Ieee std 1366-2012 (Revision of ieee std 1366-2003) ieee guide for Electric Power Distribution Reliability Indices

3.5.1 An example of using the MED definition to identify major events and subsequently 
calculate adjusted indices that reflect normal operating performance 
The following example illustrates the calculation of the daily SAIDI, calculation of the MED threshold 
T
MED
, identification of MEDs, and calculation of adjusted indices. 
Table 1 gives selected data for all interruptions occurring on a certain day for a utility that serves 2 000 
customers. 
Table 1 —Interruption data for March 18, 1994 
Date Time 
Duration 
(min) 
Number of 
customers 
Interruption Type 
Mar 18, 1994 
18:34:30 
20.0 
200 
Sustained 
Mar 18, 1994 
18:38:30 
1.0 
400 
Momentary 
Mar 18, 1994 
18:42:00 
513.5 
700 
Sustained 
Note that although the third interruption (at 18:42:00) was not restored until the following day, its total 
duration counts in the day that the interruption began. Note also that SAIDI considers only sustained 
interruptions.
For March 18, 1994, daily SAIDI (assuming a 2 000 customer utility) is given in Eq. (30). 
(
) (
)
min
73
.
181
2000
700
5
.
513
200
20
SAIDI
=
×
+
×
=
(30) 
One month of historical daily SAIDI data is used in the following example to calculate the MED threshold 
T
MED
. Five years of historical data is preferable for this method, but printing that many values in this guide 
is impractical, so only one month is used to illustrate the concept. The example data is shown in Table 2. 
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IEEE Std 1366-2012 
IEEE Guide for Electric Power Distribution Reliability Indices 
Copyright © 2012 IEEE. All rights reserved. 
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