Electric utility service interruptions last year ticked up due to more storm activity, but remained well below long-term averages, according to the Public Utilities Regulatory Authority.
Outages for Eversource and Avangrid customers increased in both duration and frequency compared with 2015, but reliability was on the better end of the past 20 years.
PURA reports the data annually to the legislature. It has data sets including and excluding major storms.
There were six major storms for each utility last year, by PURA’s definition, up from one each in 2015.
With storms included, the two utilities experienced respective highs in service interruptions in 2011 and 2012, due to a Halloween snowstorm and Superstorm Sandy, respectively.
PURA measures reliability using two metrics — system average interruption duration index (SAIDI) and system average interruption frequency index (SAIFI).
SAIDI is the sum of customer interruptions in minutes divided by customers served, while SAIFI is total number of customers interrupted divided by number of customers. In each case, a lower reading indicates better reliability.
Including storms, Eversource’s highest SAIDI reading in the past two decades was in 2011, at 8,279. Last year it was 202, the fifth lowest in 20 years. Avangrid’s peak SAIDI was 2,763 in 2012. Last year, it was 70, the fourth lowest over the two decades.
Including storms, Eversource’s highest SAIFI was 3.15 in 2011 while UI’s was 1.63 in 2012. Those indices were at 1.05 (2nd lowest in 20 years) and 0.64 (tied for third lowest), respectively, last year.
