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2.5 Cautions Relating to Harmonic Component, Noise, and Leakage Current
(1) Harmonic component
Input current to an inverter includes a harmonic component, which may affect other loads and power factor
correcting capacitors that are connected to the same power source as the inverter. If the harmonic component
causes any problems, connect a DC reactor (option) to the inverter. It may also be necessary to connect an AC
reactor to the power factor correcting 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.
- Install the inverter onto 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 or ground.
- Connect a surge absorber in parallel with a coil or solenoid of the magnetic contactor.
(3) Leakage current
Harmonic component current generated by insulated gate bipolar transistors (IGBTs) switching on/off inside the
inverter becomes leakage current through stray capacitors of inverter input and output wires or a motor. If any of
the problems listed below occur, take an appropriate measure against them.
Table 2.12 Leakage Current Countermeasures
Problem Measures
An earth leakage circuit
breaker* (a ground fault circuit
interrupter) that is connected
to the input (primary) 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 (a ground fault circuit interrupter) that
has a longer sensitive current than one currently being used.
4) Use an earth leakage circuit breaker (a ground fault circuit interrupter) that
features measures against harmonic 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 relay built in the inverter, instead of an external
thermal relay.
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