HOUSTON (Reuters) - A drop in wind generation late on Tuesday, coupled with colder weather, triggered an electric emergency that caused the Texas grid operator to cut service to some large customers, the grid agency said on Wednesday.

Electric Reliability Council of Texas (ERCOT) said a decline in wind energy production in west Texas occurred at the same time evening electric demand was building as colder temperatures moved into the state.

The grid operator went directly to the second stage of an emergency plan at 6:41 PM CST (0041 GMT), ERCOT said in a statement.

System operators curtailed power to interruptible customers to shave 1,100 megawatts of demand within 10 minutes, ERCOT said. Interruptible customers are generally large industrial customers who are paid to reduce power use when emergencies occur.

No other customers lost power during the emergency, ERCOT said. Interruptible customers were restored in about 90 minutes and the emergency was over in three hours.

ERCOT said the grid’s frequency dropped suddenly when wind production fell from more than 1,700 megawatts, before the event, to 300 MW when the emergency was declared.

In addition, ERCOT said multiple power suppliers fell below the amount of power they were scheduled to produce on Tuesday. That, coupled with the loss of wind generated in West Texas, created problems moving power to the west from North Texas.

ERCOT declares a stage 1 emergency when power reserves fall below 2,300 MW. A stage 2 emergency is called when reserves fall below 1,750 MW.

At the time of the emergency, ERCOT demand increased from 31,200 MW to a peak of 35,612 MW, about half the total generating capacity in the region, according to the agency’s Web site.

Texas produces the most wind power of any state and the number of wind farms is expected to increase dramatically as new transmission lines are built to transfer power from the western half of the state to more populated areas in the north.

Earlier on Tuesday, grid problems led to a blackout in Florida that cut power to about 1 million electric customers across that state for as much as four hours.