With the changing generation mix in North America prompting examinations of frequency response from FERC and others, NERC on May 17 said that frequency response performance of the bulk power system in 2015 was stable, but something that will be closely examined in the coming years.
The growth of renewable resources could have reliability implications in that maintaining stable voltage on the grid through frequency response will become more important, James Merlo, vice president of reliability risk management at NERC, said May 17 during a conference call with reporters about NERC’s latest “State of Reliability” report.
The report examined activities in 2015 and found improved reliability metrics, with fewer outages caused by human error and improved generator performance in the face of severe weather, such as tornadoes, high winds and extreme cold.
Key recommendations in the report for NERC and the power industry to focus on in the coming years are enhanced monitoring of the changing generation mix, improved awareness of cyber and physical security and sharing of timely information in order to strengthen power grid reliability.
Frequency response, or the ability of grid operators to match supply and demand amid fluctuations or disturbance in generation and load, has been a concern mentioned by the California ISO and FERC, which is gathering comments on its notice of inquiry (NOI) on the issue.
Grid operators strive to maintain balanced frequency on the grid at about 60 Hz, and while frequency response performance has generally been stable from 2012 through 2015, changes in the generation mix will be examined and NERC will take a closer look at it in 2016 and 2017, Merlo said during the call.
The performance of generators providing frequency response services, such as setting governor controls in accordance with good utility practices, are some of the issues being examined by FERC and the power industry in different forums, he said.
In its NOI, FERC sought comments on whether generator interconnection agreements should require all new generation resources to have frequency response capabilities as a precondition for connecting with the grid.
Another focus for NERC will be grid security, with Merlo commenting that both cyber and physical security will be areas of “high vigilance” for NERC. He mentioned that there were no cyber events that led to a loss of load during 2015 and one physical security breach that led to a loss of 20 MW of load in 2015.
While the report termed the event a physical attack, Merlo said the incident was more akin to vandalism. He did not provide details on the incident, and a NERC spokesperson said that the organization will not identify the utility that experienced the event.
The report noted that although there was only one physical security incident that led to a loss of load during 2015, that does not suggest that the risk of a physical security event is low. The number of reportable events as a result of physical security threats and those reportable events that result in physical damage or destruction to a facility have increased by about 50 percent in 2015 compared with 2014, NERC said in the report.
Following lessons learned from Polar Vortex events in the winter of 2013-14, “we made sure generators were prepared for severe storms,” Merlo said during the call. Severe weather events that caused generator outages in the past did not produce as many outages during 2015, with preparations and reports from NERC improving the resiliency of the grid, Merlo said.
Transmission line outages caused by human error were down to 0.028 outages per circuit in 2015, compared with 0.039 in 2014 and 0.047 in 2013, indicating that improved training and other steps are having positive results, Merlo noted in a presentation on the report.
A reduced number of what NERC termed “misoperations” in 2015 also indicates improved reliability trends, NERC said in a statement on the report. Misoperations can include incorrect settings on transmission line relays that cause a breaker to trip and lead to an outage, Merlo explained during the call. Over the past year, the industry has focused on relay settings and tests and the relay misoperation rate decreased to 9.4 percent in 2015 from 10.4 percent in 2014, according to the report.
“While protection system operations improved in 2015, misoperations continue to be one of the largest contributors to transmission outage severity and should remain an area of focus,” NERC said in the report.
Enhanced modeling and grid simulation activities have helped NERC be able to see the effects of coal-fired generation retirements or other changes in the bulk power system and address them before they pose reliability challenges, Merlo said during the call.
“Our greater understanding of bulk power system reliability and the root causes of protection system misoperations, which showed marked improvement in 2015, is largely due to our enhanced event analyses,” Merlo said in the NERC statement.