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A number of reliability indexes are used in the electric industry to make it easier to compare <br /> performance of electric utilities. These reliability indexes are: <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 was <br /> available to the total customer minutes available in a time period. This is normally expressed <br /> as a percentage. <br /> ERMU's 2012 ASAI is 99.999% Availability. Last year was 99.994% Availability. <br /> 2. CAIDI (customer average interruption duration index) <br /> This is defined as the average length of an interruption weighted by the number of customers <br /> affected. It is calculated by summing the customer minutes off during each interruption in <br /> the time period and dividing this by the number of customers experiencing one or more <br /> sustained interruptions during the time period. The resulting unit is minutes. The index <br /> enables utilities to report the average duration of a customer outage for those customers <br /> affected. <br /> ERMU's 2012 CAIDI is 66 minutes. Last year's CAIDI was 105 minutes. <br /> 3. SAIDI (system average interruption duration index) <br /> This is defined as the average interruption duration for customers served during a specified <br /> time period. It is determined by summing the customer minutes off for each interruption <br /> during a specified time period and dividing that sum by the average number of customers <br /> served during that period. The unit is minutes. This index enables the utility to report how <br /> many minutes' customers would have been out of service if all customers were out at one <br /> time. <br /> ERMU's 2012 SAIDI is 7.7 minutes. Last year's SAIDI was 31.1 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 interrupted <br /> in a time period by the average number of customers served. The resulting unit is <br /> "interruptions per customer." <br /> ERMU's 2012 SAIFI is 0.117. Last year's SAIFI was 0.296. <br /> Another statistic staff gets concerned about is the average length of any outage. Elk River <br /> Municipal Utilities' 2012 average length of outage is 119.32 minutes. Last year the average <br /> length of outage was 126.00 minutes. Electric utilities with a high percentage of underground <br /> facilities will exhibit higher length of outage time than electric utilities with more overhead <br /> facilities. <br /> P O W E R E D et 1 I <br /> Page 2 of 3 NATURE <br /> Reliable Pablic <br /> Power Provider P O W E R E D T o SERVE <br />