1.3 Precautions for Using Inverters
1-10
[ 4 ] PWM converter for correcting the inverter input power factor
Using a PWM converter (High power-factor, regenerative PWM converter, RHC series) corrects the inverter power
factor up to nearly “1.”
When combining an inverter with a PWM converter, disable the main power down detection by setting the function
code H72 (main power detection) to “0” (default). If the main power down detection is enabled (H72 = 1, factory
default), the inverter interprets the main power as being shut down, ignoring an entry of a run command.
[ 5 ] Molded case circuit breakers (MCCB)/earth leakage circuit breakers (ELCB)
Install a recommended MCCB or ELCB (with overcurrent protection) in the primary circuit of the inverter to protect
the wiring. Since using an MCCB 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.
Failure to observe this could result in fire.
[ 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 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 issued on
inverter's programmable output terminals. This sequence minimizes the secondary damage even if the
inverter breaks. When this sequence is employed, connecting the MC's primary power line to the
inverter's control power auxiliary 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 if 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 on 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 (secondary) circuit breaks the inverter. To avoid this, employ
an interlock to ensure that the magnetic contactor at the commercial power supply side does not turn ON at the
same time as the magnetic contactor at the inverter output side.
[ 8 ] Surge absorber/surge killer
Do not install any surge absorber or surge killer in the inverter's output (secondary) lines.
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