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 megawatts (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 megawatts 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.

ADDITIONAL BACKGROUND 

Alert (pre-EECP) – When reserves fall below 2500 MW, ERCOT Operations will:

•  Start Reliability-Must-Run units
• Instruct generation owners to suspend testing
• Deploy non-spin reserves
• Dispatch quick-start capacity

EECP Step 1 – When reserves fall below 2300 MW, ERCOT Operations will:

• Instruct all available generation to come online
• Secure emergency power from neighboring electrical grids through direct-current ties

EECP Step 2 – When reserves fall below 1750 MW, ERCOT Operations will:

• Drop customers who have been paid to accept the risk of interruption (known as "Load acting as a Resource," or LaaR)
• Transfer load to neighboring grids through block-load transfers
• Issue a media appeal, if not already done, asking the public for voluntary energy conservation

ECP Step 3 – When reserves continue trending downward or if needed to maintain system frequency at 60 Hertz (Hz), ERCOT Operations will:

• Drop additional interruptible loads (known as "Emergency Interruptible Load"), if available 

ECP Step 4 – To maintain system frequency at 59.8 Hz or greater, ERCOT Operations will:

• Instruct local utilities to implement rotating outages to reduce load