Six weeks after a mass outage that stopped electricity for nearly the entire population of Spain and Portugal, along with parts of France, the Spanish government and grid operator Red Electrica have released separate reports detailing the cause of the event and recommendations for future preventive measures.
The outage lasted 18 hours, starting on the afternoon of April 28. In the immediate aftermath of the event, many asked what could have caused such a sudden loss of power. Some speculated that a cyberattack was to blame, while others suggested the disaster occurred because of the high proportion of renewable energy on Spain’s grid at the time, leaving insufficient traditional synchronous generation to provide voltage control. (See NERC Offered to Help with Iberia Outage Investigation, Robb Says.)
Speaking with ERO Insider, Michael Goggin, vice president of Grid Strategies, noted the reports — whose authors he said “did a really good job with the data they [had] available” while producing “solid engineering analysis” — largely laid such ideas to rest. According to Goggin’s analysis of both reports, the blackouts occurred because traditional synchronous generation could not provide adequate control of high voltage resulting from the grid operator’s efforts to control frequency oscillations that were exacerbated by a faulty power plant controller.
At the time of the blackout, 11 thermal generation plants were available for voltage control — four nuclear, one coal-fired and six natural gas-fired — along with an unspecified amount of “hydraulic generation,” as noted in the government report. The plants had trouble managing the grid’s voltage, which experienced swings of about 10% in the hours leading up to the blackout. Some of the worst voltage control performance was at a thermal plant in southern Spain.
To combat the fluctuating voltage, Red Electrica reversed a switch for static reactive devices, which reduced system voltage but left the operator with less flexibility because of the stepwise “all-or-nothing” nature of the devices. The grid operator also ordered two gas combined cycle plants to start up in hopes of dynamically managing voltage; however, the start-up process would have required 1.5 hours at one plant and at least two hours at another. The process was interrupted by the beginning of the blackout 10 minutes later.
Renewables out of Voltage Control Picture
One surprising item in the reports, Goggin said, was the fact that Spain’s electricity regulations do not allow renewable energy resources and battery energy storage systems to provide voltage control. Currently only synchronous generators can provide this function in Spain.
“That was kind of amazing,” Goggin said. “I wasn’t aware that, given the amount of renewables that Spain has, and particularly on this day [when] two-thirds of generation was wind and solar … they’re still not letting those resources regulate voltage. They’re basically keeping the thermal resources online purely to regulate voltage.
“It’s very inefficient,” he continued. “You’re having to pay these … thermal plants to run even though … the generation is not needed or economic.”
Goggin noted in his analysis that battery resources “can start up and begin controlling voltage or frequency almost instantly. Moreover, many modern [inverter-based resources] can be configured so that their power electronics can regulate voltage without even generating real power.”
He further observed that FERC Order 2023’s “strict generator ride-through requirements … ensure IBRs remain online for voltage disturbances of this magnitude in the U.S.”
Goggin also pointed out NERC reliability standard PRC-024-3 (Frequency and voltage protection settings for generating resources) forbids generator protective relays from tripping any type of generator for voltages 10% above normal, while PRC-029-1 (Frequency and voltage ride-through requirements for IBRs), currently awaiting FERC approval, requires IBRs to remain online indefinitely for voltages up to 10% above normal and for one second for voltages 10 to 20% above normal.
These measures are one reason this type of event is unlikely to occur in the U.S., he said. Another is the absence in the U.S. of what the Spanish government referred to as a “Christmas tree” arrangement, in which multiple unaffiliated generators are connected to the grid via a single transformer. This type of setup is common in Spain “for economic and environmental efficiency … and to minimize impact and costs,” but the disconnection of one such transformer caused a significant loss of generation, causing a chain reaction that ultimately led to the blackout.
Goggin said he believed the government and Red Electrica reports will not be the final word on the Iberian outages, particularly in the U.S., where NERC Chief Engineer Mark Lauby is scheduled to present the ERO’s findings on the event at FERC’s open meeting June 26.
The report’s recommendations included several ideas that U.S. regulators may consider. One of these is to retool how generators are compensated for providing reactive power services to counteract voltage fluctuations through a market approach. Another is to examine the role that transmission expansion can play in helping to maintain reliability.
“I think [we] can be doing better at both of those. … The reactive compensation doesn’t really exist here. It’s … something [utilities are] supposed to provide, but if you don’t pay people to provide it, they’re not going to do a very good job of it,” Goggin said.
“Also, as we expand interregional transmission, most of the focus has been on localized shortfalls of generation. But there’s a similar story on the voltage-control capabilities with HVDC lines and how to use that to improve stability,” he added. “I think we can learn the value of those things for preventing a whole host of reliability concerns, including the ones that were the problem here.”