Idiomas disponibles
Idiomas disponibles
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 cal-
culate 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
possible 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.
Starter Terminals L1
Motor Leads
R
T3
Example:
T3-R = 51 amps
T1-B = 46 amps
T2-W = 53 amps
Total = 150 amps
4 ÷ 50 = .08 or 8%
INSULATION RESISTANCE READINGS
Normal Ohm and Megohm Values between all leads and ground
Condition of Motor and Leads
A new motor (without drop cable).
A used motor which can be reinstalled in well.
Motor in well. Readings are for drop cable plus motor.
New motor.
Motor in good condition.
Insulation damage, locate and repair.
Insulation resistance varies very little with rating. Motors of all HP, voltage and phase ratings have similar values of
insulation resistance.
Insulation resistance values above are based on readings taken with a megohmmeter with a 500V DC output.
Readings may vary using a lower voltage ohmmeter, consult factory if readings are in question.
Hookup 1
L2
L3
B
W
T1
T2
÷ 3 = 50 amps
– 46 = 4 amps
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 (fur-
thest 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 pow-
er lead, most of the unbalance is coming from the power
source.
Contact your local power company to resolve the imbalance.
Hookup 2
L1
L2
L3
W
R
B
T2
T3
T1
T2-W = 50 amps
T3-R = 48 amps
T1-B = 52 amps
Total = 150 amps
÷ 3 = 50 amps
– 48 = 2 amps
2 ÷ 50 = .04 or 4%
Ohm Value
20,000,000 (or more)
10,000,000 (or more)
2,000,000 (or more)
500,000 - 2,000,000
Less than 500,000
Hookup 3
L1
L2
L3
B
W
R
T1
T2
T3
T1-B = 50 amps
T2-W = 49 amps
T3-R = 51 amps
Total = 150 amps
÷ 3 = 50 amps
– 49 = 1 amps
1 ÷ 50 = .02 or 2%
Megohm Value
20 (or more)
10 (or more)
2 (or more)
.5 - 2
Less than .5
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