5.2. ERMUSR 01-11-2011 - Laserfiche WebLink

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A number of reliability indexes are used in the electric industry to make it easier to compare performance of electric utilities. These reliability indexes are: 1. ASAI (average service availability index) ASAI is a measure of the average availability of the sub-transmission and distribution systems to serve customers. It is the ratio of the total customer minutes that service was available to the total customer minutes available in a time period. This is normally expressed as a percentage. ERMU's 2010 ASAI is 99.989%. Availability 2. CALDI (customer average interruptiou duration index) This is defined as the average length of an interruption weighted by the number of customers affected. [t is calculated by summing the customer minutes off during each interruption in the time period and dividing [his by the number of customers experiencing one or more sustained interruptions during the time period. The resulting unit is minutes. The index enables utilities to report the average duration of a customer outage for those customers affected. ERMU's 2010 CAIDI is 108 minutes. Last year's CAIDI was 137 minutes. 3. 5AIDI (system average interruptiou duratiou iudex) This is defined as the average interruption duration for customers served during a specified time period. [t is determined by summing the customer minutes off for each intemrption during a specified time period and dividing that sum by the average number of customers served during that period. The unit is minutes. This index enables the utility to report how many minutes customers would have been out of service if all customers were out at one time. ERMU's 2010 SAIDI is 57.2 minutes. Last year's SAIDI was 5.1 minutes. 4. SAIFI (system average iuterrupHon frequency index) This is defined as the average number of timers that a customer is interrupted during a specified time period. [t is determined by dividing the total number of customers interrupted in a time period by the average number of customers served. The resulting unit is "interruptions per customer." ERMU's 2010 SAIFI is 0.527. Last year's SAIFI was 0.037. Another statistic staff gets concerned about is the average length of any outage. Elk lover lvlunicipai Utilities' 2010 average length of outage is 105.8 minutes. Last year the average length of outage was 109.3 minutes. Electric utilities with a high percentage of underground facilities will exhibit higher length of outage time than electric utilities with more overhead facilities. Staff reviews these statistics in detail to find ways to continually improve our system. 'these statistics are very good compared to other utilities. Attached for you reverence are graphs depicting our ASAI, CA[Dl, SAIDI, and SA1FI numbers. Animals and branches continue to cause the greatest number of outages. Animals contributed to 21 outages in 2010 and branches contributed to 14 outages. Underground faults were also a contributing factor. The single greatest incident impacting the report was the squirrel that caused the Substation 14-3 transformer to go off line one Sunday morning in August. This outage affected 3,000 customers for 75 minutes resulting in a 225,000 minute component, or 42.8%, of the total 526,144 minutes of outage. The specific area where this squirrel caused the flashover between feeders has been on our capital projects 2012 forecast for modifications that help to prevent this type of outage. hi the short term until this system improvement is made, there have been some system protective relays setting improvements made. To proactively reduce the number of outages directly related [o branches, and sometimes indirectly related to animals, staff continues to do tree trimming. Overall, our electric distribution system is robust and our reliability is very high. ACTION REQUESTED: No action is required.