MISO is to roll out a new transmission warning declaration to give its members advanced notice when scarce transmission capacity is raising the risk of load shed.
Speaking at a Nov. 20 MISO Reliability Subcommittee meeting, Clayton Umlor, a MISO manager of reliability coordination, said a transmission emergency warning would establish “more transparency around transmission risk,” especially when load loss is imminent.
The RTO wants to put the new system in place sometime in the first quarter of 2026.
Umlor said MISO would institute the warning only after it has exhausted all normal congestion management procedures without relief, including generation redispatch, transmission loading relief and reconfiguration plans. The RTO alo would try deploying units’ emergency ranges and calling on its emergency-only units and load-modifying resources before sounding the alarm, he said.
MISO intends to use the warning when 100 MW or more of load is at risk after those actions, or when it finds transmission facilities rated above 100 kV have post-contingent flow greater than or equal to 115%.
Umlor said MISO would issue warnings when a reliability coordinator believes “system conditions warrant heightened awareness of potential transmission risk,” such as when load is being served radially due to a forced transmission outage or when a real-time flow of a transmission facility rated more than 100 kV is expected to exceed 100% of transfer capability.
The RTO would call off warnings once risk recedes.
Umlor said the new warnings would require software changes for its operator interface and some stakeholder training. “We want this to be a meaningful communication tool,” Umlor said, adding that MISO doesn’t want to issue the warnings so frequently that it becomes a “boy who cried wolf” situation.
He asked stakeholders to provide opinions on MISO’s proposed 100-MW threshold.
‘A Lot of Stakeholder Confusion’
The new warning category is the latest change MISO is pursuing after a May 2025 load-shedding event in New Orleans in which 600 MW was forced offline abruptly to avoid exceeding an interconnection reliability operating limit (IROL) on Entergy’s transmission system. (See MISO Mulling New Way to Convey Spate of Advisories in South.)
MISO has said an IROL “is the point when operational congestion becomes a reliability risk; crossing it isn’t just a violation — it’s a systemwide emergency.”
The RTO told its Board of Directors following the blackout that it could have done more to convey the danger it perceived ahead of time. (See MISO Says Public Communication Needs Work After NOLA Load Shed.)
An Entergy representative at the RSC meeting said MISO’s designated actions during close calls aren’t always consistent.
Entergy associate general counsel Matt Brown said one shift of MISO operators could make one decision on a transmission plan of action while another shift could revoke that decision, even though criteria and conditions are unchanged.
“What it leads to is a lot of stakeholder confusion about what the risk level might be,” Brown said.
Brown said he understood MISO operators are under “tremendous pressure,” but added they sometimes make ambiguous declarations or split-second decisions the RTO struggles to explain afterward.
Umlor reiterated that the warning system is a “tool for communication that should be used infrequently enough that it is meaningful.” He said the set of criteria should be clear enough that the warning conveys real and present danger. MISO must be “vigilant to make this calibrated properly,” Umlor said.
Bill Booth, a consultant to the Mississippi Public Service Commission, asked if the warnings would come with any corrective actions for members.
“What’s the value of this warning if it doesn’t come with a directive?” Booth asked. He said when MISO delivers a capacity advisory, for instance, it comes with zero instructions.
Umlor said requests for action would come separately from MISO and not be tied to the warnings themselves.
John Harmon, MISO senior operations director of reliability, said the grid operator isn’t looking to change the existing action plans that it and utilities have in place — or their approach to public appeals for conservation.
Harmon said the intent is to “create an additional risk trigger instead of going straight to an emergency.”
Because transmission emergencies can involve shedding load, he said, it’s useful to add a layer of communication before outages that other MISO members can see. He added that MISO communicates directly in real time with utilities directly tied to the risk.
MISO has been declaring transmission and capacity advisories — mainly for its South region — since the springtime load shed.
Shedding Timed IROL Analyses
Relatedly, MISO plans to expand its IROL study timeline so it isn’t pressed to evaluate potential transmission emergencies in 15 minutes or less.
Harmon said the RTO would remove a 15-minute time limit to conduct cascade analyses from its emergency transmission procedures.
The grid operator’s current rules require it to complete an analysis on the possibility of cascading outages within 15 minutes before declaring a temporary IROL.
Harmon said MISO would be removing “an artificial time limit” and that additional minutes would allow it and its transmission owners to study, agree on and implement mitigation strategies before declaring a temporary IROL.
MISO said it’s “overly prescriptive” to assign a specific time limit on conducting studies. While the limit is “well intentioned,” it could rush decision-making and cause it to declare an IROL too quickly, especially in situations where load shed is pre-contingent, the RTO said.
