Protective relaying action associated with widespread system disturbances

Major widespread electrical system disturbances can significantly challenge protective relaying systems. The particular areas of concern include: 1) tripping of transmission lines on load at lower than normal system voltages, 2) appropriately responding to system out-of-step conditions, 3) automatic reclosing circuit breakers following protective relay operations, and 4) responding to system changes resulting from over or underfrequency conditions. In addition, the performance of the generator excitation system and the prime mover controls are important during a system disturbance. Coordination between these systems and system protection as well as control strategies are needed to avoid system collapse. This talk discusses these key issues and their relation to the blackout.