Why is it called a rolling blackout?

It is called a rolling blackout for a reason. The goal is to reduce load by impacting a minimal amount of the system for a designated amount of time and then returning power to the affected area and moving to a different area of the system. The way this will be accomplished on our systems will be by deenergizing the entire substation and not just picking and choosing among individual members. The outage should last no longer than an hour and then the substation will be re-energized and another substation in the system will be turned off.