Weather Events Dominate Electrical Disturbances

EIA has reviewed the last 5 years of reported electrical disturbance data (sourced from DOE's Electric Emergency Incident and Disturbance Report ). The data reviewed are composed of electrical disturbance reports submitted by electric utilities. Electric utilities are required to submit such reports if they meet any one of 12 established criteria (for reporting criteria see page 6 of Form OE-417 Instructions  and Form OE-417 ). For instance, customer outages are reported when more than 50,000 customers are without power for at least one hour. As such the reported data may not capture all electrical disturbances but it certainly captures all major electrical disturbances.

The review reveals that weather-related events (e.g., winter storms, thunderstorms, high winds, hurricanes, flooding, etc.) were the main cause of major electrical disturbances in the United States in the years 2007 to 2011 and 2012 (June YTD). Reported disturbances ranged from 76 in 2007 to 307 in 2011. Although reported disturbances increased year-over-year between 2009 and 2011, it is not obvious that this is indicative of a longer-term trend towards more disturbances. One constant in the data, however, is that weather appears to be the main cause of the reported disturbances, with 54% (454 of 838 total reported disturbances) of reported disturbances during the 2007 to 2012 time frame being weather-related.

The influence of weather can be readily seen when by examining the number of customer outages and the duration of the outages. Between January 2007 and June 2012, there were in excess of 93 million customer outages (A customer outage is when any given customer experiences an outage in electrical service. Note, that a given customer could have experienced more than one outage during any particular time frame examined. Further, a "customer" may actually represent a family sharing the same space). Both 2008 and 2011 standout from the other years, with in excess of 27 million and 26 million customer outages, respectively (see figure above).

Weather drives customer outages with 88% of all customer outages occurring due to weather-related events over the time period. The relative magnitude of weather impacts on customer outages becomes even clearer when you look at average number of customers affected by event type. During the 2007 to 2012 (June YTD) timeframe, weather-related outages averaged in excess of 181,000 customer outages per event, while non-weather-related events averaged about 29,000 customer outages per event. Or expressed as a ratio, weather-related events resulted in excess of six times more customer outages per event than non-weather-related events.

Weather also has a very strong impact on the duration of the disturbance. During the 2007 to 2012 (June YTD) period, there were in excess of 36,000 hours of reportable disturbance time, with about 78% of reportable disturbance time (28,335 hours) resultant from weather-related events. As with customer outages, disturbance duration was greatest in 2008 and 2011 (both in excess of or close to 10,000 hours) (see figure above).

If the data, however, are reduced further by denominating them in average duration by event type, weather's influence is further evident. The average disturbance duration for weather-related events (62 hours per event) was about three times longer than the average disturbance duration for non-weather-related events (21 hours) (see figure below).

Principal Contributor: Paul McArdle (Paul.mcardle@eia.gov)

Co-Contributor: M. Tyson Brown (Michael.brown@eia.gov)