Nevada Power Company (NEVP), FERC Docket No. NP15-29-000 (May 28, 2015)
Reliability Standard: BAL-005-0.2b
Violation Risk Factor: Medium
Violation Severity Level: Severe
Issue: NEVP self-reported that, after the Area Control Error (ACE) value became incorrectly calculated due to a loss of transmission line telemetry, NEVP's operator turned off the line's Automatic Generation Control (AGC) and failed to manually adjust generation to maintain the Net Scheduled Interchange (NSI). The AGC was off for 57 minutes.
Finding: WECC found that this issue posed a moderate, but not a serious or substantial, risk to BPS reliability because failure to maintain the NSI could result in differences in the amount of generation required and the amount of generation produced. In turn, this could result in unintended flows across balancing area interconnections. Loss of the transmission line was also possible due to the combination of unmaintained NSI and the loss of visibility of the line's power flow. NEVP's operator failed to use existing procedures to control AGC, but NEVP's Emergency Management System (EMS) would have detected a line loss and NEVP would have been able to notify system operators. To mitigate the violation, NEVP (1) provided the employee who had ineffectively controlled generation after disabling AGC with coaching and counseling, (2) trained appropriate personnel on the requirements of BAL-005-0.2b, and (3) changed the EMS's program so that when AGC is disabled, its label reads "monitor" instead of "off."
FERC Order: FERC approved the settlement on June 26th, 2015.