Xylem IM117 R01 5 and Larger Submersible Pump User Manual
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THREE PHASE POWER UNBALANCE
THREE PHASE POWER UNBALANCE
A full three phase supply consisting of three individual
transformers or one three phase transformer is recom-
mended. “Open” delta or wye connections using only two
transformers can be used, but are more likely to cause poor
performance, overload tripping or early motor failure due to
current unbalance.
Check the current in each of the three motor leads and
calculate the current unbalance as explained below.
If the current unbalance is 2% or less, leave the leads as
connected.
If the current unbalance is more than 2%, current readings
should be checked on each leg using each of the three pos-
sible hook-ups. Roll the motor leads across the starter in the
same direction to prevent motor reversal.
To calculate percent of current unbalance:
A. Add the three line amp values together.
B. Divide the sum by three, yielding average current.
C. Pick the amp value which is furthest from the average
current (either high or low).
D. Determine the difference between this amp value
(furthest from average) and the average.
E. Divide the difference by the average.
Multiply the result by 100 to determine percent of
unbalance.
Current unbalance should not exceed 5% at service factor
load or 10% at rated input load. If the unbalance cannot be
corrected by rolling leads, the source of the unbalance must
be located and corrected. If, on the three possible hookups,
the leg farthest from the average stays on the same power
lead, most of the unbalance is coming from the power
source.
Contact your local power company to resolve the imbalance.
Hookup
1
Hookup
2
Hookup
3
Starter
Terminals L1 L2 L3 L1 L2 L3 L1 L2 L3
Motor
Leads
R B Y Y R B B Y R
T3 T1 T2 T2 T3 T1 T1 T2 T3
Example:
T3-R = 51 amps
T2-Y = 50 amps
T1-B = 50 amps
T1-B = 46 amps
T3-R = 48 amps
T2-Y = 49 amps
T2-Y = 53 amps
T1-B = 52 amps
T3-R = 51 amps
Total = 150 amps
Total = 150 amps
Total = 150 amps
÷ 3 = 50 amps
÷ 3 = 50 amps
÷ 3 = 50 amps
— 46 = 4 amps
— 48 = 2 amps
— 49 = 1 amps
4 ÷ 50 = .08 or 8%
2 ÷ 50 = .04 or 4%
1 ÷ 50 = .02 or 2%