ML20058B915
| ML20058B915 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 11/16/1993 |
| From: | Marsh W SOUTHERN CALIFORNIA EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9312020279 | |
| Download: ML20058B915 (18) | |
Text
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jftf28 Southem Califamia Edison Company 23 PAFtKER ST HEET IHVINE. CALtFOHNIA 92718 November 16, 1993 wAar n c uAnss nu,._
MA84 AGE M CW NUCLE.AH RE GULA e (44 Y Ap F AHS (714) 454 <4403 U.S. Nuclear Regulatory Commission Attention: Document Control Desk I
Washington, D.C. 20555 Gentlemen:
Subject:
Docket Nos. 50-361 and 50-362 a
Additional Information for Amendment Applications 136 and 120 Degraded Grid Voltage Protection San Onofre Nuclear Generating Station Units 2 and 3
References:
1)
June 3, 1977, letter from A. Schwencer (NRC) to J. B. Moore (SCE).
Subject:
"Re:
San Onofre Nuclear Generating Station" 2)
September 29, 1993 letter from R. M. Rosenblum (SCE) to Document Control Desk (NRC).
Subject:
Amendment Applications 136 and 120, Proposed Change to Technical Specification 3/4.3.2 Enclosed is additional information regarding the planned enhancement to the undervoltage protection scheme at San Onofre Units 2 and 3 in support of the proposed Technical Specification change provided in Reference 2.
The NRC requested an evaluation of how the modified degraded voltage protection scheme and proposed Technical Specification changes will comply with the guidance in Reference 1.
Based on the enclosed evaluation, Southern California Edison concludes that the degraded voltage protection scheme meets the guidance of Reference 1 and will ensure acceptable operation of the Engineered Safety Feature loads.
If you have any questions regarding this matter, please let me know.
Sincerely, ske&
Enclosure I
i 9312020279 931116 PDR ADDCK 05000361 v
P PDR zov-
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Document Control Desk
-2 cc:
B. H. Faulkenberry, Regional Administrator, NRC Region V NRC Senior Resident Inspector's Office, San Onofre Units 1, 2, and 3 M. B. Fields, NRC Project Manager, San Onofra Units 2 and 3 i
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ENCLOSURE-
-l DEGRADED VOLTAGE PROTECTION l
Additional Information for Amendment Applicatons 136 and 120 f
Proposed Change No. 429 San Onofre_ Units'2 and 3 i
1.
PURPOSE This evaluation provides an assessment of how the San Onofre Units 2 and' 3 enhanced degraded voltage protection scheme and-related proposed.
Technical Specification changes (ref. PCN 429) comply with the guidance i
of the NRC to Southern California Edison (SCE) letter dated June 3, 1977, concerning "second level" undervoltage protection.:
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1 2.
BACKGROUND with the permanent shutdown of; Unit 1 in 1992, SCE performed a new Grid:
Stability and Voltage study to confirm that 218:kV-will be maintained at j
the San Onofre 230 kV switchyard under all required. scenarios. A:
minimum value of 218 kV switchyard voltage is assumed in <the electrical-i
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design basis calculations.
!y Based on the study, the switchyard voltage. of '218 kV or above will be maintained under all required scenarios except. for six multiale contingency scenarios. These six scenarios could occur.if ' tie following conditions are met:
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- 1) one San Onofre unit is off-line; and-
- 2) a major transmission line or tower is lost; and l
- 3) system loads exceed specified thresholds.
Should a subsequent trip of the operating unit occur under these g
conditions, voltage levels at the 230 kV switchyard would drop below the l
minimum analyzed value of 218 kV.
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l SCE has implemented procedure changes as a prompt compensatory action to ensure that adequate voltage is maintained to' support accident loads under the conditions noted above. These' procedures ~ require the SCE-Energy Control Center Operator to notify.the San Onofre: Control' RoomL i
whenever the three conditions stated above' exist. The San Onofre'
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Control Room Operator would then declare _the preferred power. source:.
1 (offsite power source) INOPERABLE and enter the appropriate' action?
statement. The Class IE buses in the operating unit.will then~be manually transferred from their Reserve Auxiliary; Transformer to the-Unit Auxiliary Transformer. This ensures that the Class-1E buses' willi shed their loads during a Loss of Voltage Signal (LOVS); condition,.and 1
automatically transfer to their respective Emergency DiesellGenerators (EDGs).
1 As a long term measure to ensure that adequate voltage,is maintained at ~
f the Class IE buses.under the-conditions stated above, an: enhancement of.-
the existing degraded voltage protection' scheme is being implemented to i
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. provide more reliable protection against_ a degraded grid. This-enhancement will also transfer each 4.16 kV Class IE bus-directly_ to the standby power source when a loss of voltage or degraded voltage condition exists. concurrent with a Safety Injection Actuation Signal l
(SIAS). This eliminates the time' delay inherent in the existing scheme-l wherein the logic first seeks the alternate preferred power source:
before transferring the buses to the standby power source.. This enhancement requires installation of new relays to perform the degraded voltage trip function (see section 4.2.2 below).
3.
EVALUATION CRITERIA The evaluation criteria are based on the NRC staff positions defined in-section B, position-1 and position 2 of the NRC' letter to SCE, dated June 3, 1977.
l The evaluation for the enhanced design is provided in section 5 below.
The evaluation for the existing design is included in the San.Onofre 2 and 3 Updated Final Safety Analysis. Report (UFSAR) section 8.3, Responses to NRC Questions 040.45 and 040.46.
4.
PROPOSED DESIGN CHANGES The objective of this modification is to provide an enhanced degraded voltage scheme which detects a degraded grid voltage below the current analyzed value of 218 kV for the worst case post accident' Class 1E~
distribution system loading and alignment.- This enhancement will-transfer each 4.16 kV Class 1E bus. directly to the-standby power' source (EDG) when a loss of voltage or degraded voltage condition exists concurrent with an SIAS. The new configuration ensures.that-adequate voltage is maintained at the Class 1E 4.16 kV buses for. all cases except 2
one. For this one case only, SCE plans to continue'using the-procedures that are currently in place as compensatory' actions. SCE and San Diego Gas and Electric (SDG&E) are evaluating grid improvements l
which may eliminate this concern.
This proposed change modifies the existing LOVS logic and installs a separate degraded voltage detection scheme.
4.1 FIRST LEVEL OF VOLTAGE PROTECTION (LOSS OF PREFERRED POWER) r The first level of voltage protection relays-are.u'ed to detect complete s
loss of voltage to the 4.16 kV class'IE buses.
1This one case is the Loss of the Southwest Power Link (SWPL). _ In the grid reliability study this contingency is represented by loss of the Imperial-Valley - Miguel line and the Imperial Valley - Rosita Line.
In this case the system is postulated to undergo unpredictable voltage oscillations for which any enhancement to the degraded voltage detection system is not a practical solution.
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4.1.1 Existina Scheme Figure 1 depicts the simplified one line diogram of the existing undervoltage detection scheme, l
Four undervoltage relays 127F-1,127F-2,1277-3, and 127F-4 (Westinghouse type CV-2, induction disc relay elements with inverse time characteristics) are connected to each of 4.16 kV class IE buses. Once undervoltage is detected by two-out-of-four undervoltage relays, with or without SIAS, the operation of the undervoltage relays initiates LOVS to effect the following in each load group:
a.
After a fixed delay of approximately 1 second (time delay for CV-2 relay dropout for a complete loss of voltage), trip the 4.16 kV i
class 1E bus normal preferred power supply breaker, and send a start signal to the associated load group's EDG.
i b.
Transfer the 4.16 kV class 1E bus to the alternate preferred power source (companion Unit), if this source is available, via the cross-tie breakers after residual voltage at the affected bus has decayed to approximately 30% (four residual voltage relays are i
i used in a two-out-of-four logic scheme to provide a residual voltage signal on the 4.16 kV class 1E bus).
c.
If step b is unsuccessful, 4 seconds after the LOVS, shed all loads, except 480 V Class 1E load centers and High Pressure Safety Injection Pump, if connected. Approximately 10 seconds after the LOVS, the EDG breaker closes if the EDG is at sufficient voltage and frequency.
4.1.2 Proposed Scheme The existing undervoltage relays as described in section 4.1.1 are also i
used in the proposed scheme.
The existing LOVS logic function without SIAS will remain the same as described in sections 4.1.1 a, b, c, and d.
However, with the new j
configuration, LOVS with SIAS will transfer the 4.16 kV class IE bus to the standby power source (EDG) without first seeking the alternate preferred power source.
4.2 SECOND LEVEL OF VOLTAGE PROTECTION (SUSTAINED DEGRADED VOLTAGE CONDITION)
Degraded voltage protection relays at the 4.16 kV Class IE bus ensure that acceptable voltages are maintained at the the terminals of all 4.16 kV and 480 V Engineered Safety Feature (ESF) loads during all modes of plant operation, and during accident conditions. The proposed relay settings will establish a new minimum available voltage at_the Class 1E buses, and will provide a basis for future voltage calculations.
Adequate voltage for 120 VAC vital loads is ensured through use of -
inverters and batteries. Acceptable operation of the ESF loads is therefore ensured.
) i 4.2.1 Existina Scheme Loss of voltage and degraded voltage protection are currently provided i
by the same set of relays described in section 4.1.1.
For a degraded voltage condition, the scheme initiates a delayed LOVS. The LOVS actuation time would be dependent upon the severity of the degraded voltage condition at the 4.16 kV class 1E bus.
l On detection of degraded voltage at the 4.16 kV class 1E bus with or without an SIAS, the operation of the undervoltage relays initiates delayed LOVS to effect the following in each load group:
e a.
After a delayed LOVS,. trip the 4.16 kV class IE bus normal j
preferred power supply breaker and send a start signal to the associated load group's EDG, i
b.
Transfer the 4.16 kV class IE bus to the alternate preferred power j
source (companion Unit), if this source is available, via the cross-tie breakers after residual voltage at the affected bus has decayed to approximately 30%.
c.
If step b is unsuccessft.1, 4 seconds after the delayed LOVS, shed all loads, except 480 V Class IE load centers and High Pressure Safety Injection Pump, if connected. Approximately 10 seconds after the delayed LOVS, the EDG breaker closes if the EDG is at rated voltage and frequency.
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i 4.2.2 Proposed Scheme l
Figure 2 depicts the simplified one line diagram of the proposed undervoltage detection scheme.
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The logic diagram for the new configuration is shown in Figure 3.
i The degraded voltage condition will be detected by new fixed time delay solid state relays 1270-1, 127D-2, 127D-3, and 127D-4.
The 1270-1, 127D-2, 1270-3, and 127D-4 relays will be connected to the same set of-bus potential transfonners as the existing 127F-1,127F-2,127F-3, and l
127F-4 relays.
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Sustained Degraded Voltage Protection The 127D-1, 1270-2, 1270-3, and 127D-4 relays associated with the timing relays 162D-1, 162D-2,- 162D-3, and 162D-4, respectively, are used for sustained degraded voltage protection when the EDG is not supplying the 4.16.kV Class IE bus (see Figure 3). A~two-out-of-four initiation signal generates the Sustained Degraded Voltage Signal (SDVS). SDVS is initiated approximately 120' seconds after a degraded voltage condition is detected by the 127D relays.
SDVS without SIAS performs the following:
a.
Approximately 120 seconds after detection of a degraded voltage condition, SDVS trips the 4.16 kV Class 1E bus j
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signal to the associated load group's EDG.
b.
Transfers the 4.16 kV Class 1E bus to the alternate preferred power source (companion Unit), if this source is available, via the cross-tie breakers after residual voltage at the affected bus has decayed to approximately 30%.
j c.
If step b is unsuccessful, 4 seconds after the SDVS, sheds all loads, except 480 V Class 1E load centers and High Pressure Safety Injection Pump, if connected. Approximately 10 seconds after the.SDVS, the EDG breaker closes if the EDG
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is at rated voltage and frequency.
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l SDVS with SIAS performs the following:
t-a.
SIAS transfers the affected Unit.'s cross-tie breaker close i
circuit from automatic mode to manual mode. This prohibits j
automatically seeking the alternate preferred power source, which is likely to be experiencing a degraded voltage condition as well.
b.
Approximately 120 seconds after detection of a degraded voltage condition, SDVS trips the 4.16 kV class IE bus preferred power supply breaker and sends a start signal to the associated load group's EDG.
(The EDG also receives a start signal from SIAS.)
c.
Within 2 to 10 seconds after the SDVS, the EDG breaker closes if the EDG is at rated voltage and frequency.
2.
Degraded Grid Voltage Protection with SIAS The 1270-1, 127D-2, 127D-3, and 127D-4 relays, in conjunction with the timing relays (162S-1, 162S-2, 162S-3, 162S-4, 162T-1, 162T-2, 162T-3, and 162T-4), will detect the Degraded Grid Voltage with SIAS. A two-out-of-four initiation signal generates the Degraded Grid Voltage with SIAS Signal (DGVSS). DGVSS is-initiated in I
approximately 5 seconds following SIAS if a degraded voltage condition is detected by the 127D relays.
DGVSS performs the following:
a.
SIAS transfers the affected Unit's cross-tie breaker close circuit from automatic mode to manual mode. This prohibits-automatically seeking the alternate preferred power ' source, which is likely'to be experiencing a degraded voltage condition as well.
b.
DGVSS trips the 4.16 kV class 1E bus preferred power supply breaker and sends a start signal-to the associated load group)'s EDG.(The EDG also receives a start signal fromj SIAS.
t c.
Approximately 10 seconds after the SIAS, the EDG breaker closes if the EDG is at rated voltage and frequency.
4.3 LOSS OF V0LTAGE OR SUSTAINED DEGRADED VOLTAGE CONDITION ALARM The 127D-1, 127D-2, 127D-3, and 127D-4 relays are also used for annunciation of a sustained degraded voltage condition in conjunction l
with five seconds timer 162A. Therefore, a 4.16 kV Class 1E bus Undervoltage Low alarm will be initiated with a fixed time delay of approximately seven seconds. The existing 127L undervoltage annunciation will be deleted.
4.4 RELAY TYPE AND SETTING The logic diagram for the new configuration using the following relays is shown in Figure 3.
l RELAY TAG N0.
MODEL NO.
SETPOINT ALLOWABLE VALUES 127D-1, 127D-2, ABB TYPE 27N RESET:
121.4V 121.4 1.35V 127D-3 & 127D-4 411T5375-HF l
i DROP 0UT. 120.8V (4228V) 120.8 1.35V (4228i47V)
DELAY:
2.0 SEC 2 i 0.2 SEC l
l 162S-1, 162S-2, ABB TYPE 62T 4.3 SF.C 4.3 0.19 SEC l
162S-3 & 1625-4 417T2170
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162T-1, 162T-2, AGASTAT 1.5 SEC 1.5 0.15 SEC 162T-3 & 162T-4 E7012PB 162D-1, 162D-2, AGASTAT 120 SEC 120 12 SEC 162D-3 & 162D-4 E7012PKL DGV-1, DGV-2, GEN ELEC N/A N/A DGV-3, & DGV-4 12HFA151A2H 162A AGASTAT 5 SEC 5
0.5 SEC E7012PC 127F-1, 127F-2, Westinghouse 105V (3675V) 105V 3.3%
127F-3, 127F-4 CV-2 (3675 i 121V)
(existing) l Delay: 1 second for 1.0 2 0.05SEC.
l complete loss of l
voltage l
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EVALUATION i
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5.1 NRC Renuirement (Position 1.a of June 3.1977 letter)
"The selection of voltage and time set points shall be determined from an analysis of the voltage requirements of the safety-related loads at i
all onsite system distribution levels."
Evaluation The time set points for the new degraded voltage protection scheme are discussed in detail in Section 5.3 below.
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The degraded voltage relay (127D) setting is selected to ensure minimum acceptable bus voltages at the 4.16 kV Class IE buses, 480V load center, and 480V MCC buses for all modes of plant operation and for accident conditions. These minimum bus voltages are necessary to ensure that (1) motor terminal voltage will remain at or above 90% of motor rated voltage at steady state conditions and (2) in the event of an SIAS all Class IE motors will start and continue to operate satisfactorily to -
mitigate the consequences of an accident.
Relays 127D-1, 1270-2, 127D-3, and 127D-4 are set with a dropout value of 4228 47 volts and with a fixed time delay setting of 2 0.2 seconds. This voltage setting will assure adequate operation of the ESF loads. The setting of 4228 V is below the normally expected voltage (4360 V or above) with the switchyard voltage of 230 kV.
Therefore, i
under normal operating conditions a spurious actuation is not expected.
l Trip and allowable values for the degraded voltage relays are included in the Technical Specification Table 3.3-4 " Engineered Safety Features Actuation System Instrumentation Trip Values" of Proposed Change Number (PCN) 429.
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5.2 NRC Requirement (Position 1.b of June 3.1977 letter)
"The voltage protection shall include coincidence logic to preclude spurious trips of the offsite power source."
Evaluation A two-out-of four coincidence logic is selected for the new degraded voltage detection scheme to preclude spurious trips. This will also
' l provide ca) ability for testing during power operation. At any time:one relay can 3e removed (or bypassed) from service for maintenance, testing, calibration, or replacement.
5.3 NRC Requirement (Position 1.c of June 3.1977 letter)
"The time delays selected shall be based on the following conditions:
1.
The allowable time delay, including margin, shall not exceed the maximum time delay that is assumed in the FSAR accident analyses; y
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The time delay shall minimize the effect of short duration disturbances f' rom reducing the availability of the offsite power source (s); and i
3.
The allowable time duration of a degraded voltage condition at all 1
distribution system levels shall not result in failure of safety systems or components."
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Evaluation i
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The DGVSS scheme The time delay settings of the DGVSS detection timing relays (162S-1,1625-2,162S-3,1625-4,162T-1,162T-2,162T-3,and 162T-4) are selected to comply with the design objective described in section 4.2.2.2 with due consideration to the tolerances associated with these timers, Emergency Safety Feature (ESF) load sequencing timing relays, and the response time of the degraded voltage relays (127D-1, 1270-2, 127D-3, and 127D-4).
Timing relays 1625-1, 162S-2, 1625-3, 1625-4 These timers are used to "open" the DGVSS window. The DGVSS window opening time has been analyzed to be adequate time for the grid voltage to recover from a short term voltage drop from a motor start transient.
ESF load group 2 starts at 5 seconds after initiation of an SIAS.
ESF load l
sequencing uses Agastat relays with a tolerance of 10% (+
l 0.5 seconds for the second load group). Therefore, the 162S timing should be less than 4.5 seconds after initiation of an SIAS so that the DGVSS window opens before load group 2 sequencing begins. With a setting of 4.3 sec, the DGVSS window could open any time between 4.11 seconds and 4.49 seconds after initiation of an SIAS.
e Timing relays 162T-1, 162T-2, 162T-3, 162T-4 i
These timers are used to "close" the DGVSS window. The timers must be set to ensure that 1) load shedding and transfer of the bus to the EDGs occurs within the time allowed in the safety analyses, and 2) the voltage dip caused by the starting of the ESF load group 2 does not generate a spurious DGVSS.
Therefore, a time delay setting of 1.5 0.15 sec. is chosen. With this time delay setting the earliest the DGVSS window could close is 5.46 seconds after initiation of an SIAS (4.3 sec - 0.19 sec + 1.5 sec 0.15 sec = 5.46 sec).
The latest the DGVSS window could close is 6.14 seconds after initiation of an SIAS (4.3 sec +
0.19 sec + 1.5 sec + 0.15 sec = 6.14 sec).
The DGVSS window will enable detection of the degraded voltage in the first ESF load group sequence and will not be affected by the subsequent ESF load starting transients.
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The DGVSS trips the 4.16 kV Class IE source breakers.
Because the latest a DGVSS bus trip may be initiated is 6.14 seconds af ter initiation of an SIAS, all ESF loads werc analyzed for operation with a complete loss of voltage condition for up to 6.14 seconds and found acceptable.
Following initiation of a DGVSS, there is an additional time i
delay of 2.0 0.20 sec. provided for load shedding.
Following the 2 second time delay, the EDG breaker will i
close provided the EDG has attained normal voltage and speed. The EDG breaker will close within 10 seconds after initiation of an SIAS, which is the safety analysis time limit for EDG breaker closure.
e The SDVS scheme For a sustained degraded voltage condition, the proposed maximum response time requirement of 135 seconds (based on a time delay of 2.010.2 seconds for the 127D relays plus 120 12.0 seconds for the degraded voltage timing relays 1620) will ensure that permanently connected Class IE equipment will not be damaged and i
allow the operator a short period of time to restore bus voltages j
to an acceptable value.
l Following this period if the voltage has not recovered adequately, l
the relay will separate the 4.16 kV Class IE bus from the preferred power source. With this second time delay the 4.16 kV and 480 V Class IE buses may experience a degraded voltage condition if the voltage at the 4.16 kV Class IE bus dips below l
4181 V, which is the minimum dropout voltage for the 127D relay, l
for a period of approximately 135 seconds. Based on analysis, the Class IE motors can be operated at 80% of rated voltage for a duration of 140 seconds. However, if voltage at the 4.16 kV Class 1E buses drops below 80%, the Class IE motors will still be l
protected because at the lower voltages the CV-2 relays used for l
loss of voltage protection will trip within approximately 10 l
seconds, which is much sooner than the SDVS relays. This is due i
to the inverse time-voltage characteristic of the CV-2 relays.
This delayed CV-2 trip will also separate the 4.16 kV Class IE bus from the preferred power source.
The response time for SDVS is included in PCN 429 in the Technical Specification Table 3.3-5 " Engineered Safety Features Response Times."
l 5.4 NRC Requirement (Position 1.d of June 3.1977 letter)
"The voltage monitors shall automatically initiate the disconnection of offsite power sources whenever the voltage setpoint and time delay limits have been exceeded."
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. Evaluation Once a sustained degraded voltage is detected on 4.16 kV Class IE buses by one-out-of four degraded voltage relays following a time delay of 7 seconds, an alarm in the control room will alert the operator to the degraded condition. The existing design uses a Westinghouse inverse time delay relay CV-7 for the 127L alarm relay. Therefore, annunciator response time is dependent on the magnitude of the voltage sensed by the relay. The new design uses 1270 for sensing the bus voltage which is a fixed time (time delay of two seconds) relay. This two second delayed undervoltage signal is further delayed five seconds by timer 162A.
i Therefore, the Undervoltage Low alarm will be initiated with a fixed time delay of approximately seven seconds. This time delay will ensure that there will be no spurious actuation of-the alarm due to motor.
starting or system (switchyard) transients.
Following this alarm SDVS will automatically disconnect the preferred power source as described in section 4.2.2.1.
l DGVSS will disconnect the preferred power source as described in section 4.2.2.2.
5.5 NRC Reauirement (Position 1.e of June 3.1977 letter)
"The voltage monitors shall be designed to satisfy the requirements of IEEE std. 279-1971, " Criteria for Protection Systems For Nuclear Power Generating Stations.
I Evaluation
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This proposed scheme will provide undervoltage protection which complies with IEEE 279-1971 for single failure considerations, testing 1
provisions, and indication requirements.
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J For the proposed degraded voltage scheme the new ABB 27N and ABB 62T relays and associated timers and auxiliary relays listed in'section 4.4 are qualified for Class IE applications. All of these relays satisfy the requirements in IEEE standards 323 and 344.
An independent undervoltage detection scheme is provided for each of Train A and Train B Class 1E load groups. Train A and Train B relays are located at the 4.16 kV Class IE switchgear A04 (Train A) and A06 (Train B), respectively.
Each independent undervoltage detection scheme utilizes a two-out-of--
four coincidence logic as in the existing design to preclude spurious trips of thc-preferred power source.
IEEE 279 4.13 states, " Indication of Bypasses.
If the protective action of some part of the system has been bypassed or deliberately rendered i
inoperative for any purpose, this fact shall be continuously indicated in the control room."
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IEEE 279 4.14 states, " Access to Means 'or Bypassing. The design shall permit the administrative control of the means for manually bypassing channels or protective functions."
Neither the design of the existing nor the proposed scheme incorporates any operating bypasses.
Local test knife switches or wire jumpers would be used for manually placing a channel in tripped condition or bypassed j
mode for maintenance or testing. A channel placed manually in tripped condition will be annunciated in the control room (Low Voltage Alarm).
A manually bypassed channel also requires entry into Technical Specification ACTION statement.
Therefore, existing administrative controls will be used to monitor the status of a bypassed channel.
Also, control power to the circuitry is monitored and alarmed in the control room. These alarms and controls meet the intent of IEEE 279, l
and therefore meet the guidance of this NRC position.
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5.6 NRC Requirement (Position 1.f of June 3.1977 letter)
"The Technical Specification shall include limiting conditions for operation, surveillance requirements, trip set points with minimum and maximum limits, and allowable values for the second-level voltage i
protection monitors."
l Evaluation Proposed Change Number (PCN) 429, Change to Technical Specifications 3/4.3.2, " Engineered Safety Features Actuation Systems," dated September 30, 1993, requests NRC approval for the revised limiting conditions for operation, surveillance requirements, trip setpoints, and allowable values for the second-level voltage protection relays.
5.7 NRC Requirement (Position 2 of June 3.1977 letter)
)
" Interaction of Onsite Power Sources with Load Shed Feature.
"We require that the current system designs automatically prevent load shedding of the emergency buses once the onsite sources are supplying l
power to all sequenced loads on the emergency buses. The design shall also include the capability of the load shedding feature to be automatically reinstated if the onsite source supply breakers are tripped. The automatic bypass and reinstatement feature shall be j
verified during the periodic testing identified in Position 3.
J "In the event an adequate basis can be provided for retaining the load l
shed feature when loads are energized by the onsite power system, we l
will require that the setpoint value in the Technical Specifications, which is currently specified as "... equal to or greater than..." be amended to specify a value havir9 maximum and minimum limits. The licensees' bases for the setpoints and limits selected must be l
documented."
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Evaluation LOVS Scheme:
j In the proposed scheme the new LOVS logic will' also be' active while:the f
EDG'is supplying power to the 4.16 kV Class IE bus, the same as in the existing condition. The CV-2 relay setting is such that the relay will i
not dropout (trip) on bus load sequencing due to the inherent inverse l
time delay characteristics of an induction disc type relay. Dynamic studies show that the bus voltage will always recover above the relay pickup (reset) value prior to the start of the next load sequencing cycle and the duration of the voltage dip during any motor startup l
(including the start of the largest motor starting on a fully loaded bus) will not cause a trip of the CV-2 relay.
Therefore, with the EDG supplying the 4.16.kV Class'1E bus a LOVS will only.be generated for a loss of voltage (complete loss of voltage).
i However, in the unlikely scenario where the bus has insufficient voltage for either accelerating or for continuous operation of the Class.1E motors, tu generation of delayed LOVS and a subsequent separation of the EDG e W rable.
If the load shedding feature were locked out, the affecteo W
and subsequent motor sequencing to the bus would remain at locked rotor current condition, eventually tripping their associated i
circuit breakers. This could result in damage to the motors. 'The i
affected motor breakers would have been locked out due to overcurrent trip and subsequent starting of the motors would not be possible before i
manual resetting of the lockout relay.
Because the load shed feature is retained for this protection scheme, i
l the proposed Technical Specification will provide a maximum and. minimum
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allowable value for the voltage setpoint of the LOVS trip. The maximum allowable value is 3796 V.
The minimum allowable value is 3554 V.
This allowable value range is based on the setpoint of 3675 V plus or minus ~ a 3.3% (121 V) tolerance. The bases for these setpoints are documented in calculation E4C-098, "4kV Switchgear Protection Relay Setting Calculation.
SDVS Scheme:
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SDVS is disabled when the EDG is supplying power to the 4.16 kV Class IE bus. Therefore, bus load shedding by SDVS is automatically prevented once the EDG is supplying power to the Class IE bus and-automatically reinstated if the EDG breaker is open.
DGVSS Scheme:
DGVSS is a short duration signal which is generated during the first load sequencing cycle concurrent with initiation of an SIAS, only if the 4.16 kV Class IE bus experiences a degraded voltage coi.iition. This signal will be blocked after a short duration'(see section 5.3) and will not generate a DGVSS even if a degraded voltage condition exists during subsequent load sequencing cycles. Therefore, this scheme prevents l
l t
_ -...,. _. ~.., _. ~, _.
..~.-,m.-
. automatic load shedding of the Class IE bus when the EDG is supplying power and is automatically reinstated with an SIAS reset.
5.8 NRC Reauirement (Position 3 of June 3.1977 letter)
"Onsite Power Source Testing" (Not repeated here)
Evaluation i
This requirement deals with onsite sources, which are not affected by the planned enhancement to the degraded voltage protection scheme.
Therefore, this position is not applicable to this evaluation.
6.
CONCLUSION i
Based on the above evaluation, the degraded voltage protection scheme l
meets the NRC guidance provided in the June 3, 1977 letter and will ensure acceptable operation of the Engineered Safety Feature loads.
i
u I
4 TO S'titTCHYARD 220kV l
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r;OTES:
- 1. RELAYS 127 F1,2,3,4 ARE WESTINGHOUSE TYPE CV-2 IrJDUCTION DISC UNDERVOLTAGE RELAYS.
l
- 2. RELAY 127 L IS A WESTINGHOUSE TYPE CV 7 INDUCTION DISC UNDERVOLTAGE RELAY.
Updated SAN ONOFRE NUCLEAR GENERATING STATION l
Units 2 & 3 l
CLASS 1E 4160 VOLT EUS i
UNDERVOLTAGE DETECTION SCHDIE i
(2A04 SHOW)
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t NOTES:
- 1. RELAYS 127F1, 2, 3 & 4 ARE WESTINGHOUSE TYPE CV-2 s
INDUCTION DISC UNDERVOLTAGE RELAYS.
j
- 2. RELAYS 127D1, 2, 3 & 4 ARE ASEA BROWN BOVERI TYPE 27N DEFINITE TIME SOLID STATE UNDERVOLTAGE RELAYS.
- 3. RELAYS 16201, 2, 3 & 4 ARE ACASTAT TIME DELAY RELAYS TYPE E7012PLK.
I
- 4. RELAY 162A IS AGASTAT TIME DELAY RELAY TYPE E7012PC.
^
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