ML18219D985
| ML18219D985 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 11/17/1976 |
| From: | Tillinghast J Indiana Michigan Power Co, (Formerly Indiana & Michigan Power Co) |
| To: | Rusche B Office of Nuclear Reactor Regulation |
| References | |
| Download: ML18219D985 (17) | |
Text
U.S. NUCLEAR REGULATORYi
'IMISSION NRC FonM 195 y.m >
NRC DISTRIBUTIGN FoA PART 50 DOCKET MATERIAL DOCKET NUMBER FILE NUMBER Mr Rusche
@/LETTER ISORIGINAL Q COPY IINOTORIZED IIUNCLASSIFIED PROP INPUT FORM M'ndiana & Michigan Pwr Co Hew York, NY J T Tillinghjast DATE OF DOGUMENIT1 DATE RECEIVED
]l 19 76 NUMSER OF COPIES RECEIVED one signed DESCRIPTION Ltr notarized 11-17-76....trans the following, in response to our 8-13-76 1'tr ~ ~ F ~
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ENCLOSURE
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Analyses of the effect of degraded grid voltage on the operability of safety re-lated equipment......
3WQ..l" PLANT NAME'C COOK
$Pl AlCKXllg'ii'~'ji',DrpD SAFETY ASSIGNED AD:
FOR ACTION/INf0RMATION ASSTr.NFD IITI.
11-19-76 ehf BRANCH CHIEF:
PROJECT
>IANAGER:
LIC ASST a~n (5 P OE KEG-SXXRE NRC PDR I&E2-OELD GOSSXCK & STAFF MIPC CASE INTERNALD SYSTEMS SAFETY HEINEIIAN SCHROEDER ENGINEERING MACCARRY KNIGHT SXHMEIL PAWLICKX ISTRI BUTION BENAROYA IPPOLITO K RKWOO e
OP~RRATYN
~ RFAC ORS SITE A
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INDIANA R MICHIGAN POWER COMPANY P. O. BOX 18 BOWLING GREEN STATION NEW YORK, N. Y. 10004 November 17, 1976 Donald C.
Cook Nuclear Plant Unit No. 1 Docket No. 50-315 DPR No.
g8 Mr. Benard C. Rusche, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C.
205(5 Cry 9
Dear Mr. Rusche:
This letter transmits the results of analyses of the effect of degraded grid voltage on the operability of safety related equipment in response to Mr. Dennis L. Ziemann's request of August 13, 1976.
Due to the complexity of the analyses, on September 17, 1976 we requested a 60-day extension in order to provide'all the necessary information.
Enclosed please find 40 copies of Attachment A which addresses Enclosure 2 of Mr. Ziemann's letter of August 13, 1976.
Very truly yours, ZT:vp Sworn and subscribed to before me this 17th day of November 1976 in New York County, New York a
ice President
~Mr Qusiiired in Queens County Cettlffcoto filed in Now York County r qounotiurr uxprres lurch 30, 19r 1 cc:
{see next page) oocxottt usttttr.
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W. Jurgensen BrMgman R. S. Hunter 0
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ATTACHMENT A
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Evaluation of the Design of Cook Plant Class XE u'lectrical Distribution System An evaluation was made of the operability of,safety related equipment, including associated control ciicuitry and instrumenta-tion as requested in your Enclosure 2.
'The numbering 'below corresponds to Enclosure-2. --
la.
Plant conditions under which the plant auxiliary systems (safety and non-safety related) will be supplied by offsite (reserve power) are the following:
during startup; during shutdown; and during periods when auxiliary power supplied by unit generator (26/4 kV transformer (s)) is unavailable.
Accordingly, it is estimated that for 2,3 percent of "narmal plant operating
. time" the auxiliary buses will be powered from an offsite source (reseive power transformer(s)).
Xn reaching this percentage figure the following definitions have been adopted.:
ae b.
F L'
f of auxiliary buses to auxiliary transformers after paralleling.
Shutdown time.
From transfer of the auxiliary buses.to the reserve source to the time when the reactor is not critical.
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Auxiliar Transformer (s) unavailable:
Cook Plant experience in this mode being zero, the following as sumo tion was adopted:
one auxiliary transformer out of service for 3 months during the entire life of the unit (40 years),
Total "normal plant operating time" equals total "reactor critical time".
lb.
Normal operating range of grid system voltage is 355 kV
+3 kV.
The corresponding voltage values at the safety related buses with the auxiliaries powered. from the reserve source is as follows-Max Min 4.
kv kV 4 kV 600 Volt 358
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35 5
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4160 591 352 35 0 4090 5/8 lc.
'i1ith the generating unit out of service, the 34-5 kV system voltage is expected to be within the normal range of 352 to 358 kV.
- However, a combination of
~ contingencies well beyond normal planning criteria and more severe than actual experience was chosen so as to produce a very extreme but highly unlikely range of network voltage levels.
600 Volt The voltage profile at the safety related buses for the auxiliary full load and auxiliary minimum load conditions on the system (assuming this extreme'range of grid voltage) with the auxiliaries powered from the reserve source is as follows:
4 kV 4.
kV 4 kV
- 1) Full Auxiliary Load. 4 l6,n. Grid 322 Voltage 31 9 3.66 510
- 2) Min. Auxiliary
'Load. 6 Max.
Grid Voltage
, 369 36.9 631 These were calculated usiog the transformer taps currently in use.
The transformers which supply the 'auxiliary buses within the plant have five fixed taps which're set in such a manner as to provide the optimum voltage profile for the full range of anticip ated oper at ing conditions.
Case 1 represents "Hot Standby load" with the unit out of service and minimum grid voltage (322 kV).
Case 2 represents "Cold Shutdown load."
(minimum conceivable load) and. maximum grid voltage (369 kV).
Case 1 shows a 600 volt bus voltage of 510 volt, (.887 p.u.
on a 575 volt base).
Since it is proposed to operate all ESS equipment within the NEbl~ rating of
+10/~, the ESS buses will be taken off the reserve source before this voltage level of 510 is reached.
Xn Case 2 the 4 kV bus voltage of 4440 volt (1.11 p.u.)
and the 600 volt bus voltage of 631 volts.(1.09 p.u.)
do not significant+exceed NFHA rating and are acceptable.
ld.
Assuming auxiliary loads are being carried by the station generator, voltage profiles at the safety buses for grid voltage at the normal maximum value and the normal minimum value are as follows:
4 kV 26 kV 4-kV 600 Volt Grid Volt Norm Max.
358 Value 25 5
4.10 573 Grid Volt 352 Norm. Min.
Value
- 26. 7
. 4.32 613
Xf the generator terminal voltage is brought as low as
.9g p.u.
(24.7 kV) the ESS buses*voltage levels are still satisfactory, that is,
.989 p.u.
(3960 volt) at the 4 kV buses and
.927 p.u.
($77 volt) at 600 volt buses.
Safet Buses Volta e Profile '/hen Grid Volta e is at De raded.
Conditions which would re uire enerator trio Automatic generator trip for degraded grid. voltage conditions is not provided.
Under these conditions unit output would be reduced tb obtain additional reactive capability to sustain generator terminal voltage.
Mhen operating the generator at its reactive capability limits and terminal voj,Cage below 95/, operation would continue while monitoring generator temoeratures and the auxiliary buses voltage limits.
See Paragraph "4a".
- However, we know of no system condition Chat would require this type of oper ation.
le.
The undervoltage sensors (G-E-NGV relays) will sense a voltage failure, disconnect the emergency buses from the offsite power source and start the diesel generators.
These undervoltage sensors are listed. in Table 1 below.
The trip setpoint for Cook Plant loss of offsite power is set at 60fp (2400 volt) voltage.
The reason for the selection of such a low value is that it is voltage failure Chat is being monitored and not abnormal voltage.
There is no undervoltage trip at present.
See Paragraph "4b" for proposed new scheme.
Table I Undervolta e Rela (G-E-NGV') Locations il Undervoltage 4 kV Bus monitored Rela Desi nation Electrical Location TllA TllA T3,1B
,TllB TllC T11C TllD T11D"
- Engineered Hafeguards buses.
27-TllA 27-1-TllA 27-TllB 27-1-TllB 27-TllC 27-1-Tllc 27-T11D 27-1-TllD System Buses.
Also referred 41-42 42-43
, 41-42 42-43 41-42 42-43 41-42 42-43 to as safety related
lf.
Assuming operation on offsite power and degradation of the grid system voltage:
a 0 4
kv The voltage value at the safety related buses corresponding to the maximum value of grid voltage is as follows:
4..
kV
,4kV 600 Volt 369 b.
- 36. 9 4.44 631 The degraded grid voltage corresponding to the undervoltage trip setpoint proposed (see Paragraph "4b") is 327 kV.
The profile is given below:
4 kV 4.
kV 4 kV 600 Volt 327 32.4.
3 74.
518 lg.
The voltage range over which the safety and non-safety related components can start and operate continuously in the performance of their designed functions is as follows:
NEHa Rating
+10'~
4000 Volt Class 600 Volt Class 8afety Re 1 aCed Load s 4400-3600 632 5-517 5*
- Safety related equipment rating is 4.000 volts and.
575 volts therefore 90$
- and, 110/o values are based on 4000 volt and 575 volt, respectively.
The above voltages apply for power requirements for all motor sizes.
For motor sizes larger than 100 hp, controls operate from the 250 V DC batteries.
Battery chargers~are subject to no derating for source voltage variation of ~105.
Reactor instrumentation and protection equipment are also fed from 250 V DC through inverters and are not affected by degradation of the grid voltage.
Control power for motor sizes less than 100 hp comes from AC control transformers installed within the r'4CC's.
Voltage level ranges required for the control of these smaller motors is as follows'.
From TQ Motor Starter Size 1
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II Jl 2
tl 3
4, 460 volts 512 g4.2g g g33QQ 632. g volts
- Review and. analysis of control circuits for size 3
and 4 starters demonstrated that for bus voltages below g4.2 and f33 volts respectively reliable contactor operation on energizing could not be assured.
As these voltages are above the, 518 volt minimum for the 600 volt bus
.voltage listed in response to question "lf", we propose to modify these starters (see paragraph 4d) to enable them to operate for voltages as low as 480 volts (80/o of r ated).
lh.
The bus voltage monitoring and abnormal voltage alarms available in the control room are as follows:
Table IX (a)
List of Bus Volta e Monitorin in the Control Room (Voltmeters)
Bus Monitored 4 kV buses 1A and. 1B 4 kV buses TllA and. TllB 4 kV buses 1C and 13 4 kV buses T11C and. T11D 600 V buses llA and llB 600 V buses 11C and.
11D 34.5 kV bus 1
Voltmeter Location Station Auxiliary Panel PI II
.II Generator Panel "G"
II S~~ll (b)
Currently, there are no undervoltage alarms available in the control room (see Paragraph "4a" for alarms to be added).
2.
Description of load shedding feature at Cook Plant.
On undervoltage trip, the logic initiates the following actions:
a.
The auxiliary bus source is disconnected from the emergency power system.
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b.
Existing loads are shed from the 4 kV emergency buses.
c.
Onsite emergency power sources (diesel generators) are started.
d.
Sequencing of the emergency loads is initiated.
At present the load shedding feature is retained after the diesel generators are connected to the emergency buses.
Retention of the load shedding function after the diesel generators are connected to the emergency buses is based on the following:
Voltage failure (V6607o) causes the load shedding relays to be energized and the load shedding function activated.
At such a low voltage the system cannot operate; removal of the load shedding function was not considered..
However as a result of this analysis we are proposing to revise our load shedding scheme as outlined in Paragraph "4c" below ~
3.
Operating limits are given by the generator capability curve.
As indicated in the PSM, the D.
C ~ Cook Unit No.
1 has no operating constraints imposed by transient stability performance considerations.
Mith the unit operating at full load steady'tate stability considerations limit the underexcited reactive power to approximately 3)0 NVAR's.
The overexcited reactive power output at full load is limited to approximately.
600 N/AR' by generator thermal design considerations.
iVote
---that-the Unit operattes at its overexcizawion reactive oower limit of 600 MVAR's when the D. C.
Cook 345 kV bus voltage is at normal minimum of 3)2 kV or at the lowest credible voltage of 33/ kV.
Similarly the unit operates at its under-excitation reactive power limit of 350 iVliZ's for the conditions
'hen the D.
C.
Cook 34$ kV voltage is at normal maximum of 358 kV or at the highest credible voltage of 369 kV.
The generator capability curve applies for voltages between 953 and 105/a of rated generator terminal voltage.
For frequencies between g8 and 59 HZ the operator is instructed to load reject the unit within 30 min. If frequency decreases to. 58 HZ the operator is instructed to load reject the unit immediately.
For voltage below 9gfo operation would b'e as de-
-scribed in P ar agr aph (ld )
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As a result of the analysis performed in response to Items 1-3 above, 'the following modifications are proposed at Cook Plant.
a.
Addition of low voltage alarms on the 600 volt
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Issuance of operating instructions to be used for operation of the generator at voltages other than rated.
b.
Addition of automatic circuitry to insure that the ESS bus loads cannot be disabled by a degraded offsite power supply.
This will be accomplished by:
Installation of potential transformers and.
under voltage relays on the reserve source (34.5 kV).
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Interlocking will be installed to initiate ESS bus load shed and Diesel Generator start for 34.g kV voltage less than 94/ (32.4 kV) when the 4 kV reserve bus feeders are closed.
This circuit will have a two second time delay to avoid spurious operation due to grid transient conditions.
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Revision of the Diesel Generator, load shedding circuit to remove the recycle capability now inherent in the circuit.
The new revision will insure that no load shedding can take place once FSS load has been transferred to the Diesel Generator.
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d.
Hodification of the control circuitry for motor starter sizes 3 and 4-. It is proposed to equip these contactors with 600 volt rated starter coils.
An interposing relay will be used for energization of the starter coil, and allow reliable starter operation well below the
)3.8 volt bus limit.
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