Measuring And Maintaining Reliability
We use several measures to track our transmission and distribution reliability performance. The System Average Interruption Duration Index (SAIDI) measures how many minutes the average customer experiences an interruption in their electric service in a given year. During 2012, the AEP System SAIDI was 193 minutes, a 15 percent improvement from 2011, when it was 228. While 2012 presented its share of challenges with the derecho and Super Storm Sandy, the number of smaller weather-related outage events declined significantly.
Another reliability performance metric, the System Average Interruption Frequency Index (SAIFI), represents the number of interruptions the average customer experiences in a year. During 2012, the AEP system’s SAIFI was 1.317, an 11 percent improvement over the previous year and the second best annual performance the AEP system has achieved during the past 7 years.
A third industry-wide reliability metric, the Customer Average Interruption Duration Index (CAIDI), represents the average length of time it takes to restore service when an average outage occurs. AEP's 2012 CAIDI was 146.6 minutes, a 5 percent improvement over 2011. While 2012 performance improved, AEP's CAIDI has slowly trended unfavorably over the past several years, reflecting a long-term rise in the length of time it takes to respond to the average outage. This is due to a combination of factors, including a favorable reduction in the number of shorter duration outages that historically affected larger counts of customers that skew the metric upward (and subsequently resulted in an improvement in SAIDI and SAIFI). It is also due to an increase in non-major storm events combined with fewer internal resources available to respond. Vegetation management and equipment failure remain the most significant challenges to AEP's service reliability.