Power outage frequency and average power outage duration (EU27–28)

Vattenfall’s electricity distribution operation strives to provide high quality service with uninterrupted power supply and consistent voltage. However, power outages occur, most of which are for planned maintenance, although some are also unplanned, for example due to extreme weather conditions.

System Average Interruption Frequency Index (SAIFI)

SAIFI is the average number of interruptions that a customer would experience and is measured in units of interruption per customer. It demonstrates the reliability of Vattenfall’s electricity supply.

SAIFI =(total number of customer interruptions)/(total number of customers served). For Vattenfall’s Nordic distribution operation, the accumulated SAIFI for 2008 was 2.40 interruptions/year.

System Average Interruption Duration Index (SAIDI)

SAIDI is the average outage duration for each customer served, and is measured in units of time. Duration demonstrates Vattenfall’s ability to restore power in a timely manner.

SAIDI = (sum of all customer interruption duration)/(total number of customers served). For Vattenfall’s Nordic distribution operation in 2008, average interruption time per customer was 236 minutes.