ML17212B465

Advises That CV-2 Undervoltage Relay to Be Installed, Although Probability of Operating for Significant Time Period During Undervoltage Condition Small

ML17212B465
Person / Time
Site:	Saint Lucie
Issue date:	03/18/1982
From:	Robert E. Uhrig FLORIDA POWER & LIGHT CO.
To:	Clark R Office of Nuclear Reactor Regulation
References
L-82-105, NUDOCS 8203240193
Download: ML17212B465 (6)

Text

+~4 REGULATORY ORMATION DISTRIBUTION SY M (RIDS)

AC'CESSION NBR 0 820324 0 1 93 DOC ~ DATE 82/03/ 1 8 NOTAR XZED WO FAOIL:50-335 St. Lucie Plantr Unjust 1~ Flor ida Power 8 Light Co.

AUTH~ NAME AUTHOR AFFILIATION UHRIGeR ~ E ~

Florida 'Power 8 Light Co+

R E'C IP ~ NAME RECIPIENT AFFILIATION CLARKpR ~ AD Operating Reactors Branch 3

I SUBJECT; Advises that CV 2 undervoltage relay to 'be installed although probability of operating for significant <time period during undervoltage condition small.

DISTRIBUTION CODE:

AOI5S COPIES RECEIVED:LTR.J ENCL J SIZE:

TITLE: Onsite Emergency Power Systems NOTES:

DOCKET 05000335 RECIPIENT ID CODE/NAME ORB P3 BC 01 INTERNAL: AEOD IE 06 NRR/DL/DRAB 12 NRR/DS I/PSB 14 RGN2 COPIES LTTR ENCL 7

7 1

1 1

1 1

1 1

1 1

1 RECIPIENT ID CODE/NAME ELD 1'7 MPA 18 N

DSI/ICSB 09 00 COPIES LTTR ENCL 1

1 1

1 1

1 1

1 EXTERNAL: ACRS LPDR NSIC 16 10 10 03 1

1 05 1

1 INPOEJ ~ STARNES NRC PDR 02 NTIS 1

1 1

1 1

1 TOTAl NUMBER O'F COPIES REjGUIRED:

L'TTR 31 ENCL 31 I

f

l(

a

$(

f 1

1 N

g 1

e P.O. BOX 529100 MIAMI,F L 33152 FLORIDAPOWER & LIGHT COMPANY March 18, 1982 L-82-105 Office of Nuclear Reactor Regulation Attention:

Mr. Robert A. Clark, Chief Operating Reactors Branch g3 Division of Licensing U.S.

Nuclear Regulatory Commission Washington, D.C. 20555 Dear Mr.

Cl ark:

Re:

St.

Luci e Unit 1

Docket No. 50-335 Degraded Grid Volta e

@~A CCl F

Florida Power 8 Light has reviewed the NRC letter, dated November 30, 1981, concerning degraded grid voltage at St.

Lucie Unit 1.

We have studied the NRC information and Technical Specification request as it pertains to our grid stability and power distribution operating practices.

As described in the attached

response, the probability of operating for any significant time period during an undervoltage condition is small and therefore does not warrant additional bus undervoltage protection.

However, we will install a

second CV-2 undervoltage relay as requested in the referenced NRC letter.

In order to preclude a severe undervoltage condition, either momentary or sustained, we have provided undervoltage protection for the 480 V buses as described in the attached response.

Ver uly y urs, o ert E. Uhrlg Vice President Advanced Systems 8.Technology REU/PLP/mbd cc:.

J.P. O'Reilly, Region II Harold F.

Rei s, Esquire PD(5 S

8203240f93 820318 PDR ADOCK 05000335 PEOPLE... SERVING PEOPLE

In response to NRC letter dated November 30, 1981 RE:

Degraded Grid Voltage St. Lucie Unit f/1

References:

1)

FPL R.E. Uhrig letter, L-79 of ll/9/79 to NRC Mr. Gammil 2)

FPL R.E. Uhrig letter L-80-304 of 9/12/80 to NRC Mr. Eisenhut 3)

FPL R.E. Uhrig letter L-80-212 of 7/3/81 to NRC Mr. Clark 4)

NRC R.A. Clark letter of ll/30/81 to FPL R.E. Uhrig FPL's letter of ll/9/79 (reference

1) provided our operating experience t'.hat an undervoltage condition at a level which would preclude proper equipment operation has an extremely low probability.

Voltage conditions in the grid system less than 230 KV are shown by experience to be short term and transient in nature with recovery or collapse of the system expected to occur in a short time period. If a general system voltage reduction were initiated, it would be accomplished at the distribution level and not by a reduction of plant output voltage.

Thus, the only probable undervoltage conditions which can exist will be transient in nature, i.e., the voltage will either completely collapse or recover wi.thin a short period.

Prolonged operations at lower voltage cond'itions are not practical.

Thus operation of the undervoltage relays on the'afety related buses is precluded by grid practices.

The above not withstanding, anadditional level of undervoltage protection as discussed in FPL's ll/9/79 letter (reference" 1), was added to the 480V buses'uring the last refueling outage (Octbber, 1981).

This further assures that, in the unlikely event of a sustained degraded grid voltage concurrent with a safeguard

signal, the manufacturer's guaranteed rating of the Motor Control Center contactors (the most limiting equipment) is not exceeded.

The modifi-cation added an undervoltage relay to each of the safety related 480 volt load centers.

'i%en actuated, after a short time delay, it will strip the bus, start diesel generator and sequence the loads on the effected train.

Since there does not exist any electrical or mechanical intertie between buses, the bus shedding and load sequencing in one bus will not affect the other.

Approximately 0.2 second after the diesel generator has started and its breaker has closed, the undervoltage relays are bypassed.

They remain so until the diesel br'eakers open, at which time they are reinstated.

0

Response

to NRC letter dated ll/30/81 RE:

Degraded Grid Voltage St. Lucie Unit //1 Pa e

2 A testing circuit has been engineered into the undervoltage relay logic to provide the capability of functionally testing the undervoltage relays.

A similar test circuit exists in the 4 KV safety related bus undervoltage protection logic utilizing the Westinghouse CV-2 relays.

In reference 2, it was stated that the addition of the undervoltage relays in the safety related 480 V buses will ensure sufficient voltage'o meet the manufacturer's guaranteed pickup point of the most limiting piece of equip-ment, the motor control center contactors.

A setpoint of 429 volts with a 1 second delay has been chosen.

The 1 second time delay is to prevent false actuation which may be caused by relay chattering.

This setpoint assures the HCC voltage will be above the manufacturer's guaranteed pick-up voltage in case of a safeguard actuation and adequately protects the equip-ment from starting during an unlikely sustained degraded voltage condition.

I Due to independence and redundancy (see reference 3), the undervoltage protection logic of the 4160 and 480, volt busks provides protection against spurious trips of the Class 1E bus'es-lfrom off-site power.

Furthermore, in order to prevent tripping of any safety related power train from its offsite power source due to spurious actuation or failure of a single CV-2 undervoltage relay as suggested in reference 4,

a design modifica-,

tion is in progress to add an undervoltage relay to each of the 4160 volt buses.

The new relay will parallel the existing undervoltage relays with their normally-closed contacts series connected.

This modification is expected to be installed during the next scheduled refueling outage in 1983.

L

'