SAIDI
The system average interruption duration index (SAIDI) is commonly used as a reliability index by electric power utilities. SAIDI is the average cumulative outage duration for each customer served, and is calculated as: SAIDI = ∑ U i N i N T {\displaystyle {\mbox{SAIDI}}={\frac {\sum {U_{i}N_{i}}}{N_{T}}}} where N i {\displaystyle N_{i}} is the number of customers and U i {\displaystyle U_{i}} is the annual outage time for location i {\displaystyle i} , and N T {\displaystyle N_{T}} is the total number of customers served.