How many Black Start units are required for critical load/TO zone?

The requirement for Black Start units in a critical load or Transmission Owner (TO) zone is based on the need for reliability and stability of the electric grid during a system restoration scenario. Black Start units are capable of starting up without needing electricity from the grid, making them essential for restoring power in the event of a widespread outage.

Having two Black Start units is typically mandated because redundancy is crucial—relying solely on one unit introduces significant risk. If that single unit fails or is unavailable, there wouldn’t be a backup to ensure that the critical loads can be restored. Two units provide a safeguard to ensure that at least one can be operational to initiate the recovery process. This redundancy enables a more resilient restoration strategy so that essential services can be brought back online safely and effectively.

This requirement takes into account the various factors that could affect the operability of the units, such as maintenance, reliability, and the potential for unexpected outages. Therefore, two units are required to ensure the reliability of the restoration process in critical areas.