GE Digital Energy Multilin 239 Instruction Manual page 140

7–102
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EXAMPLE: CALCULATING THE PERCENT OF UNBALANCE
Find the percent unbalance given the following information:
PRIMARY SECONDARY (5A)
I = 73 A 3.65 A
a
I = 100 A
b
I = 100 A
c
The average of the three phase currents is:
I I I
+ +
a b c
I
------------------------
= =
av
3
Now, since I < I , we have percent unbalance given by:
av FLC
I I
–
 
m av
-------------------- -
%UB
=
 
I
FLC
Therefore, the percent unbalance in this case is 18%.
5 A
5 A
73 100 100 273
+ +
------------------------------------- - A -------- - A
=
3 3
73 91
 
–
× -------------------- - ×
100% 100%
=
 
100
239 MOTOR PROTECTION RELAY – INSTRUCTION MANUAL
CHAPTER 7: TESTING
91 A
=
18%
=