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2.3 Other Wiring; Power Supply Harmonics; Inverter-generated Noises And Their Reduction Techniques - Mitsubishi Electric FR-A500 Instruction Manual

Transistorized inverter.
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2.3 Other wiring


Power supply harmonics

Power supply harmonics may be generated from the converter section of the inverter, affecting power supply
equipment, power capacitors, etc. Power supply harmonics are different in generation source, frequency and
transmission path from radio frequency (RF) noise and leakage currents. Take the following measures.
The differences between harmonics and RF noise are indicated below:
Quantitative understanding
Generated amount
Immunity of affected device
Example of safeguard
The harmonic current generated from the inverter to the
power supply differs according to various conditions such as
the wiring impedance, whether a power factor improving
reactor is used or not, and output frequency and output
current on the load side.
For the output frequency and output current, the adequate
method is to obtain them under rated load at the maximum
operating frequency.
Note: A power factor improving capacitor or surge suppressor on the inverter's output may overheat or
be damaged due to the harmonics of the inverter output. Also, since an excessive current flows in
the inverter to activate overcurrent protection, do not provide a capacitor and surge suppressor on
the inverter output side when the motor is driven by the inverter. To improve the power factor,
insert a power factor improving reactor on the inverter's primary side or in the DC circuit.
For details, refer to the FR-A500/E500 series technical information.

Inverter-generated noises and their reduction techniques

Some noises enter the inverter to malfunction it and others are radiated by the inverter to malfunction
peripheral devices. Though the inverter is designed to be insusceptible to noise, it handles low-level signals,
so it requires the following basic measures to be taken. Also, since the inverters chops outputs at high carrier
frequency, that could generate noise. If these noises cause peripheral devices to malfunction, measures
should be taken to suppress the noise. These techniques differ slightly depending on noise propagation
1) Basic techniques
Do not run the power cables (I/O cables) and signal cables of the inverter in parallel with each other and
do not bundle them.
Use twisted pair shielded cables for the detector connection and control signal cables, and connect the
sheathes of the shielded cables to terminal SD.
Earth (Ground) the inverter, motor, etc. at one point.
Normally 40th to 50th degrees or less, (up
to 3kHz or less)
To wire paths, power impedance
Logical computation is possible
Approximately proportional to load capacity
Specified in standards for each device.
Install a reactor
High frequency (several 10kHz to 1GHz order)
Across spaces, distance, laying paths
Occurs randomly, quantitative understanding is difficult.
According to current fluctuation rate (larger with faster
Differs according to maker's device specifications.
Increase the distance.
Power factor
improving AC
RF Noise
Power factor
improving DC
Do not insert power factor
improving capacitor


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