Ohio Power Company
(AEP) - Annual performance compared to standard
Excludes major events and transmission outages
Average interruptions per customer served
Average minutes per customer interruption
Rule 4901:1-10-10 (Rule 10) of the Ohio Administrative Code requires Ohio’s investor-owned electric utilities to file an annual report of their distribution reliability performance. Specifically, Rule 10 requires the electric utilities to report their performance using the following two reliability measures (called “indices”).
The System Average Interruption Frequency Index (SAIFI) represents the average number of interruptions per customer. This index measures how often an “average” customer’s power is interrupted in a year and includes both those customers experiencing several interruptions per year as well as those whose power is not interrupted at all. SAIFI is calculated using the following formula:
SAIFI = Total number of customer interruptions ÷ total number of customers served
The Customer Average Interruption Duration Index (CAIDI) represents the average interruption duration. In other words, CAIDI is the average time it takes for the electric utility to restore service following a power interruption. This index measures the electric utility’s average restoration time, and therefore only includes those customers who experience power outages during the year. CAIDI is calculated using the following formula:
CAIDI = Sum of customer interruption durations ÷ total number of customer interruptions
Interruptions – As used in the calculation of SAIFI and CAIDI, an interruption is defined as a complete loss of a customer’s electric power for more than five minutes.
Major Event and Transmission Exclusions – Rule 10 requires utilities to exclude “major events” and transmission outages from their reliability data before calculating their CAIDI and SAIFI performance. Major events are unusually severe weather or other events that stress the company’s distribution system and cause untypical outages. Days that qualify as major events are excluded from reliability performance calculations for the year. Major events are calculated using the IEEE Standard 1366-2003 (except that transmission outages are excluded). Outages caused by the company’s transmission lines, which are not part of the distribution system, are similarly excluded to concentrate on measuring only the performance of the distribution system.
Performance Standards and Rule Violations – Rule 10 requires each electric utility to file performance standards for approval by the Public Utilities Commission of Ohio. The approved standards are minimum performance levels, and missing a standard for two consecutive years constitutes a rule violation. Performance standards can be revised if the utility files an application that is approved by the Commission following a legal process that is open to interested persons. Performance standards can also be revised by Commission order.