We track our transmission and distribution reliability performance with several metrics that are used industrywide. These indicators show us how reliable our system is and how our customers are impacted when it is not. The investments we are making in our transmission and distribution system improve reliability and operating efficiency and prepare the system for new technologies in the future.
The System Average Interruption Duration Index (SAIDI) measures how many minutes the average customer experiences an interruption in electric service in a given year. During 2013, the AEP System SAIDI was 200.2 minutes, a 3.7 percent increase from 2012. The growth of vegetation contributed to about 33 percent of SAIDI results and impacts to equipment accounted for about 20 percent.
The System Average Interruption Frequency Index (SAIFI) represents the number of interruptions the average customer experiences in a year. During 2013, the system’s SAIFI was 1.329, a 0.9 percent increase from 2012.
The Customer Average Interruption Duration Index (CAIDI) represents the average length of time it takes to restore service when an outage occurs. AEP’s 2013 CAIDI was 150.6 minutes, a 2.7 percent increase from 2012. A combination of factors are responsible, including a reduction in the number of shorter-duration outages that historically affected larger numbers of customers that skew the metric upward and an increase in non-major storm events.
Vegetation-related outages and equipment failure are among the biggest challenges to AEP’s service reliability. Managing vegetation on our rights of way (ROW) is key to maintaining transmission and distribution system reliability. AEP manages the trees and vegetation around power lines using a combination of performance-based (such as targeting low performing circuits) and cycle-based maintenance strategies. Maintaining a regular tree-trimming cycle is a significant expense that directly affects customer bills. During the past five years, AEP has invested more than $1 billion in vegetation management, including $221.8 million in 2013. The issue of reliability has prompted several states to consider or implement shorter intervals between tree trimming programs.
Going forward, we are looking for opportunities to use an integrated vegetation management approach to ROWs for new transmission lines. This would involve addressing key ecological concerns while maintaining reliable transmission service. Reducing the need for herbicides, controlling invasive species, and providing greater natural species diversity are examples of practices under such an approach that could potentially reduce long-term vegetation maintenance costs.
One way we will do this is to identify potential partnerships with organizations that have experience with habitat conservation. In March 2014, AEP was among 32 private companies and five states that committed to enroll more than 3.6 million acres in the Lesser Prairie-Chicken Range-Wide Conservation Plan. This three-year plan is a collaborative effort to support habitat conservation for the bird, which is being considered for listing under the Federal Endangered Species Act. As we seek to build new transmission facilities across our service territory, we are mindful of potential environmental and ecological impacts we might have. Working with organizations such as the Western Association of Fish & Wildlife Agencies – which is overseeing this plan – helps us understand the issues, support habitat preservation and take appropriate actions to mitigate our impacts.