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1.4.2 Notes on inverters
Over-current protective function
The inverter has an over-current protective function. The current for this protection is adjusted
to the maximum current rating of the applicable motors by default. Therefore, when the
inverter is used to control a motor with a relatively small capacity, it is necessary to readjust the
over-current protection level and the electronic thermal protective function. In such a case,
follow the procedure specified in 5.13 to readjust them.
Inverter capacity
An inverter with a small capacity (kVA) must not be used for a motor with a relatively large
capacity even if the motor is operated under a small load. If an inverter is used this way, the
output peak current rises high because of a current ripple, thus causing the motor to trip easily.
Power factor improving capacitor
No power factor improving capacitor should be connected on the output side of the inverter.
When the inverter is used for a motor equipped with a capacitor for power factor improvement,
remove the capacitor from the motor. Connecting such a capacitor causes the inverter to break
down and the motor to trip, or breaks the capacitor itself.
Use of an inverter at a voltage other than the rated one
There is a need to connect it to a power unit supplying a voltage different from the rated
voltage, increase or reduce the supply voltage to the inverter's rated voltage, using a
transformer, etc.
Use of a set of inverters, which requires circuit-breaking devices
Circuit-breaking of defective inverter
When two or more inverters are connected to the same power line as shown above, it is
necessary to select a circuit-breaking characteristic ensuring that, for example, if a short circuit
occurs in INV 1, only MCCB2 trips but not MCCB1. If it is difficult to select a proper characteristic,
then insert a breaking fuse between MCCB2 and INV 1 in this case.
Note on the disposal of inverters
Be sure to dispose of inverters as industrial wastes, when they become unnecessary.
Remove the power factor improving
capacitor and the surge absorber, if any.
Power factor improving capacitor
U
V
W
Inverter
IM
Breaking fuse)