Average Service Availability Index

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

$$\mbox{ASAI} = \frac{\sum{N_i} \times 8760 - \sum{U_i N_i}}{\sum{N_i} \times 8760}$$

where $$N_i$$ is the number of customers and $$U_i$$ is the annual outage time (in hours) for location $$i$$. 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)

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