Heuristics: An attempt to identify catastrophic days

The Major Event Day identification process used in distribution reliability calculation described in IEEE Standard 1366-2003 is based on computing a threshold from the prior five years of daily SAIDI data. Infrequent events, such as a hurricane, severe ice storm, or earthquake can appreciably increase the Major Event Day threshold value. This will usually reduce the number of Major Event Days over the next five years and increase the value of annual SAIDI by a small, but not insignificant amount. The Catastrophic Event Task Force of the Distribution Reliability Working Group has explored methods to identify Catastrophic Events to exclude them from the calculation of the Major Event Day thresholds. The Heuristic Method, based on the original work that developed the 2.5 Beta Method for calculating the Major Event day thresholds, is presented.