By Rory D. Sweeney
PJM ordered its first load-shed event since implementing Capacity Performance in 2015 after a transmission line in Indiana tripped offline on May 29.
It was also the RTO’s first trigger for the significant performance-related bonuses and penalties introduced with CP.
The 30-minute event occurred at the Jackson Road substation in American Electric Power’s transmission zone, west of South Bend, Ind. PJM’s Adam Keech explained that a transformer and a transmission line unexpectedly tripped out of service about 1:20 p.m., creating a load on the facility above its ratings.
As part of its response procedures, PJM simulated the effect on the system of losing that facility. The RTO’s procedures call for continuing that analysis for facilities that subsequently would become overloaded and simulating their loss as well. If that continues for five steps without mitigation, or if it hits a larger issue and can’t be resolved, PJM pre-emptively sheds load “before anything else tripped that would potentially create a cascading outage,” Keech said during a special Markets Implementation Committee meeting Friday on updating the variable resource requirement curve.
For this situation, grid operators ordered a reduction of 71 MW of load, he said. However, the transformer kicked back into service, “so the total requested amount was never actually shed … because the equipment came back that quickly.”
No demand response was called, Keech said. PJM later confirmed the actual load shed was 21 MW.
The situation triggered the first performance assessment interval (PAI) under the CP capacity construct, which analyzes the performance of generators that were paid for a capacity commitment to supply power in that region. Units that outperformed their commitments are eligible to receive bonus payments, while those that underperform receive stiff financial penalties. The analysis compares the supply needed to the units that have commitments and only includes units that were able to help by raising their output, Keech said.
PJM is limited in how much information it can release, he said, because the event affected only a small number of generation owners. The RTO’s confidentiality rules restrict what information staff can release if fewer than four generation owners were affected, he said.
Keech noted that some stakeholders expressed concerns with how the incident was communicated and said staff plan to revise procedures to address them.
“I think when we envisioned PAIs, the discrete, very localized load-shed event wasn’t on everybody’s mind. But now that we’ve got it, we should learn to handle it a little bit better,” he said.
The event will have implications for several other markets and reliability calculations, including the balancing ratio and default market seller offer cap. (See “Balancing Ratio,” PJM Market Implementation Committee Briefs: May 2, 2018.)