves will be operating at less than 110 percent of rated voltage when equipment opera-tion is initiated by an SFAS due to voltage drop in the electrical system.

e.

The maximum voltages calculated will produce a torque that is only slightly greater than the torque that would be produced at the nominal maximum voltage of 110 percent.

However, due to voltage drop during starting and operation of a motor, the maximum voltage at the terminals of the motor and the increase in torque will be reduced. The MOV circuits I.B-8 :

have minimal voltage drop during starting and operation.

Therefore, it is possible for the MOV's to produce a slightly greater torque than that produced at 110-percent voltage.

However, operation of the MOV is limited by a torque switch.

Therefore, the excessive torque is not applied to the valve and operation during the overvoltage condition is acceptable.

f.

The motor manufacturers contacted did not expect any adverse effect to their equipment due to the slight overvoltage levels being considered. Operating instructions published by one motor manufacturer

• indicate the following character-istics for operation of their motors above rated voltage.

Percent of Full Load Percent of Full Load Percent Percent Temp.

1 Rated Voltage Efficiency Current Torque Rise 100 100 100 100 110 101.5-102 93 121

(-)3 to (-)4'C 120 100+

89 144

(-)5 to (-)6*C From the above data, it is indicated that motors are not particularly sensitive to overvoltage. Efficiency at 120-percent voltage, for example, is even better than at rated voltage.

g.

Overvoltage alarm relaying is being added to the 480-V safety buses to alert the operator should an unusual over-voltage condition (greater than 110 percent of 460V) occur.

Battery Chargers - The battery chargers are qualified to operate at full load with a maximum input voltage of 528 volts (114 percent of 460V) which is above the maximum calculated voltage of 521 volts.

Il Heat Tracing System - The heat tracing system for the safety-related pipes, tanks, and valves containing boric acid consists of strip type resistance heating tape, transformers and thermostats. All of this equipment should be capable of operating at the maximum calculated voltage 1

of $21 volts.

MCC Control Circuits - The control voltage for each 480-volt MCC

' feeder circuit is obtained from a feeder line tap through a 480 to 120 volt stepdown control power transformer. The maximum voltage rating for the most limiting component is 132 volts. The maximum calcu'.ated voltage on t

the component is 130 volts which is less than the maxim"2 voltage rating.

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• Installation, Operation and Care of " Duty Master" Nuclear Service Class IE

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Integral Horsepower Induction Motors, Reliance Electric Instruction Manual 1

i B-3645, December, 1977.

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Overvoltage Relav Setpoint - In case the maximum calculated voltage is exceeded the analysis indicates that the District's overvoltage relay should be set at 4580 volts (110 percent of 4160V) which, assuming a no load condition, corresponds to a maximum of 112 percent of 460 volts on the 480-V system. This setpoint is equivalent to a voltage of 242kV in the switchyard. With this setpoint, the relay will protect the safety-related equipment The relay is set a higher voltage than the maximum expected voltage and will not cause spurious trips.

It has a definite time delay set at 3 seconds and operates in series with an external time delay relay set at 0.5 seconds.

GUIDELINE #12 Voltage-time settings for undervoltage relays shall be selected so as to avoid spurious separation of safety buses from offsite power during plant startup, normal operation and shutdown due to startup and/or operation of electric loads.

RESPONSE TO GUIDELINE #12 The setting for the undervoltage relay was selected to assure protection of the safety equipment as explained in the response to Guide-line #10. The setting selected avoids spurious separation of the safety buses from offsite power during plant startup, normal operation and shut-1 down due to startin3 and/or operation of loads providing the switchyard voltage is above 218kV. This level is below the 221-kV voltage defined as the normal minie zm voltage for the switchyard.

GUIDELINE #13 Analysis documentation should include a statement of the assump-tions for each case analyzed.

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RESPONSE TO GUIDELINE #13 For the cases analyzed the District's assumptions have been included. The following statements describe the general assumptions used in the computer analysis.

a.

The computer modeled running loads and motors as having a constant volt-ampere characteristic.

b.

Starting motors are modeled as having a constant impedance characteristic.

c.

The load data for the non-Class IE 4.16-kV system (and subsystems) and safety motors greater than 60 hp was based on actual field measurements (under simulated accident condi-tions, if applicable); for other loads, field test data, manufacturers' data and typical motor / load data were utilized.

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d.

Impedance data for transformers was based on the actual nameplate or test report data.

e.

Impedance data for bus duct was based on manufacturers published data.

f.

Impedance of cables was modeled for Class IE 4160-480V 3

transformer primary and secondary cables, MCC feeders and worst-case loads. Other loads were lumped together at their supply point.

g.

Cable impedance was calculated based on the actual cable length pulled and cable type.

3 h.

The impedance of switching equipment (switchgear, breakers, etc.) is negligible and was not included.

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TABLE 1 NUCLEAR SERVICE BUS (EACH) AUTOMATIC LOADING SEQLT.NCE Acc.

Offsite Power System Time i

Loading Sequence Quantity Sec.

Description Block 1 - Energize at:

0 + 0 see 1

0.9 Decay heat pump (low pressure inj.)

2 5.3 Reactor Building upper dome air circulators 1

1 1

Motor control center (miscellaneous load) 0 + 3 sec*

1 0.7 Makeup pump (high pressure inj.)

Block 2 - Energize at:

0 + 16 sec 2

4.2 Reactor Building Emer-gency air cooler 1

1 0.6 Nuclear service cooling water pump Block 3 - Energize at:

0 + 26 see 1

0.6 Nuclear service raw water Pump 2

5.8 Diesel generator room supply and exhaust fans Block 4 - Energize at:

1 3

Auxiliary Feedwater Pump 1

(Train A only) 0 + 36 see Block 5 - Energize at:

0 + 300 see 1

0.5 Reactor Building spray system including pump

• Start of the make-up pump (high pressure inj ) is delayed 3 seconds to allow its bearing lube oil flow to get started.

I.B-12

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-J

4 SRI!CH 2 CASE 1A BUS 4A ON STARTUP TRANSFORMER NO.1 STEADY STATE AFTER SEQUENTIAL LOADING 214 KV SWITCHYARD VOLTAGE 220 KV SWITCHYARD STARTUP TR ANS. N O.1 214 KV 221 - 12.47 - 6.9 KV H

TAP - 230 KV ww H WINDING - 38.6 MVA X WINDING - 10 MVA Y WINDING - 34.6 MVA 5.6 MVA X

Y TO 6.9 KV SUSSES SA & 68 TO CANAL _PUMPtNG SUB 273 MVA 11.5 KV w

y NUCLEAR SERVICE SUPPLY TRANSFORMER 7.5 M A ESF SYSTEM 178 MVA 4160 V BUS 4A 3922 V

(.94 0F 4160 V)

STATION SERVICE w

w TRANS. X34A 3910 V 4160-480V MOTOR mm

(.94 0F 4160 V)

TAP-4260V 1.12 MVA J7 MVA o

480 V BUS 3A 421 V

(.910F 460 V)

OTOR 0 0F 460 V) 480 V MCC 2A1 419 V (J10F 460 V) 407 V M01wA

(.89 0F 460 V)

NOTES:

1. MOTORS CONNECTED TO A 4160V BUS ARE RATED 4160V. THE 480V SYSTEM MOTORS ARE RATE 0 460V.

2. THE MOTO RS SHOWN ARE ELECTRICALLY THE MOST DISTANT MOTORS FROM THE SUSSES SHOWN. ALL OTHER MOTORS ON THESE BUSSES WILL OPERATE AT A VOLTAGE BETWEEN THAT OF THE SUS. AND THAT OF THE MOST DISTANT MOTOR.

I.B-14 l

m

SKE!Cli 3 CASE 18 BUS 48 ON STARTUP TRANSFORMER NO. 2 STEADY STATE AFTER SEQUENTIAL LOADING 214 KV SWITCHYARD VOLTAGE 220 KV SWITCHYARD 214 KV H

STARTUP TRANSFORMER NO.2

%w 221 - 4.36-4.36 KV TAP -230 KV

&M&T H WINDING - 42.6 MVA Y

Z Y WINDING - 24 MVA Z WINDING - 22.6 MVA T0 4160 V BUSSES 4E1 & AE2 -

14.0 MVA 14.1 MVA TO 4160 V BUSSES 4C & 40 3734 V ESF SYSTEM 4160 V BUS 48 3790 V

( 910F 4160 V)

STATION SERVICE D N 160-480 V MOTOR (.778Y 3

' ' ' TAP - 4260 V 910F 4160 V 1.12 MVA 1.03 MVA o

480 V BUS 38 404 V

(.88 0F 460 V) l 396 V MOTOR

(.86 0F 460 VI i

480 V BUS 281 402 V

(.87 0F 460 V)

)

i MOTOR 396 V NOTES:

(.86 0F 460 V)

1. MOTORS CONNECTED TO A 4160V BUS ARE RATED 4160V. THE 480V SYSTEM MOTORS ARE RATE 0 460V.

2. THE MOTORS SHOWN ARE ELECTRICALLY THE MOST OlSTANT MOTORS FROM THE BUSSES SHOWN. ALL OTHER MOTORS ON THESE BUSSES WILL OPERATE AT A VOLTAGE BETWEEN THAT OF THE BUS, AND THAT OF THE MOST DISTANT MOTOR.

I.3-15 e e v=

-,n

SKETCH 4 CASE 2 SUS 4A & 4B ON STARTUP TRANSFORMER NO.1 STEADY STATE AFTER SEQUENTIAL LOADING 214 KV SWITCHYARD VOLTAGE 220 KV SWITCMYARD

~

STARTUP TR ANS. NO.1 214 KV 221 - 12.47 KV H

TAP-230 KV ww H WINDING - 38.6 MVA ymym X WIN 0 LNG - 10 MVA Y WINDING - 34.6 MVA Y

8.30 MVA X

TO 6.9 KV 8USSES 6A & 68 m

TO CANAL PUMPlNG SUB 11.4 ?.V W MVA WW NUCLEAR SERVICE m

% SUPPLY TRANSFORL ER 12.47-4.36 KV 6.89 MVA 7.5 MV A o

4160 V BUS 4A ESF SYSTEM 4160 V BUS 4E 3805 V 3801 V l 910F 4160 VI

(.310F 4160 V) 3789 V

(.910F 4160 VI STATION SERV.

STATION SERV.

TR ANS. X43A ww 3793V MOTOR TR ANS. X438 W#

M3 TOR 4160 - 480 V ym

(.910F 4160 V) 4160 - 480 V r1-O TAP - 4260 V TAP - 4260 V d

1.12 MVA

.97 MVA 1.12 MVA

.37 MVA 480 V BUS 3A 480 V BUS 38 406 V 407 V

(.88 0F 460 VI

(.88 0F 460 V) 399 Y

(.87 0F 460V)

MOTOR M010R F40V) 480 V MCC 2A1 480 V MCC 281

~

405 V 406 V

(.88 0F 460 V)

(.88 0F 460 V) 399 V

(.87 0F 460 V)

MOTOR MOT 01

(.85 OF 460) iOTES:

1. MOTORS CONNECTED TO A 4160V BUS ARE RATED 4160V. THE 48CV SYSTEM MOTORS ARE RATED 460V.

2. THE MOTORS SHOWN ARE ELECTRICALLY THE MOST OISTANT MOTORS FROM THE 8USSES SHOWN. ALL OTHER MOTORS ON THESE BUSSES WILL OPERATE AT A VOLTAGE BETWEEN THAT OF THE BUS. AND THAT OF THE MOST DISTANT MOTOR.

I.3-16

~ ' ' '

c.

SmcH 5 CASE 3 BUS 4A & 4B ON STARTUP TRANSFORMER NO. 2 STEADY STATE AFTER SEQUENTIAL LOADING 214 KV SWITCHYARD VOLTAG E 220 KV SWITCHYARO 214 KV Hww STA RTU P TR ANS. N O. 2 m

,q m m 221 - 4.36-4.36 KV TAP -230 KV Y

Z H WINC!NG -42.6 MVA T0'4160 V BUSSES 4E1 & 4E2 Y WINDING - 24 MVA Z WIN 0!NG - 22.6 MVA 14.1 MVA 17.0 MVA

~

TO 4160 V BUS 4C TO 4160 V BUS 40 3745 V 3740 V

~

ESF SYSTEM 4160V BUS 4A 4160 V BUS 48 3743 V l

3737V

(.90 0F 4160 V)

(.30 0F 4160 V)

STATION SERV. WW STATION SERV.

TRANS X43A TR ANS. X43B MOTOR 3731 V 4160 - 480 V 4160 - 480 V MOTOR TAP - 4260 V

(.90 0F 4160 V)

TAP - 4230 V 1.12 MVA 1.12 MVA 3725 V J7 MVA

(.S0 0 F 4160 V)

_g7 y 480 V BUS 3A 480 V BUS 3B 339 V 339 y

(.87 0F 460 V)

(.h* OF 460 V)

MOTOR 3

85 0F 460 V) 391 V

(.85 0F 460 V) 480 V MCC 2A1 480 V MCC 2B1 397 V 398 V

(.86 0F 440 V)

(.87 0F 460 V)

OTOR OTOR F 460 V)

NOTES:

38I

(.85 0F 460 V)

1. MOTORS CONNECTED TO A 4160V 8US ARE RATED 4160V. THE 480V SYSTEM MOTORS ARE RATED 460V.

2. THE MOTORS SHOWN ARE ELECTRICALLY THE MOST DISTANT MOTORS FROM THE BUSSES SHOWN. ALL OTHER MOTORS ON THESE BUSSES l

WILL OPERATE AT A VOLTAGE BETWEEN THAT OF THE BUS, AND THAT OF THE MOST DISTANT MOTO R.

I.3-17

SKETCH 6 CASE 4A BUS 4A ON STARTUP TRANSFORMER NO. 2 STEADY STATE AFTER SEQUENTIAL LOADING 214 KV SWITCHYARD VOLTAGE 220 KV SWITCHYARD 214 KV H

STARTUP TR ANSFORP.!ER NO 2 wW 221 - 4.36-4.36 KV

&m mm TAP - 230 KV Y

Z H WINDING - 42.6 MVA

{g,lN W

NG - M TO 4160 V BUSSES 4E1 & 4E2 gDINg _2 S M A 13.6 MVA TO 4160'V BUS P.

TO 41S3 V BUS *O 3823 V

~

ESF SYSTEM

_160 V BUS 4A 4

38G1 V

(.310F 41SO /)

STATION SERV.

4160 8V WW TAP-4250 V

&T 37I9 v MOTOR 1.12 MVA L910F 4160 V)

J7 EVA 480 V BUS 3A 406 V

(.88 0F 460 V) 400 V MOTOR I.87 0F 460 V) 480 V MCC 2A1 404 V

(.88 0F 460 V)

MOTOR (392 V

.85 0F 460 V)

N 3 TIS-

1. NOTORS CONNECTED TO A 4160V SUS ARE RATED 4160V. THE 440V SYSTEM MOTORS ARE RATED 460V.

2. THE MOT 3RS SriOWN ARE ELECTRICALLY THE MOST DISTANT MOTORS 7 ROM THE BUSSES OHOWN. ALL OTHER MOTORS ON THESE BUSSES WILL OPERATE AT A VOLTAGE BETWEEN THAT OF THE BUS, AND THAT OF 'HE MOST OlSTANT MOTOR.

1 I.3-18 W=a e

SKETCH 7 CASE 4B BUS 4B ON STARTUP TRANSFORMER NO.1 STEADY STATE AFTER SEQUENTIAL LOADING 214 KV SWITCHYARD VOLTAGE 220 KV SWITCHYARO 214 KV STARTUP TR ANS. N O.1 221 - 12.47-4.3 KV H

TAP - 230 KV ww H WINDING - 38.6 MVA ym,,,,,3 X WINDING - 10 MVA X

Y Y WINDING. 34.6 MVA TO 8.9 KV BUSSES 6A & 68 5.64 MVA TO CAN AL PUMP!NG SUB 27.9 MVA 11.47 KV NUCLEAR SERVICE R

JJ SUPPLY TRANSFORMER mm 12.47 - 4.36 KV 7.5 MVA 3.53 MVA o

ESF SYSTEM 4160 V SUS 48 3918 V

(.94 0F 4160 V)

STATION SERV. w w T 3906 V TRANS X438 mm MOTOR

~

4160-480 V TAP-4260 V 1.03 MVA 480 V EUS 38 419 V (J10F 480 V) 412V

(.90 0F 460 V)

MOTOR 480 V MCC 281 418V

(.910F 480 V) 412 V NOTES:

MOTOR

1. MOTORS CONNECTED TO A 4180V BUS ARE RATED 4160V. THE 480V SYSTEM MOTORS ARE RATED 460V.

2. THE MOTORS SHOWN ARE ELECTRICALLY THE MOST DISTANTiiOT08tS FROM THE LUSSES SHOWN. ALL OTHER MOTORS ON THESE BUS $ES-WILL OPERATE AT A VOLTAGE BETWEEN THAT OF THE BUS, AND THAT OF THE MOST OlSTANT MOTOR.

I.5-19

S H8 CASE 3

' BUS 4A & 48 ON STARTUP TRANSFORMER NO. 2 VOLTAGE DURING BLOCK LOADING OF EMERGENCY BUSSES (BLOCK 1., T = 0 SEC.)

START DECAY HT REMOVAL PP. RB UPPER DOME FANS AND MISCELLANEOUS MCC LOADS 220 KV SWITCHYARD 214 KV STARTUP TRANSFORMER NO 2 H

221 - 4.36-4.36 KV

• ^n*J TAP - 230 KV H WIN 0 LNG -42.6 MVA TO 4160 V BUSSES 4E1 & 4E2 Y WINDING - 24 MVA y

Z Z WINDING - 22.6 MVA

_ TO 4160 V BUS 4C TO 4160 V BUS 40 3739 V 3734 V

~

ESF SYSTEM 4160 V BUS 4A 4160 V BUS 4B 3738 V 3731 y

(.90 0F 4160 V)

(.30 0F 4160 V) m8 V

(.90 0F 4160 V)

STAT!ON SERV.

TR ANS. X43A 3735 V STATION SERV.

(STARTING) 4160 - 480 V

(.90 0F 4160 V)

TR ANS. X438 WW

]

TAP - 4250 V MOTOR (STARTING) 4160 - 480 V MOTOR) 1.12 MVA TAP - 4260 V 1.12 MVA

~

480 V BUS 3A 480 V BUS 38 398 V 395 V

(.87 0F 460 V)

(.86 0F 460 VI i

==

480 v MCC 2A1 480 V MCC 281 393 V 381 V

(.85 0F 460 V)

(.85 0F 480 V) 363 V 376 V MOTOR (.79 0F 460 V)

(.82 0F 460 V) MOTOR (STARTING)

(STARTING)

NOTES:

1. MOTORS CONNECTED TO A 4160V BUS ARE RATED 4160V. THE 440V SYSTEM MOTORS ARE RATED 460V.

2. THE MOTORS SHOWN ARE ELECTRICALLY THE MOST OlSTANT MOTORS FROM THE BUSSES SHOWN. ALL OTHER MOTORS ON THESE SUSSES WILL OPERATE AT A VOLTAGE SETWEEN THAT OF THE BUS. AND THAT OF THE MOST DISTANT MOTOR.

I.B-20 a-.

SCCH 9

)

CASE 3 BUS 4A & 4B ON STARTUP TRANSFORMER NO. 2 VOLTAGE DURING BLOCK LOADING OF EMERGENCY BUSSES (BLOCK 1.,T = 3 SEC.)

START HP INJECTION PP, THE RB DOME FANS CONTINUE STARTING 220 KV SWITCHYARO 214 KV STARTUP TR ANSFORVER NO 2

,,--H, 221 -4.36-4.36 KV

. AP - 230 KV

&%my H WINDING -42.6 MVA TO 4160 V BUSSES 4E1 & 4E2 Y WINDING - 24 MVA y

Z Z WINDING - 22.6 MVA

_ TO 4160 V SUS *C TO 4160 V BUS 40 Vs3 V 3667 V

~

ESF SYSTEM 4160 V BUS 4A 4160 V BUS 4B 3672 V 3663 V

(.88 0F 4160 VI

(.88 0F 4160 V)

(.88 0F 4160 V)

STATION SERV.

TR ANS. X43A 3667 V STATION SERV.

(STARTING) 4160 - 480 V

-i, ii

(.88 0F 4160 V)

TR ANS. X43B WW TAP -4260 V MOTOR (STARTING) 4160 - 480 V

&M MOTOR 1.12 MVA TAP - 4260 V 1.12 MVA 480 V BUS 3A 480 V BUS 3B 402 V 3i1 V

(.87 0F 460 V)

(.87 0F 460 V) 480 V MCC 2A1 480 V MCC 281 389 V 397 Y

(.87 0F 460 V)

(.86 0F 460 V) 368 V 381 V MOTOR (.80 0F 460 V)

(.83 0F 460 V) MOTOR (STARTING)

(STARTING)

NOTES:

1. MOTORS CONNECTED TO A 4160V BUS ARE RATED 4160V. THE 480V SYSTEM MOTO RS ARE RATED 460V,

2. THE MOTORS SHOWN ARE ELECTRICALLY THE MOST DISTANT MOTORS FROM THE BUSSES SHOWN. ALL OTHER MOTORS ON THESE BUSSES WILL OPER ATE AT A VOLTAGE SETWEEN THAT OF THE BUS, AND THAT l

OF THE MOST DISTANT MOTOR.

1.5-21

SKETCH 10 CASE 3 BUS 4A & 4B ON STARTUP TRANSFORMER NO. 2 VOLTAGE DURING BLOCK LOADING OF EMERGENCY BUSSES (BLOCK 2., T = 16 SEC.)

START NUCLEAR SERVICE AIR COOLERS AND NUCLEAR SERVICE COOLING WATER PUMPS 220 KV SWITCHYARD 214 KV STARTUP TRANSFORMER NO 2 H

221 - 4.36-4.36 KV TAP - 230 KV m%&M H WINDING - 42.6 MVA TO 4160 V BUSSES 4E1 & 4E2 Y WINDING - 24 MVA y

Z Z WINDING - 22.6 M*.*A T0 4160 V BUS 4C T0 4160 V BUS 40 3732 V 3727 V ESF SYSTEM 4160 V BUS 4A 4160 V 8US 48 3731V 3724 V

(.90 0F 4160 VI

(.90 0F 4160 V) 3721 V STATION SE RV.

(.90 0F 4160 V)

TR ANS~ X43A 3728 V STATION SERV.

4160 -480 V

(.90 0F 4160 V)

T R ANS. X438

%W TAP - 4260 V MOTOR 4160 - 480 V MOTOR 1.12 MVA TAP - 4260 V 1.12 MVA 480 V BUS 3A 480 V BUS 3B 369 V 366 V

(.80 0F 460 V)

(.80 0F 460 V) 344 V

(.75 0F 460 V) f.76 0F 480 V)

(STARTING)

MOTOR (STARTING)

M OT,0 R f

480 V MCC 2A1 480 V MCC 2B1

~

367 V 384 V

(.80 0F 480 V)

(.79 0F 480 V) 354 V 357 V MOTOR (.77 0F 480 V)

(.78 0F 460 V) MOTOR l

BOTES:

1. MOTORS CONNECTED TO A 4160V BUS ARE RATED 4180V. THE 480V SYSTEM MOTORS ARE RATED 460V.

2. THE MOTORS SHOWN ARE ELECTRICALLY THE MOST DISTANT MOTORS FROM THE BUSSES SHOWN. ALL OTHER MOTORS ON THESE BUSSES WILL OPERATE AT A VOLTAGE BETWEEN TAAT OF THE BUS, AND THAT OF THE MOST DISTANT MOTOR.

I.3-22

SKUCH 11 CASE 3 BUS 4A 0 4B ON STARTUP TRANSFORMER NO. 2 VOLTAGE DURING BLOCK LOADING OF EMERGENCY BUSSES (BLOCK 3., T = 26 SEC.)

START THE NUCLEAR SERV RAW WATER PUMPS AND THE DIESEL-GENERATOR ROOM VENT FANS 220 KV SWITCHYARO 214 KV STARTUP TR ANSFORVER NO 2 H

221 - 4.36-4.36 KV.

L* 1*

TAP-230 KV

&%&M H WINDING - 42.6 MVA TO 4160 V BUSSES 4E1 & 4E2 Y WINDING - 24 MVA y

Z Z WINDING - 22.6 MVA l

TO 4160 V BUS 4C TO 4160 V BUS 40 3692V 3685 V

~

ESF SYSTEM 4160 V BUS 4A 4160 V BUS 4B 3690 V 3681 V

(.89 0F 4160 V)

(.88 0F 4160 V) 3648 V L OF M W STATION SERV.

T R ANS. X43A 3656 V STATION SERV.

(STARTING) 4160 - 480 V

(.88 0F 4160 V)

T R ANS. Xs3B WW TAP - 4260 V MOTOR (STARTING) 4160 - 480 V

&M MOTOR 1.12 MVA TAP - 4260 V 1.12 MVA 480 V BUS 3A 480 V BUS 3B 386 V 382 V (J4 0 F 460 V)

(.83 0F 460 VI 370 V

(.80 0F 460 V)

(STARTING) y (20 0F 460 V)

MOTOR (STARTING)

MOTOR 480 V MCC 2A1 480 V MCC 2B1 384 V 381 V

(.83 0F 460 V)

L83 0F 460 V) 374 V 371 V (J10F 460 V) MOTOR MOTOR (J10F 460 V)

BUTES:

1. MOTORS CONNECTED TO A 4160V BUS ARE RATED 4160V. THE 480V SYSTEM MOTORS ARE RATED 460V.

2. THE MOTORS SHOWN ARE ELECTRICALLY THE MOST OISTANT MOTORS FROM THE BUSSES SHOWN. ALL OTHER MOTORS ON THESE BUSSES WILL OPERATE AT A VOLTAGE SETWEEN THAT OF THE BUS, AND THAT OF THE MOST OLSTANT MOTOR.

I.B-23

S N 12 CASE 3 BUS 4A & 4B ON STARTUP TR AMSFORMER NO. 2 VOLTAGE DURING BLOCK LOADING OF EMERGENCY BUSSES (BLOCK 4., T = 36 SEC.)

START AUX FEED WATER PUMPS 220 KV SWITCHY ARD 214 KV STARTUP TR ANSCOR"!2 NO 2 H

221 -4.36-4.36 KV WW TAP - 230 KV

&P&P H WINDING - 42.C MVA TO 4160 V BUSSES 4E1 & 4E2 Y WINDING - 24 MV A y

Z Z WINDING - 22.6 MVA

_ TO 4160 V BUS 4C TO 4160 V BUS 40 3556 V 3547 V ESF SYSTEM 4160 V BUS 4A 4160 V BUS 42 3553 V 3541 V

(.85 0F 4160 V)

(.85 0F 4160 V) 3431 V

(.64 0F 4160 V)

STATION SE RV.

T R ANS. X43A 3523 V STATION SERV.

(STARTING) 4160 - 480 V WN

(.85 0F 4160 V)

T R ANS. X438 WW TAR - 4260 V MOTOR (STARTING) 4160 - 480 V

&M MOTOR 1.12 MVA TAP - 4250 V 1.12 MV A 480 V BUS 3A 480 V BUS 3B 384 V 380 V

(.84 0F 460 V)

(.83 0F 460 V) 372 V

(.810 F 460 V) 37g y

(.82 0F 460 V)

MOTOR MOTOR 480 V MCC 2A1 480 V M CC 281 383 V 379 V (J3 0F 460 VI

(.82 0F 460 V) 370 V 372Y MOTOR (.80 0F 460 V)

(.810F 450 V) MOTOR NOTES:

1. MOTORS CONNECTED TO A 4160V BUS ARE RATED 4160V. THE 480V SYSTEM MOTORS ARE RATED 460V.

2. THE MOTORS SHOWN ARE ELECTRICALLY THE MOST DISTANT MOTORS o

FROM THE BUSSES SHOWN. ALL OTHER MOTORS ON THESE BUSSES WILL OPERATE AT A VOLTAGE BETWEEN THAT OF THE SUS. AND THAT OF THE MOST DISTANT M3 TOR.

I.3-24

CASE 3 SFITCH 13 BUS 4A G 4B ON STARTUP TRANSFORMER NO. 2 VOLTAGE DURING BLOCK LOADING OF EMERGENCY BUSSES (BLOCK 5., T = 300 SEC.)

START REACTOR BUILDING SPRAY PUMP l

220 KV SWITCHYARD 214 KV STARTUP TR ANSFORMER NO 2 H

221 - 4.36-4.36 KV I

i Lin' TAP - 230 KV H WINDING - 42.6 MVA TO 4!60 V BUSSES 4E1 & 4E2 y

Y WIN 3ING - 24 MVA Z

Z WINDING - 22.6 MVA

_ TO 4160 V BUS 4C TO 4160 V BUS 40 3699 V 3693 V

~

~

ESF SYSTEM 4160 V B"S 4A 4160 V BUS 4B 3698 V 3689 Y

(.89 0F 4160 V)

(.89 0F 4160 V)

STATION SERV.

3679 V TR ANS' X43A 3688 V STATION SE RV.

(*89 0F 4160 V) 4160 - 480 V NN

(.89 0F 4160 V)

TR ANS. X438

%W TAP - 4260 V MOTOR 4160 - 480 V TM MOTOR 1.12 MVA TAP - 4260 V l

1.12 MVA 480 V BUS 3A 480 V BUS 3B 369 V 365 V

(.80 0F 480 VI

(.79 0F 460 V) 353 V

(.77 0F 460 V) 357 V (STARTING)

(.78 0F 460 V)

MOTOR (STARTING).

MOTOR 480 V MCC 2A1 480 V MCC 2B1 367V 364 V

(.80 0F 480 V)

(.79 0F 460 V) 353 V 356 V MOTOR (.77 0F 460 V)

(.77 0F 460 V) MOTOR NOTES:

1. MOTORS CONNECTED TO A 4160V BUS ARE RATED 4160V. THE 480V SYSTEM MOTORS ARE RATED 460V.

2. THE MOTORS SHOWN ARE ELECTRICALLY THE MOST DISTANT MOTORS FROM THE BUSSES SHOWN. ALL OTHER MOTORS ON THESE BUSSES WILL OPERATE AT A VOLTAGE BETWEEN THAT OF THE BUS. AND THAT 0F THE MOST DISTANT MOTOR.

I.3-25

SKE CH n CASE 3 BUS 4A & 48 ON STARTUI 7".XsSFORMER NO. 2 VOLTAGE DURING START OF CONDENSATE PUMP 220 KV SWITCHY ARO 214 KV ST A RTUP TR ANSr0 R*.'E m NO 2 H

221 - 4.36-4.36 KV WW TAP - 230 KV H WINDING - 42.6 MVA TO 4160 V BUSSES 4E1 & 4E2 Y WINDING - 24 MV A y

Z Z WINDIN G - 22.6 MVA TO 4160 V BU; 4C TO 4160 V BUS 40 3462 V 3448 V ESF SYSTEM 4160 V BUS 4A 4160 V BU3 48 3461 V 3445 V

(.83 0F 4160 VI

(.83 0F 4160 V) 3432 V STATION SERV.

( 82 0F 4160 V)

TR ANS. X43A 3447V STATION SERV.

4160 - 480 V

(.83 0F 4160 V)

TR ANS. X43B WW TAP - 4260 V MOTOR 4160 - 480 V

&M MOTOR 1.12 MVA TAP - 4260 V 1.12 MV A 480 V BUS 3A 480 V BUS 3B 365 V 364 V

(.79 0F 460 V)

(.79 0F 460 V) 355 V OF 460 W 358 V

(.78 0F 460 V)

MOTOR MOTOR 480 V MCC 2A1

_80 V MCC 281 4

363 V 363 V L79 0F 460 V)

(.79 0F 460 V) 349 V 355 V MOTOR (.7g OF 460 V)

L77 0F 460 V) MOTOR i

NOTES:

1. MOTORS CONNECTED TO A 4160V BUS ARE RATED 4160V. THE 480V SYSTEM MOTORS ARE RATED 460V.

2. THE MOTORS SHOWN ARE ELECTRICALLY THE MOST DISTANT MOTORS FROM THE BUSSES SHOWN. ALL OTHER MOTORS ON THESE BUSSES WILL OPERATE AT A VOLTAGE BETWEEN THAT OF THE BUS. AND THAT O F THE MOST DISTANT MOTOR.

3. CONDENSATE PUMP STARTING TIME IS LESS THAN 2 SECONOS.

I.5-26

r-ENCLOSURE I PART C Evaluation of the Rancho Seco Offsite Power System for Compliance to General Design Criterion 17 (Refer to NRC Letter William Gammill to Power Reactor Licensees Dated nugust 8, 1979) t

\\

The NRC's August 8, 1979, letter to all Reactor Licensees (except Humbolt Bay) requested the District "To review the electric power systems of your nuclear station to determine if there are any events or conditions which could result in the simultaneous or consequential loss of both required circuits to the offsite network to determine if any z

potential exists for violation of GDC-17 in this regard."

The District has completed a review of the electrical power l1 system for Rancho Seco and has determined that the District's electrical power supply system is in compliance with GDC-17. The basis for this con-clusion is contained in what follows.

The power distribution system from the transmission network to the i

onsite safety related electrical distribution system consists of:

a.

Five overhead lines b.

Start-up transformers #1 and #2 and the nuclear service trans forme rs.

Bus duct from the start-up transformers to the onsite c.

safety related electrical distribution system.

d.

Protective relays, circuit breakers, control panels, batte-ries, and power and control cables associated with the operation of the distribution system.

The following assumptions were made by the District in determining events which could result in simultaneous or consequential loss of both required circuits.

(For a one line diagram of the Rancho Seco distribution system refer to Sketch 1.)

a.

All switchyard breakers are closed and in service.

b.

All five lines that connect the switchyard to the transmission system are in service.

Safety Bus 4A is connected to start-up transformer #1.

c.

d.

Safety Bus 4B is connected to start-up transformer 62.

e.

Only a single event or failure is assumed to occur unless it could be deominstrated that the single event could lead to multiple failures.

Based on the following assumptions, the District has analyzed the following events to determine if they could cause loss of both required circuits.

I.C-1

FIRE It is possible for a single fire either in a control cabinet, cable tray or conduit to involve the control circuits for all the circuit breakers required for both offsite sources, and cause the circuit breakers to trip. However, this loss of power would only be temporary since the required circuit breakers can be quickly closed manually without any elec-trical poder.

The District has minimized to the extent practical the likelihood of this event by:

1.

Using flame retardant cable for all cable between the plant and switchyard.

2.

Installing a fire detection and suppression system in the plant and switchyard where the circuits of concern are routed.

3.

Providing a manual method of choosing the circuit breakers.

Therefore, this event is not a violation or potential violation of GDC-17.

SEISMIC EVENT A design basis earthquake may cause the loss of both offsite However, the District has designed and located equipment so as to sources.

minimize to the extent practical the likelihood of loss of both required circuits during a seismic event by including a seismic load in the design of supports for equipment required to be in service to provide offsite power. Therefore, loss of both required offsite power sources during an earthquake is not a violation or potential violation of GDC-17.

RANDOM SINGLE FAILURES The District has analyzed the power distribution system from the transmission system to the onsite safety electrical distribution system for single failures that can cause loss of both required offsite circuits. The review indicated that there are no single failures that can cause the loss of both required offsite sources. This analysis included the following items.

[L a.

Short circuits b.

Breaker failures c.

Switchyard battery failure d.

Relay failures e.

Transformer failures f.

Lightning strikes I.d-2

)

i i

TokIR FAILURIS.

The District has analyzed the transmission system for compliance with GDC-17 and determined that there is no single tower failure that could 1

cause the loss of all offsite power. Therefore, failure of a transmission tower is not a violation or potential violation of GDC-17.

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Enclosure II SACRAENTO MUNICIPAL UTILITY DISTRICT RANCHO SECO NUCLEAR GENERATING-STATION, UNIT NO. 1 RESPONSE TO:

NUCLEAR REGULATORY CO.TfISSION REQUEST FOR INFORMATION REGARDING ENCLOSURE 1 0F NRC TO SMUD LETTER DATED JUNE 3, 1977 TITLED SAFETY EVALUATION AND STATEMENT OF STAFF POSITIONS RELATIVE TO THE EMERGENCY POWER SYSTEMS FOR OPERATING REACTORS Issued: July 19, 1977 Revision 1: August 1, 1980 I

Listed below is a response to each position listed in Enclosure 1

" Safety Evaluation and Statement of Staff Positions Relative to the Emergency Power Systems for Operating Reactors" of NRC's Robert W. Reid to J. J.

Mattimore, letter dated June 3, 1977.

POSITION 1: SECOND LEVEL UNDER0 ROVER VOLTAGE PROTECTION WITH A TIME DELAY Ws require that a second level of voltage protection for the onsite power system be provided and that this second level of voltage protection shall satisfy the following criteria.

a)

The selection of voltage and time set points shall be determined from an analysis of the voltage requirements of the safety-related loads at all onsite system distribution levels; b)

The voltage protection shall include coincidence logic to preclude spurious trips of the offiste power source; c)

The time delay selected shall be based on the following conditions:

(1) The allowable time delay, including margin, shall not exceed the maximum time delay that is assumed in the FSAR accident analyses; (2) The time delay shall minimize the effect of short duration distribances from reducing the availability of the offsite power source (s); and (3) The allowable time duration of a degraded voltage condition at all distribution system levels shall not result in failure of safety systems or components; d)

The voltage monitors shall automatically initiate the disconnection of offsite power sources whenever the voltage set point and time delay limits have been exceeded; e)

The voltage monitors shall be designed to satisfy the 1

requirements of IEEE Std. 279-1971, " Criteria for Protection Systems for Nuclear Power Generating Stations"; and f)

The Technical Specification shall include limiting condtions for operation, surveillance requirenents, trip set points with minimum and maximum limits, and allowable values for the second-level voltage protection monitors.

RESPONSE TO POSITION 1 The second level of voltage protection for the onsite power system is not necessary since equivalent protection is afforded by a single inverse time-undervoltage relay type.

II-1

?

a a) _ The selection of voltage and time settings was determined by analysis of the voltage requirements of the safety-related loads. The undervoltage relay settings are analyzed in the response to Guideline #10 of Enclosure I.

The overvoltage relay settings are analyzed in the response to Guideline #1 of Enclosure I.

l))

A scheme incorporating coincidence logic is proposed to preclude spurious trips of the offsite power system. The circuit proposed in shown in Figure 1.

Three potential transformers will be used to monitor the bus voltage. Each potential transformer will monitor a different line-to-line voltage.

Connected to the secondary of each potential transformer (PT) will be an undervoltage relay, overvoltage relay and a voltmeter.

The contacts from the undervoltage and overvoltage relays are connected such that if either relay is removed, an alarm will be received in the control room on the plant annunciator and plant computer. A normally-closed contact from the overvoltage relay and a normally-opened contact from the undervoltage relay on the same PT are connected in series to operate an auxiliary relay (4AUL1, 4AUL2 and 4AUL3). The auxiliary relays are deenergized for either an undervoltage or overvoltage condition. The contacts from the auxiliary relays are arranged in a two-out-of-three logic. This logic 4

string is used to operate an existing time delay energize-deenergize relay (62A). A time delay close (TDC) contact from this relay is used to initiate bus load shedding and diesel starting in the existing scheme.

The 62B relay is a time delay on energizing relay that prevents an accidental bus unloading when the logic circuit 1

is initially energized. The 125V de to terminals 7 and 8 on the overvoltage and undervoltage relays is the control power to the relays.

{

c)

The time delay setting was based on thefollowing conditions:

(1) The undervoltage relay will trip in less than one second on a complete loss of voltage (see Figure 2).

This, combined with the 62A relay definite time delay, is appreciably less than 5-second maximum delay shown in the FSAR. Time requirements for overvoltage trip delay are not addressed in the FSAR.

(2).The time delays selected have been analyzed to verify that short-duration disturbances caused by motor starting and short circuits will not cause inadvertent disconnec-tion of the offsite power source.

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(3) The time duration that a degraded voltage _ condition is allowed to persist before tripping of the voltage relays has been analyzed to verify that failure of safety system or components will not occur.

d)

The voltage monitors will automatically initiate the discon-nection of offsite power sources whenever the voltage set-

-point and time delay limits have been exceeded.

e)

The voltage monitors were designed to satisfy the requirements of IEEE 279 except independence between channels of the same train is not provided since the sensing and protective action functions relate only to that train. However, independence is provided between redundant portions of the safety systems (i.e.: between Train A and Train B) in accordance with the requirements for independence established in IEEE 603.

f)

Technical Specifications will be revised to include limiting conditions for operation, surveillance requirements, trip set points with maximum and minimum limits, and allowable values.

Refer to Attachment I for a description of the Technical Specification modifications being considered by the District.

POSITION 2:

INTERACTION OF ONSITE POWER SOURCES WITH LOAD SHED FEATURE We require that the current system designs automatically prevent load shedding of the emergency buses once the onsite sources are supplying power to all. sequenced loads on the emergency buses. The design shall also include the capability of the load shedding feature to be automatically reinstated if the onsite source supply breakers are tripped. The automatic bypass and reinstatement feature shall be verified during the periodic test-ing identified in Position 3.

In the event an adequate basis can be provided for retaining the load shed feature when laods are energized by the onsite power system, we will require that the setpoint value in the Technical Specifications, which is currently specified as "... equal to or greater than..." be amended to specify a value having maximum and minimum limits. The licensees' bases for the setpoints and limits selected must be documentea.

RESPONSE TO POSITION 2 The existing Rancho Seco design complies with this position; consequently, no changes are necessary.

The existing scheme functions as follows:

1.

After exceeding the voltage setpoint a contact of the 62A relay closes energizing a set of load shedding relays.

II-3

2.

The load shedding relays perform the following functions:

A.

Trip the normal offsite supply breaker to the safety features.1160 volt buses.

B.

Trip the load breakers on the 4160 volt buses.

C.

Set up the load sequencing timing circuit.

D.

Start the emergency diesel generators.

3.

When the diesel driven generator reaches the required voltage, its circuit breaker will automatically close connecting it to the 4160 volt bus, and the step loading sequence will automatically commence if a safety features actuation signal exists.

4.

An auxiliary "b" contact from the generator circuit breaker opens to disable the load shedding feature of the circuit.

Consequently, the. voltage sensing relay cannot re-initiate the load shedding feature of the scheme so long as the generator circuit breaker remains closed.

5.

Should the gene.rator circuit breaker be opened for any reason the load shedding and loading sequences would be re-initiated as described in Items 2 and 3 above.

POSITION 3: ONSITE POWER SOURCE TESTING We require that the Technical Specifications include a test requirement to demonstrate the full functional operability and independence of the onsite power sources at least once per 18 months during shutdown.

The Technical Specifications shall include a requirement for tests:

(1) simulating loss of offsite power in conjunction with a safety injection actuation signal; and (2) simulating interruption and subsequent reconnec-tion of onsite power sources to their respective buses. Proper operation shall be determined by:

a)

Verifying that one loss of offsite power the emergency buses have been de-energized and that the loads have been shed from the emergency buses in accordance with design requirements.

b)

Verifying that on loss of offsite power the diesel generators start from ambient condition on the autostart signal, the emergency buses are energized with permanently connected loads, the autoconnected emergency loads are energized through the load sequencer, and the system operates for five minutes while the generators are loaded with the emergency loads.

II-4

c)

Verifying that on interruption of the onsite sources the loads are shed from emergency buses in accordance with design

. requirements and that subsequence loading of the onsite sources is through the load sequencer.

RESPONSE TO POSITION 3

' Refer to Attachment I for a description of the Technical Specifi-cation modifications being considered by the District.

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' ' UNDERVOLTAGE RELAY TIME-VOLTAGE CHARACTERISTIC TRIP SETTING 03065 12 I

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0 0.2 0.4 0.6 0.8 1.0 VOLTAGE IN PER UNIT OF 4150 V NOTE: AN EXTERNAL TIME DELAY RELAY (62A) SET AT 0.5 SECOND OPER ATES IN SERIES WITH THIS RELAY.

II,7

ATTAC1DfENT 1 E CEICAL SPECIFICATION HODIFICATIONS The modifiestions described herein have been drafted in response to NRC positions and guidelines.

They are being considered by the District for inclusion in the Technical Specifications and are submitted to the NRC for preliminary review.

Upon NRC approval of the voltage protection system modifications, a proposed Technical Specification change will be submitted for NRC approval.

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ATTACHMENT 1 3.

LIMITING CONDITIONS FOR OPERATION 3.7 AUXILIARY ELECTRICAL SYSTEMS Specification 3.7.1 The reactor shall not be brought critical unless the following conditions are met:

Add paragraph 3.7.1 (I) as follows:

I.

The switchyard voltage is 218 kV or above.

3.7.2 -The reactor shall not remain critical unless all of the following requirements are satisfied.

Add paragraph 3.7.2 (H) as follows:

H.

If the switchyard voltage is below 218 kV for less than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, no corrective action is required. After 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, if the voltage has not increased above 218 kV, both diesel generators will be started, connected to the. nuclear service buses, and the startup transformers removed from the nuclear service buses.

Switchyard voltage above 218 kV will allow unrestricted plant operation.

Add paragraph 3.7.4 as follows:

1 3.7.4 The voltage protection system trip setting shall be as stated in Table 3.7.1.

Add paragraph 3.7.5 as follows:

\\

3.7.5 Voltage Protection System Limiting Conditions j

i A.

Startup and operation are not permitted unless the minimum requirements and action statements of Table 3.7.5 are met.

B.

In the event the number of protective channels falls below that listed in Table 3.7.5, the plant will be brought to a hot shutdown within 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />.

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t II-9 i.

ATTACHMENT I Bases Add the following paragraph to Bases.

The. voltage protection system is designed to isolate the nuclear service buses

~

from the startup_ transformers when the bus voltage exceeds the allowable operating limits of the equipment. The allowable operating range for the 4160-V nuclear service buses is 3731 to 4626 volts and 397 to 521 volts for the 480-V nuclear service buses.

This-corresponds to a switchyard voltage range of 214 to 244kV.

This range of switchyard voltage encompasses the normal operating range of 221 to 239kV.

L II-10

TABLE 3.7.1 VOLTAGE PROTECTION SYSTEM RELAY TRIP VALUES l

Trip Value Time Delay l

l Undervoltage (Note 2) l a.

Dropout 3771 1 38V Note 1 b.

75 percent of 4160V 3120 1 31V 1.9 1 0.2s c.

Complete loss 0

1.5 1 0.2s Overvoltage 4580 1 46V 3.0 1 0.3s Note 1 - Dropout voltage is calibrated with relay on its minimum time dial settings.

f Note 2 - The relay voltage values shown have been converted by the PT ratio (40:1) for review convenience.

U l

S TABLE 3.7.5 Minimum Total Number Channels Channels Action Functional Unit of Channels to Trip OPERAllLE (Note 1)

Undervoltage 3/ Bus 2/ Bus 2

A Overvoltage 3/ Bus 2/ Bus 2

A Action Statements Action A -

With the number of OPERABLE channels one less than the Total Number of Channels operation may proceed provided both of the following conditions are satisfied:

The inoperable channel is placed in the tripped condition within one hour.

a.

b.

The Minimum Channels OPERABLE requirement is met; however, one additional channel may gy be bypassed for up to 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> for surveillance testing.

U Note 1: The above table is not applicable when the plant is in cold shutdown.

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AITACHMENT 1 4.

SURVEILLANCE STANDARDS 4.1 OPERATIONAL SAFETY REVIEW TA3LE 4.1-1 INSTRlT.ENT SURVEILLANCE REQUIREMENT.i Add item 48 to Table 4.1-1.

Channel Description Check Test Calibrate Remar'ks 48.

Voltage Protection S

Compare voltmeter readings a.

Undervoltage R

R b.

Overvoltage R

R c.

Time Delay R

R 4

S = Each Shift l

M = Monthly R = Once during the refueling interval 4.6 EMERGENCY POWER SYSTEM PERIODIC TESTING Specification Substitute 4.6.2 with the following:

4.6.2 During each refueling interval, a test of the diesel generators and emergency start circuits shall be performed to verify that these emergency power sources and associated equipment are operable by:

A.

Simulating a loss of offsite power in conjunction with a safety injection actuation signal, and:

1)

Verifying deenergization of the nuclear services buses and opantion of the load shedding circuitry.

i 2)

Verifying the diesel starts from ambient condition on the auto-start signal and energizes the nuclear services buses, and by verifying proper operation of the automatic load sequencing circuitry. The diesel generators will be oprated for at least 5 minutes in this condition.

1 J'

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ATTAODfENT 1 3)

Verifying that on diesel generator trip, the load shedding circuitry operates properly and the diesel restarts on the auto-start signal, and by verifying proper operation of the automatic load sequencing circuitry. The diesel generator will be operated for at least 5 minutes in this condition.

B.

Load testing the diesel generators to SFAS capacity.

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