ML19339A885

Submits Info Re Auxiliary Power Sys Per 760812 Request. Facility Does Not Have Conventional Auxiliary Power Sys Consisting of Unit Auxiliary Transformers & Reserve Auxiliary Transformers

ML19339A885
Person / Time
Site:	Yankee Rowe
Issue date:	09/16/1976
From:	Groce R YANKEE ATOMIC ELECTRIC CO.
To:	Office of Nuclear Reactor Regulation
Shared Package
ML19339A886	List: ML19339A885 ML19339A887
References
WYR-76-96, NUDOCS 8011050643
Download: ML19339A885 (9)

Text

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r Taliphone 617 366-9011 Regulatory Docketj

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YANKEE ATOMIC ELECTRIC COMPANY m

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7'ki/"gf N Attention:

Reference:

1.

L'. cense No. DPR-3 (Docket No. 50-29) 2.

NRC letter dated August 12, 1976

Dear Sir:

As required in Reference 2, we are providing the following information.

The item numbers used are identical to the numbers in your request.

The Yankee Nuclear Power Station (Yankee Rowe) does not have a conventional auxiliary power system consisting of unit auxiliary transformers, reserve auxiliary transformers and associated transfer Therefore some questions in your facilities between the two sources.

for informatien are not quite applicable to Yankee Rowe.

request 1 shows the main one line diagram at the Yankee Attachment No.

Electric power from the transmission network Nuclear Power Station.

to the onsite electric distribution system is supplied by two physically independent circuits.

One is the 115 kV Cabot line (Y-177) and the (Z-126).

Both of the lines occupy the other the 115 kV Harriman line same switchyard which is located in close proximity to the turbine generator building.

The 115 kV incotiing lines (Z-126, Y-177) are tapped on the line sides of the circuit breakers near the switchyard and are connected 2 and 3 respectively, to the 115/2.4 kV station service transformers No.

The secondaries of the two station service with overhead lines.

transformers are connected directly to the 2400 volt indoor metal clad 2 and 3, and also to the 480 volt switchgear, via switchgear buses No.

volt station service transformers (No. 5 and No. 6).

two 2400/480 When energized, the two 115 kV incoming lines are both available p

~enerator.

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E The two cuter buses (2400V buses 2 and. 3) are thus always connected to of fsite The center bus (2400 volt bus 1) is connected to the main generator Power is restored power.

and is without power immediately following a generator trip.

by manually closing a tie breaker unless the trip is caused by a fault in the generator at which time the center bus is automatically tied to bus No. 3 When the main generator is connected to the grid, the voltage at the When the main switchyard is essentially controlled by the generator.

generator is disconnected from the grid, the voltage at the switchyard is I

controlled by the grid, f

1 The a-c power systems that are safety related and which require emergency 4

onsite power following the loss of normal. power, consist of the three separate 480 volt emergency buses, their power supplies and their loads.

The normal and emergency supplies to these buses are shown in The normal power supply for each emergency bus is an attachment No. 1.

An emergency diesel generator is connected 4

individual 480 volt station bus.

to each emergency bus to provide emergency power in the event that normal This arrangement assures that sufficient sources of power power is lost.

are available at all times tc start and supply the safety related loads which require <5 r2ency onsite power following the loss of normal power.

mitage is lost on an emergency bus, the circuit breakers

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When supplying normal power receive a signal to open and the emergency diesel When norm 1 voltage is reached generator receives a signal to start.

the generator terninals, the emergency generator circuit breaker is atautomatically closed onto the dead bus, thus providing the emergency bus with a source of onsite power.

The plant auxiliary systems are supplied by offsite power when the 1.a From the time of main generator is not connected to the grid.

initial startup in 1960 through July 1976, the plant auxiliaries have been supplieu by offsite power for apprcaimately 20% of the time.

The nominal value of the grid voltage at Yankee Rowe is 115 kV.

1.b The normal operating range of grid system voltage with the generator connected to the grid is 113 to 115 kV.

The corresponding values the emergency buses are from 454 to 462 volts.

at transformer tap settings have been chosen by analysis l.c The present of the bus voltages over the operating period of Yankee Rowe.

The only conditions where the auxiliary system is fed directly by f

offsite power is when the generator is not connected to the grid.

Under this condition, the range of grid voltages is 109 to 117 kV.

The corresponding voltages at the emergency buses are from 442 to 474 volts.

It is apparent that the voltage profiles at the safety related buses are-satisfactory for operation of all connected safety related equipeent (see item 1.g).

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. tn With the generator operating (the plant distribution system B

f 1.d supplied by the generator) and grid voltages of 113 kV and 115 kV, the corresponding voltages on the emergency buses are 454 and 4

462 volts.

There are no identifiable' degraded conditions that would require a gene'. tor trip.

On each 480 volt emergency bus, there is one undervoltage relay.

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Each relay is located on the safety injection panel in the main i

control' room, and is supplied bus potential from a 480 to 120 volt potential transformer located in the 480V emergency switchgear.

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The relays are Westinghouse type CV-7 electromagnetic induction disc l

relays with a tap setting of 105 volts and a time dial setting of 2.

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These relays will trip in 1.8 seconds if the voltage drops to zero.

With 69 volts at the relay (277 bus volts), the relays will trip in 3.0 seconds; with 92.4 relay volts (370 bus volts), the relays will trip in approximately 7.0 seconds. These relays initiate the following action when tripped:

4 (a) start the diesel engine (b) trip the incoming power feeder breakers (c) closa required load breakers in a predetermined sequence.

4 The undervoltage relays provided on the 480 volt emergency buses have to assure pickup in 1.8 seconds on complete loss of power been set (dead bus) and to initiate the action described. The tap setting chosen (105 volts) corresponds to 399 volts on the bus or 83.25% of the nom!nal 480 bus voltage and is considered adequate to prevent nuisance tripping due to starting of large auxiliary motors, and transitory disturbances on the transmission system.

Due to the configuration of the auxiliary power system at Yankee l.f Rcwe, this item is considered not applicable.

See introductory statement for an explanation. The undervoltage trip set point is 83.25% of nominal; the value of grid voltage corresponding to this setpoint is 98.8 kV.

On emergency and non-emergency buses, a wide range of motors exists.

l.g NEMA Some are rated 480' volts, some 460 volts, and some 440 volts.

MG-1 requires that motors operate successfully with a var;. tion in voltage of +10% of the rated voltage. The range for each motor voltage would be:

FROM TO MOTOR 480V 432 528 460V 414 306 440V 396 484

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{l to the manufacturer's data, the a.c. contactors on emergency and a

According

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non-emergency' buses are' guaranteed for a minimum pickup voltage of_77% (370 bus volts). Tests performed at Yankee Rowe have verified this capability.

l Yankee Rowe's safety related instrumentation is normally fed by the Therefore, 125 volt D.C. battery system through a motor-generator set.

the safety related instrumentation is not affected by a short or long term degradation in the grid system voltage.

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The' bus voltage corresponding to the undervoltage relay tap. setting a

1 of-83.25% is obviously below the operating range for some equipment.

However, as shown in item Ic the expected bus voltages, when connected l

to offsite power, are well within the range required for continuous l

operation of the equipment.

In the control room, the following bus voltages are continously monitored 4

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by the operators via panel meters.

Generator Volts 115 kV Z-126 Line 115 kV Y-177 Line 2400 Volt bus 1 2400 Volt bus 2 4{

2400 Volt bus 3

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48 Volt bus 4-1 480 Volt bus 5-2 480 Volt bus 6-3 In addition, 2400 volt buses 1, 2 and 3 are individually alarmed and annunciated in the control room for low voltage.

The functional safety requirements-of the undervoltage trips is to l

2.

the loss of offsite power system voltage and to initiate the detect necessary actions required to transfer safety related buses to the At Yankee Rowe, a loss of voltage to the onsite power system.

emergency 480 volt buses for more than 1.8 seconds will result in j

initiation of automatic load shedding and load sequencing.

j Connected to each 480 volt emergency bus is an undervoltage relay.

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i, When this relay senses a voltage below its setpoint, a high speed, electrically resetable (by manual action) relay is operated.

l lock out, This relay initiates the following action:

i The diesel generator is started, a.

the bus is isolated by tripping all incoming power feeder breakers b.-

required load breakers are closed in a predetermined sequence.

c.

The bus load. shedding features as described, ensure that a low voltage subsequent te initiation of load shedding and diesel generator l

load sequencing will not interfere with, or prevent any safety related load from performing its safety function.

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Li Page Five September 16, 1976 e

r The operating procedures for Yankee Rowe require adherence to the 3.

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following limits:

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Voltage (kV) lll dee Attachment No. 2, Generator Capability Curve MW See Attachment No. 2, Generator Capability Curve ju MVARS 60 Frequency (Hz) 60 j'

These limits were determined in accordance with the generator's F

capability.

We have analyzed voltage data taken at Yankee Rowe over the 4.

last five years of operation.

1 The normal voltage range of the grid during plant shutdowns ranged The lowest recorded voltage occurring on the from 109 to 117 kV.

This grid was 106 kV which occurred during a plant shutdown.

corresponds to a voltage of 430 volts on the 480 volt emergency 430 volts is adequate to ensure successful operation of all bus.

sa.ety related components.

i Our analysis has shown that the grid in the vicinity of Yankee Rove with its associated ceneration and transmission system has a capacity sufficiently large enough to preclude a low voltage situation similar to that which occurred at Millstone 2.

This is accomplished through the proper scheduling and supervision of the generation and transmission system by the dispatcher, (REMVEC-Rhode Island, Eastern Massachusetts and Vermont Energy Control).

therefore, believe that the degraded voltage conditions We, described in your letter are a combination of events pertinent to the auxiliary system at Millstone and its load dispatching and are not typical of, or applicable to, the transmission facilities grid at Yankee Rowe or the auxiliary system at Yankee Rowe.

However, as a precautionary measure, we are proposing to install at the next refueling outage an additional undervoltage relay on each energency bus. -These relays will be set to respond to a voltage above'the minimum required to ensure operation of safety related They will have a time delay of several seconds duration equipment.

to eliminate spurious pick-up due to short duration voltage In the transients on the grid and the auxiliary system.

unlikely event that these relays actuate, an annunciator will be activated in the control room.

The operators will have i

instructions to manually start the diesel generators and synchronize them to the bus experiencing los voltage. After synchronization, the off-site supply will be disconnected, thus 4

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f-i;.S. Nuclear Regulatory Commission Page Six September 16, 1976 4

As an alterrative, supplying the bus with on-site errergency power.

procedures may require the operators to trip the incoming feeder j

breaker so as to initiate a no-voltage condition on the emergency i

bus.

k'e trust that you find this information satisfactory; however,'should l

l you desire additional information, please contact us.

l Very truly yours, YANKEE ATOMIC ELECTRIC COMPANY f{Y

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R. H. Groce 4

Licensing Engineer 4

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PART 50 DOCKET MATERI AL NRC DISTRIBUTION FOR DATE OF DOCUMENT FROM: YAEC fo: NRC Westborough, Mass. 01581 9-I4-76 J.L. French DATE RECEtVE D 9-20-76 NU.MBER OF COPIES RECEIVED JNPUT F ORM rROP ONOTORizED

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