SAIFI

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

${\mbox{SAIFI}}={\frac {\sum {\lambda _{i}N_{i}}}{\sum {N_{i}}}}$

where $\lambda _{i}$ is the failure rate and $N_{i}$ is the number of customers for location $i$. In other words,

${\mbox{SAIFI}}={\frac {\mbox{total number of customer interruptions}}{\mbox{total number of customers served}}}$

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.

Sources

• Layton, Lee (2004). "Electric System Reliability Indices" (PDF). www.egr.unlv.edu.