2.5 Beta Methodology—Impact of “Zero SAIDI” Days

The IEEE Standard 1366-2003-2.5 Beta Methodology was developed to provide a methodology to define a Major Event Day (MED) with respect to distribution reliability performance. The method applies to utilities experiencing interruptions every day or just some days of the year. According to the methodology, days without interruptions are eliminated from the threshold calculation. This letter endeavors to illustrate that actual data variations in the number of “Zero SAIDI” days has a significant impact on the threshold for data sets of 24 utility units and may also apply to other utilities. The issue that arises is that there is a large variation in the thresholds and number of MEDs, depending on the number of “non-zero” days a utility may encounter from year to year as a result of slightly deteriorating daily performance. This condition can cause significant shifts of the MED thresholds and the resulting number of defined MEDs.