What is "saidi"

The System Average Interruption Duration Index (SAIDI) 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 is the number of customers and U is the annual outage time for location i, and N 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.