L-79-324, Submits Evaluation Results in Response to NRC 790723 & 0808 Ltrs Re Offsite Power & Onsite Distribution Sys. Evaluations Currently Under Review to Determine Need for Addl Tech Specs
| ML17207A567 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 11/09/1979 |
| From: | Robert E. Uhrig FLORIDA POWER & LIGHT CO. |
| To: | Gammill W Office of Nuclear Reactor Regulation |
| References | |
| L-79-324, NUDOCS 7911160537 | |
| Download: ML17207A567 (10) | |
Text
DOCKET 05000335 REGULATORY
'FORMATION DISTRIBUTION SY M (RIDS) t Al;CESSION NBR:7911160537 DOC ~ DATE: 79/11/09 NOTARIZED:
NO FACIE:50-33S St ~ Lucie Planti Unit'i Florida Power 8 Light Co.
"AUTH~ NRPlE
'UTHOR AFFILIATION uHRIC Floirida Power 8 Light Co, RECIP ~ NAME RECIPIENT AFFILIATION GAAAYLL,H,P.
"Assistant Director fol Standard 8
Advanced Reactors SUBJECT!
Submits evaluation results in response to NRC 790723 790808 ltrs te offsite power 8 onsite distribut/on sy Evaluations currently under review to determine need addi Tech Specs'ISTRIBUTION CODE:
A015S COPIES RECEIVED:LTR 9 ENCL Q SIZE TITLE: Ons>te Emergency Power Systems ES C% ~
V OTLS.
~
K W
s ~for ACTION'NTERNAL:
EXTERNALS RECIP IENT IO CODE/LIAME 05 BC'+B 4'f 0
REG FILE 1
15 OELD 17 AOX1L SYS BR 20 ENGR BR 22 PLANT SYS BR 2Q PIER SYS
'OR'6 TONOIiD 29 BRINKMAN S
HANAUER 03 LPDR 31 ACRS COPIES L'TTR ENCL 7
7 1-1 iii 1
1 1
ii 1
1 1
1 1
1 1
16 ib RECIPIENT ID CODE/NAME LA gag Wg 02 NRC PDR 13 I8E 16 MPA 18 18C SYS BR 21 REAC SFTY BR 23 ADV REAC BA 25 NAMBACH T 27 MCDONALOiD 30 EEB 00 NSIC COPIES LTTR ENCL 1
0 1
1 2
2 1
1 1
1 1
1 1
1i 1
1 TOTAL NUMBER OF COPIES REQUIRED:
LTTR 46 ENCL 45
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tP. O. BOX 529100, MIAMI,F I 33152 gygll/g~
A FLORIDAPOWER & LIGHTCOMPANY November 9, 1979 L-79-324 Office of Nuclear Reactor Regulation Attn:
Mr. William Gammill Acting Assistant Director for Operating Reactors Projects Division of Operating Reactors U.S. Nuclear Regulatory Commission Washington, D., C.
20555
Dear Mr. Gammill:
Re:
St. X.ucie Unit 1 Docket No.
50-335 Station Electric Distribution S stems As a result of NRC letters dated July 23 and August 8, 1979, we have performed evaluations (attached) related to offsite power and the onsite distribution system at St. Iucie Unit l.
Our operating department is now reviewing the evaluations to determine the need for additional Technical Specifications.
If such Specifications are needed, we will provide a -schedule
'for their submittal by December 15, 1979.'ased on the results of the'valuations and proposed plant modifications we have deferred scheduling a distribution system test pending NRC review of this submittal.
Please call if you,have'additional questions on this subject.
Very truly yours, Robert E. Uhrig
.Vice President Advanced Systems 6 Technology REU/MAS/mid cc:
R.
W. Reid, Operating Reactors Branch I4 Harold Reis, Esquire "II'911 1 60 PEOPLE..
~ SERVING PEOPLE
4
Xn response to ItRC letter to FPL dated. July 23, 1979, Request for Additional Xnformation St. Lucie De raded Grid. Volta e.
The following response addresses, the-adequacy of the undervoltage setpoints and time delays regarding the operation of 480V safety
,equipment as required in the above referenced.
Request for Additional
~Xnformation.
- Also,,as requested, this response details the coincident
~logic for undervoltage protection, describes how XEEE 279-1971 requirements are satisfied.,
and resolves the discrepancy noted.'between our letters of September 22, 1976 and, July,'25, 1977.
Our September 22, 1976 letter stated that it 'is improbable that the voltage on the'480 volt bus would remain between the undervoltage setpoint and. the nominal equipment ratings.
This is due to the fact that orily transients would cause the voltage to pass through this region.
Therefore, equipment would not be required,to operate at such a voltage.
Since 1977 when the original concern was raised, FPL in the.normal course of review 'of plant operational data and experience has changed. the tap setting of the 4.16kV/480V safety related transformers.
Considering actual loads, this then brings the HCC bus average voltage corresponding to the 88.3%
4.16kV undervoltage relay setting to approximately 85,".
Considering cable to equipment voltage drops and actual operating conditions, equipment can be demonstrated to continue to operate without damage at 85% of,480V.,
Exc'ept. for motor operated valves the maximum cable voltage drops do not cause device terminal voltage to drop below 400 Volts while the equipment is running.
Tne low voltage operating<~point of equipment given by our September 22, 1976 is the nominal lowest point at which the. manufacturer rates operation of thc. equipment..
The equipment,
- however, was specified with conservati.s,m which allozrs continued. operation at oven lower voltages..
A discussion of the various 480 volt equipment is given below:
Pum and. Fan Motors These motors are specified. as 460'volt, 1.15 service factor, Clas B motors capable of starting and accelerating their connected.
load, at 755 of nameplate terminal voltage.
Furthermore, continu'ous operation at +105 of the nameplate voltage of 460 volts is also requirecL.
'Since the motors are designecL with sufficient torque to accelerate their load.
at 755 voltage, operation at 755 from a torque requirement is possible.
Continuous operation at this lower voltage (345V) however, wou1d require a
corresponding increase in current of approximately 1.,33 times the nominal 460 volt current.: This increased current would cause the motors to run hotter than the Class B 1.15 service factor temperature rise of'0 C, which for extendecL.periods of time would shorten the lifo of the motor.
- However, operation at ll5g of rated current is within the temperature rating of the motors.
Considering this satisfactory, full output continuous operation could be expected at 400 volts which is 83.3g of 480 volts.
This voltage is considered to be conservative since the full output horse-power of the motor is not generally required. to po~er the driven loacL.
The.
general philosophy used in sizing these motors is to select the.next largest.
standard size motox above the highest point on the lo ds operating curve.
Valve motors Motor operated valves employ special torque motors for their operation.
Manufacturer's data and. plant tests reveal that these motors can start at 368 volts and. generally operate near or in the saturated region.
That is, with a decrease in voltage the current also decreases.
Therefore, at low voltages there is less temperature rise and. thermal over-heating is not a problem.
Therefore, continued operation below 400 volts is possible without equipment damage.
Each MOV operating voltage was calculated.
and none fell below 368 volts.
Motor Control Center Contactors - 'The motor control center contactors are powered from 480/120 volt transformers.
These transformers are oversized, with 50 VA being used for size 1 and. 2 starters and. 500 VA for size 3 and 4.
Tests were performed on severa1 contactors and the highest'pickup voltage required on any size starter'was 95.2 volts.
The highest drop out voltage was 74.8 volts.
Considering the above transformer. ratio and typical transformer impedance, operation at 400 volts is acceptable.
Batte Char.,ers The battery charger manufacturer indicates that similar type chargers have been tested, at 400 volts AC input and. still obtained the full range of regulation.
Readings taken at the plant indicate that the connected. load on the chargers is less than half its rating, therefore, operation down to 400 volts is acceptable.
Boric Acid Heat Tracin This system was specified. to operate at a minimum 80(~ of 120 volts.
Considering transform r drops this system would be.capable of 'operation down to at least 394 volts input to the heat tracing transformer.
As demonstrated, by the above analysis, in the unlikely event that equipment would be required, to continue-to operate at the undervoltage setpoint for a long period of time, it could do so without damage.
As stated in our previous responses, St. Lucie Plant incorporates a Uestinghousc, type CV-2 undervoltage relay on each of the safety related 4.16 kV busses.
Upon actuation of the relay the offsite power source is disconnected, the bus is stripped and the diesel starting sequence is initiated.
These relays are induction disc ype which inversely relate time and voltage.
That is, the lower the bus voltage the faster the relay responds.
Therefore, this relay provides protection against sustained low voltage conditions as well as complete loss of power since the relay response is very fast, on complete loss of power and much slower on low voltage conditions.
Since its time response to low voltage is slower it wi3,1 not be actuated by motor starting or other transient
'conditions which might cause spurious relay actuation if such a feature were not used.
The CV-2 relays are connected to the 4.16 kV busses through 4200/120 volt potential transformers.
The relays are of the 55 to 140 volt range and are set at, the 105 volt tap.
This corresponds to 88.3%
of 4.16 kV.
Time dial 1 was selected for the time characteristic..
The relay is designed such that; the induction disc begins to move at the tap voltage.
For example, if the bus voltage rem ined at 79.5f. of 4.16kV for approximately 6 seconds, the relay would actuate.
Xf the voltage were at 707'f 4.16kV the relay would. actuate in approximately 3 seconds.
This then allows motor starting without spurious actuation. o'f the bu., under-voltage relay.
To avoid spurious loss of all offsite power and to provide the required.
redundancy, each safety related 4.16 kV bus has individual undervoltage relay and. logic circuits for 'diesel starting.
There is one undervoltage relay on each 4.16 kV safety related bus.
Actuation of that relay will start the diesel on that bus.
In addition, there is no intertie between A and 3 undervoltage bus stripping logic.
Should a relay malfuncti'on occur, it would effect one bus.
The other bus would r'emain connected. to the offsite powe source.
In.view of the above and the fact that the re'ays are on separate
- busses, their cabling and associated. logic are 'separated and. they activate separate diesels, the redundancy, single failurk and separation requirements of IEEE 27/-1973. are met.
The FPL letters dated September 22, 1976 and July 25, 1977 and the 'latest wiring diagrams, have been reviewed.
The latest circuit design concurs with
" the statement made in the July 25, 1977 letter.
For 'each train, approximately 0.2 seconds after the 'diesel generator breake. is closed, the 4.16 kV bus undervoltage relay is bypassed.
The circuit design also provides for automatic reinstatement of the 4.16 kV bus undervoltage relay (and hence
'load shedding capabilities)'when the diesel generator breaker is tripped.
Xn xespon e to NRC letter to FPL dated August 8, 1979 Re=
Ade uac of Station Electric Distribution Systems Volta<<es The folloving xesponse addresses the NRC concern that the offsite power sys.Cem (grid) and on-site electrical distribution system is of sufficient capacity and. capa'bility to automatically start and operate all required safety 1oads.
Specifically, the NRC required. confirmation that potential overloading due to transfers of either safety or'on-safety loads
- and, potential starting transient problems do not result in unacceptably degraded voltage to safety loads or spurious shedding of safety loads from the offsite electrical grid.
During 1978 and. 1979, the steady voltage experienced on the tr nsmission system at St. Lucie varied betveen 230 kV and. 244 kV.
On ICay 16, 1977, the loss of FPL Turkey Point Unit 3 necessitated.
a large import of power
'nto southeast Florida.
The subsequent loss of a major transmission line resulted, in a blackout south of Ranch Substation.
During the intexval between loss of Turkey Point Unit 3 and the transmission fault, the St. Lucie transmission bus voltage varied between 240 kV and 219 kV for approximately 10 minutes before collapse of the grid south of Hidway Substation.
On October 3, 1979, St. Lucie 1 tripped off the line and the switchyard voltage subsequently dipped to 216 kV, recovering to approximately 222 kV within seconds.
The voltage recovered to 230 kV within approximately 90 minutes.
- However, from experience, voltages less than 230 kV at St. Lucie are considered to be short term and transient in nature with recovery or collapse of the system expected to occur in a short period of time.
Florida Power 5 Light has no contingency plans to lover transmission voltages to reduce load,.
A progxam is in progress vhich villlower only distribution voltage for load, reduction.
Because either a unit trip or safety injection signa1 initiates automatic transfer of the onsite distribution system from the auxiliary transformer
'o the start-up transformer, the voltage analy"es vere performed. assuming connecCion to the start-up transfoxmer.
Two cases were analyzed,,
one arith.
normal running 'oads being supplied by the start-up transformex. (unit trip) and the other vith -safety loads being simultaneously started vithout.tripping
~
the normal running loads (accident condition).
All automatic actionswere
,assumed to occur as designed.
and no credit vas taken for manual. load. shedding.
The following assumptions vere made for the calculations.
1)
The normal loads used were measured.
values vith the plant at full load.
2)
The power factor of the rupning loads vere, assumed as
.85 3)
. The measured normal running loads vere assumed. to include the following safety related. loads; the intake cooling vater pumps and component cooling water pumps on the 4 kV system; containment fan. coolers, RM3 exhaust fan and charging pumps on the 480V load center; and all safety xelated loads
'(such as battery chargers etc.) on the 480V motor control centers except for motor operated valves.
4)
The starting power factor of the 4 kV mot'ors was assumed as.22.
The starting current used. was from nameplate data.
5)
The starting power factor of the 480V motor operated. valves was
- assumed, as.60.
The starting current used was ta'en froth the. oxiginal plant start up test data.
- 6) All currents were assumed. to remain constant fox the calculation.
Considering the above assxunptions the voltage at all safety related. equipment would be sufficient for theix'ontinued operation should the plant trip ancl
- all loads'ransfer to the startup transformer.
Should, there be a concurrent safeguard signal with the transfer, there would be sufficient voltage to start.;
the, required. safety'elated. motor's.'he voltage at the. safety related motor control centers would not drop below 400 volts.
Although 400Y is below the minimum pick-up point guaranteecl by the contactor manufacturer, tests wexe p rformed whose results indicate this to be consexvatiue.
The motor control center contactors are powered from 480/1ZO volt transformers.
These transformers axe oversized.;
150 VA is used. for size 1 and 2 starters and 500 VA for 'size 3 and. 4.
Results of these tests on several contactors xevealed.
the highest pickup voltage required. on any size.starter was'. 95.2 volts.
The highest drop out voltage was 74.8 volts.
Considering the above transformer ratio and, typical transformer impedance,operation at 400 volts is acceptable..
In order to further assure that'egraded grid voltage would not prevent safety equipment from starting, a design modification is planned to add undervoltage relays to the 480V busses.
Actuation of these undervoltage relays concurrent with a safeguards signal will transfer the safety loads to the diesel-generator.
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