ML20053A595
| ML20053A595 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 05/18/1982 |
| From: | Bordine T CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20053A596 | List: |
| References | |
| NUDOCS 8205260286 | |
| Download: ML20053A595 (5) | |
Text
6 Consumers Power Company Generet Offices: 212 West Michison Avenue, Jackson, MI 49201 * (517) 788-0550 May 18, 1982 Dennis M Crutchfield, Chief Operating Reactors Branch No 5 Nuclear Reactor Regulation US Nuclear Regulatory Commission Washington, DC 20555 DOCKET 50-155 - LICENSE DPR BIG ROCK POINT PLANT - STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES By letter dated January 13, 1982, Consumers Power Company provided a status report describing the progress of a new station voltage analysis. The analyses has been completed and is provided as an enclosure to this letter.
The system grid voltage analysis used a computer simulation to determine minimum and maximum expected voltages for station power equipment during various plant operating conditions. The analysis results (preliminary and final), conditions found, and actions taken have been incorporated in the i
report. This report is provided for your information in response to the verbal telephone requests from Mr Richard Emch of your staff.
/ Thomas C Bordine Staff Licensing Enginee'r CC Administrator, Region III, USNRC NRC Resident Inspector-Big Rock Point Attachment t
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BIG ROCK POINT STATION ELECTRIC DISTRIBUT10N SYSTEM VOLTAGE REPORT This report addresses the adequacy of the station power voltages for all possible operating conditions at the Big Rock Point Plant. Attachment 1, included in this report, is the preliminary study which uncovered several undervoltage (UV) and overvoltage(OV) conditions and made preliminary recommendations as to how these conditions could be eliminated. Attachments 2 and 3, provided for your convenience, are lists of the UV and OV conditions found and the preliminary recommendations made to correct those conditions, respectively. This report describes what actions were ultimately taken to correct the UV and OV situations and the results of those actions.
Recommendations a, b, and c of Attachment 3 were implemented. Referring to and Table 3 of Attachment 1, it can be seen that these tap changes alleviated the UV conditions for sections 1.a.1,1.a.3,1.b.1,1.b.2 and part of 1.a.2.
The tap changes, however, did not completely eliminate the UV condition at the input of the battery chargers or at the input of the I&C power supplies. Additional analysis showed that the minimum voltage at the input of the battery chargers (at bus 2A) in this condition (with the tap changes made) was 0.897 per unit (pu), leaving an UV condition of only 0.3%
which was considered insignificant.
It should be noted that the battery charger manufacturer states that the chargers will provide rated output given input voltages within 10% of its rating.
The UV condition at the input of the I&C power supplies was also determined to be insignificant. The minimum voltage at the input of the power supplies was 0.882 pu af ter the taps had been changed. To be conservative, additional analysis was performed on the power supply with the highest minimum voltage rating. The analysis was performed on power supply ES-8512B which has a minimum rating 0.901 pu.
(It should be noted that Attachment 1, page 9, lists ES-2108 with a minimum voltage of 0.910 pu.
This power supply was listed in error. A review of plant records shows that this supply does not exist.) The additional power supply analysis proved that given an input of 0.882 pu at ES-8512B, the loop transmitter output would be insignificantly affected and would continue to maintain an output current proportional to its pressure input.
From the above information, it can be seen that there are no significant undervoltages present with the 2400 V voltage regulator out of service.
It is therefore concluded that plant operation with the 2400 V regulator out of service need not be restricted as Item d of Attachment 3 originally recommerded.
Referring to Attachment 3, Recommendation e, the emergency diesel generator pre-load voltage was adjusted at the regulator from 490 V to 485 V during a recent surveillance test.
The surveillance test procedure was modified to incorporate the pre-load voltage of 435 V and to include a voltage requirement of 485 V (+0, -10 V) for loaded conditions during the test. The selection of the pre-load voltage requirement and the loaded voltage range was based on :
- 1. the known emergency diesel generator voltage reduction as a function of
- load,
- 2. the known load during surveillance testing,
- 3. the maximum expected step load during an accident and
- 4. the generator's own voltage rating (480 V nu0582-0013c142
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+5%).
The selection of these voltages insures that the diesel generator will supply all station power equipment with adequate voltage once the diesel generator has automatically assumed the maximum expected step load af ter an accident and that the generator is operated within its own voltage limits during test and actual operation. Both the pre-load voltage and the load voltage range are verified every three days.
In addition to revising the diesel generator surveillance test procedures, plant operating procedures regarding the emergency diesel generator were also revised to ensure (along with the three-day surveillance test pre-load and load voltage verification) that the generator output is between 485 V and 456 V to ensure that the generator is operated within its own voltage ratings and that all statica power system equipment is provided with voltage within the equipment rated limits anytime the generator supplies the system. As a result, the regulator adjustment and the procedural revisions corrected the overvoltage condition 2.a.1 (see Attachment 2).
Recommendation f of Attachment 3 refers to the standby diesel generator.
Recommendation f called for operating the generator at a terminal voltage of 483 V during minimum and maximum voltage conditions, Further analysis, however, based on known standby diesel generator output voltage at known load revealed that if the generator was adjusted to provide 480 V when test loaded to 200 kW, the station power system would be provided with adequate voltage such that no equipment would be overvoltaged or undervoltaged. The standby diesel generator voltage regulator will be adjusted at the earliest opportunity to provide such a voltage while loaded as described. Given the aforementioned analysis, the generator is expected to provide between 472 V and 490 V for the station power system after automatically responding to the maximum expected step load after an accident. Generator voltages within this range will result in station power system equipment voltages which are adequate and within the equipment minimum and maximum ratings.
In addition to revising the standby diesel test procedures, plant operating procedures were also revised to ensure that the standby diesel generator output voltage is maintained between 472 V and 490 V whenever the generator is loaded with station power system equipment.
It should be noted that although 490 V exceeds the manufacturer's nominal rating of the generator which is 460 V +5%
(resulting in the upper voltage rating of 483 V), the manufacturer (Caterpillar) has indicated that infrequent generator operation at such voltage values would not detrimentally affect the generator. As a result of the aforementioned regulator adjustment and the procedural revisions. the overvoltage and undervoltage conditions described in Items 2.b.1 and 2.b.2 of are eliminated.
It should be noted that page 29 of the attached report (Attachment #1) incorrectly states that undervoltages occur at buses IA and 2B when the standby diesel generator is operating at 460 V and the station power system represents a maximum load on the standby diesel generator. To correct the record, it should be stated that the reference to bus 28, as stated above, is incorrect. As concurred by the author of the report, the report should state that buses IA and 2A are undervoltaged and not IA and 2B.
The final preliminary recommendations g and h of Attachment 3 deal with the ability of the emergency diesel generator to start and accelerate the fire pump with a preload of 160 kVA.
This deals with Section 2.a.2 of Attachment nu0582 0013c142
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'3 2.
Starting the 100 hp fire pump using the 480 V, 250 kVA emergency diesel generator was examined with a generator preload of 160 kVA and the recommended operating generator terminal voltage of 480 V (1.0 pu) presented in Part IVB of Attachment 1.
As can be seen in Table 7 of Attachment 1, the motor terminal voltage drops to 65.8% which is below the assumed 70% minimum starting voltage rating of the motor. Though below the assumed 70% minimum starting voltage rating of the motor, the 65.8% motor terminal voltage was determined to be sufficient to breakaway and accelerate the fire pump.
It was calculated that a voltage of 65% of maximum developed a starting torque of 42%
full load torque (FLT), while the pump manufacturer (Worthington) indicated the Big Rock Point fire pump required only 20% FLT. With this in mind, it is expected that the fire pump motor will start and begin rotating the pump when automatically started on the preloaded generator given 65% voltage at the motor's input.
It is also expected that the motor will accelerate to running speed as the motor voltage should return to normal within a few seconds.
The above data suggests that the originally assumed 70% minimum starting voltage rating of the motor was a conservative figure and that 65% is more reasonable. Consumers Power plans to conduct alternative tests to verify this once suitable procedures have been prepared and reviewed by the appropriate departments. At a future outage, once these test procedures have been completed, a test can th=n be conducted with the diesel generator preloaded to 160 kVA, maintained au 480 V and the electric fire pump started. This will veriiy Section 2.a.2 cf Attachment 2 will be satisfied. This test has been placed on the plant praject list.
Another fact to be noted is that should the electric fire pump fail to start and accelerate as expected when called upon by an automatic start signal during operation of the emergency diesel generator preloaded to 160 kVA, the diesel fire pump servec as a backup.
The diesel fire pump automatically starts upon decreasing fire header pressure as does the electric fire pump.
Like the electric fire pump, the diesel fire pump is capable of passing 1000 GPM at a dis. charge pressure of 110 psi.
This report has shown that the station power auxiliary voltages at the Big Rock Point Plant have been analyzed and any discrepancies that were found have been either corrected or are in the process of further analysis. The following is a list of the final actions taken.
SUMMARY
OF FINAL ACTION 1.
The main transformer tap was changed from the 145/13.5 kV tap to the j
140/13.5 tap.
2.
The No. 11 transformer tap was changed from the 2400/480 V tap to the 2340/480 V tap.
3.
The No 22 transformer tap was changed from the 2400/4870 V tap to the 2340/480 V tap.
4.
Additional analysis established that the undervoltage of the power supplies and battery chargers of initial concern is insignificant when the 2400 V, 250 kVA voltage regulator is out of service.
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4 5.
The emergency diesel generator voltage regulator has been adjusted and testing and operating procedures have been revised to ensure that the diesel generator will provide the station power system equipment with voltage within the equipment ratings. Also, the adjustment and procedural changes ensure that the emergency diesel generator is operated within its i
own voltage limits 6.
The standby diesel generator voltage regulator will be adjusted and operating procedure 3 have been revised to ens-tre that the diesel generator j
will provide the station power system equipnent with voltage within the l
equipment ratings. Also, the adjustment and revisions to operating and test procedures inave been made which ensure that the standby diesel generator operates with output voltage levels which do not detrimentally affect the generator.
7.
Analysis has been performed which indicates that the electric fire pump can be successfully started by a pre-loaded emergency diesel generator with a terminal voltage of 480 V.
An actual test, to verify such, is planned.
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