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8. Electrical installation
Warning
Make sure that the power supply cannot be
accidentally switched on during the electrical
installation.
8.1 General information
Operating voltage and operating frequency are stated on the
motor nameplate. Check that the motor is suitable for the power
supply available at the installation site.
The voltage quality for MG motors, measured at the motor
terminals, must be ± 10 % of the rated voltage during continuous
operation (including variation in the supply voltage and losses in
cables).
Warning
The motor must be connected to an external mains
switch.
8.1.1 Motor protection
Single-phase motors
Single-phase motors are supplied with built-in thermal protection,
according to IEC 60034-11, against thermal overload with both
rapid and slow variation.
Three-phase motors
Three-phase motors must be protected by a motor-protective
circuit breaker according to local regulations.
MG motors as from 3.0 kW are supplied with thermal switches
(PTC) as standard and protected against thermal overload with
both rapid and slow variation. The motor protection is stated on
the nameplate.
Warning
Whenever motors incorporating a thermal switch or
thermistors are to be repaired, make sure that the
motor cannot start automatically after cooling.
8.2 Electrical connection
The electrical installation should be carried out by authorised
personnel in accordance with local regulations.
The wiring diagram is located in the terminal box cover.
Warning
Before removing the terminal box cover and before
any dismantling of the motor, switch off the power
supply.
The terminal box of single-speed motors normally contains six
winding terminals and at least one earth terminal.
Warning
The motor must be earthed.
Do not connect the motor to the voltage supply until
the connection to earth has been carried out in
accordance with local regulations.
8.2.1 Single-phase motor
Connect single-phase motors to the mains in accordance with the
instructions located in the terminal box cover.
8.2.2 Three-phase motor
Three-phase motors can be connected in star (Y) or delta (D)
according to IEC 60034-8. See the wiring diagram in the terminal
box cover.
Voltage and connection are stated on the nameplate.
Example: 380-415 D/660-690 Y
•
If the voltage supply is 380-415 V, the motor must be
connected in delta.
•
If the voltage supply is 660-690 V, the motor must be
connected in star.
9. Start-up
9.1 Measuring the insulation resistance
Measure the insulation resistance before start-up and in case of
any risk of moisture in the windings.
Warning
When measuring the insulation resistance, carefully
follow the safety regulations of EN 50110-1
(operation of power plants) and the instruction
manual for measuring and test equipment.
Calculate the minimum permissible insulation resistance, R, by
multiplying the rated voltage (in kV) of the motor with the constant
0.5 megohm/kV.
Stop using the motor immediately if the insulation resistance falls
below this value.
Example
If the rated voltage is 690 V, the measured resistance must be
higher than 0.69 kV x 0.5 megohm/kV = 0.35 megohm.
Measure the minimum permissible insulation resistance at a
winding temperature of 25 °C (± 15 °C).
Procedure:
•
Connect the megaohmmeter between phase and earth at a
measuring voltage of 500 V DC.
•
Read the value on the megaohmmeter.
Warning
During and immediately after the measurement,
there will be a risk of electric shock. Do not touch the
terminals until the windings are de-energised.
If the minimum insulation resistance is not attained, the windings
are too moist and must be oven-dried.
The oven temperature must be 90 °C for 12-16 hours and then
105 °C for 6-8 hours.
Remove any drain plugs before heating.
Note
9.2 Direction of rotation
The direction of rotation is clockwise, seen from the motor drive
end when the mains conductors are connected in accordance
with the diagram located in the terminal box cover. The direction
of rotation can be changed by switching two random mains
conductors.
Some MG motors have a properly directed fan. The
Caution
direction of rotation must be as stated on the motor.
10. Operation
Warning
During operation, the motor surface may be so hot
that it may cause personal injury.
10.1 Max. number of starts per hour
See page 10.
7
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