05000280/LER-1998-002, :on 980202,automatic Turbine Trip Resulted in Automatic Reactor Trip.Caused Degraded Generator Voltage Regulator sub-component Failure.Placed Plant in Safe Hot SD & Replaced Intermittent Relay & Relay Socket
| ML18153A225 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 03/04/1998 |
| From: | Christian D VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | |
| Shared Package | |
| ML18153A224 | List: |
| References | |
| LER-98-002, LER-98-2, NUDOCS 9803100233 | |
| Download: ML18153A225 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(viii) 10 CFR 50.73(a)(2)(iv), System Actuation |
| 2801998002R00 - NRC Website | |
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NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB NO. 3150-0104 (4-95)
. EXPIRES 4/30/98 ESTIMATED BURDEN.PER RESPONSE TO COMPLY WITH THIS MANDATORY INFORMATION COLLECTION REQUEST: 50.0 HRS.
LICENSEE EVENT REPORT (LER)
REPORTED LESSONS LEARNED ARE INCORPORATED INTO THE LICENSING PROCESS AND FED BACK TO INDUSTRY. FORWARD COMMENTS REGARDING BURDEN ESTIMATE TO THE INFORMATION AND RECORDS MANAGEMENT BRANCH (T-6 F33),
(See reverse for required number of digits/characters for each block)
U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON, DC 20555-0001. AND TO THE PAPERWORK REDUCTION PROJECT (3150-010-4),
OFFICE OF MANAGEMENT AND
- BUDGET, WASHINGTON, DC 20503.
FACILITY NAME (1)
DOCKET NUMBER (2)
PAGE(3)
SURRY POWER STATION, Unit 1 05000 - 280 1 OF5 TITLE (4)
Turbine:.Generator Trip Due to Loss of Generator Excitation Power Results in Reactor Trip EVENT DATE (5)
LER NUMBER (6)
REPORT DATE (7)
OTHER FACILITIES INVOLVED (8)
SEQUENTIAL REVISION FACILITY NAME DOCUMENT NUMBER MONTH DAY YEAR YEAR MONTH DAY YEAR 05000-NUMBER NUMBER 02 02
. 98 1998 002 00 03 04 98 FACILITY NAME DOCUMENT NUMBER 05000-OPERATING THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check one or more) (11)
MODE (9)
N 20.2201(b) 20.2203(a)(2)(v) 50.73(a)(2)(i) 50.73(a)(2)(viii)
POWER 20.2203(a)(1) 20.2203(a)(3)(i)
- 50. 73(a)(2)(ii)
- 50. 73(a)(2)(x)
LEVEL (10) 100 %
20.2203(a)(2)(i) 20.2203(a)(3)(ii)
- 50. 73(a)(2)(iii) 73.71 20.2203(a)(2)(ii) 20.2203(a)(4)
X 50.73(a)(2)(iv)
OTHER 20.2203(a)(2)(iii) 50.36(c)(1)
- 50. 73(a)(2)(v)
Specify in Abstract below 20.2203(a)(2)(iv) 50.36(c)(2).
- 50. 73(a)(2)(vii) or in NRC Fenn 366A LICENSEE CONTACT FOR THIS LER 112 NAME I
~;;;;N;~;:;~;~de Afea Code)
D. A. Christian, Site Vice President COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)
CAUSE
SYSTEM COMPONENT MANUFACTURER REPORTABLE
CAUSE
SYSTEM COMPONENT MANUFACTURER REPORTABLE TONPRDS TONPRDS X
TL RG W893 y
SUPPLEMENTAL REPORT EXPECTED (14)
EXPECTED MONTH DAY YEAR I
YES 1x NO SUBMISSION (If yes, complete EXPECTED SUBMISSION DATE).
DATE ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines) (16)
On February 2, 1998, at 0526 hours0.00609 days <br />0.146 hours <br />8.69709e-4 weeks <br />2.00143e-4 months <br />, with Surry Unit 1 at 100% reactor power and 855 Mwe, an 'Excitation Loss Of Power' annunciator was received followed immediately by a 'Generator Differential Lockout Relay Trip' annunciator.
This caused an automatic trip of the Unit 1 main generator followed by an automatic turbine trip. The automatic turbine trip resulted in an automatic reactor trip.
The most probable cause of the loss of generator excitation power was a degraded generator voltage regulator sub-component failure. At the time of the trip the generator voltage regulator was in the manual base adjust position due to a malfunction in the automatic circuit. Extensive testing of the voltage regulator circuitry and its sub-components did not result in the identification of a specific failed component. A root cause evaluation has been initiated to determine the cause of the Loss of Field and Main Generator Lockout annunciators, evaluate corrective actions from previous events, and provide recommended corrective actions to prevent recurrence.
No conditions adverse to safety resulted from this event and the health and safety of the public were not affected.
event is being reported pursuant to 10 CFR 50.73(a)(2)(iv).
9803100233 980304 PDR ADOCK 05000280 S
PDR This
,r.=========================================;i NRC F~RM 366A e
e. NUCLEAR REGULATORY COMMISSION (4-95)
FACILITY NAME (1)
LICENSEE EVENT REPORT (LER)
TEXTCONTINUATION DOCKET LER NUMBER (6)
Surry Power Station, Unit 1 YEAR I SEQUENTIAL I REVISION NUMBER NUMBER 05000-280 1998 002 00 PAGE (3) 20F5 TEXT (If more space is required, use additional copies of NRC Form 366A) (17) 1.0 DESCRIPTION OF THE EVENT At 0526 hours0.00609 days <br />0.146 hours <br />8.69709e-4 weeks <br />2.00143e-4 months <br /> on February 2, 1998 with Unit 1 at 100% reactor power and 855 MWe, a
!Excitation Loss of Power' annunciator [EIIS-TL-ANN] was received followed immediately by a 'Generator Differential Lockout Relay Trip' annunciator [EIIS-TB-ANN]. This caused the Unit 1 main generator [EIIS-TB-GEN] and turbine [EIIS-TA-TRB] to automatically trip. The
- automatic turbine trip resulted in an automatic reactor trip.
At the time of the trip, the generator voltage regulator [EIIS-TL-RG] was in the manual base adjust position due to a malfunction in the automatic circuit.
The automatic circuit malfunctioned in June 1997 and the regulator was placed in base adjust at that time. The decision was made to remain in base.adjust and not repair the automatic circuit while on line.
A review of industry events identified numerous occurrences of plant trips when attempts were made to repair voltage regulators on line.
Approximately one minute prior to the trip, the Unit 1 operator made an adjustment to the main generator base voltage switch [EIIS-TL-EIS] to lower the 230 KV bus voltage from 233 KV to 230 KV. Response to the adjustment appeared to be normal to the operator.
Approximately 10 seconds after making the adjustment, a computer alarm indicated gen~rator voltage was low at 20.8 KV.
The operator acknowledged the alarm and proceeded to the generator control panel to check the voltage.
He noted the generator voltage was 17 to 18 KV. The generator voltage appeared to be moving slightly up and down. As the operator started to announce that the generator voltage was extremely low, annunciators 'Excitation Loss of Power' (KLF Relay) and 'Generator Differential Lockout Relay Trip' (86-G Relay) actuated. This caused the Unit 1 main generator and then the turbine to automatically trip. The automatic turbine trip resulted in an automatic reactor trip.
Upon the receipt of the trip signal, the Reactor Protection System (RPS) actuated as designed and the operator backed-up the automatic trip with a manual trip.
Both Motor Driven Auxiliary Feedwater (MDAFW) pumps [EIIS-BA-P] and the* Turbine Driven Auxiliary Feedwater (TDAFW) pump [EIIS-BA-P] automatically started as designed on low-low steam generator (SG) level. Approximately 15 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br /> after the trip, annunciator 'NIS Source Range Hi Flux' [EIIS-IG-ANN] was received and it was noted that detector N-31 had increased from 250 counts per second (cps) to 2000 cps. The appropriate annunciator procedure was entered.
Redundant indications on detector N-32 and the gammametrics source range detectors showed no indications of an increased count rate.
A four hour non-emergency report was made to the NRC Operations Center at 0814 hours0.00942 days <br />0.226 hours <br />0.00135 weeks <br />3.09727e-4 months <br /> in accordance with 1 OCFR50. 72(b )(2)(ii) due to a manual or automatic engineered safety feature (ESF) actuation.
- (4-95) e e. NUCLEAR REGULATORY COMM;SSION LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME (1)
DOCKET.
LER NUMBER (6)
Surry Power Station, Unit 1 YEAR I SEQUENTIAL I REVISION NUMBER NUMBER 05000-280 1998 002 00 TEXT (If more space is required, use additional copies of NRC Form 366A) (17)
PAGE (3) 30F5 Troubleshooting was performed by the system engineer and station electricians on the generator base adjust control switch and the voltage regulator motor operated potentiometer for base adjust. No problems were found and the readings were correct for these switches.
Additionally, the KLF and 86-G relays were tested satisfactorily. On February 3, 1998, a vendor representative with the assistance of system engineering and electricians performed tests of the voltage regulator circuits using vendor test equipment. All the circuits again
_ tested satisfactorily.
The automatic circuit was tested. An intermittent relay was identified and the relay and relay socket were replaced. This was believed to have been the original problem that required operating in base adjust.
No equipment failures were found during any of the tests that would have caused the step decrease in excitation which caused the Unit trip. A root cause evaluation has been initiated to determine the cause of the _Loss of Field and Main Generator Lockout annunciators, evaluate corrective actions from previous events, and provide recommended corrective actions to prevent recurrence.
On February 4, 1998, a final test which involved making voltage adjustments in automatic and manual modes was performed. The results of the test were satisfactory. Unit 1 was tak~n critical at 0507 hours0.00587 days <br />0.141 hours <br />8.382936e-4 weeks <br />1.929135e-4 months <br /> on February 4, 1998, and returned to 100% power at 0530 on February 5, 1998. The unit is now operating with the regulator in the automatic mode.
This report is being made pursuant to 1 OCFR50.73(a)(2)(iv), due to the initiation of an engineered safety feature (ESF), including the reactor protection system (RPS).
2.0 SAFETY CONSEQUENCES AND IMPLICATIONS
Upon the receipt of the reactor trip signal, the RPS actuated and functioned* as designed.
The control rods inserted into the core and neutron flux was verified-to be decreasing.
Station operating personnel acted promptly to place the unit in a safe, hot shutdown condition in accordance with the proper procedures. The shutdown margin was calculated using the appropriate procedure and the critical safety function status trees were monitored to verify that unit conditions were acceptable. Plant response was as expected and the unit stabilized at hot shutdown. No conditions adverse to safety resulted from this event and the health and safety of the public were not effected.
" (4-95) e FACILITY NAME (1)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION DOCKET e. NUCLEAR REGULATORY COMMISSION LER NUMBER (6)
. PAGE (3)
Surry Power Station, Unit 1 YEAR I SEQUENTIAL I REVISION NUMBER NUMBER 05000 - 280 1998 002 00 4 OF 5 TEXT (If more space is required, use additional copies of NRC Form 366A) (17)
3.0 CAUSE
Although no specific component failure was identified during the troubleshooting of the regulator, the most probable cause of the loss of generator excitation power was a degraded generator voltage regulator sub-component failure. At the time of the trip the generator voltage regulator was in the manua( base adjust position due to a malfunction in the automatic circuit. The automatic circuit malfunctioned in June 1997 and the regulator was placed in base adjust at that time.
Although testing by plant personnel and the vendor representative did not identify any problems with the regulator manual circuitry, a sub-component failure of this equipment remains as the most probable cause f9r the event. A root cause evaluation (RCE) has been initiated to determine the cause of the equipment failure.
4.0 IMMEDIATE CORRECTIVE ACTIONS
Following the reactor trip, Control Room Operators acted promptly to place the plant in a safe hot shutdown condition in accordance with emergency and other operating procedures.
The Shift Technical Advisor calculated the shutdown margin and monitored the critical safety function status trees to verify that the unit conditions were acceptable. Plant response was as expected and the unit was stabilized at hot shutdown.
5.0 ADDITIONAL CORRECTIVE ACTIONS
A root cause evaluation has been initiated to determine the cause of the Loss of Field and Main Generator Lockout annunciators, evaluate corrective actions from previous events, and
. provide recommended corrective actions to prevent recurrence.
A vendor representative with the assistance of system engineering and electricians began troubleshooting the voltage regulator circuits using vendor test equipment.
The circuits tested satisfactorily.
The base adjust switch in the main control room was checked for binding or sticking.
No problem was found with the switch.
The firing drawers and redundant circuits were tested individually and as a unit with no problems identified.
The automatic circuit was tested. An intermittent relay was identified and the relay and relay socket were replaced.
This was determined to be the original problem that required operating in base adjust.
T, (4-95) e NUCLEAR R:GULATORY COMMISSION LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME (1)
DOCKET LER NUMBER (6)
Surry Power Station, Unit 1 YEAR I SEQUENTIAL I REVISION NUMBER NUMBER 05000-280 1998 002 00 TEXT (If more space is required, use additional copies of NRC Form 366A) (17)
PAGE (3) 50F5 A work order was submitted to troubleshoot and repair the N-31 source range detector condition. The high voltage power supply was replaced and this corrected the problem. The detector was satisfactorily tested and returned to service.
6.0 ACTIONS TO PREVENT RECURRENCE Recommendations from RCE 98-0280 necessary to prevent recurrence will be implemented when the evaluation is completed.
7.0 SIMILAR EVENTS
LER 50-281/93-004-00, "Unit 2 Turbine-Generator Trjp Via the Loss of Field Relay." The trip was caused by a loss of excitation field for the main generator. Troubleshooting of the voltage regulator identified a failed phase shifter card was discovered and replaced.
8.0 ADDITIONAL INFORMATION
Unit. 2 was not affected by this event and remained stable at 100% power.