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

T
MED
 
Major Event Day threshold 
3.2 Sustained interruption indices 
3.2.1 SAIFI: System Average Interruption Frequency Index 
The System Average Interruption Frequency Index (SAIFI) indicates how often the average customer 
experiences a sustained interruption over a predefined period of time. Mathematically, this is given in Eq. 
(1). 
SAIFI = 
Served
Customers
of
Number 
Total
d
Interrupte
Customers
of
Number 
Total
∑
(1) 
To calculate the index, use Eq. (2). 
SAIFI = 
N
i
N
T
∑
= 
T
N
CI
(2) 
3.2.2 SAIDI: System Average Interruption Duration Index
The System Average Interruption Duration Index (SAIDI) indicates the total duration of interruption for the 
average customer during a predefined period of time. It is commonly measured in minutes or hours of 
interruption. Mathematically, this is given in Eq. (3). 
SAIDI = 
Served
Customers
of
Number 
Total
on 
Interrupti
of
Minutes
Customer 
∑
(3) 
To calculate the index, use Eq. (4). 
SAIDI = 
T
N
i
N
i
r
∑
= 
T
N
CMI
(4) 
3.2.3 CAIDI: Customer Average Interruption Duration Index
The Customer Average Interruption Duration Index (CAIDI) represents the average time required to restore 
service. Mathematically, this is given in Eq. (5). 
CAIDI = 
d
Interrupte
Customers
of
Number 
Total
on 
Interrupti
of
Minutes
Customer 
∑
=
CI
CMI
(5) 
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IEEE Std 1366-2012 
IEEE Guide for Electric Power Distribution Reliability Indices 
Copyright © 2012 IEEE. All rights reserved. 
6
To calculate the index, use Eq. (6). 
CAIDI = 
r
i
N
i
N
i
SAIDI
SAIFI
∑
∑
=
(6)