On June 8, 2017, the North American Electric Reliability Corporation (“NERC”) released a report on the August 2016 Blue Cut Fire, which resulted in the loss of 1,200 megawatts (“MW”) of solar photovoltaic (“PV”) power generation.  NERC’s report contains recommendations for avoiding similar incidents by reconfiguring solar inverters, the devices that convert solar energy from direct current to alternating current.

On August 16, 2016, the Blue Cut Fire erupted in Southern California’s Cajon Pass, near a significant transmission corridor containing three 500 kilovolt (“kV”) lines owned by Southern California Edison (“SCE”) and two 287 kV lines owned by the Los Angeles Department of Water and Power (“LADWP”).  During the incident, the fire interrupted solar PV power generation in the transmission corridor by inducing faults on the transmission system.  In total, the SCE lines experienced 13 faults and the LADWP lines experienced two faults.  The most significant event resulted in the loss of 1,200 MW of solar PV power generation.  The fault events did not de-energize any of the solar PV facilities; instead, the facilities ceased output in response to the faults perceived on the system.

In the fire’s aftermath, NERC convened a task force, comprised of representatives from the Western Electricity Coordinating Council, the Federal Energy Regulatory Commission, affected registered entities, industry experts, and inverter manufacturers, to analyze the event and develop recommendations for avoiding similar incidents in the future.

The task force made two key findings regarding the incident, which are explained in additional detail in NERC’s report.  First, the solar PV resources disconnected as a result of an inaccurate perception of the system’s frequency.  The system’s inverters, which were set to trip instantaneously in response to a simultaneous reading of a lower or higher than normal frequency, erroneously tripped upon perceiving the faults on the system.  The task force recommended that inverters be reconfigured to impose a time delay in such situations to avoid erroneous instantaneous trips.  Second, the inverters, which were configured to momentarily cease current injection in response to readings of certain voltage levels, returned to pre-disturbance operation levels too slowly.  The task force recommended that, when inverters cease output due to voltages outside of their continuous operating range, such inverters should be set to delay the restoration of output by no more than five seconds.

The task force also recommended that NERC send out an alert to Generator Owners and Generator Operators about the pending inverter changes and the potential for incidents like the Blue Cut Fire to affect solar PV power generation.  Further studies on the potential effects of current and potential inverter settings on reliability were also recommended.

NERC’s full report is available here.