ML19296D298
| ML19296D298 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 02/25/1980 |
| From: | Goodwin C PORTLAND GENERAL ELECTRIC CO. |
| To: | Schwencer A Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8003030347 | |
| Download: ML19296D298 (3) | |
Text
.
s
/s m
D i= Portlard C,enem! Electric Ccnyany
-J i
s i
February 25, 1980 Trojan Nuclear Plant Docket 50-344 License NPF-1 Director of Nuclear Reactor Regulation ATTN:
Mr. A. Schwencer, Chief Operating Reactors Branch #1 Division of Operating Reactors U. S. Nuclear Regulatory Commission Washington, D. C.
20555
Dear Sir:
Pursuant to the telephone conversation on February 11, 1980 between Portland General Electric Company (PGE) and your staff, the attached supplemental information concerning the effects of Degraded Grid Voltage at the Trojan Nuclear Plant is submitted.
The attached supplemental information not only provides additional data on the bus-voltage profile for 230 kV grid voltage but also clarifies the point of inconsistency questioned by your staff in our October 5, 1979 and our January 11, 1980 submittals.
It should be noted that, as explained in the attachment as well as in the January 11, 1980 submittal, the information in our January 11 letter was based on slightly different load calculations than those used for the October 5, 1979 submittal.
These revised load calculations had concluded that a lower grid voltage (230 kV) can be tolerated before safety-related equipment will be adversely affected by the undervoltage condition.
Sincerely, s
C. Goodwin, Jr.
AssistantVicePres[ dent Thermal Plant Operation and Maintenance CG/K!!/4mg9A18 Attachment g
c:
Mr. Lynn Frank, Director State of Oregon Department of Energy 00 03030 3+ {
s ATTACHMENT 1 Trojan Nuclear Plant Supplemental Information to PGE Submittal of January 11, 1980 on Degraded Grid Voltage The PGE letter of October 5, 1979 responded to the NRC letter of August 8,1979, concerning the effects of a postulated grid undervoltage on the Plant safety equipment assuming the onsite power source being unavailable. The January 11, 1980 PGE letter responded to the October 1, 1979 NRC letter (and June 3,1977 NRC letter) which requested instal-lation of a second level undervoltage protection system. These two separate responses were to two interrelated letters but basically different problems.
The initial grid stability analysis, conducted for the PCE response of October 5, 1979, had showed that, at 100 percent PGE system load, the grid voltage will drop to 236 kV at the Trojan switching station.
Since the historical minimum voltage observed was slightly less than 236 kV (235 kV was observed twice during the last half of 1978), a conservative grid system voltage of 232 kV was chosen and analyzed with acceptable results as shown in Table 11 of the October 5, 1979 PGE letter. In conducting this analysis, we had assumed a situation in which the grid voltage stabilized below 232 kV with Trojan off line (as it would be following a Plant trip). The possibility of having such an occurrence is considered to be very remote based on the operational experiences at the Trojan plant. This operational experience had led us to conclude that 232 kV was a minimum expected value of grid voltage at the Trojan plant.
Subsequently, based on the NRC letter dated October 1,1979, another load flow calculation was conducted with more realistic transformer tap ratios and bus loadings. The results of the revised calculation indi-cated that a grid voltage of 230 kV can be tolerated before safety-related equipment has the potential for being adversely affected by the undervoltage condition; i.e.,
230 kV is the minimum grid voltage value that can be tolerated without degrading continuous operating capabili-ties of any of the safety-related loads. Below this value, continuous operation of safety-related loads could jeopardize the equipment. The ESF equipment which might be jeopardized are nominal 480-V loads (Service Water Booster Pumps and Containment Air Cooler Fans). Nevertheless, at a switchyard voltage of 230 kV, sufficient margin exists to preclude potential damage to these voltages.
The 480-V ESF loads are the limiting equipment in this analysis due to the significant voltage drop (5-15 V) in the long cable run from the MCC's to the motors. Therefore, 230 kV was used as the grid voltage for the proposed second level of the under-voltage protection system, described in detail in the January 11, 1980 PGE submittal, to protect the safety-related equipment.
Table 1 tabulates a listing of the Plant bus profile for both 230 kV and 232 kV switchyard voltages per the resised load flow program used in our January 1980 submittal. The values for 232 kV were also included in the table for the purpose of comparison with a similar table in the October 5, 1979 PCE submittal.
KH/4sa9A16
Table 1 Grid Voltage: 230 kV and 232 kV Offsite Power Source: Startup Transforrrar Calculated Voltages kV Bus Normal Loads Normal Loads Running and Designation Running All DBA Loads Running 230-kV Switchyard 230 230 232 12.47-kV Bus H1 11.6 11.5 11.6 g4.16-kV Bus Al 3.91 3.85 3.90 Service Water Pump on Bus A1 Containment Spray Pump l on Bus A1 3.85 3.90 i
I Component Cooling Water l Pump on Bus A1 i
i Charging Pump on Bus A1 3.85 3.90 3.86 3.90 SI Pump on Bus A1 3.86 3.90 RHR Pump on Bus A1 480 LC Bus B01 0.4411 0.4306 0.4367 Containment Air Cooler on Bus B01 0.4262 0.4157 0.4217 480 LC Bus B03 0.443 0.4363 0.442 Containment Air Cooler on Bus B03 0.4286 0.4214 0.4274 480-V MCC Bus 21 0.4406 0.430 0.4359 Service Water Booster l
0.4354 0.4248 0.4308 Pump on Bus 21 480-V MCC Bus B23 1
0.4406 0.4296 0.4358 I
480-V MCC Bus B25 0.4421 0.4353 0.4409 i
Service Water Booster 3 Pump on Bus B25 0.4378 0.4306 0.4364 RAY /3jr3.2A14