|V.C. Summer Nuclear Station, Unit 1|
|Reporting criterion:||10 CFR 50.73(a)(2)(iv)(A), System Actuation|
|3952017004R00 - NRC Website|
|Person / Time|
|From:||Lippard G A|
South Carolina Electric & Gas Co
Document Control Desk, Office of Nuclear Reactor Regulation
|Download: ML17313B092 (4)|
comments regarding burden estimate to the Information Services Branch (7-2 F43). U.S. Nuclear Regulatory Commission. Washington, DC 20555-0001, or by e-mail to NEOB-10202, (3150-0104), Office dl Management and Budget, Washington. DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number. the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
05000- V.C. Summer Nuclear Station, Unit 1 395 1.0 EVENT DESCRIPTION At 1648 on September 11, 2017, VCSNS Unit 1 was operating in Mode 1 at 100% reactor power when a storm induced perturbation on the off-site power system occurred which resulted in reduced voltage on the 1DA vital bus. The 'A' emergency diesel generator (EDG) started on loss of voltage signal, but it did not load since the low voltage condition cleared within the designed recovery time limit.
A fault on the Killian-Pineland 115kV line occurred as a result of high winds from hurricane Irma. The fault resulted in depressed voltages on both the 115kV and 230kV systems. The duration of the fault was longer than it should have been due to a malfunction of a transmission system relay.
There were two reasons for the delayed clearing of the fault. First, the high speed relay communication scheme on the Killian-Pineland line failed. Second, the relay incorrectly interpreted the fault as a power swing condition and blocked the tripping function that would have cleared the fault.
The 'A' EDG was returned to standby at approximately 1742.
2.0 EVENT ANALYSIS The EDGs automatically start upon receipt of an undervoltage signal from the associated bus from either the loss of voltage relays or degraded voltage relays, or upon receipt of a safety injection signal. The 7.2 kV ESF buses are each provided with 3 loss of voltage relays set at approximately 81% of the nominal bus voltage level and 3 degraded voltage relays set at approximately 91% of the nominal bus voltage level. Operation of a set of loss of voltage or degraded voltage relays will initiate a diesel generator start.
All three XSW1DA loss of voltage relays sensed a 3-phase fault on the Killian-Pineland 115kV line caused by high winds from hurricane Irma. The voltage remained less than 81% on all three phases for greater than 0.25 seconds resulting in the 'A' EDG starting. Following the diesel start signal, a time delay relay allows 2 seconds for the voltage to recover prior to initiating the load sequencer. Voltage recovered to greater than 81% 1.55 seconds after the 'A' EDG started. Because the sequencer did not initiate, XSW1DA offsite feeder breakers did not open, the diesel output breaker did not close, and loads did not sequence onto the bus.
3.0 SAFETY SIGNIFICANCE Since plant equipment responded as designed, there was no PRA risk impact from this event. This event had no effect on baseline Core Damage Frequency or Large Early Release Frequency.
4.0 PREVIOUS OCCURRENCE No previous occurrence within the last three years.
Infccollects.Resource@nrc.gov, and to the Desk Off:cer, Office of Informaton and Regulatory Affairs, used :3 impose an information collection does not display a currently valid OMB control number, the NRO may not conduct or sponsor, and a person is no: required to respond to, the information collection.
05000- V.C. Summer Nuclear Station, Unit 1 385 5.0 CORRECTIVE ACTIONS The high speed relay communication scheme on the Killian-Pineland line has been repaired. Corporate Power Delivery and the Relay Department is working with the relay manufacturer to make adjustments to the relay to ensure that future faults are cleared prior to propagating to the station.