IEEE Power & Energy Magazine - May/June 2018 - 46

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Daily
SAIDI (min)

2,000
1,500
1,000
500
0

Date
(a)

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(b)

figure 1. Line plots of daily SAIDI values: (a) all SAIDI values and (b) the 20 highest SAIDI values are excluded.

Annual SAIDI (in Minutes) by Root Cause
70
60
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Predictive Outage
and Reliability Analytics

10
0

2008 2009 2010 2011 2012 2013 2014 2015 2016
Other
Accident

Unknown
Animal

Electrical Failure
Weather

figure 2. The annual SAIDI by root cause. Contributions
to the sum of SAIDI values over the nine-year period are
weather (29%), electrical failure (28%), animal (19%), unknown (15%), accident (8%), and other (1%).

this case study, we will adopt the simplified Beta method to
exclude 20 days from the nine-year period for further analysis because that helps us answer questions about the utility's
underlying reliability trend by uniformly removing extreme
events across the entire data set.
many factors may lead to a distribution outage. the stacked
bar chart in figure 2 shows the sum of annual saiDi values for each outage root cause during the past nine years.
46

the legend lists the categories in the ascending order of the
saiDi share during the nine years. the largest category is
weather, which includes subcategories of tree, storm, and
wind. the other categories, such as electrical failure, animal,
unknown, and accident, do not have weather as a main driving factor. in this article, we focus on weather-related outages, which contribute to about one third (29% in this case)
of the saiDi value over the nine-year period.

ieee power & energy magazine

We can further relate the root causes of outages to some
weather variables. for instance, we can use wind speed and
gust to describe wind; we can use precipitation and wind
speed to describe a storm. although tree faults are not always
weather driven, many are due to windblown trees falling on
overhead lines. sometimes a moist tree branch bridges two
conductors and gradually dries out due to the small current,
which can eventually lead to a short circuit. Weather conditions such as wind, precipitation, humidity, and temperature
are often the real root causes of the tree faults. therefore,
we merge tree faults with the other weather-related outages
in this article to conduct the analysis. out of 3,268 days, or
nine full years minus the top 20 saiDi days, this category
includes 375 days with weather-related outages.
the major weather service providers in the united states
have been reporting weather variables hourly for many major
weather stations, including the one close to this lDc. in
this case study, we take the following 11 quantitative weather
may/june 2018



Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - May/June 2018

Contents
IEEE Power & Energy Magazine - May/June 2018 - Cover1
IEEE Power & Energy Magazine - May/June 2018 - Cover2
IEEE Power & Energy Magazine - May/June 2018 - Contents
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IEEE Power & Energy Magazine - May/June 2018 - Cover3
IEEE Power & Energy Magazine - May/June 2018 - Cover4
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