Disturbance Analysis: Key Findings
In recent years, several transmission system disturbances have provided valuable information regarding the ability of inverter-based resources to ride-through and recover.
In August 2016, the Blue Cut Fire in California caused a fault on the Southern California transmission system. It was cleared normally. However, it resulted in a significant number of solar PV resources erroneously tripping due to miscalculated frequency. An investigation found that many other resources were operating in a previously unknown mode called “momentary cessation.”
A coordinated event analysis and disturbance report published in June 2017 concluded that this is a systemic issue requiring action by industry. NERC issued a Level 2 Alert to collect data on the extent of the reliability risk and to provide recommended performance improvements for existing and new solar PV resources connecting to the Bulk Power System (BPS).
In October 2017, the Canyon 2 Fire in California resulted in a transmission disturbance that again triggered the loss of solar PV resources as a result of a fault that was cleared normally. In this case, the predominant cause of tripping was attributed to sub cycle transient over-voltages resulting in inverter tripping at solar PV facilities.
Momentary cessation was also a contributing factor. NERC ERO, working with California ISO and Southern California Edison, published a disturbance report in February 2018 to outline key findings and recommendations. A Level 2 NERC Alert was issued to provide recommended performance improvements and to initiate modifications to eliminate momentary cessation for existing resources to the greatest possible extent.
As the NERC Alert for the Canyon 2 Fire disturbance was being rolled out, two additional disturbances occurred, related to the April 2018 Angeles Forest Fire and May 2018 Palmdale Roost Fire. NERC issued a disturbance report to document the primary contributors to solar PV output reduction in these events. The causes were similar in nature to the Canyon 2 Fire disturbance. However, a unique finding in these two events was that some amount of DER also tripped in the local area, causing a net load increase after the disturbance.
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