CAISO to require equipment improvements for inverter-based generation

Dive Brief:

The California Independent System Operator (CAISO) will require equipment improvements for renewable energy resources, requiring inverter-based generators to inject reactive current during low-voltage conditions in order to maintain grid reliability.
The Federal Energy Regulatory Commission (FERC) approved the ISO's tariff revisions in a July 2 order. The change is designed to allow increased integration of wind and solar power.
The ISO said the decision also means inverter-based generators larger than 20 MW will be required to record and store data for all frequency and voltage events, to assist with subsequent investigations.

Dive Insight:

As the volume of inverter-based resources rises, California's grid operator says it faces difficulties maintaining reliability through its transmission services.

The new requirements stem from a 2016 event where smoke from California's Blue Cut Fire tripped several transmission lines and caused almost 1,200 MW of solar energy to go offline unexpectedly. FERC's decision follows recommendations developed by a North American Electric Reliability Corp. task force that was convened to address the issue.

"The approval will now require inverter-based generator resources to inject reactive current during low-voltage conditions to allow for a minimum delay for frequency tripping and a quick return to support the bulk power system reliability," the ISO said in a statement.

The volume of inverter-based generators interconnecting within the California ISO balancing authority area has increased "dramatically" in recent years, and now includes more than 18,000 MW, according to FERC's order.

Inverters change direct current or variable frequency alternating current to 60 Hz alternating current for the transmission and delivery of electricity that generators produce, while also monitoring grid conditions and providing controls to ensure electricity from the generator is deliverable.

Many generator owners have reconfigured their inverters and protective relays to avoid unnecessary trips that caused previous reliability events, according to federal regulators. But the commission said the new tariff is necessary until all of those generators make similar changes.

"CAISO maintains that the risk of future events will remain until all inverter-based generators are required to program their inverter internal protection and protective relays consistently," FERC said in its order.