Average Service Availability Index

The Average Service Availability Index (ASAI)¹² is a reliability index commonly used by electric power utilities. ASAI is calculated as

${\displaystyle {\mbox{ASAI}}={\frac {\sum {N_{i}}\times 8760-\sum {U_{i}N_{i}}}{\sum {N_{i}}\times 8760}}}$

where ${\displaystyle N_{i}}$ is the number of customers and ${\displaystyle U_{i}}$ is the annual outage time (in hours) for location ${\displaystyle i}$. ASAI can be represented in relation to SAIDI (when the annual SAIDI is given in hours, 8760 is the number of hours in a year)

${\displaystyle {\mbox{ASAI}}=1-{\frac {\mbox{SAIDI}}{8760}}}$