Extra power was needed to keep the regional’s electricity grid going for a half hour on Wednesday

Brutal heat combined with a sudden shortfall in imported electricity caused the operators of New England’s power grid to fire up extra generators for a half hour on Wednesday.

The shortfall in electricity production versus demand, known as a capacity deficiency, began shortly after 6 p.m. as a “transmission equipment failure significantly reduced imported electricity coming to New England.” The six-state region can import or export electricity from New York, Quebec and New Brunswick as needed; details of the failure were not available Thursday.

Demand for electricity production by power plants often spikes at around 6 p.m. on a summer weekday because people turn on air conditioning as they get home from work and the region’s solar production – which on a sunny afternoon now generates three times as much electricity as Seabrook Station nuclear plant – begins to wind down.

This combination on Wednesday resulted in more demand for electricity than was scheduled to be produced by power plants, leading ISO-New England, which operates the grid, to implement Actions 1 and 2 under Operating Procedure No. 4. That includes ordering immediate generation from some units that can fire up quickly, such as two kerosene-fired combustion turbines at Merrimack Station in Bow.

“The capacity deficiency was mitigated within 30 minutes,” ISO-NE wrote in a report, although a problem caused the website and mobile app to show abnormal operations for several more hours.

The deficiency was never great enough to request the public to voluntarily reduce usage, a form of demand response that has proved effective in past summer surges.

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