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

3.2.7 CEMI
n
: Customers Experiencing Multiple Interruptions
The Customers Experiencing Multiple Interruptions Index (CEMI
n
) indicates the ratio of individual 
customers experiencing n or more sustained interruptions to the total number of customers served. 
Mathematically, this is given in Eq. (13). 
CEMI
n
= 
Served
Customers
of
Number 
Total
ons
interrupti
sustained
more
or 
n 
d
experience
that 
Customers
of
Number 
Total
(13) 
To calculate the index, use Eq. (14). 
CEMI
n
= 
T
N
n)
(k
CN
≥
(14) 
NOTE—This index is often used in a series of calculations with n incremented from a value of 1 to the highest value of 
interest. 
3.2.8 CELID: Customers Experiencing Long Interruption Durations 
The Customers Experiencing Long Interruption Durations Index (CELID) indicates the ratio of individual 
customers that experience interruptions with durations longer than or equal to a given time. That time is 
either the duration of a single interruption (s) or the total amount of time (t) that a customer has been 
interrupted during the reporting period. Mathematically, the Single Interruption Duration equation is given 
in Eq. (15) and the Total Interruption Duration equation is given in Eq. (17). 
Single Interruption Duration: 
CELID-t = 
Served
Customers
of
Number 
Total
duration 
hours
more
or 
S
d
experience
that 
Customers
of
Number 
Total
(15) 
To calculate the index, use Eq. (16). 
CELID-s = 
T
N
S)
(k
CN
≥
(16) 
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IEEE Std 1366-2012 
IEEE Guide for Electric Power Distribution Reliability Indices 
Copyright © 2012 IEEE. All rights reserved. 
8
Total Interruption Duration: 
CELID-t= 
Served
Customers
of
Number 
Total
duration 
hours
more
or 
T
d
experience
that 
Customers
of
Number 
Total
(17) 
To calculate the index, use Eq. (18). 
CELID-t = 
T
N
T)
(k
CN
≥
(18)