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2008 Electric Outage Report <br />Page 2 of 3 <br />1. ASAI (average service availability index) <br />ASAI is a measure of the average availability of the sub-transmission and distribution <br />systems to serve customers. It is the ratio of the total customer minutes that service <br />was available to the total customer minutes available in a time period. This is <br />normally expressed as a percentage. <br />ERMU's 2008 ASAI is 99.997%. This is a very good percentage for any utility! <br />2. CAIDI (customer average interruption duration index) <br />This is defined as the average length of an interruption weighted by the number of <br />customers affected. It is calculated by summing the customer minutes off during each <br />interruption in the time period and dividing this by the number of customers <br />experiencing one or more sustained interruptions during the time period. The <br />resulting unit is minutes. The index enables utilities to report the average duration of <br />a customer outage for those customers affected. <br />ERMU's 2008 CAIDI is 28 minutes. Last years CAIDI was 63 minutes! <br />3. SAIDI (system average interruption duration index) <br />This is defined as the average interruption duration for customers served during a <br />specified time period. It is determined by summing the customer minutes off for each <br />interruption during a specified time period and dividing that sum by the average <br />number of customers served during that period. The unit is minutes. This index <br />enables the utility to report how many minutes customers would have been out of <br />service if all customers were out at one time. <br />ERMU's 2008 SAIDI is 17.3 minutes. Last years SAIDI was 7.4 minutes! <br />4. SAIFI (system average interruption frequency index) <br />This is defined as the average number of timers that a customer is interrupted during a <br />specified time period. It is determined by dividing the total number of customers <br />interrupted in a time period by the average number of customers served. The <br />resulting unit is "interruptions per customer." <br />ERMU's 2008 SAIFI is .618. Last years SAIFI was .118! <br />