ML17053D975

Safety Evaluation Re Motor Starting Voltages During Diesel Generator Load Sequence Testing

ML17053D975
Person / Time
Site:	Nine Mile Point
Issue date:	07/18/1983
From:	NRC
To:
Shared Package
ML17053D974	List: ML17053D973 ML17053D975
References
NUDOCS 8307290387
Download: ML17053D975 (14)

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. UNITED S'FATES NUC R REGULATORY COMMISSION WASHINGTON, O. C. 20555 SAFETY EVALUATION NINE MILE POINT 1

DOCKET NO, 50-220 MOTOR STARTING VOLTAGES DURING DIESEL GENERATOR LOAD SEQUENCE TESTING BACKGROUND The 4 KV 450 HP core spray pump motor no, 111 is a permanently connected load to the 4

KV Class lE bus.

The system is designed such that upon transfer from offsite power Co onsite power (diesel generators),

all safeguard loads are shed except the permanently connected load.

The diesel generator load sequence tests conducted on June 29, 1981 indicated that only 52,5 percent (2100 volts) of its rated 4000 volts was available to the 450 HP core spray motor during starting, i.e. at the instant of starting this motor, the voltage drops down to 52.5 percent.

In general, when a motor is started, a high reactive starting current depresses the source voltage, depending on the source impedance.

As the source voltage

drops, the inrush current drops in direct proportion and the motor torque goes down as the square of the terminal voltage.

Due to the lower torque, the accelerating torque is less and the accelerating time is increased.

If there is not sufficient accelerating torque available to the motor, it may stall and eventually fail.

The concern relating to the permanently connected 450 HP core spray motor and other safeguard motors at this plant is whether there is sufficient voltage available to successfully start these motors without degradation and within the requirements of the safeguard equipment.

8307290387 830718 PDR ADOCK 05000220 P

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ANALYSIS AND EVALUATION The results of the diesel generator load sequence tests performed on June 29, 1981 are documented in Niagara Mohawk Power Corporation submittal dated January 28, 1983.

These test results show that the generator output circuit breaker (R1022) is closed at 5.9 seconds after starting the diesel generator This immediately starts the 450 HP core spray pump motor (no. 111) which pulls the bus voltage down to 2100 V (52,5X of 4000 V),

However, the diesel generator. excitation system is able to provide the necessary field to raise the..bus voltage to 3780 volts (94.5X of 4000 volts) within 1,7 seconds.

The 450 HP core spray motor produces sufficient tor que at 52,5X rated voltage (2100 volts) to accelerate its load from zero speed to rated speed without an adverse effect on the diesel generator output voltage, The motor reaches its rated speed within 1,9 seconds at which time the bus voltage is up to 4200 volts.

Since the motor successfully starts without any adverse effects (i.e.

no indication of motor stalling or continued depressed voltage condition),

it appears that the motor is properly applied, Further, this motor has been exercised since the plant has been in operation without any adverse effects, This indicates that the core spray pump motors can start with 52,5 percent voltage and can accelerate their load without any adverse affects.

However, NRC Regulatory Guide 1,9 (Rev. 2),'Selection,

Design, and gualification of Diesel-Generator Units Used as Standby (Onsite) Electric Power Systems at Nuclear Power Plants," requires that the voltage decrease be no less than 75 percent of nominal during load sequencing.

This Regulatory Guide is not applicable to the Nine Mile Point 1, Because the 450 HP core spray is permanently connected to the bus and the voltage drops below the 75 percent limit when the generator output breaker is closed, and it does not affect other

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loads sequenced on later.

Further, the diesel generator has the capability to supply power within limits so as not to degrade the performance of this permanently connected load below design minimum requirements.

The remaining safeguard loads are sequenced on starting at 8 seconds after diesel generator starts with the lowest starting bus voltage of 3150 volts (78.75K of 4000 volts) occurring at 14 seconds when 450 HP core spray pump 121 starts.

The test results indicate that during load sequencing of this motor the voltage is maintained above the 75 percent limit.

The strip charts show the starting line voltages and phase cur'rents for the 450 HP core spray pumps nos.

111 and 121, and demonstrate successful starting of these motors.

In addition to the 450 HP core spray pump motor no, ill, a 1000

KVA, 4160-600 volt transformer is also permanently connected to the 4160 volt bus, This transformer supplies power to 550 volt Class lE loads, The permanently connected load on the 600 volt bus is a 250 HP control rod drive pump motor.

The licensee has assured us in our telephone conversation of 5/23/83 that there are no starting problems or adverse effects on this motor when the 1000 KVA transformer is energized when the generator output breaker is closed.

Further, the licensee has agreed to furnish starting voltage test data on this motor in the near future for documentation.

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4 CONCLUSION Based on our review of the above data, we conclude that the bus voltage of 5Z.5 percent for starting of a permanently connected 450 HP core spray no.

111 and 1000 KYA transformer is adequate and will not result in degradation of equipment performance or challenge the minimum design requirements of other safeguard equipment as presently designed.

Principal Contributor:

A. Gill Dated:

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~I chment 1

DIESEL GENERATOR 102 LOAD SEtlUENCE TEST 6/29/81 0 Time Bus Supply Breaker R1012 Tripped 5.9 sec.

Generator Breaker R1022 Closed 450 Horse Power Core Spray Pump ill Starts (Breaker remained closed)

Bus Voltage During Starting-Start Time 0 volts C

2100 volts min. 3780 volts in 1.7 sec.

1.9 sec.

8 sec. 350 Horse Power Bus Voltage During Start Start Time Core Spray Topping Pump 111 Starts 4200 volts 3360 volts min. to 3890 volts at peak current 1.05 sec.

14 sec. 450 Horse Power Core Spray&ump 121 Starts Bus Voltage During Start Start Time 4410 3150 volts min - 3890 volts in peak current

'1.26 sec.

20.8 sec. 350 Horse Power Core Spray Topping Pump 121 Starts

~ Bus Voltage During Start Start Time 4410 3520 min - 3890 volts at peak current 1.05 sec.

26 sec. 350 Horse Power Containment Spray Pump ill Bus Voltage During Start Start Time 4250 3255 min - 3890 volts at peak current 0.8 sec.

31 sec. 350 Horse Power Containment Spray Pump 121 Bus Voltage During Start Start Time 4250 3255 min - 3890 at peak current 0.8 sec.

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