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

<math>\mbox{SAIFI} = \frac{\sum{\lambda_i N_i}}{\sum{N_i}}</math>

where <math>\lambda_i</math> is the failure rate and <math>N_i</math> is the number of customers for location <math>i</math>. In other words,

<math>\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.

Sources

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