SAIFI

The System Average Interruption Frequency Index (SAIFI) is commonly used as a reliability indicator by electric power utilities. SAIFI is the average number of interruptions that a customer would experience, and is calculated as

[math]\displaystyle{ \mbox{SAIFI} = \frac{\sum{\lambda_i N_i}}{N_T} }[/math]

where [math]\displaystyle{ \lambda_i }[/math] is the failure rate, [math]\displaystyle{ N_i }[/math] is the number of customers for location [math]\displaystyle{ i }[/math] and [math]\displaystyle{ N_T }[/math] is the total number of customers served. In other words,

[math]\displaystyle{ \mbox{SAIFI} = \frac{\mbox{total number of customer interruptions}}{\mbox{total number of customers served}} }[/math]

SAIFI is measured in units of interruptions per customer. 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 1.10 interruptions per customer.

See also

• Average Service Availability Index (ASAI)
• ASIDI
• ASIFI
• ASUI
• CAIDI
• CAIFI
• CTAIDI
• MAIFI
• SAIDI
• SAIFI