The interconnected power systems serving two-thirds of the United States and Canada are projected to maintain system frequency for at least the next five years, despite a changing resource mix that could affect this capability, according to a report issued recently by the Eastern Interconnection Planning Collaborative (EIPC).
The EIPC, a coalition of 19 major transmission planning coordinators responsible for the planning of the bulk power grid throughout the Eastern Interconnection (EI), conducted its second detailed power system frequency response analysis for the North American Electric Reliability Corp. (NERC). In response to a request from the NERC, the EIPC in July 2017 began providing forward-looking frequency response reviews. A report on the initial Frequency Response Working Group (FRWG) study was released in April 2019.
"The EIPC has completed its second review of the expected frequency response of the EI over the next five years. As the generation resource mix continues to evolve over time to incorporate new and emerging technologies and address energy and environmental policies, it is essential to understand how the EI will be poised to maintain system frequency under a wide range of operating conditions," said Keith Daniel, senior vice president of transmission policy at Georgia Transmission Corp. and chairman of the EIPC Executive Committee. "The EIPC's FRWG will update its analysis in the years ahead, in support of the NERC request. The EIPC is also engaged in additional analysis on broader power system modeling issues for the EI. We are pleased that the EIPC organization is able to conduct power system analyses that provide critical information to maintain the reliability of the bulk electric power system and to inform state and federal regulators and policy makers."
Frequency is one measure of the state of the power system. Electricity generation and electricity consumption must remain in almost perfect balance to maintain system stability.
If a generator trips offline, electricity generation will be lower than electricity consumption, or load, and system frequency will drop. If the frequency drops too far and too quickly, load may be shed automatically, or by grid operators, to mitigate the imbalance between load and generation and prevent more widespread impacts. Traditional synchronous generators on the power system respond automatically (inertial response) by slowing down slightly and releasing more energy into the grid, helping to arrest frequency decline. The asynchronous characteristics of newer wind and solar power generators can make them less responsive to frequency variations unless they have been designed and equipped to provide some form of frequency control.
With the planned retirements of synchronous resources (such as oil, coal, and nuclear) that automatically respond to arrest frequency variations, combined with the addition of non-synchronous generation (such as wind, solar, and other renewables), there are concerns about the continuing ability of large interconnections to properly maintain frequency. The EIPC has been tasked with identifying and understanding how future generation contingencies could lead to under frequency load shedding (UFLS) events on the EI because of the reduction of frequency support from the changing generation resource mix.
"Our updated analysis has demonstrated the EI's resource mix over the next five years will retain sufficient system inertia to maintain adequate frequency response, with the generation resource mix, load, and interchange levels modeled," said Jonathan Glidewell, project manager of the transmission planning stability group for Southern Company Services and chairman of the EIPC FRWG. "Our efforts to track the interconnection's inertial response has established a framework and baseline for system planners. In coordination with other industry groups, the EIPC will continue its work to improve the models and techniques used for this critical analysis to provide sufficient notice when the changing resource mix could have an adverse effect on frequency response and to develop solutions to those adverse effects."
The 2020 FRWG report is available here.