Unlike most commodities, electricity must be consumed at virtually the same instant it is produced. On the power grid, that means supply and demand must be kept in balance at all times to avoid problems that could severely damage generation and transmission equipment and lead to a blackout.
Unexpected events like a widespread power outage could result in the system having significantly more supply than demand. ISO New England system operators must react quickly to correct the imbalance by reducing supply.
All generating resources have an output level below which it is not economical to operate, called their economic minimum or ecomin. Correcting a system imbalance may require generators to operate at or below their ecomin.
Depending on the possibility of anticipating these conditions, ISO-NE system operators may declare either a Minimum Generation Warning or a Minimum Generation Emergency.
The effects of a system imbalance can reach beyond New England into neighboring grids. In the event of a Minimum Generation Warning, ISO-NE will notify grid operators in New York, Québec, and New Brunswick. System operators may also direct energy resources within New England to reduce output, as well as reducing energy imports from outside the region. Pumped storage units may be dispatched to absorb excess energy.
Procedures during a system imbalance are detailed in CROP.25005 Minimum Generation.
No action is required. System imbalance alerts are notifications primarily for power generators and other organizations with direct connections to the New England electrical grid.
