SAIDI

The System Average Interruption Duration Index (SAIDI) is commonly used as a reliability index by electric power utilities. SAIDI is the average outage duration for each customer served, and is calculated as:



\mbox{SAIDI} = \frac{\sum{U_i N_i}}{N_T} $$

where $$N_i$$ is the number of customers and $$U_i$$ is the annual outage time for location $$i$$, and $$N_T$$ is the total number of customers served. In other words,


 * $$\mbox{SAIDI} = \frac{\mbox{sum of all customer interruption durations}}{\mbox{total number of customers served}}$$

SAIDI is measured in units of time, often minutes or hours; it is usually measured over the course of a year. According to IEEE Standard 1366-1998, the median value for North American utilities is approximately 1.50 hours. According to the U.S. Energy Information Administration Annual Electric Power Industry Report, it is 2.0 hours, rising to the range of 3.5 to 8 hours, when "major events" are included.

Comparison of SAIDI by country
The following is a table of SAIDI for different countries, calculated using the methodology in the World Bank's Doing Business 2016-2020 studies: