Fluke 43B - Scope

Motor Loads
Induction Motors
4
39
5
Calculate the voltage imbalance (fill in your measurement results):
a
First calculate the average voltage:
Average Voltage:
___ V
1-3
+ ___ V
2-3
+ ___ V
1-2
___ V
= = _____ V
AVERAGE
33
b
Second, calculate the maximum deviation from the mean.
Ignore the minus signs:
Maximum Deviation:
V
1-3
- V
AVERAGE
= ___ V
V
2-3
- V
AVERAGE
= ___ V Largest deviation: ___ V
DEVIATION
V
1-2
- V
AVERAGE
= ___ V
c
Finally, calculate the voltage imbalance:
Voltage Imbalance:
___ V
DEVIATION
x 100% = _____ %
___ V
AVERAGE
Voltage imbalance for three-phase motors should not exceed 1%. Voltage
imbalance may be caused by bad connections, contacts or fuses; or is caused
by problems at the source transformer.
Example
a
403 V
1-3
+ 391 V
2-3
+ 406 V
1-2
1200 V
= = 400 V
AVERAGE
33
b
403 V
1-3
- 400 V
AVERAGE
= 3 V
391 V
2-3
- 400 V
AVERAGE
= -9 V Largest deviation: 9 V
DEVIATION
406 V
1-2
- 400 V
AVERAGE
= 6 V
c
9 V
DEVIATION
x 100% = 2.25 %
400 V
AVERAGE