Grundfos CR Series User Manual

29
English (US)
18. 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.
19. Disposal
This product or parts of it must be disposed of in an
environmentally sound way:
1. Use the public or private waste collection service.
2. If this is not possible, contact the nearest Grundfos company
or service workshop.
Subject to alterations.
Note
Note
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
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 Series Specifications

General

Type	Centrifugal pump
Material	Stainless steel
Motor range	0.37 kW to 22 kW
Applications	Water supply
Impeller Material	Stainless steel
Connections	Flanged
Speed	2900 rpm
Temperature range	-20°C to +120°C (depending on model and material)