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The System Average Interruption Duration Index (SAIDI)[1] is commonly used as a reliability indicator 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, and according to IEEE Standard 1366-1998 the median value for North American utilities is approximately 1.50 hours.

See also[edit]


  1. ^ Yeddanapudi, Sree. "Distribution System Reliability Evaluation". Iowa State University. Retrieved 18 June 2011.