Despite concerns raised by the Trump administration, officials with the North American Electric Reliability Corp. said nothing in their new report indicates that retirements of coal-fired and nuclear power plants posed a reliability threat to the power grid in 2017.
"Every adequate level of reliability was met," James Merlo, vice president and director of reliability risk management at NERC, said at the June 21 release of the electric reliability organization's "State of Reliability 2018" report. The assessment recapped and analyzed reliability risk trends of the bulk power system in 2017.
"We found nothing in our backwards review that would make us concerned about any one fuel more than another," said Merlo. "It's just more about what is the performance of the grid."
NERC is also assessing the potential impacts that generation retirements could have on the bulk power system. That assessment is slated to be released in November. Concerned about the potential grid resilience impacts of recent and future coal-fired and nuclear power plants, President Donald Trump on June 1 directed the U.S. Department of Energy to take "immediate steps" to prevent the loss of "fuel-secure power facilities," including coal and nuclear plants.
But the only "forward-looking" risks NERC identified in the "fuel-agnostic" study were some resource challenges in Texas that already had been addressed in a recent summer report, Merlo said. NERC's territory encompasses the continental United States; most of Canada; and Baja California, Mexico.
NERC's latest report said the bulk power system experienced no major events other than the two NERC "Category 5" events that occurred when hurricanes Harvey and that battered Texas and Florida in August and September of 2017, respectively. Even though power was lost to a record number of Florida customers, NERC said storm-impacted areas recovered in half the time it took to bounce back following Hurricane Wilma in 2015.
Merlo attributed the faster recovery efforts to money well-spent on "hardening the grid" since Wilma and on "human capital" and ingenuity that helped get the lights back on in hurricane-damaged areas, including the use of drones for assessing damaged power lines. "These are great measures of the resiliency [of] the most complicated machine in the world, [which] resides largely outside," he said.
The report also said North America's power grid suffered no loss-of-load from cyber or physical attacks in 2017, despite near-constant cyberattacks and "continually evolving" threats. Even though the report's current metrics do not address the number of successful cyberattacks or how many were thwarted or aborted, Merlo said NERC is looking at ways to collect, assess and include that data in future reports.
In addition, the report said 2017 saw the number of transmission outages caused by failures of protection system or alternating-current substation equipment or by human error continued to decline for the fifth year in a row. But, Merlo said, human error is a growing concern as equipment becomes more complex to operate.
NERC said frequency response performance rates varied in 2017 by interconnection but nonetheless remained acceptable. Protection systems misoperation rates also remained significant although they declined for the fifth consecutive year to an overall rate of 7.1% in 2017 from 8.3% in 2016. NERC said the three largest causes of misoperations in 2017 were the same as in 2016: incorrect settings, logic and design errors, relay failure or malfunctions, and communication failures.
The year 2017 also saw NERC identify a previously unknown reliability risk of inverter-based resource controls tripping and disconnecting from the bulk power system during transmission disturbances. Merlo attributed the problem to the growing proliferation of solar generation.
The issue first came to NERC's attention during an August 2016 wildfire in San Luis Obispo County, Calif., when a 500-kV line fault resulted in a reduction of 1,000 MW grid-connected solar photovoltaic resources in California ISO's market. Then, a similar situation occurred during the Canyon 2 Fire east of Los Angeles in October 2017 when a 220-kV and a 500-kV line each suffered phase-to-phase faults with normal clearing that led to a reduction of over 900 MW of solar photovoltaic across the service territory of Edison International subsidiary Southern California Edison Co.
NERC found that the majority of such inverter-based resources tripped and disconnected thanks to subcycle transient overvoltages and instantaneous protective action at the inverters. A significant number of the inverters "also entered momentary cessation during and following the fault events," NERC said.
The power grid reliability organization has issued two alerts to resolve the issues and is working with stakeholders on a reliability guideline that Merlo said will look at how such "small events" could impose reliability risks going forward.