System Average Interruption Frequency Index (SAIFI)

The System Average Interruption Frequency Index (SAIFI) is the average number of interruptions that a customer experiences, and is calculated as:

SAIFI = total number of customer interruptions / 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.

The System Average Interruption Duration Index (SAIDI) is the average outage duration for each customer served, and is calculated as:

SAIDI = sum of all customer interruptions / total number of customers served

SAIDI is measured in units of time, often minutes or hours. 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 1.50 hours.

Calculated Values for SAIFI and SAIDI for Nairobi (11/2014 – 10/2015)

SAIFI: 16.5 outages/year

SAIDI: 162.3 hours/year