NLS9100446, Application for Amend to License DPR-46,consisting of Proposed Change 98,changing Tech Specspage 55 Re Voltage Relay Setting Limits

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Application for Amend to License DPR-46,consisting of Proposed Change 98,changing Tech Specspage 55 Re Voltage Relay Setting Limits
ML20082B889
Person / Time
Site: Cooper Entergy icon.png
Issue date: 07/10/1991
From:
NEBRASKA PUBLIC POWER DISTRICT
To:
Shared Package
ML20082B887 List:
References
NLS9100446, NUDOCS 9107170116
Download: ML20082B889 (5)
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NLS9100446 Attachment 1 Page 1 of 5 Emergenty Technical Specification Change Proposed Change No. 98 (Revised Loss of Voltr3e Relay - Setting Limits)

Technical Specification Page 55 Refereace: 1) Telecon between J . M. Meacham (NPPD) and John Zwolinski (NRC) on July 9,1991, Request for Waiver of Compliance

2) Letter from G. Lear (NRC) to J. M. Pilant (NPPD) dated April 11, 1978, CNS Amendment No. 43 to CNS Technical Specifications
3) Letter from J. M. P11 ant (NPPD) to D. K. Davis (NRC) dated July 18,1977, Electrical Under Voltage Protection BACKGROUND License Amendment No. 43 (Reference 2) approved, among other things, the addition of and setting limits for the first level undervoltage relays or (loss of voltage relays) 27/1FA-1, 27/lF-1, 27/1CB 1, 27/1G-1, and 27/ET-1 (27/ET-2 was added by Amendment 75), Also this Amendment approved the addition of and the setting limits for the second level undervoltage or (degraded voltage relays) 27/lF-2, 27/1FA-2, 27/10-2, and 27/lGB-2. These relays and settings limits were included in the CNS Technical Specifications in response to an NRC request (Reference 3).

This request addressed the susceptibility of the on-site emergency power system to sustained degraded grid voltage conditions at the offsite power source and the interactions between the offsite and on-site emergency power systems, lt also requected modifications be made if necessary and that Technical Specification changes be submitted to comply with the Staff's position.

During the course of the District's Design Basis Review of the Standby AC Power System, the design settings of Loss of Voltage Relays were determined to be outside of the settings limits specified in the CNS Technical Specifications. By Reference 1. the Nebraska Public Power District requested a Walver of Compliance to the Cooper Nuc! ear Station (CNS) Technical Specifications regarding the CNS Loss of Voltage Relays setting limits. During this telecon the District was granted an Oral Waiver of Compliance. The Nuclear Regulatory Commission, in Reference 1, notified the District that an Emergency Technical Specification Change would be necessary to resolve this concern.

The critical buses (lF and 1G) are monitored for loss of voltage conditions by the first level (loss of voltage) relays. This protective function utilizes inverse time delay relays. There are two settings associated with these relays.

The tap setting determines the point that the relay will actuate and the time dial setting determines the prescribed time delay curve. The combination of these parameters uniquely identifies the operating characteristics which form an inverse time-voltage curve. This setting limit is currently listed in the Technical Specification as 2900 V 5 Percent, 5 seconds i 1 second time delay.

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NLS9100446 Attachment 1 Page 2 of 5 The first level undervoltage (loss of voltage) relays for buses IF and IG (27/1F-1, 27/1G 1) perform the following two actions: a) Initiate load shedding of the 4160 volt motor loads on Bus IF and 1G; and b) Provide a start signal to the emergency diesels. The remaining first level undervoltage (loss of voltage) relays (27/1FA-1, 27/lGB 1) have a slightly longer time delay and trip the tie breakor from Bus lA/1B to-Dus 1F/lG. This extra time delay is to allow the shedding of loads prior to closing breakers IFS /1GS (which close immediately after tripping IFA/1GB), The second level undervoltat,e logic will only trip the tie breaker IFA/1GB, which will initiate the first level undervoltage relays to accomplish actions a) and b).

The functions of relays 27/ET-1, and 27/ET-2 are to: a) Provide an interlock to prevent the closing of Emergency Transformer (ET) Tie Breakers IFS and ICS, respectively, during loss of the ET and, b) Trip breakers IFS and 1GS if a loss of the ET occurs while operating from the ET The Emergency Transformer also has second level undervoltage protection that provides an interlock to prevent the closing of Breakers IFS and 1GS during degraded voltage conditions on the ET and its 69kV feeder line.

SAFETY EVALUATION

[ The relays at issue (first level) monitor the Gritical AG bus.s for a loss of l voltage condition and were installed as part of the original de. sign of GNS. Later modifications added the second level undervoltap protectior (Reference 2), The original design setpoints (tap and time dial setting) were determined by Burns and Roe calculation 2.09.06. Thesc two settings identify a unique time voltage curve that 6 scribes the operation of the relay.

The design - bases for the first level relaya a9 oefined in Burns and Roe calculation 2.09.06 are:

1) Both 27-1F1/27-101 and 27-1FA1/27-1GB1 must ride through (i.e. not pick up-and time out) during motor starting cycles at 70% voltage for 5 seconds.

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2) 27-1Fl/27 1G1 must initiate motor trips: immediately and initiate a permissive signal to load the diesel generator on the bus in 8.5 seconds if-the offsite supply voltage has not stabilizad.
3) 27-lFAl/27-1GB1 must trip breaker 1FA/lGB which autom stically closes breaker 1FS/ LGS to the emergency transformer.
4) The emergency transformer tie breaker 1FS/1G5 must close on the bus

. after it is cleared of motors and before the diesel generator breakers attempt to close.

5) 27/1FA-1 (27/1GB-1) contacts should actuau approximately 1 seconds after 27/1F-1 (27/10-1) close in the 70% bus voltage range, and sooner for lower voltages to allow for motor trips and voltage collapse before re energizing with the emergency transformer.

j NLS9100446 Attachment 1 Page 3 of 5 These relays are inverse time relays and are calibrated every 18 months per CNS Surveillance Procedure 6.2.2.1.9. This procedure calibrates and tests the relays at four points which lie on the time-voltage curves specified by the original Burns and Roe setting calculation 2.09.06. The subject relays are calibrated and adjusted to function as designed. However, during the design basis review of the

. Standby AC Power -System, it was determined that the Technical Specification setpoint'is not the same as the original design basis setpoint. These relays were added to Tsble 3.2.B (with the published setpoint) in Amendment 43 of the CNS Technical Specifications (Reference 2). Although there was extensive communication with the NRC concerning the operation of these relays the basis for the published setpoint is unclear. It is believed _ to be a result of a incorrect translation of the original Burns and Roe calculation.

V'.th the addition of the second level undervoltage protection (Reference 2), the I

fu st level undervoltage relays need only detect a loss of voltage and not l degraded voltage conditions. CNS Technical Specification Table 3.2.B lists the subject relays as " Emergency Buses Mss of Voltagt Relays" as compared to a

" Emergency Buses Undervoltage Relays (degraded voltage)" that describe the second

, level relays.' The actual setpoint of the first level (loss of voltage) relays is somewhat arbitrary, provided the setpoint does not create spurious transfers, or diesel starts, and does initiate load shedding in the required ti.ne, The actual setpoint translates to 'a lower voltage point for the. relay logic to actuate. It should be _noted that the second level undervoltage relays independently trip the tie breaker. The trip of the tie breaker will create a complete loss of voltage.

When this loss of voltage occurs, the loss of voltage relays, as currently set

in the plant, will respond as designed and quickly clear the buses. The Emergency AC System will respond as described in the USAR and the CNS Technical Specification Section 3.9 BASES, because there is no loss of function over the

{ entire range of voltage (normal to zero).

Although the first level undervoltage relays are not adjusted or calibrated to i

the published setpoint described in the CNS Technical Specification Table 3.2.B, they continue to perform their safety function. This safety function is described 4- in the BASES of section 3.9 of the CNS Technical Specifications, and in the USAR.

- The . original design calculations that established _ the setting have not been l superseded or determined to be inadequate; however, the setting reflected in the

, Technical Specifications does rmt agree with the original design basis setting, i

In summary, the District requests the following change:

1) On page 55, for the Emergency Bus Loss of Voltage Relays, change the setting limit from 2900V 5 percent, 5 second i 1 second time delay to 2300V i 5% and 0 to 5 second time delay.

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EVALUATION OF THIS REOUEST WITH RESPECT TO 10CFR50.92
The requested license amendment is judged to involve no significant hazards based upon the following:

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NLS9100446 Attachment 1 Page 4 of 5

1. Does the proposed license amer.dment involve a significant increase in the

-probability or consequences of an accident previously evaluated?

Evaluation The previously evaluated cccident for the existing undervoltage protection at CNS t for the offsite power sources and the emergency buses is as follows:

"The startup transformer and the emergency transfarmer are the offsite power t Surces to CNS. Their voltages are monitored by undervoltage relays which provide low voltage protection for the emergency buses. Whenever the voltage setpoint and time delay limit for the undervoltage relays have been exceeded, the emergency

-buses are. automatically disconnected from the offsite power sources".

" Voltages on the 4160 volt bus IF (1G) are monitored by loss of voltage relays 27/1F-1 (27/10-1),-which is set to operate on decreasing voltage at about 2900 volts _i 5 %, 5 reconds i 1 second delay. Each relay initiates tripping of-all

motor breakers on the bus, starts its associateo diesel ,enerator, and isolates its bus".

The District has determined that the Loss of Voltage Relay settings listed in the Technical Specifications are misstated. This proposed amendment will change the voltage < and time settings to correspond with the original existing loss of voltage relay setting of 2300 volts i 5 percent, with a 0 to 5 second time delay.

4 The relays will still begin to operate at less than 2900 volts decreasing and for loss of voltage the safety actions should be complete within 5 seconds depending on the rate of voltage loss. The settings will accurately reflect calibration points . on the curves to prove - operability. These revised voltage . and time settings are within the Plant Design . Basis, and are consistent with the JOperational Transient and Accident Analyses as documented in the USAR. The proposed amendment will not negate the ability of the first level undervoltage (loss of voltage) relays to satisfy the previu..-., evaluated and accepted criteria. The District has determined _that there is no safety significance resulting from inis change, as the electrical distribution system will continue to operate within the Design Basis assumed in the Operational Transient and

. Accident Analysis.'The proposed amendment will incorporate the original design basis settings of the subject relays and therefore will not involve a significant

increase in the probability or consequence of any accident previously evaluated.
2. Does the proposed license amendment create the possibility of a new or different kind of accident from any accident previcusly evaluated?

Evaluation The proposed amendment will make changes to the setting limits on the first level

- undervoltage (loss of voltage) relays, to correspond with the original existing

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j NLS9100446 Attachment 1

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Page 5 of 5 loss of voltage relays, voltage and timer sottings of 2300 volts i 5%, with a 0 to 5 second time delay. These revised voltage and timer setpoints are within the Plant Design Basis, and are consistent with the Operational Transient and Accident Analysis of the USAR. The original design setpoints (tap and time dial setting) were determined by Butns and Roe calculation 2.09.06. These two settings identify a unique time voltage curve that describes the operation of the relay.

The function and operation of the first level undervol: age relays remains the same, and the previously evaluated safety function remains in effect. The Emergency AC System will continue to respond as described in the USAR and the CNS Technical Specification Section 3.9 BASES. The proposed amendment will not create a new mode of plant operation and will not create the possibility of a new or different kind of accident from any accident previously evaluated.

3. Does the proposed amendment involve a significant reduction in the margin of safety?

Evaluation The safety function of the first level undervoltage (loss of voltage) relays is described in the BASES of section 3.9 of the CNS Technical Specifications, and in the USAR. With the revised Technical Specification voltage and time settings, the safety function and operation of the first level undervoltage (loss of vcltage) relays remain the same. Also, with the addition of the second level undervoltage protection, the first level undervoltage (loss of voltage) relays need only detect a loss of voltare and not degraded voltage conditions. It should be noted that the second levd undervoltage relays independently trip the _

tie breakers. The trip of the tie breakers will create a complete loss of voltage. When this loss of voltage occurs, the loss of voltage relays, as currently set in the plant, will respond as designed and quickly clear the buses.

The Emergency AC System will continue to respond as described in the USAR and the CNS Technical Specification Section 3.9 BASES, because there is no loss of function over the entire range of voltage (normal to zero). The proposed amendment will continue to allow the electrical distribution system to operate within the Design Basis assumcd in the Operational Transient and Accider*.

Analysis. This proposed amendment will not involve a significant reduction in ' ne margin of safety.

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