ML20136D826
| ML20136D826 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 03/24/1993 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20136C539 | List:
|
| References | |
| FOIA-96-485 NUDOCS 9703130032 | |
| Download: ML20136D826 (6) | |
Text
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ENCLOSURE EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION UNDERVOLTAGE RELAY SETPOINT FOR DEGRADED GRID VOLTAGE i
I FLORIDA POWER AND LIGHT COMPANY i
ST. LUCIE UNIT 1
- DOCKET NO. 50-335
1.0 INTRODUCTION
The existing ~undervoltage protection scheme at St. Lucie consists of three sets of two (2) solid state undervoltage definite time relays. One set provides a " loss of voltage" function (trip at 2900 +/- 29 volts, 1 +/- 0.5 seconds) and the other two sets ( undervoltage device #1 and undervoltage device #2) serve as " degraded voltage" sensors (trip at 3675 +/- 36 volts, 7
+/- 1 minutes; and 3592 +/- 36 volts, 18 +/- 2 seconds respectively). This design provides undervoltage/ degraded voltage protection for the 4160 and 480 volt system equipment under non-accident conditions.
In addition, each 480 volt Class lE bus has one set of two (2) solid state undervoltage relays with internal adjustable timers (set at 429 +5, -0 volts; 7 +/- 1 seconds) to provide " degraded voltage" protection for the 4160 and 480 volt system equipment during accident conditions. Florida Power and Light Company (FPL) re-analyzed their station auxiliary system and determined that an improvement to the undervoltage relay setpoints could be made. By letter dated November 30, 1992 FPL proposed a revision to the Technical Specifications Tables 3.3-3, 3.3-4, and 4.3.2 to change the setpoints for the emergency bus undervoltage protection scheme relays for both accident and non-accident conditions.
2.
EVALUATION i
The licensee used Ebasco Services Incorporated computer program AUXSYS4078 to analyze the system and equipment voltages for both steady-state and transient conditions for the station auxiliary system. Analysis of the " Arkansas 9703130032 970301 PDR FOIA BINDER 96-485 PDR
k Scenario" (NRC Information Notice 79-04), which postulates starting all safety injection actuated signal (SIAS) initiated loads with the auxiliary system under full power operation, was performed in two stages: (1) the first stage j
assumed simultaneous starting of all large SIAS loads. The results were used to evaluate the adequacy of the system voltages for starting large 4000 volt and 460 volt motors and to verify that voltages at the 480 volt motor control centers (MCC) did not reach contactor dropout levels. The time period of the first stage was considered to be approximately 5 seconds (based on j
manufacturer's acceleration time data for large motors); (2) the second stage j
examined the start of smaller 460 volt motors after system voltages had stabilized following start of the large motors. The licensee states that nominal setpoints and tolerances are calculated considering test instrument, relay, and potential tonsformer errors.
The licensee has proposed to change the trip and allowable values for the 4.16 kV emergency bus undervoltage (loss of voltage) relay set points from 2900 +/-
29 volts to greater than or equal to 2900 volts with no change to the existing time delay of 1 +/- 0.5 seconds. We have determined that this change duplicates the format presently used in the corresponding Technical Specifications for St. Lucie Unit 2 and the change is, therefore, acceptable.
1 The licensee's re-analyses also indicated that two different trip setpoints for 4.16 kV undervoltage Device #1 and undervoltage Device #2 which were required for equipment protection are no longer required. Rather, a single setpoint is sufficient to assure that acceptable voltages are available to Class IE equipment during non-accident conditions of degraded grid voltage.
The licensee has proposed to modify the undervoltage Device #1 to alarm the undervoltage conditions in the main control room, and the setpoint and the associated time delay will provide an early warning of the sustained grid voltage disturbances. The licensee has proposed to change the trip setpoint of the undervoltage Device #2 from 3592 +/- 36 volts to not less than 3831 volts with no change to the existing time delay range of 18 +/- 2 seconds.
The licensee has determined that this is the voltage level at or above which (equivalent to 415 volts at the 480 volt load center bus under normal operating load conditions and minimum expected transmission system voltage of
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.- 2 230 kV), operation of all the station auxiliary equipment under non-accident conditions is assured. The time delay of 18 +/- 2 seconds allows start of the largest 4000 volt motor (4000 HP condensate pump) on the fully loaded auxiliary system without causing a spurious trip. These settings assure that the Class IE equipment will not t,e subjected to sustained degraded voltages
- i under non-accident conditions and the settings are, therefore, acceptable.
4 In addition, the licensee has proposed to change the 480 volt emergency bus undervoltage (degraded voltage) setpoints under accident conditions from 429
+5 -0 volts with a 7 +/- 1 second time delay to greater than or equal to 415 volts with a less than or equal to 9 second time delay. This will assure adequate starting voltage and continued safe operation of equipment under I
accident conditions (415 volts at the 480 volt load center which corresponds to 3850 volts on the 4.16 kV bus coincident with SIAS). The time is sufficiently long to allow bus voltage recovery following start of all required safety equipment and does not exceed the time delay assumed in the accident analyses for connecting the emergency bus to the diesel generator.
We find this to be acceptable.
The licensee has also evaluated the proposed change. with respect to overload protection of systems and motors. The setpoint changes will not result in inadvertent actuation of overload protective devices for the individual loads.
With the new settings, all the 480 volt system motors will be operating with terminal voltages not less than 400 volts (not more than 115% of rated current). The thermal overload (TOL) devices for the motors are set to trip at 125% of the overload heater rated current which assures that the TOL devices will not trip under degraded voltage conditions.
The licensee further states that the proposed trip and allowable values are provided in a " greater than/ equal' or " lesser than/ equal" format to specify only the limiting values for the undervoltage/ degraded voltage protective function. This type of value specification duplicates the format presently used in corresponding Technical Specifications for St. Lucie 2.
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I The staff has evaluated the licensee's submittal and has concluded that the i
new undervoltage relay setpoints offer full protection to the Class IE systems j
and equipment during-both accident and non-accident conditions. The proposed J
trip and allowable values for the 4.16 kV emergency bus undervoltage (Loss of Voltage) in a " greater than/ equal" fermat duplicates the format presently used 1
in corresponding Technical Specifications for St. Lucie 2 and the change-is, therefore, acceptable. The proposed trip and allowable values for the 4.16 kV.
emergency bus undervoltage (degraded voltage) relay setpoints under non-accident conditions will alert operators to the sustained undervoltage conditions and will initiate separation from the offsite power and transfer to the onsite sources if the voltage does not recover to acceptable levels within the allotted time periods This is in accordance with the Branch Technical Position PSB-1 and the proposed change to the degraded voltage setpoints is, therefore, acceptable. The proposed trip and allowable values for the 480 volt emergency bus undervoltage ( degraded' voltage) relay setpoints during accident conditions will protect the 4160 volt and 480 volt systems equipment, will assure adequate starting voltage and continued safe operation of all the j
equipment.and the proposed change is, therefore, acceptable.
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i FACILITY NAME:
St. Lucie 1 l
SUMARY OF REVIEW / INSPECTION ACTIVITIES
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' EELB/DE/NRR conducted a review of the revision to the Technical Specifications to change the undervoltage relay setpoints in Tables 3.3-3, 3.3-4, and 4.3-2.
The staff has reviewed the licensee's submittal and has concluded that the licensee has provided adequate justification for these changes and the changes are, therefore, acceptable.
NARRATIVE DISCUSSION OF LICENSEE PERFORMANCE FUNCTIONAL AREA: ENGINEERING / TECHNICAL SUPPORT SE of March 15, 1993, involved a technical issue that overlapped into operations and design of electrical power system. The licensee has adequately addressed all aspects of the issue without NRC prompting to close the TAC.
This achievement indicated good departmental communications, a technically qualified staff, and responsiveness to NRC issues.
i Author:
N. K. Trehan Date:
March 15, 1993.
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