Survey Questions - Edison Electric Institute

Chapter 2: Storms and Outages
Types of Storms
The next several figures will present the categories of storms that are most frequent, that affect the most
customers, and that causes the largest amount of outage hours. The EIA data captures the “Type of
Disturbance” for each outage; however, they have not created a standardized list of disturbances for
uniformity in the data. For example, summer storms associated with rain, lighting, wind, and thunder have
47 different types of listings. In an effort to manage the data, this report has assigned each of the events to
one of the following seven categories:
� Earthquake
� Flooding
� Heat Storm
� Hurricane/Tropical Storm
� Summer Storm (Lightning/High Winds)
� Wildfire
� Winter Storm (Ice/Snow)
Of these types of events, hurricanes/tropical storms, summer storms, and winter storms together make up
more than 97.8 percent of all the events recorded. This report has included earthquakes, flooding, and
wildfires in the listing because they are naturally-occurring events.
Figure 2.7, Percentages of Outage Hours, Storms Types, and Customers Out, is comprised of three charts
showing the percentage breakdown for the Total Outage Hours, Type of Storms, and Total Customers Out
for the summation of all events from 2003 to 2011. The data in the three pie charts consistently demonstrates
that summer storms are the leading cause of electrical grid outages. However, because of fewer
hurricanes/tropical storms over the last few years, summer storms have increased in their share of the
percentage of all storms. The percentage difference between hurricanes/tropical storms and winter storms is
minimal except when looking at the number of customers affected by the events. Again, it is worth
reiterating that this data is only for major outage events reported to EIA.
14 Edison Electric Institute