Motor Loads
Induction Motors
4
41
5
Calculate the current imbalance. Use the same formula as in the
previous section but substitute current for voltage.
Current imbalance for three-phase motors should not exceed 10%.
Example
a
33 A
1
+ 29 A
2
+ 34 A
3
= 96 A
TOTAL
= 32 A
AVERAGE
3
b
33 A
1
- 32 A
AVERAGE
= 1 A
29 A
2
- 32 A
AVERAGE
= - 3 A Largest value: 3 A
DEVIATION
34 A
3
- 32 A
AVERAGE
= 2 A
c
3 A
DEVIATION
x 100% = 9.4 %
32 A
AVERAGE
Note
To detect single phasing, always check the current on all three
phases. When a voltage measurement is made at the motor
terminals, the voltages will read close to normal as motor action is
inducing voltage into the open winding.
To Next Page
Loading...
