ML19275A178
| ML19275A178 | |
| Person / Time | |
|---|---|
| Site: | Haddam Neck File:Connecticut Yankee Atomic Power Co icon.png |
| Issue date: | 09/24/1979 |
| From: | Counsil W CONNECTICUT YANKEE ATOMIC POWER CO. |
| To: | Ziemann D Office of Nuclear Reactor Regulation |
| References | |
| TASK-08-01.A, TASK-8-1.A, TASK-RR NUDOCS 7910030275 | |
| Download: ML19275A178 (8) | |
Text
e CONNECTICUT YANKEE ATO M IC POWER COMPANY BERLIN. CO N N E C TIC U T P. O BOX 270
$1 A RTFORD. CONN ECTICUT 06101 T e t senon s 203 666 6911 September 24, 1979 Docket rc. 50-213 Director of Nuclear Reactor Regulation Attn:
Mr. D. L. Ziemann, Chief Operating Reactors Branch //2 U. S. Nuclear Regulatory Commission Washington, D. C.
20555
References:
(1)
D. C. Switzer letter to A. Schwencer dated July 21, 1977.
(2)
D. L. Ziemann letter to W. G. Counsil dated July 24, 1979.
Gentlemen:
Haddam Neck Plant Emergency Power Systems In Reference (J ), Connecticut Yankee Atomic Power Company (CYAPCO) proposed certain modifications in response to NRC Staff concerns regarding degraded grid voltage effects on emergency power systems (diesel generators) at the Haddam Neck Plant.
In Reference (2), the NRC Staff stated that they required additional information in order to continue their review of Reference (1).
It was requested that this information be submitted within 45 days of the date of Reference (2).
In a phone conversation on September 6,1979, CYAPCO informed the NRC Staff tha:. members of the Northeast Utilities Service Company (NUSCO) Staff were involved in the emergency reetoration of electrical service in the aftermath of the passage of tropical storms through the Northeast Utilities' service region.
Since these circumstances affected those who were. involved in preparing the response to Reference (2), CYAPCO requested a revised due date of September 21, 1979. The NRC Staff stated that this would be acceptable.
Accordingly, CYAPC0 hereby provides the attached additional information in response to Reference (2).
Very truly yours, CONNECTICUT YANKEE ATOMIC POWER COMPANY
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W. G. Counsil Vice President Attachment 7010080
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a DOCKET No. 50-213 ATTACIDIENT HADDAM NECK PLANT EMElGENCY POWER SYSTEMS ADDITIONAL INFOILMATION
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v3, SEPTEMBER, 1979
ADDITIONAL INFORMATION
References:
(1)
D. L. Ziemann letter to W. G. Counsil dated July 24, 197')
(2)
D. C. Switzer letter to A. Schwencer dated July 21, 1977 Ql. Our position (i.e., of our letter of June 3,1977) is that the voltage nonitors shall be designed to satisfy the requirements of IEE1 Std. 279-1971, " Criteria for Protection Systems for Nuclear Power Generating Station." State your compliance with this position and in.lu :e sufficient description for us to verify compliance of your design.
Al. Refer to the attached sketch SKJRF083179A. One level-one scheme and one level-two scheme are supplied from each side of the redundant off-site supplies. The level-one scheme in each division consists of three phase-to-phase connected electromechan' cal undervoltage relays. The level-two scheme in each division consists of three phase-to-phase connected solid-state undervoltage relays.
Failure of the supply to any one of the undervoltage relays will result in that relay assuming the fail-safe mode (i.e., the relay wil1 provide an undervoltage output). An output from any undervoltage relay will initiate an alarm. Operation of the undervoltage schemes is described in Reference (2). Also, cable runs for the level-two schemes will be separated by division.
mjz 054 Q2. CYAPC0 letter dated July 21, 1977, states that the second level of voltage protection will only initiate the disconnection of the offsite power source when:
1.
the voltage level is below the setpoint of 3871 volts; 2.
the time delay of 9 + 1 seconds has timed out; 6nd 3.
an accident signal is present.
It was also stated that operator action would be required to protect certain ESF loads (from degraded voltage) when an accident signal is not present. Our position (l.d. of our letter of June 3,1977) is that the voltage monitors shall automatically initiate the disconnection of offsite power sources whene.er the voltage set point and time delay limits have been exceeded. We request that you propose a design description and scheaule for installation of a modification to conform to our position and eliminate the need for operator action.
A2. The only ESF motors capable of st..rting automatically during the degraded voltage condition are the charging pumps and the service water pumps.
Prior to the undervoltage condition, one charging pump and at least two service water pumps would be running as part of the normal station load. The following points are our justification for not disconnecting from the offsite source as soon as the voltage relays drop out and the timing relays time out:
1C12 055
a.
The motors wili run continuously at voltage levels down to 3660 volts without violating the vendor's specified operating capability.
This level corresponds to the minimum acceptable voltage for operation of the motors on the 480-volt busses (406 V).
It is not desirable to start motors in the voltage range between 3660 and 3871 volts because the starting of the motor may cause the voltage to dip below the spet Fied capability of the motor. However, the charging and service water pumps are loaded well below their full capability and would suffer little, if any, from a degraded voltage start.
It should be noted that during testing, a serv 4 e water pump at CYAPC0 has been started at considerably less than 90%
voltage with no discernible increase in starting time.
This test was conducted at 328 volts (75% Jtage).
b.
The probability of the system voltage dropping below the 6
3871 volt level is remote. Also, the probability of an automatic start juring the proposed four-hour period is remote. However, if the de3raded voltage situation were to occur, starting of the charging and service water pumps could be administratively prevented. This action would eliminate any concern over possible damage to the motors during degraded voltage starts.
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0,3U c.
The protective relays for these motors have been calibrated to protect the motors from thermal damage by setting the time dial on the relay below the thermal overload curve
for the motor.
In the event of an attempt tc start the motor, the relays would trip the circuit breaker supplying the motor if the current drawn during starting exceeded the motors' thermal capability.
d.
As discussed in paragraph 5, part 4 of Reference (2),
tripping the Haddam Neck Plant due to low voltage may further degrade the transmission-system voltage to the point where another nuclear plant with a similar under-voltage scheme will trip. Operations of this nature unnecessarily threaten the integrity of the transmission system.
Q3. Clarify the discrepancy in the two statements in your proposed Technical Specifications change regarding equipment capability -
that of operating without damage at 3660 volts for 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> and that of the second level voltage protection set point of 3871 volts for 9 seconds.
A3. The significance of the 3660 volt limit is that voltage below this level will be below the 90% voltage requirement for operation of the motors on the 480-volt busses if the motors are in the running mode. This level corresponds to 406 volts on the 480-volt busses.
Motors on the 4160-volt busses could run at voltage as low as 3620 volts, but are limited because of the voltage requirements ca the 480-volt busses. The 3871-volt limit is the level required prio.
1E;2 057
5-to starting safeguards loads so that once all the ESF loads are running, we will have at least 3660 volts on the 4160-volt bus.
In essence, the plant could operate continuously at voltages down to 3660 volts on the 4160-volt busses if no safety-related motors were required to start.
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