ML18026A355
| ML18026A355 | |
| Person / Time | |
|---|---|
| Site: | Susquehanna  |
| Issue date: | 05/15/1981 |
| From: | Curtis N PENNSYLVANIA POWER & LIGHT CO. |
| To: | Youngblood B Office of Nuclear Reactor Regulation |
| References | |
| PLA-781, NUDOCS 8105190497 | |
| Download: ML18026A355 (14) | |
Text
REGUI A TL 1NFORMAT ION 0 ISTHIBU T IOr4 "TEN (R IDS)
ACCESSION r4dR:810519049/
DOC ~ DATE: 81/05/15 NOTARIZED:
NO FACIL:50-3d7 Susquehanna Steam E I ectric Station~
Uni t 1< Pennsyl va 50"388 Susquehanna Steam Electric Stations Unit 2i Pennsylva AUTH DNA'4IE AUTHVR AFF lLIATION CURTIS'
~'i.
Pennsylvania Power ir Light Co ~
R EC I P ~ 9 A>~E REC IPIEN'T AFF ILIATION YOUNGBLOODrB ~ J ~
Licerising Branch 1
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SUBJECT; Forwards revision to Question 40,6 re degraoed grid voltages closing SER Outstanoing Issue 49, D IS TR IOUTIOr4 CODE:
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TWO NORTH NINTH STREE'T, ALLENTOWN, PA.
18101 PHONE: (215) 821 ~ 5'I51 NORMAN W. CURTIS Vice President Engineering 8 Construction 821 5381 May 15, 1981 Mr. B. J. Youngblood, Chief Licensing Branch No.
1 U.S. Nuclear Regulatory Commission Washington, D.C.
20555 Docket Nos.
50-387 50-388 SUSQUEHANNA STEAM ELECTRIC STATION SER OUTSTANDING ISSUE 49 ER 100450 FILE 841-2 PLA-781
Dear Mr. Youngblood:
Attached is a revision to Question 40.6 which addresses degraded grid voltage.
This revised response completes our action to close SER Outstanding Issue 49.
Very truly yours, N.
W. Curtis Vice President-Engineering and Construction-Nuclear CTC/mks Attachment cc:
R.
M. Stark NRC poor
)h PENNSYLVANIA POWER 8
LIGHT COMPANY
SSES-PSAB Becent operating experience has shown that adverse effects on the safety-related power system and safety related equipment and loads can be caused by sustained low or high grid voltage conditions.
Ae therefore require that your design of the safety related electzical system meet the following staff positions.
Supplement the description of your design in the PSAR to show how it meets these positions or provide appropriate analyses to
)ustify non-conformance with these positions.
Ve require that an additional level of voltage protection for the onsite power system be provided and that this additional level of voltage protection shall satisfy the following criteria
{a)'he selection of voltage and time set points shall be determined from an analysis of the voltage requirements of the safety-rela ted loads a t all onsite system distribution levels; (b)
The voltage protection shall include coincidence logic on a per bus basis to preclude spurious trips of the.
offsite power source;
{c)
The time delay selected shall be based on the following conditions The allowable time delay, including margin, shall not exceed the maximum time delay that is assumed in the PSAH accident analyses; (iii)
The time delay shall minimize the effect of short duration disturbances from reducing the availability of the offsite power souzce{s);
and The allowable time duration of a degraded voltage condition at all distribution system levels shall not result in failure of safety systems or components; 1)
The voltage sensors shall automatically initiate the disconnection of offsite power sources whenever the voltage set point and tiae delay limits have been exceeded; 2)
The voltage sensors shall be designed to satisf y the applicable requirements of IEEZ Std 279-1971,
~~Criteria for Protection Systems for Nuclear Power Generating Stations";'and
I 4 SSZS-FSA3 3) he Technical Specifications shall include limiting condition for operation surveillance requirements, trip set points vith minimum and maximum limits, and allowable values for the second-level voltage pzotection sensors and associated time delay devices.
Re require that the current system designs automatically prevent load shedding of the emezgency buses once the onsite sources are supplying pover to all sequenced loads on the emergency buses.
The design shall also include the capability of the load shedding feature to he automatically zeinstated if the onsite source supply breakers are tripped.
The automatic bypass and reinstatement feature shall.be verified during the periodic testing identified in Position 3 0 In the event an adequate basis can be provided for retaining the load shed feature vhen loads aze energized by the onsite pover system, we vill require that the setgoint value in the..
Technical Specifications, which is currently specific as
"...equal to or greater than..."
he amended to specify a
value having maximum and minimum limits.
Your bases foz the selected setpoints and limits must be documented.
Me require that the Technical Specifications include a test requirement to demonstrate the full functicnal operability and independence of the onsite pover sources at least once per 18 months during shutdown.
The Technical Specifications shall include a requirement for tests:
(1) simulating loss of offsite power; (2) simulating loss of offsite pover in conjunction vith a safety feature actuation signal; and
{3) simulating interruption and subsequent reconnection of, onsite pover sources to their respective buses.
Propez operation shall he determined by:
(a)
Verifying that on loss of offsite power the emergency buses have been de-energized and that the loads have been shed from the emergency buses in accordance vith design requirements (b)
Verifying that on loss of offsite pover the diesel generators start on the autostart signal, the emergency buses are energized vith permanently connected
- loads, the auto-connected shutdovn loads are energized thzough the load sequencer, and the system operates for five minutes vhile the generators aze loaded vith the shutdovn loads.
{c)
Verifying that on a safety features actuation signal (vithout loss of offsite pover) the diesel generators 000 6-2
SSES-ESTAB start oa the autostart signal and operate on standby for five minutes.
(d)
Verifying that on loss of offsite power in conjunction with a safety features actuation signal the diesel generators start on the autostart signal, the emergency buses are energized vith permanently conaected
- loads, the auto-connected emergency (accident) loads are energized through the load sequencer, aad the system operates foz five minutes vhile the generators are loaded with the emergency loads.
(e)
Verifyiag that on interruption of the onsite sources the loads are shed from the emergency buses in accordance with design requirements aad that subsequent loadiag of the onsite sources is through the load sequencez.
(4)
The voltage levels at the safety-related buses should be optimized for the full load and minimum Load conditions that are expected throughout the anticipated range of voltage variations of the offsite pover source by appropriate adjustment of the voltage tap settiags of the intervening transformers.
Qe requize that the adequacy of the design in, this xegazd be verified by actual measurement and by correlation of measured values vith analysis results.
Provide a description of the method fo" making this verification; before initial reactor pover operation, provide the documentation required to establish that this verification has been accomplished.
MSPONSZ Befer to Pigures 8.3-1, 8.3-2, 8.3-3 and 8.3-15 for the followiag discussion on undervoltage detection aad transfer logic+
The primary bus transfer on loss of offsite pover is initiated at the 13.8 kV staztup svitchgeaz and at each Class 1Z 4.16kV svitchgear bus aligned to the lost offsite source.
Refer to Subsection 8.3 for discussion on bus arrangement and the intezconnection of the offsite pover supplies aad the on-site distribution system.
040.6-3
1 Each 13 8 kV startup bus is provided with an offsite power supply and the capability of connecting to the second offsite power supply by the closing of the 13.8 kV tie breaker
{breaker 52-10502).
The undervoltage detection system at each 13.8 kV svitchgear bus consists of (1) incoming feeder (offsite power supply) undervoltage relays device 27AI, (2) bus undervoltage relay device
- 27A2, and
{3) tie, bus andervoltage relay device 27kl.
(a)
Device 27AI-initiates tzipping of the incoming feeder Device 27AI is an instantaneous plunger type relay with pickup setting at 93.6 volts
{78% of the rated 120 volts)
Tvo independent single phase relays.
aze used to monitor the A-B and E-C phase voltages.
The incoming breaker is tripped on coincidence logic of the tvo undervoltage relays at 91.7 volts vith 30 cycle time delay.
{b)
Device 2741-Provides the permissive for closing of tie breaker Device 27kl is a long time induction disc type undervoltage relay set at 82 volts
{68% of rated) and time dial 1/2.
Tvo single phase relapare provided for,monitoring the availability of the alternate offsite pover supply at, the 13.8 kV level and provide a coincidence logic for the closing of the tie breaker.
(c)
Device 27A2 initiates the bus transfer 2%
Device 27k2 is a 3 phase instantaneous plunger type relay vith three full vave bridge rectifiers.
The relay is set to drop out at 30 volts {25%, of rated).
Bus transfer is completed by the closing of the tie breaker
{permissive by device 27A1).
Each 4.16 kV class 1Z svitchgear bus is provided with a preferred and an alternate
{offsite) gower supply and one diesel generator feeder as discussed in Subsection 83 13 The undervoltage detection and backup bus transfer on loss of offsite pover oz sustained degraded voltage on the bus is provided by (1) incoming feeder undervoltage relay-device
- 27hZ, and (2) bus undervoltage relay device 27A, and (3) degraded voltage protection relays.
devices 27Bl, 27B2,
- 27B3, and 27B4.
The devices settings for the Class IZ bus undervoltage protection aze summarized in the folloving Table 40 6-1 040.6-4
. ~
SSES-ESAB (a)
Device 27hZ - provides the permissive for closing of the incoming breaker c
Device 27AI is two single phase definite time delay relays set at.
92% dropout voltage.
These relays are used to monitor the availability of the offsite power supply at the class 1E 4. 16 kV level Device 27A - initiates the bus transfer Device 27A is a 3 phase instantaneous plunger type relay with three full wave rectifiers.
The relay is set to drop out at 18 volts or 15% of rated bus voltage.
The 4.16 kV bus transfer is initiated vith a time delay of 10 cycles by tripping of the preferred incoming feeder breaker.
The transfer is completed if the alternate offsite power supply to this 4.16 kV bus is available (permissive by device 27AI).
In case the alternate offsite power is not available, the standby diesel generator is initiated to start with a 0.5 second delay.
(c)
Devices 27Bl, 27B2,
- 27B3, and 2784 initiate bus transfer and undervoltage alarm.
These undervoltage relays are solid-state, single phase vith definite time delays
{ITE 27D type definite..
long time).
The additional level voltage protection for each 4.16 kV Class IE bus is provided to assure that voltage levels at all Class IE distribution buses meet the minimum requirement of all safety related eguipment to the extent practical.
In the event of loss of voltage on the 4.16 kV
&lass-IE bus, the bus undervoltage relay (27A) initiates bus transfer pez paragraph (b) above.
In addition, relays
- 2731, 27B2,
- 27B3, and 27B4 provide back up protection for alarms and initiating bus transfer.
If a degraded voltage condition cccurs on the 4.16 kV Class IE bus, with no LOCA signal present
{see Piguze 8.3-15),
which is below the setting of relays 27B1 and 27B2, an alarm (coincidence logic) vill.he initiated after 10 seconds.
The relays will initiate the bus transfer after a 5 minute time delay during non-LOCA conditions.
A LOCA signal bypasses the 5 minute time delay.
The 10 second time delay is provided to preclude spurious alarms and tzips for motor start transients The 040.6-5
SSES-FSAR 5 minute timer is provided for operators to initiate corrective actions during non-LOCA conditions.
Relays 27Bl and, 27B2 initiate an alarm when the diesel generator is supplying power but do not trip the diesel generator breaker.
Zn addition, relays 27B3 and 27BO trip the offsite supply breakers after a time delay of 3 seconds when the bus voltage falls below their setting.
These two relays are also connected in a coincident logic Their setting is, based on coordination with overcurrent relays to prevent false trips due to. transient voltage dips from fault currents These relays have no function when the diesel generator is supplying bus power.
040.6-6
I
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If the alternate offsite power is not available, the emergency diesel generat<<, will be started automatically with a 0.5 second delay and connected to the respective bus within 10 seconds per section 8.3.1.4.1.
Selection of all voltage relay settings is based on the cn-site distribution system load flow study and, is f
d by preoperational tests.
The continuous o crating voltage at each distribution voltage v
e level is opera i maintained at
+ 10'f the rated voltage level over the entire transmission grid operating range Tripping of the offsite power supply at, the 13 8
kV 1 v 1 is accomplished by a coincidence logic of two independent single phase undervoltage relays.s The backup tripping of the same offsite gower supply to the, Class 1E 4. 16 kV switchgear is provided by a 3 phase full wave rectifiers type undervoltage relay for minimizing nuisance tripping such as loss of a single control fuse in the detection cizcuit.
The total time delay allowed by restarting (starting) of class 1E equipment after a
DBA is 13 seconds as shown on Table 8.3-1 10 seconds is reserved for diesel generator starting Therefore, 3 seconds is allocated for voltage sensing and bus transfer.
Pre-operating tests will verify that the time delay on the bus tzansfez does not exceed the allowable time.
ks discussed in (I) of above, offsite power supply is automatically disconnected at the 13.8 kV level.
This forces a loss of power to the 4
kV busses connected to the offsite supply and a
4 kV transfer to,the alternate offsite supply, if available, or to the diesel generators.
The undervoltage detection sensors and circuits aze designed in accordance with IEEE std 279-1971 040.6-7
SSES-PSAR All loads on each 4.16 kV Class 1E switchgear bus except the 480 volt load center feeder aze shed on loss of power to the. bus.
Once the bus is re-energized, the 4 16 kV Class 1E loads are loaded in accordance with the pre-set time delay.
Load shedding and reloading of 4.16 kV class 1E loads are repeated as discussed above whenever the bus becomes de-energized.
{3)
Refer to Chapter 16 for Technical Specification.
(4)
Transformer tap settings are selected for optional operating voltage levels foz all loading conditions under'he anticipated voltage variation of the offsite power supplies.
The continuous operating vqltage at each level is maintained within + 107 of rated.
Pre-opezational tests verify the actual voltage levels.
ZTZ Belay Settings:
The function and settings of undezvoltage relays are determined in consideration of the full load, minimum load, and the largest motor starting conditions that are expected throughout the anticipated range of voltage variations for the offsite power sources.
The settings of the degraded voltage protection relays are selected to prevent spurious trips of the offsite power supplies and to provide protection against damaging effects of degraded voltage.
The settings are constrained by motor start transients and relay characteristics.
The following design criteria are used:
(1)
The maximum allowable voltage at no load -or the minimum load conditions is 110% of the motor rated voltage.
(2)
The minimum voltage under the maximum running load condition is 90% of the bus rated voltage.
(3)
The minimum starting voltage is 80% of motor rated voltage See Table 40.6-1 040.6-8
SSZS-PSAR B
040 6
Device Ho.
27AE (preferred)
Punction Permissive to close. the preferred power incoming Breaker.
AIazm Yes Voltage Setting Time Setting 92% dropout 1 sec.
27AZ
)alternate)
Pezmissive to close the alternate incoming Breaker Yes 92% dzopout 1 sec.
27A Initiate bus transfer Tzip the incoming closed breaker Yes 10 cycl~
59/27 27Bl 27B2 27BlX 27B2X
~
~
Bus over/under voltage (alarm only 8 located in load center)
Undervoltage alarm and initiate bus transfer vith time delay re1ays.
Time delay relays vith 27BI 6 2732 to initiate bus transfer.
Yes Yes 110$/90$
10 sec.
84% dropout, 10 sec.
~
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~
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- 5. min 27B3 27B4 Enitiate bus transfer on LOCA condition 65%
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