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

3.4.2 MAIFI
E
: Momentary Average Interruption Event Frequency Index 
The Momentary Average Interruption Event Frequency Index (MAIFI
E
) indicates the average frequency of 
momentary interruption events. This index does not include the events immediately preceding a sustained 
interruption. Mathematically, this is given in Eq. (25). 
MAIFI
E
= 
Served
Customers
of
Number 
Total
Events
on 
Interrupti
Momentary 
Customer 
of
Number 
Total
∑
(25) 
To calculate the index, use Eq. (26). 
MAIFI
E
= 
T
mi
E
N
N
IM
∑
(26) 
3.4.3 CEMSMI
n
: Customers Experiencing Multiple Sustained Interruption and Momentary 
Interruption Events
The Customers Experiencing Multiple Sustained Interruption and Momentary Interruption Events Index 
(CEMSMI
n
) is the ratio of individual customers experiencing n or more of both sustained interruptions and 
momentary interruption events to the total customers served. Its purpose is to help identify customer issues 
that cannot be observed by using averages. Mathematically, this is given in Eq. (27). 
CEMSMI
n
= 
Served
Customers
of
Number 
Total
ons
Interrupti
More
or 
n 
ng
Experienci
Customers
of
Number 
Total
(27) 
To calculate the index, use Eq. (28). 
CEMSMI
n
= 
T
N
n)
(k
CNT
≥
(28) 
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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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