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4)

Harmonic suppression techniques

In the PWM type inverter, a surge voltage attributable to wiring constants is generated at the motor terminals. 
Especially for a 400V class motor, the surge voltage may deteriorate the insulation. When the 400V class motor is 
driven by the inverter, consider the following measures:
z

It is recommended to take either of the following measures.

(1) Rectifying the motor insulation

For the 400V class motor, use an insulation-enhanced motor. Specifically,
1) Specify the "400V class inverter-driven, insulation-enhanced motor".
2) For the dedicated motor such as the constant-torque motor or low-vibration motor, use the "inverter-driven, 

dedicated motor".

1

Reactor installation
(ACL, DCL)

Install a reactor (ACL) on the AC side of the inverter or a reactor (DCL) on its DC side or 
both to suppress outgoing harmonic currents.

2

High power factor 
converter
(FR-HC)

The converter circuit is switched on-off to convert an input current waveform into a sine 
wave, suppressing harmonic currents substantially. The high power factor converter (FR-
HC) is used with the standard accessory.

3

Installation of power 
factor improving capacitor

When used with a series reactor, the power factor improving capacitor has an effect of 
absorbing harmonic currents.

4

Transformer multi-phase 
operation

Use two transformers with a phase angle difference of 30° as in  -delta, delta-delta 
combination to provide an effect corresponding to 12 pulses, reducing low-degree 
harmonic currents.

5

Passive filter
(AC filter)

A capacitor and a reactor are used together to reduce impedance at specific frequencies, 
producing a great effect of absorbing harmonic currents.

6

Active  filter

This filter detects the current of a circuit generating a harmonic current and generates a 
harmonic current equivalent to a difference between that current and a fundamental wave 
current to suppress a harmonic current at a detection point, providing a great effect of 
absorbing harmonic currents.

addition to the above countermeasures to operate the inverter.  (Refer to page 112 for Pr. 240 "Soft-
PWM selection".)