Transmission Outage Performance Prediction: Unit or Component Approach?

The key information required for quantitative evaluation of bulk power system reliability includes frequency and duration of multiple transmission line outages that cause system problems. Two fundamental approaches to reporting and analyzing transmission performance data to predict these multiple outages have evolved in the industry. These have been referred to as "unit" and the "component" approaches. A third approach "hybrid" has also been suggested. This paper interprets these approaches and discusses their relative advantages. Their relative accuracies are also discussed applying these approaches to Commonwealth Edison Company\´s 345 kV transmission outage data.