ML20039D614

Application for Amend to Licenses DPR-24 & DPR-27,responding to NRC 811218 Telecopied Request for Addl Info on 811203 Tech Spec Change Request 74 Re Emergency Power Undervoltage Relay Protection

ML20039D614
Person / Time
Site:	Point Beach
Issue date:	12/30/1981
From:	Burstein S WISCONSIN ELECTRIC POWER CO.
To:	Clark R, Harold Denton Office of Nuclear Reactor Regulation
References
TAC-12955, TAC-12956, TAC-47404, TAC-47405, NUDOCS 8201050267
Download: ML20039D614 (3)

Text

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I Wisconsin Electnc mmcome 231 W. MICHIGAN, P.O. BOX 2046, nelLWAUMEE, WI 53201 December 30, 1981 c)

Mr. Harold R. Denton, Director 4

ff Office of Nuclear Reactor Regulation U.

S. NUCLEAR REGULATORY COMMISSION nECgNED 3

Washington, D.

C.

20555 gp Attention:

Mr. Robert A. Clark, Chief h manamaruttaE88 4 Operating Reactors Branch 3 8883 f "

Gentlemen:

DOCKET NOS. 50-266 AND 50-301 EMERGENCY POWER UNDERVOLTAGE RELAY PROTECTION TECHNICAL SPECIFICATION CHANGE REQUEST NO. 74 POINT BEACH NUCLEAR PLANT, UNITS 1 AND 2 On December 18, 1981, Mr. Colburn of your Staff tele-copied to Wisconsin Electric a request for additional information concerning Point Beach Nuclear Plant Technical Specification No. 74 which was submitted to the NRC with our letter dated December 3, 1981.

The specific inquiries and our responses to those questions are provided in this letter.

Prior to addressing your questions, additional clari-fication of the minimum expected voltage values presented in our June 1, 1981 submittal on the adequacy of statiou distribution system voltages is necessary.

The minimum expected voltage values which.were given in the first paragraph of that letter were expressed as a percent of the nominal system voltage (4,160 volt or 480 volt).

Since the safety-related loads on these systems have voltage ratings lower than the nominal ~

system voltage, the voltage available at the load as a percent of the motor voltage rating will be greater than that shown in our June 1, 1981 submittal.

In addition, the minimum voltage expected at the terminals of any 480 volt system load was calculated based on some very conservative assumptions.

These calculations have been recently refined.

Based on the same conditions expressed in paragraph one of our June 1, 1981 submittal, the minimum expected voltage at the terminals of any 4,160 volt system load is 3,839 volts or 95.9% of the 4,000 volt motor rating.

The minimum expected voltage at the terminals of any 480 volt system load is 418.7 volts or 91% of the 460 volt motor rating.

These values are above the 9CM of rated voltage which is the minimum required running vonage in ANSI C50.41-1977.

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8201050267 811230 DR ADOCK 05000266 0\\h PDR

Mr. Harold R. Danton Dactmbar 30, 1981 Concerning your question as to the percentage of the setting for which the trip is defined, the relays utilized for the undervoltage relaying proposed in Technical Specification Change No. 45 are of the ITE-27D type with a definite time curve.

This type of relay has a fixed time delay which is defined from 0 to 100% of the trip setting.

Please note that the trip setting is that which is defined in Table 15.3.5-1 of the Technical Specifications.

Concerning your question as to whether the temperature limits defined in paragraph 9.3 of ANSI C50.41-1977 are maintained when running a motor with a service factor of 1.15, loaded to the rated horsepower, and operating at a voltage less than the 90% of the rated voltage, we have the following comments.

A motor running at rated horsepower will draw less current than it would if it were run at a load corresponding to a 1.15 service factor. This effect would offset the increase-in current which results when running a motor at rated load with less than 90% of rated voltage.

The result of these offsetting factors is that a motor with a 1.15 service factor running at rated horsepower could run on voltage less than 90% of nominal without exceeding the temperature rise values given in Table 2 of ANSI C50.41-1977.

At this time, however, we have no firm basis (such as heat rise test data) for determining the minimum voltage level at which a motor, operated as described above, will demonstrate temperature rise characteristics less than those allowed by Table 2 of ANSI C50.41-1977.

We do not wish to set undervoltage relay settings at a level that would strip the safeguards equipment loads unnecessarily.

Accordingly, we would propose to modify our Technical Specification Change Request No. 74 to change the trip setting limit of the degraded grid voltage relays, as given in item 9 of Table 15.3.5-1 to

>3,762 v. + 2

= 3,839 v. minimum 4,160 v. system voltages mInu% (3,762 v.

s 2% relay tolerance). This setting will maintain a minimum voltage of 89% of nameplate rating at all safety-related loads which we believe to be entirely adequate.

It is our intention to determine the ultimate capability of safety-related loads to operate at reduced voltage and submit a future Technical Specification change' based on this determination, if appropriate.

Concerning your question as to the adequacy of the loss of voltage relays to protect safety-related loads from operation at less than adequate voltage for the sixty seconds it would require for the degraded bus voltage relays to operate, we have the following comments.

It is our best engineering 4

judgment that the possibility of low voltage levels for a period of sixty seconds or less is not a significant concern.

This judgment is based on the following facts:

The safety-related motors are capable of running at 75% of their rated voltage for at least one minute per paragraph 14.3 of ANSI C50.41-1977 (72% of 4,160

~

volts and 72% of 480 volts).

+

Mr. Harold R. Danton D:ccmbar 30, 1981 As described in our September 17, 1976 submittal,

" Adequacy of the Class IE Distribution System", there are two additional undervoltage relaying schemes which provide undervoltage protection in addition to the degraded grid voltage protection.

Both schemes provide the same protective action as the degraded grid voltage relays.

The first scheme is actuated in 2.6 seconds at 0 volts and 13.6 seconds at 3,255

~

volts (78% of 4,160 volts).

The second scheme is actuated in twenty cycles at 0 volts and 1.2 seconds at 2,450 volts (59% of 4,160 volts).

F There is no known or postulated system or plant condition which would lead to voltages less than 75%

of nominal on the 4,160 volt or 480 volt systems except total loss of voltage.

The voltage level required to cause actual stalling oof motors or opening of contactors is significantly less than 75% of rated voltage.

Based on our operating experience, sixty seconds is much too short a time to cause any significant temperature rise to take place in the safeguards motors or motor contactors.

We understand that the Staff has not completed its review of the acceptability of our proposed setpoint of sixty,

seconds for the time delay feature of the degraded grid voltage relay.

We, therefore, would propose a time delay setpoint for-these relays of less than thirty seconds for an. interim period until the Staff shall have completed its review and we may have the benefit of any further evaluation we are now making.

As noted in our letter of May 30, 1981, relay settings for the degraded grid voltage relays for Point Beach Unit 2 will be made when the new relay equipment is installed.

As specified in the Commission's regulations, we are providing three signed originals and forty copies of this license amendment application.

Should you have any questions concerning the contents of this application, please notify us so that we may address your concerns.

Very truly yours,

- Sol Burstein Exe utive Vice President Copy to NRC Resident Inspe~ tor Subscribed and sworn to before me this day of Dece r 4 1.

n Notary Publiq, hte of Wisconsin My Commission g pirca~nM

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