2-20
2.3.8 Cautions relating to harmonic component, noise, and leakage current
(1) Harmonic component
Input current to an inverter includes a harmonic component that may affect other motors and
phase-advancing capacitors on the same power supply line. If the harmonic component causes any
problems, connect a DC reactor (option) to the inverter. In some cases, it is necessary to insert a
reactor in series with the phase-advancing capacitors.
(2) Noise
If noise generated from the inverter affects other devices, or that generated from peripheral
equipment causes the inverter to malfunction, follow the basic measures outlined below.
1) If noise generated from the inverter affects the other devices through power wires or grounding
wires:
- Isolate the grounded metal frames of the inverter from those of the other devices.
- Connect a noise filter to the inverter power wires.
- Isolate the power system of the other devises from that of the inverter with an insulated
transformer.
2) If induction or radio noise generated from the inverter affects other devices through power wires
or grounding wires:
- Isolate the main circuit wires from the control circuit wires and other device wires.
- Put the main circuit wires through a metal conduit and connect the pipe to the ground near the
inverter.
- Mount the inverter on the metal switchboard and connect the whole board to the ground.
- Connect a noise filter to the inverter power wires.
3) When implementing measures against noise generated from peripheral equipment:
- For the control signal wires, use twisted or shielded-twisted wires. When using
shielded-twisted wires, connect the shield of the shielded wires to the common terminals of
the control circuit.
- Connect a surge absorber in parallel with a coil or solenoid of the magnetic contactor.
(3) Leakage current
A high frequency current component generated by insulated gate bipolar transistors (IGBTs)
switching on/off inside the inverter becomes leakage current through stray capacitance of inverter
input and output wires or a motor. If any of the problems listed below occurs, take appropriate
measures against them.
Table 2.10 Leakage Current Countermeasures
Problem Measures
An earth leakage circuit
breaker* that is connected
to the input (primary) side
has tripped.
*With overcurrent protection
1) Decrease the carrier frequency.
2) Make the wires between the inverter and motor shorter.
3) Use an earth leakage circuit breaker (ELCB) with lower
sensitivity than the one currently used.
4) Use an earth leakage circuit breaker that features measures
against the high frequency current component (Fuji SG and
EG series).
An external thermal relay
was activated.
1) Decrease the carrier frequency.
2) Increase the settling current of the thermal relay.
3) Use the electronic thermal overload protection built in the
inverter.
