Power outages in Connecticut have been much shorter on average as well as less frequent for the past six years.
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Power outages in Connecticut have been much shorter on average as well as less frequent for the past six years.
The high-water mark was 2011, when two memorable storms — Tropical Storm Irene and a Halloween Nor’easter — each knocked out electricity for more than 800,000 utility customers here.
This month, the Public Utilities Regulatory issued its annual reliability report for each of the public electric utilities in the state, Eversource and United Illuminating.
The latest report, which covers 2017, shows that outage duration and frequency remain far below their 2011 peaks, though there were some upticks between 2016 to 2017, notably for Eversource.
PURA measures system reliability using two core metrics:
• System average interruption duration index (SAIDI) is the sum of customer interruptions in minutes divided by customers served. It can be viewed as the average outage duration experienced by all customers.
• System average interruption frequency index (SAIFI) is the total number of customers interrupted divided by number of customers. It can be viewed as the average outage frequency.
Counting six major storms during 2017, Eversource’s SAIFI reading was largely flat, but its SAIDI reading increased from 202 to 355. That’s the highest it has been since 2012, the year Hurricane Sandy hit.
A big part of the reason for the increase in power-outage duration was Tropical Storm Philippe (Oct. 29-Nov. 1, 2017), which resulted in 5.7 million hours of service outages.
However, excluding major storms, Eversource’s SAIDI reading dropped to its lowest (best) level since at least 1996, while its SAIFI reading was its second best since then.
Meanwhile, UI’s SAIDI reading also increased, when including storms, and its SAIFI reading dropped. When not including storms, UI, too, had a good year. Both readings were their lowest (best) since at least 1996.
PURA said Eversource has much more territory to cover than UI — 87 percent of the state’s geography vs. 7 percent for UI. Eversource also has more wooded territory and four times as many electricity customers.
