Load shedding

Load shedding (LS) is a protective method of emergency power control where, during a large disbalance between supply and demand, the demand (load) is intentionally disconnected ("shed") so that the available electricity supply within a safe timeframe can meet the remaining demand, thereby preventing a cascading collapse of the power grid.

The load shedding is activated when the line frequency becomes too low (under-frequency load shedding, UFLS) or the line voltage is below the specified level (under-voltage load shedding, UVLS). The very act of disconnecting the load introduces yet another disturbance into the grid, so the selection of the bus about to be shed is chosen based on the bus distance from the contingency location as well as economic considerations. The shedding can be shared (typical situation, especially for UFLS: multiple areas of the grid shed the load in cooperative manner) or targeted (the load shedding is concentrated in a particular area). Typically the shedding is performed automatically in multiple stages, each with a pre-programmed threshold and the load amount to shed.