IEEE Reliability Indices Standards - Major Event Day calculations and how it effects small utilities

The new IEEE "Guide for Electric Power Distribution Reliability Indices" (1366-2001) has been approved and should be released in early 2004. Among the changes from the previous Guide is a new method to calculate Major Event Days (MED). The Working Group on System Design developed a statistically based methodology that classifies reliability data into day-to-day and major event days. This newly developed methodology, the "Beta Method", utilizes daily SAIDI values in a-log-normal distribution. There have been questions of the effect of this calculation on small utilities where days with no outages are not uncommon. This has previously been unknown because of lack of data from small utilities. Recently, data has been obtained from several co-ops ranging in size from 1400 customers to 72,000 customers. This paper discusses the results of the evaluation of small utility data and encourages more utilities to use this methodology to determine MEDs and submit the data to the working group.