A Minimum Generation Emergency is a type of abnormal system condition the ISO declares when it anticipates that generation and external transactions will exceed system demand, which could result in excessively high system voltages and frequencies and unscheduled flows of power into neighboring regions. A widespread power outage that greatly reduces the region’s demand for electricity compared with the forecasted demand is one type of situation for which the ISO may declare a MinGen Emergency to reduce the excess amount of electric power available.
The ISO will issue a Minimum Generation Warning when the control room forecasters’ reliability assessment (see FAQ below) indicates that generation could exceed the region’s demand for electricity. The warning lets generators and neighboring regions know that the ISO is seeking voluntary reductions in generation and external transaction imports. Ideally, a Min Gen Warning would be declared before a Min Gen Emergency, but an emergency can be declared without declaring a warning.
Reference: Minimum Generation, Procedure CROP.25005 (December 19, 2017)
The ISO may declare a Minimum Generation Warning when the difference between the sum of fixed external transaction purchases plus all on-line generating units at the economic minimum (ecomin) limits and the projected system demand for all of New England is less than 300 MW. (The ecomin limit is the minimum amount of electric energy [in megawatts] available from a generating resource for economic dispatch.)
The ISO declares a Minimum Generation Emergency when the sum of fixed external transactions that cleared the Day-Ahead Energy Market plus the ecomin limits of all on-line generators is within 100 MW of the projected demand or greater than the projected demand. As an example, starting with regional system demand at 10,000 MW and with 9,900 MW of fixed external transactions plus generation at ecomin (supply), a Min Gen Emergency would be declared if the demand decreased or the supply increased to a point where the difference between the demand and supply were less than 100 MW, which could lead to the supply exceeding the demand.
The ISO performs the Reserve Adequacy Assessment (RAA) to ensure the proper amount of resources are scheduled in advance to meet the ISO’s demand forecast, operating reserve, and replacement reserve requirements for the next operating day and for the subsequent six days. The analysis covers supply offers; external transactions; demand bids for dispatchable asset-related demand; unit-availability information; and ISO demand forecast information, including the deviation between the ISO demand forecast and the sum of cleared demand bids and decrement bids used in the initial commitment. The focus of the RAA is reliability, and the objective is to minimize the capacity costs associated with any additional capacity that may be required. The ISO performs additional RAAs throughout the operating day, as necessary, based on updated ISO demand forecasts and updated resource availability information.
For detecting the possibility of a Minimum Generation Warning or Emergency, control room personnel review the capacity analysis for the current operating plan to determine whether actual system demand is less than the demand forecast, a potential Min Gen condition.
Reference: SOP-RTMKTS.0050.0010—Perform Reserve Adequacy Assessment (January 16, 2017)
The ISO posts Minimum Generation Warning declarations on its website calendar to notify external participants of the warning. If the ISO declares a Minimum Generation Warning for a period spanning multiple days, it reflects the event in the ISO web calendar for the subsequent day.
The ISO may take the following actions to mitigate a Minimum Generation Emergency, making exceptions for reliability or transmission outages:
If these actions do not adequately mitigate the Minimum Generation Emergency condition, the ISO declares a Minimum Generation Emergency event for all of New England.
Reference: Minimum Generation, Procedure CROP.25005 (December 19, 2017)
After the ISO declares a Minimum Generation Emergency, it sets location marginal prices to $–150 within the New England Balancing Authority Area. External transactions clearing the Day-Ahead Energy Market are subject to being reduced, and generating resources are subject to being reduced to emergency minimum limits. If additional actions are required to match supply to demand, the ISO will issue decommitment orders recognizing the priority of day-ahead committed resources compared with self-scheduled resources, minimum run time, and minimum down time, transmission constraints and reliability, expected capacity for the next operating day, and all other available information.
Declaring a Minimum Generation Emergency should occur on the hour to promote equity between external transaction cuts and generation reductions. However, the declaration may also be made within the hour, if necessary, to respond to sudden events.
The ISO system operator will not unilaterally reduce generators refusing to follow ISO dispatch instructions; these generators should remain at their bid limits and incur failure-to-follow flags, if applicable. Units that come under the Public Utility Regulatory Policies Act (PURPA) are not exempt from the curtailment process.
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