ML19253C942
| ML19253C942 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 12/10/1979 |
| From: | Herbein J METROPOLITAN EDISON CO. |
| To: | Harold Denton, Reid R Office of Nuclear Reactor Regulation |
| References | |
| GQL-1470, NUDOCS 7912120414 | |
| Download: ML19253C942 (3) | |
Text
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Metropolitan Edison Company Post Of fice Box 480 g
Middletown, Pennsylvania 17057 717 9444041 Wnter's Direct Dial Number December 10, 1979 GQL lh70 Director of Nuclear Reactor Regulation Attn:
R. W. Reid, Chief Operating Reactors Branch No. L U. S. Nuclear Regulatory Con =ission Washington, D.C.
20555
Dear Sir:
Three Mile Island Nuclear Station, Unit 1 (TMI-ll Docket No.
50-289 License No. DPR-50 Degraded Grid Voltage With regard to your letter of August ik,1979, concerning a request for additional information on degraded grid voltage, enclosed please find the responses to Items 1 and 2.
The response to Item 3 is presently undergoing review and, therefo.ce has not been included.
It is anticipated that the response vill be completed by December 21, 1979 Additionally, your letter of August ih, 1979, referred to our letter of August 19, 1977 The August 19, 1977 letter has been supplemented by an October 16, 1979 letter (GQL 12921 and should be considered an addendum to the August 19, 1977 letter. Both of these letters have been referenced in the attached responses.
Sincerely, t
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J. G, Herbein Vice President-Nuclear Operations JGE:DWR:tas 1535 259 Aos s
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Metrocactan Ec son ccmcany :s a Memcer et tne Genera' Fuenc utit es s< stem 4
7912120
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EHetOSuRn REQUEST FOR ADDITIONAL INFORMATION -
DEGRADED GRID VOLTAGE ITEM 1 Your chosen nominal set point of 353hv and minimum acceptable setpoint of 3h23V correlates to 88% and 85.6% of motor rated voltage, respectively.
As both of the voltages are below those reco= mended by ANSI C8h.1-1973 and most manufacturers, show by analysis that a postulated voltage of 89% of h000v for an indefinite time vill not cause thermal damage to the ESF otors.
RESPONSE
The undervoltage relays are set to provide the necessary protection for the following reasons:
1.
To prevent the control transformer fuses within the motor control centers from burning due to a lov voltage condition.
2.
To prevent spurious trips during the starting of large motors.
In the submittals dated August 19, 1977, and October 16, 1979, both of the above requirements have been satisfied under the worst conditions in which one (1) Aux. transformer is in operation, the grid is at 223KV, the plant operating at 100% power and one full ES train running. Under the above stated conditions, it has also been shown in the submittal of October 16, 1979 -
Exhibit 12, that the h000 volt bus vill be at 3625 volts under running conditions. This is 90.6% of the motor rated voltage.
This rating is within the limits as recommended by ANSI C8h.1-1973.
ITEM 2 Provide the time delay of the undervoltage protection at your chosen setpoint.
Provide analysis showing that the time delay for undervoltage protection vill preclude any spurious trips from starting large motors and also prevent any thermal damage to the safety related equipment. Also provide sufficient information (voltage drop analyses) to allow our independent verification that the undervoltage set point and time delay selected vill not cause spurious separation of safety buses from offsite power during all modes of plant operation (start-up, shutdown, power operation and accident condition 1 due to automatic or manual starting of large motors, bulk or sequential loading or automatic transfer of electrical loads. The analyses should include conditions when the safety buses are supplied from the Unit Auxiliary Transformer, the Start-Up/ Reserve Transformer or other available offsite connections and assuming the need for electrical power is initiated by an anticipated transient (e.g., unit trip) or an accident, whichever presents the largest load demand.
1535 260
. + ~ Request for Additional Infomation -
Derraded Grid Voltare
Response
The undervoltage relays applied on TMI Unit tio.1 class IE Equipment are 1AV51K inverse time-voltage characteristic relays. These relays presently have the following documented setting:
Pickup = 353h volts Tested set point = 6.5 seconds at 299h.7 volts Due to the inverse time characteristic of these relays the time to trip varies with the magnitude of the voltage applied. '21erefore, the defined range of operation for these relays as presently set is:
16 seconds to trip at 3h23 volts 2.1 seconds to trip at 0 volts The :EC's concerns about spurious trips during the starting of large motors and the possibility of voltages belov motor ratings under vorst case conditions were answered by the voltage study data supplied to you for the October 16, 1979 reply to the imC's inquiry on the adequacy of station distribution voltages.
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