ML19309C270

Electrical Distribution Sys Review Summary

ML19309C270
Person / Time
Site:	Crystal River
Issue date:	04/03/1980
From:	FLORIDA POWER CORP.
To:
Shared Package
ML19309C265	List: ML19309C264 ML19309C270
References
NUDOCS 8004080380
Download: ML19309C270 (1)

Text

{{#Wiki_filter:O CR-3 ELECTRICAL DISTRIBUTIo;; SYSTDf REVIEW SDUIARY 8004080350

INTRODUCTION The review of the electrical power systems at CR-3 was perf ormed in accor-dance with the NRC letter and Guidelines dated 8/8/79. The review and analys is (eee attachments) indicate that the electrical systems a re ade-quate to allow the safety-related loads to perf orm their function under all conditions as described in the letter. NOTE: The load data used in the ref erenced " Plant Auxiliary Loading Sum-cary" was developed using nameplate data and " running" loads. Actual load data taken at the plant has shown that the Loading Summary is very conser-vative and normal operating loads are about 15% lower overall. 4 KBBemhT02D47

i i 1 Page 1 VOLTAGE DROP CALCULATIONS i i ASSUMPTIONS & METHODS USED IN ttAKING CALCULATIONS: I i A. LOADS 1 [ 1. Motor loads were considered " constant kVA Loads" with power fac-l tors of 0.9. t i l 2. Other loads, such as, heaters, distribution pa nels, etc., were considered as " Constant Impedance Loads." 3. Loads taken from Crystal River Unit 3 " Plant Auxiliary Loading l Summary" revised February 15, 1977. This summary was made using nameplate voltages and currents. i 4. Safety-related loads we re taken from the Crystal River Unit 3 ^ FSAR Table 8-1 and supplemented by the Plant Auxiliary Load Sum-mary as required. B. WORST CASE CONDITIONS NOTE: The Unit 3 Auxiliary Transformer and the Unit 3 Start-up Trans-former are similar 3-winding transformers with identical ratings. The only dif ference is the high side voltage ratings which are 22. kV for 1 the Unit Auxiliary Transformer and 230 kV for the Start-up Transform-er. Normally, the Start-up Transformer only feeds the 4.16 kV ES bus-ses while the Unit Auxiliary feeds all others.. Worst Case has been I calculated considering all loads being fed f rom the Start-up Transfor-f mer. 1. Steady State a. System voltage at minimum with all coincidental unit loads, emergency block loading sequences blocks 1 thru 4 including the manually applied loads of FSAR Table 8-1.- r b. System voltage at maximum with all coincidental unit loads,- l and the emergency block loading sequence blocks 1 thru.4 in-cluding the manually applied loads of FSAR Table 8-1. l c. System voltage at minimum and maximum with emergency block loads 1 thru 4 on the Unit I and 2 Startup Transformer. 2. Dynamic The same as each of the above " Steady State" cases, in addition to starting a large motor on the 4.16 kV ES Switchgear bus. i f KBBemhT02D47 j l i l 1 e -y -t .----,--m-,- , - *, - - -, -, -, + - - - - - - +-.,-,.,---e- - -, .,--v, --y , - - = - *, - -tT'-- r," -+, w --mv-*r n--y-we-. .,r,--

1 0 e Page 2 y C. BASE VALUES 4 l l. Power:. 100 MVA = 1.0 per unit (p.u.)

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Voltage: 4.16 kV - 1.0 p.u. 2. Current: 13,879-A - 1.0 p.u. D. SYSTI21 VOLTAGE REQUIREMENTS i 1. System voltage is 240 kV nominal, however, stability studies in-dicate voltage minimum and maximum values are + 7.5% of the capa-bility of the line to the start-up transf ormer - (MTTR-2) primary which is 230 kV, therefore: i Minimum voltage to MTTR-2 is 212.75 Maximum voltage to MTTR-2 is 247.25 2. Start-up transformer (MTTR-2) tap setting is tap number 4 which is the 22450 setting. j 3. Unit 1 & 2 start-up transformer tap setting is tap number 1 which is the 235750 setting. E. COMPUTATIONAL METHODS The " Constant kVA" and " Constant Impedance" loads f rom each of the re-spective distribution busses (i.e., 6.9 kV, 4.16 kV, 0.48 kV and 480 V i MCC) were summed as kVA values. These values whe re then changed to impedance values and subsequently converted to a per unit system. The results are as shown on the attached chart and impedance diagrams. F. CONCLUSIONS I 1. Steady State a. For the minimum system voltage conditions, the results are j_ as summarized on the chart of Pages 4 and 5. Even with the worst case loading conditions,. the voltage at. the most dis-tant portion of the distribution ' system (i.e., the MCC's) is greater than 87% of the nominal voltage to the bus (i. e., 480 V). Since the nameplate voltage rating of these motors, in most ca ses, is 460 volts, the voltage to the individual motor terminals is (neglecting cable impedance) approximate-l ly 91% of the nameplate value. The same logic holds for the i 4.16 kV and 6.9 kV bus loads. b. For the maximum system voltage. conditions, the results are as summarized on the-chart of Pages 6 and 7. At the worst i case overvoltage conditions, the overvoltages are; no greater i than 4.6% on -the safety-related buses at the nominal voltage j rating. This condition,.for e xample, means - that at. the K3BemhT02D47 t i 1 wwm m. y- .c w-,-eyq m-i--y- .y

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Page 3 4.16 kV switchgear bus the motors which are nameplate rated at 4000 volts will see an 8.78% overvoltage. This overvolt-age is within NE:!A standards of +10% and, therefore, totally acceptable. c. For the alternate offsite power source, the Unit 1 & 2 start-up transformer, the voltage conditions are similar to the previous analyses for both the minimum and maximum sys-tem voltages. However, the overvoltages are only 1% over the nominal ratings. 2. Dynamic The results of starting a large motor, after the steady-state conditions described above, can be seen on the charts of Pages 8 & 9. As indicated, the voltages at the minimum and maximum sys-tem conditions are not degraded to a point where safety-related equipment cannot perform their functins properly. KBBemhT02D47

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!iRC CUIDELI!!E ITEM 8 (!iRC 8/8/79 letter) 8. (1) Automatic transfer of loads is not._ accomplished through the use of voltage relays for the 6900 V Reactor Aux. Buses 3A and 3B and 4160 V Unit Aux. Buses 3A and 3B. A transfer from the Unit 3 Aux. Transformer to the Unit 3, Start-up Transformer is initiated only with certain lockout relays and overcurrent devices which -are activated on equipment failures only. The t ransf e rs of the 6900 volt buses are immediate, automatic, high speed dead bus transfers and completed with a dead bus time of less than 100 milliseconds. If this time is exceeded, the reactor will be automa tically tripped. The automatic transfers of the 4160 volt buses will be similar to that of the 6900 volt buses except the closure of the incoming source feeder breaker is delayed 0.75 seconds f rom the time the bus voltage drops to zero. The automatic transfer of the 4160 volt ES Buses 3A and 3B from the normal of fsite power to the emergency onsite (Emergency Die-sel Generators) is initated by undervoltage relays. When the undervoltage is detected on either or both of the buses, a trip signal is initiated to trip the incoming and feeder breakers, the respective diesel generator unit is started and brought up to speed, and the respective generator incoming breakers are closed supplying power to the bus. The undervoltage relays (CE Type 1AV53K) are set at 56.5% or 2373 volts (for 4160 volt bus). A time delay does exist which is inherent with the type of relay and depends on how fast the undervoltage (loss of voltage) occurs and to what voltage the bus is reduced to. Typically, a 7.8 sec. time delay will occur if the voltage is suddenly reduced to 0 volts. (2) The undervoltage relays on the 6900 volt Reactor Aux. Buses 3A and 3B, 4160 volt Unit Aux. Buses 3A and 3B, 4160 volt ES Buses 3A and 3D, and all 480 volt buses initiate automatic load shed-ding on their respective buses. The relays on the 6900 volt bus-es are set at 63.8% and the relays on all 4160 volt and 480 volt buses are set at 56.5%. All relays have an inherent time delay as described above. (3) The automatic load sequencing for the Emergency Diesel Generator bus is accomplished through the use of timers which are initiated af ter an undervoltage on the respective bus as described ' above [8(2)] and af ter the diesel generator is connected to the bus. 7 KBBemhT02D47}}