1.3 Precautions for Using Inverters
1-9
BEFORE USE
Chap 1
[ 5 ] Molded case circuit breaker (MCCB) / residual-current-operated protective device
(RCD) / earth leakage circuit breaker (ELCB)
Install a recommended MCCB or RCD/ELCB (with overcurrent protection) in the primary circuit of the inverter to
protect the wiring. Since using an MCCB or RCD/ELCB with a lager capacity than recommended ones breaks the
protective coordination of the power supply system, be sure to select recommended ones. Also select ones with
short-circuit breaking capacity suitable for the power source impedance.
If no zero-phase current (earth leakage current) detective device such as a ground-fault relay is installed in the
upstream power supply line in order to avoid the entire power supply system's shutdown undesirable to factory
operation, install a residual-current-operated protective device (RCD)/earth leakage circuit breaker (ELCB)
individually to inverters to break the individual inverter power supply lines only.
Otherwise, a fire could occur.
[ 6 ] Magnetic contactor (MC) in the inverter input (primary) circuit
Avoid frequent ON/OFF operation of the magnetic contactor (MC) in the input circuit; otherwise, the inverter failure
may result. If frequent start/stop of the motor is required, use FWD/REV terminal signals or the / keys on
the inverter's keypad.
The frequency of the MC's ON/OFF should not be more than once per 30 minutes. To assure 10-year or longer
service life of the inverter, it should not be more than once per hour.
• From the system's safety point of view, it is recommended to employ such a sequence that shuts down
the magnetic contactor (MC) in the inverter input circuit with an alarm output signal ALM
inverter's programmable output terminals. The sequence m
inimizes the secondary damage even if the
When the sequence is employed, connecting the MC's primary power line to the inverter's auxiliary
control power input makes it possible to monitor the inverter's alarm status on the keypad.
The breakdown of a braking unit or misconnection of an external braking resistor may
cause damage
of the inverter's internal parts (e.g., charging resistor). To avoid such a breakdown linkage, introduce an
MC and configure a sequence that shuts down the MC i
f a DC link voltage establishment signal is not
issued within three seconds after the MC is switched on.
For the braking transistor built-in type of inverters, assign a transistor error output signal DBAL
inverter's programmable output terminals to switch off the MC in the inverter input circuit.
[ 7 ] Magnetic contactor (MC) in the inverter output (secondary) circuit
If a magnetic contactor (MC) is inserted in the inverter's output (secondary) circuit for switching the motor to a
commercial power or for any other purposes, it should be switched on and off when both the inverter and motor are
completely stopped. This prevents the contact point from getting damaged due to a switching arc of the MC. The
MC should not be equipped with any main circuit surge killer.
Applying a commercial power to the inverter's output circuit breaks the inverter. To avoid it, interlock the MC on the
motor's commercial power line with the one in the inverter output circuit so that they are not switched ON at the
same time.
[ 8 ] Surge absorber/surge killer
Do not install any surge absorber or surge killer in the inverter's output (secondary) lines.
To Next Page
Loading...
