MISO’s Independent Market Monitor said a MISO South September transmission emergency shows the RTO needs a better handle on constraint management within its markets.
MISO declared a local transmission emergency around 1 p.m. ET on Sept. 16 after a 500-kV transmission line was forced offline in MISO South. The IMM said the sudden outage forced two constraints into violation and congestion costs rose to $12 million.
“MISO was successful in avoiding a load shed,” MISO Independent Market Monitor staffer Robert Sinclair said during a Nov. 11 Entergy Regional State Committee meeting. He said MISO “successfully utilized the available supply to maintain reliability through the event.”
MISO confirmed that a local transmission emergency occurred in MISO South on Sept. 16.
Sinclair said MISO manually dispatched some generation to manage violated constraints and made additional resource commitments that sent some resources into their emergency ranges to increase supply by more than 700 MW.
However, Sinclair said the IMM is finding in its initial investigation that MISO should improve its transmission constraint demand curves so that the market dispatches generation instead to manage constraint violations. He said while MISO’s manual dispatch actions were effective, they are more expensive than letting the market take the wheel.
Outages of 500-kV lines in MISO South “have increased in frequency in 2025 and triggered more frequent transmission emergencies,” Sinclair added.
He promised a fuller report on the events and the IMM’s recommended course of action at the upcoming MISO Board Week in December in Indianapolis. There, MISO leadership can respond to the recommendation.
