Checking Of Motor And Cable - Grundfos BMP series Montage- Und Betriebsanleitung

18. Checking of motor and cable

1. Supply voltage
2. Current consumption
Points 3 and 4: Measurement not needed if supply voltage and current consumption are normal.
3. Winding resistance
4. Insulation resistance
19. Disposal
This product or parts of it must be disposed of in an environmen-
tally 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.
10
Measure the voltage between the phases by
means of a voltmeter.
Connect the voltmeter to the terminals at the
mains connection.
Measure the current of each phase while the
pump is operating at a constant discharge
pressure (if possible at the capacity where the
motor is most heavily loaded).
The motor full-load current appears on the
motor nameplate.
Disconnect the phase leads in the terminal
box.
Measure the winding resistance as shown on
the drawing.
Disconnect the phase leads in the terminal
box.
Measure the insulation resistance from each
phase to earth (frame).
(Make sure that the earth connection is made
carefully.)
The voltage should, when the motor is loaded, be
within ±5% of the rated voltage. The motor may burn if
there are larger variations in voltage.
If the voltage is constantly too high or too low, the
motor must be replaced by one corresponding to the
supply voltage.
Large variations in voltage indicate poor electricity sup-
ply, and the pump should be stopped until the defect
has been found.
Resetting of the motor starter may be necessary.
The difference between the current of the phase with
the highest amp consumption and the one with the low-
est amp consumption must not exceed 10% of the low-
est amp consumption.
If so, or if the current exceeds the full-load current,
check the following possible faults:
• Too high operating pressure which may overload the
motor.
• Too high speed which may overload the motor.
• Damaged pump which may overload the motor.
• The motor windings are short-circuited or partly dis-
jointed.
• Too high or too low supply voltage.
• Poor connection in leads. Weak cables.
The highest value must not exceed the lowest value by
more than 5%.
If the deviation is higher, and the supply cable is OK,
the motor should be overhauled.
The insulation resistance for a new, cleaned or
repaired motor must be approx. 10 MΩ measured to
earth.
For a given motor the critical insulation resistance
(R ) can be calculated as follows:
crit
R = U [kV] x 0.5 [MΩ/kV].
crit N
If the measured insulation resistance is lower than
R , the motor must be overhauled.
crit
Subject to alterations.