The Electric Reliability Council of Texas (ERCOT) implemented the second stage of its emergency grid procedures Tuesday evening following a sudden drop in the system frequency.

Preliminary reports indicate the frequency decline was caused by a combination of events including a drop in wind energy production at the same time the evening electricity load was increasing, accompanied by multiple power providers falling below their scheduled energy production. In addition, the drop in wind energy led to some system constraints in moving power from the generation in the north zone to load in the west zone, resulting in limitations of balancing energy availability. The wind production dropped from over 1700 MW three hours before the event, down to 300 MW at the point the emergency procedures were activated.

By moving directly to the second stage of the emergency procedures, the system operators were able to activate ERCOT’s demand response program known as Loads Acting as Resource (LAARs), which added approximately 1,100 MW of resources within a 10-minute period. LAARs are typically large industrial and commercial users who are paid to curtail their electricity use as needed for reliable grid operation. Most of the interruptible loads were restored after approximately an hour and a half.

Other than the interruptible loads, no other customers in the ERCOT region lost power due to the event.

The emergency procedures were declared at 6:41 pm and ended at 9:40 pm.

ERCOT operations will be preparing a more detailed and quantitative report on this event in the next few weeks.