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 $\text{SAIFI}=\frac{\sum {\lambda }_i{N}_i}{\sum N_i}$ where ${\lambda }_i$ is the failure rate and $N_i$ is the number of customers for location $i$. In other words, $\text{SAIFI}=\frac{\text{total number of customer interruptions}}{\text{total number of customers served}}$ 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.