Reliability lessons learned from the major Western Interconnection disturbances of 1994

In 1994, the Western interconnected bulk power system (hereafter referred to as the Western Interconnection) suffered two major disturbances. Both disturbances broke up the interconnection into smaller islands, tripped large amounts of transmission and generation, and interrupted customer service over a large area. One disturbance, on January 17, 1994, resulted from the Northridge earthquake. A second disturbance, on December 14, began with a relatively common and seemingly innocuous (by power system standards) single line-to-ground fault on a 345 kV circuit in Southern Idaho. While the initiating causes of the disturbances were different, the impacts-widespread loss of generation, transmission and interruption of customer load-were largely the same. The author describes how the investigations into the causes of, effects of, and remedies for, these two disturbances produced a set of questions-and lessons-which, while specific to these two disturbances, also apply to all interconnected power system operations