Grundfos CR 3 User Manual

33
English (US)
20. Worksheet for three-phase motors
Below is a worksheet for calculating current unbalance on a
three-phase hookup. Use the calculations below as a guide.
Current unbalance should not exceed 5 % at service
factor load or 10 % at rated input load. If the
unbalance cannot be corrected by rolling the 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. However, if the reading farthest from
the averages moves with the same motor lead, the
primary source of unbalance is on the "motor side" of
the starter. In this instance, consider if the cause can
be a damaged cable, an untight cable splice, a poor
connection, or a faulty motor winding.
Explanation and examples
Here is an example of current readings at maximum pump loads on each leg of a three-wire hookup. You
must make calculations for all three hookups. To begin, add up all three readings for hookup numbers 1, 2,
and 3.
Hookup 1
T1 = 51 amps
T2 = 46 amps
T3 = 53 amps
TOTAL = 150 amps
Divide the total by three to obtain the average.
Hookup 1
50 amps
3150 amps
Calculate the greatest current difference from the average.
Hookup 1
50 amps
-46amps
4amps
Divide this difference by the average to obtain the percentage of the unbalance.
In this case, the current unbalance for Hookup 1 is 8 %.
Hookup 1
.08 or 8 %
50 4.00 amps
Blank worksheet
Hookup 1 Hookup 2 Hookup 3
L
1
to T
1
=___ amps L
1
to T
3
= ___ amps L
1
to T
2
= ___ amps
L
2
to T
2
=___ amps L
2
to T
1
= ___ amps L
2
to T
3
= ___ amps
L
3
to T
3
=___ amps L
3
to T
2
= ___ amps L
3
to T
1
= ___ amps
TOTAL = ___ amps TOTAL = ___ amps TOTAL = ___ amps
Hookup 1 Hookup 2 Hookup 3
___ amps ___ amps ___ amps
3 ___ amps 3 ___ amps 3 ___ amps
Hookup 1 Hookup 2 Hookup 3
___ amps ___ amps ___ amps
___ amps ___ amps ___ amps
___ amps ___ amps ___ amps
Hookup 1 Hookup 2 Hookup 3
___ or ___ % ___ or ___ % ___ or ___ %
___ ___ amps ___ ___ amps ___ ___ amps

Grundfos CR 3 Specifications

General

Brand	Grundfos
Model	CR 3
Category	Water Pump
Language	English