5.3 ERMUSR 03-13-2018 - Laserfiche WebLink

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System Average Interruption Frequency Index(SAIFI) SAIFI is defined as the average number of times that a customer is interrupted during a specified time period. It is determined by dividing the total number of sustained' interrupted customers in a time period by the average number of customers served. The resulting unit is"interruptions per customer." Customer Average Interruption Duration Index(CAIDI) CAIDI is defined as the average duration (in minutes) of an interruption experienced by customers during a specific time frame. It is calculated by summing the customer minutes off during each sustained' interruption in the time period and dividing this 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. Momentary Average Interruption Frequency Index(MAIFI) MAIFI is defined as the average number of times that a customer on the system will experience a momentary interruption. It is determined by dividing the total number of momentary customer interruptions by the average number of customers served. The resulting unit is"interruptions per customer." Average Service Availability Index(ASAI) 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. Listed below in Table 1 is a summary for the 2017 reliability indexes. This table includes 2016 reliability indexes for comparison. Attached is the American Public Power Association's (APPA) eReliability Annual Report which contains published averages that can be used by utilities to better understand the performance of their electric system relative to other utilities nationally and to those within their region or size class. 2017 Electric Reliability Summary ERMU APPA Region 3 APPA Customer Class 4 Index 2017 2016 2017 2016 2017 2016 SAIDI 32.3938 41.0234 100.7792 88.3391 230.6849 85.4668 SAIFI 0.3123 0.2727 0.7275 0.6310 0.8991 0.7013 CAIDI 103.7180 150.4193 111.4538 153.2071 227.8248 116.6985 MAIFI 0.0012 0.0001 0.6860 0.5327 0.3090 0.4400 ASAI 99.9938 99.9922 99.9808 99.9839 99.9561 99.9838 Table 1 ' Only outages lasting longer than five minutes are included in the calculations, as defined by IEEE 1366. Staff reviews these statistics in detail to find ways to continually improve our system. These statistics are very good compared to other utilities. As indicated by the following pie chart and statistics list, you can see the cause of the outages that we experienced in 2017. Page 2 of 3 202