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Operating Events Insights-LOV_DVR
	ML23117A316
Person / Time
Issue date:	04/27/2023
From:	Mohammad Sadollah; NRC/RES/DE
To:	;
	M. Sadollah 301-415-6804
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ML23094A108	List: ML23117A316;
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	Download: ML23117A316 (1)
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Docket Numbe Link 247 2471999015 247 2471999015 374 3742001003 249 2491989001 251 2512013002 455 4542012001 219 2191997010 219 2192012001 237 2371990002 244 2442003002 272 2722003002 301 3011989002 249 2492010001 250 2502008001 282 2821989010 339 3382009004 331 3311994012

311 3111991008 311 3111991008 254 2542018005 498 4982017001 Inspection Reports full search of

https://lersearch.inl.gov/Index.aspx?Page=PDFView?Doc::3111991008R01.pdf LER 31191008 Y91: 4KV Vital Bus UV Relay Setpoints Found Below Minimum Tech. Spec. Allowable Value. (inl.gov)

PDFView.ashx (inl.gov)

Degraded Voltage Relay resulted in no hit

Date Summary description of Issues with 8/31/1999 event DVR/LOVR A complex event during DVR actuated maintenance of bistable in RPS logic caused trip, Actual Degraded Low voltage on 480 bus, Voltage condition striped the emergency bus and connected to EDGs. One bus tripped off due to overcurrent trip.

Post trip evaluation found that found that the actual over current trip setpoint for its 8/31/1999 Amptector was at 3200 amps, rather than the 6,000 amps setting as designed. In addition the event might have been prevented if the Station Auxiliary Transformer Tap Changer was not in manual mode due to a defective voltage control relay.

CCF (Common Cause LOVR actuated due to failures) of fuses caused fuse failures 9/3/2001 actuation of the Division 1 undervoltage No actual low voltage (UV) protective circuit condition 3/25/1989 4/19/2013 1/30/2012 8/1/1997 7/23/2012 1/16/1990 8/14/2003 7/29/2003 3/29/1989 10/11/2010 2/26/2008 7/21/1989 12/9/2009 Duane Arnold event Harmonics and Relays 10/4/1994

several repeated events Harmonics and Relays 6/3/1991 at Salem 1 several repeated events Harmonics and Relays 6/3/1991 at Salem 2 10/24/2018 Loss of Safety Bus and Automatic Actuation of a Safety System During Undervoltage Relay Surveillance 3/10/2017 Unit 1 Failure of a Timing Relay During a Technical Specification Surveillance

Docket Number Link Link Address Date 254 2542018005 PDFView.ashx (inl.gov) 10/24/2018 498 4982017001 PDFView.ashx (inl.gov) 3/10/2017 251 2512013002 https://lersearch.inl.gov/PDFView.a 4/19/2013 455 4542012001 https://lersearch.inl.gov/PDFView.a 1/30/2012 249 2492010001 https://lersearch.inl.gov/PDFView.a 10/11/2010 339 3382009004 https://lersearch.inl.gov/PDFView.a 12/9/2009 250 2502008001 https://lersearch.inl.gov/PDFView.a 2/26/2008

244 2442003002 https://lersearch.inl.gov/PDFView.a 8/14/2003 272 2722003002 https://lersearch.inl.gov/PDFView.a 7/29/2003 374 3742001003 https://lersearch.inl.gov/PDFView.a 9/3/2001 247 2471999015 https://lersearch.inl.gov/PDFView.a 8/31/1999 219 2191997010 https://lersearch.inl.gov/PDFView.a 8/1/1997 331 3311994012 Licensee Event Report Search l NRC 10/4/1994

311 3111991008 https://lersearch.inl.gov/Index.aspx 6/3/1991 301 3011989002 https://lersearch.inl.gov/PDFView.a 3/29/1989 249 2491989001 https://lersearch.inl.gov/PDFView.a 3/25/1989

Summary description of event during performance of a second level undervoltage surveillance, Class-1 E 4.16 KV Bus 13-1 tripped on an Undervoltage Protection [surveillance error causing testing insuced grounding in DC and an inadvertent UV signal]. The associated EDG started but could not load due to surveillance alignment.

Unit 1 Failure of a Timing Relay During a Technical Specification Surveillance. The PDF file is not easily readable. Main conclusion is as follows: There have been many occurrences where the as-found condition of this or similarly functioning timing relays were found out of acceptance criteria or outside Technical Specification criteria.

However all events involved the old model E7000 timers. It is important to note that the older model relays are diaphragm type designs, while the new relay timers are solid state designs. Since these timers were replaced (starting in 2012) this condition is the first case of its kind.

While doing the third harmonic test for generator relay drop off, they received a degraded voltage condition. The trip occurred as a result of degraded voltage at the 480V load centers (down to 440 volts for 60 Seconds) . Wrong procedure was use.

The electrical insulator failure resulted in a sustained open phase event and a low level ground fault occurred on the SAT 242- 1/2 side of the open phase.The 4.16 kV Engineered Safety Feature (ESF) buses undervoltage protection scheme did not satisfy due to open phase condition and it did not automatically switch over to the emergency Diesel Generators (DG).

Following a scram, the Auxiliary Power System transferred from its main power source to the reserve power source, as designed. During this transfer, the Unit 2/3 Emergency Diesel Generator automatically started. This automatic start occurred as the result of the EDG start logic momentarily sensing both the main power source breaker and the reserve power source breaker contacts being open concurrently. Since there was no undervoltage signal received, the automatic start of the EDG is considered invalid.

Electrical supply breaker was inadvertently opened, which caused the "C" Reserve Station Service Transformer (RSST) to de-energize. There was issue with calibrating the bus transfer during UV condition but not for the emergency buses. The event is generally of interest since it identifies generic calibration issues for UV relays including delay time (Part of utility Corrective Action Program (CAP), not discussed)

Both Units of Turkey Point tripped and undervoltage relays were actuated after a one second time delay. The grid voltage disturbance occurred due to human error when a Protection and Control (P&C) field engineer disabled both levels of local protection at an electrical substation which then failed to actuate when a fault occurred during equipment troubleshooting (manual clearing of the fault took 1.7 second more than 1 second time allotted).

While off-site power was lost to several on site buildings,it was never lost to the busses supplying the power block area. Although the safeguards bus voltage was swinging as a result of the grid transient, the voltage did not reach the undervoltage setpoints. However, the Operators determined that the off-site supply was unreliable, manually started the Emergency Diesel Generators (EDGs), and then manuallyt ransferred the safeguards busses to the EDGs. This resulted in declaring an Unusual Event that was terminated after power was later transferred back to the off-site sources.

On an event started by ground fault in 500 KV breaker, generator separated, turbine triped and reactor scrammed. The E-buses were transfered to preferred power source in addition of three of the Circulating Water (CW) pumps per design. The 4KV vital bus voltages dropped below the second level undervoltage setting of 95.1%. Voltage on the Salem Unit 1 4KV vital busses did not recover to the reset setpoint before the relay timeout caused the relay logic to separate the vital busses from offsite power.

CCF (Common Cause failures) of fuses caused actuation of the Division 1 undervoltage (UV) protective circuit A complex event during maintenance of bistable in RPS logic caused trip, Low voltage on 480 bus, striped the emergency bus and connected to EDGs. One bus tripped off due to overcurrent trip. Post trip evaluation found that found that the actual over current trip setpoint for its Amptector was at 3200 amps, rather than the 6,000 amps setting as designed. In addition the event might have been prevented if the Station Auxiliary Transformer Tap Changer was not in manual mode due to a defective voltage control relay.

During a bus voltage transfer from Aux. Transformer to SU transformer, A degraded voltage condition was experienced on 4160 emergency buses resulting in spearartion from offsite power. The cause of degraded voltage was the inapporpriate setting of the SU transformer voltage regulator below the Degraded voltage setting.

during the performance of an increased frequency surveillance test, 4 out of 8 Essential Bus Degraded Voltage relays were found high outside Technical Specification (TS) test using an improved calibration technique. On October 17, 1994 all 8 relays were found low outside the TS voltage limits using the improved calibration method. A 4.7 to 5.1%

power source distortion (Harmonics) was identified which subsequently equated to approximately 4.0 to 5.0 volt variance in the relay trip set points. The recommended vendor maximum distortion was 3%.

On June 3, 1991, the 91.6% sustained undervoltage relay minimum drop out trip setpoint voltage, for two (2) of the three (3) of the 2A 4KV Vital Bus undervoltage relays and for all three (3) 2B 4KV Vital Bus undervoltage relays, were found to be below the Technical Specification minimum allowable value of 91%. The lowest as-found trip setpoint, of the five subject relays was 90.5%. The causal factors of the setpoint variance are relay design inadequacy and procedure inadequacy. The 4KV Vital Bus 91.6%

undervoltage Rochester relays (both Salem Units) were replaced with ASEA Brown Boveri type 27N relays.

spurious actuation of the Unit 2 X01C phase fire deluge spray system. The spurious deluge spray apparently induced a flashover from the transformer to ground, which was detected by protective circuitry causing generator and turbine trip followed by reactor scram. The emergency diesels automatically started because of bus undervoltage. The undervoltage condition was the result of the premature actuation of the generator stuck breaker protection relay, which isolated a Unit 1 bus section cross-connection. Voltage dips to 3700 volts on the normal 4160 v system were experienced.

A phase-to-ground fault occurred, causing the loss of reserve auxiliary transformer (TR) 32 which is fed from 345 KV Bus 8. Bus 32 feed breaker transfer from TR 32 to TR 31 was slow resulting to loss of the bus.

1. DVR/LOV working status

2. Deg. Voltage or Loss of Lessons and Insights Voltage condition No LOVR/DVR actuation (but Errors during surveillance and findings are applicable) calibration of DVR/LOVR could become risk significant.

NO LOV or Degraded Voltage Condition No LOVR/DVR actuation (but It appears Solid state relays findings are applicable) generally used for DVRs are much more resillent to NO LOV or Degraded Voltage setpoint drift.

Condition DVR worked (actuated)

Degraded Voltage condition (internal causes)

LOVR did not work Response of LOVR and DVR to OPC should be evaluated.

Sustained open phase condition (OPC) not LOVR No LOVR actuation (Not Applicable)

NO LOV or Degraded Voltage Condition . Spurious EDG start No LOVR actuation (Not Applicable) Calibration methods for timing relays will be examined so that NO LOV or Degraded Voltage specific methods may be Condition required or disallowed for certain circuits.

LOVR properly actuated LOV condition (Grid fault)

DVR was not actuated but the Manual transfer should be offsite power was manually considered as a back up to DVR stripped for Grid instabilities.

Grid instability due to switching transients DVR worked (actuated) but not Design time delay and voltage as intended recovery setpoint may not have been correct. Time delay Degraded Voltage condition and voltage recovery setpoint (internal causes) should have accounted for voltage dip and recovery time caused by start of 3 CW pump.

LOVR actuated due to fuse failures No low voltage condition DVR worked (actuated)

Degraded Voltage condition (internal causes)

DVR worked (actuated)

Degraded Voltage condition (internal causes)

No LOVR/DVR actuation (but The calibration source should findings are applicable) be free from harmonics per NRC guidance. The distortion NO LOV or Degraded Voltage could be reduced by filters.

Condition The filters should attenuate higher harmonics below 3%.

IEEE std 141 should be consulted.

No LOVR/DVR actuation (but The type of relay and findings are applicable) calibration method with harmonic free source will NO LOV or Degraded Voltage affect the relay setpoints.

Condition Certain relay types such as ASEA Brown Boveri type 27N relays appear to have less setpoint drift.

LOVR actuated properly This event also highlights the (worked) potential complications that may be introduced in setting the LOVR set point if there is LOV condition (internal causes) cross connections between units.

LOVR worked (actuated)

Loss of voltage condition

Reference Information Xelon Generation, Licensee Event Report 254/2018-005-01 "Loss of Safety Bus and Automatic Actuation of a Safety System During Undervoltage Relay Surveillance," Quad Cities Nuclear Power Station Unit 1, November 21. 2019; South Texas Project Unit 1 Docket No. SIN 50-498 Licensee Event Report 2017-001-00 Unit 1 Failure of a Timing Relay During a Technical Specification Surveillance Turkey Point Unit 4 Docket No. 50-251 Reportable Event: 2013-002-00 Reactor Trip Due to Loss of Offsite Power Resulting From Generator Testing, June 18, 2013 Byron Station, Unit 1 05000454 12 OF 12 2, Docket No. 05000454, September 28, 2012 Exelon, Dresden Nuclear Power Station, Unit 3 Renewed Facility Operating License No. DPR-25 NRC Docket No. 50-249 - December 10, 2010 Virginia Electric and Power Company, North Anna Power Station ,

Docket No.: 50-338 , February 3, 2010 FPL, Turkey Point Units 3 and 4 ,05000250, April 25, 2008

RGE, LER 2003-002, Major Power Grid Disturbance Causes Loss of Electrical Load and Reactor Trip R.E. Ginna Nuclear Power Plant Docket No. 50-244 , October 9, 2003 PSEG, Salem Generating Station Unit 1, 'Reactor Trip due to Turbine Trip Caused by a 500KV Switchyard Breaker Trip' LER 272, September 24, 2003 Exelon, LaSalle County Station, Unit 2, Docket No. 50-374, October 21, 2001 Indian Point No. 2, Docket No. 05000274, "Reactor Trip, ESF Actuation, Entry into TS 3.0.1, and Notification of Unusual Event."

August 31, 1999 GPU Nuclear, Oyster Creek Nuclear Generating Station Docket No.

50-219, Licensee Event Report 97-010: Manual Reactor Scram, Engineered Safety Feature Actuation and Design Deficiencies Noted As a Result of Main Generator Exciter Preventive Maintenance, September 2, 1997 Duane Arnold Energy, DOCKET NUMBER: 05000-331, Essential Bus Degraded Voltage Relay Calibration Errors Due to Harmonics, October 14, 1994

Salem Generating Station Unit 2, DOCKET NUMBER: 05000311, "4KV Vital Bus UV Relay Setpoints Found Below Minimum Tech.

Spec. Allowable Value." EVENT DATE: 06/03/91 LER #: 91-008-01 REPORT DATE: 07/09/92 Point Beach Nuclear Plant Unit 2,Docket No. 05000301, Fire System Actuation Induced 2X01C Fault and Unit Trip, March 29, 1989 Dresden Nuclear Power Station, Unit 3, DOCKET NUMBER:

05000249, Turbine Trip and Reactor Scram on Stop Valve Closure Due to Slow Transfer of House Loads During Loss of Offsite Power, March 25, 1989

ML23117A316

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