2.3 Other wiring
INSTALLATION AND WIRING
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2.3 Other wiring
2.3.1 Power harmonics
Power harmonics may be generated from the converter section of the inverter, affecting power supply
equipment, power capacitors, etc. Power 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:
Item Harmonics RF Noise
Frequency
Normally 40th to 50th degrees or less, (up
to 3kHz or less)
High frequency (several 10kHz to MHz order)
Environment To wire paths, power impedance Across spaces, distance, laying paths
Quantitative understanding Logical computation is possible Occurs randomly, quantitative understanding is difficult.
Generated amount Approximately proportional to load capacity
According to current fluctuation rate (larger with faster
switching)
Immunity of affected device Specified in standards for each device. Differs according to maker’s device specifications.
Example of safeguard Install a reactor Increase the distance.
•
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.
NFB
IMInverter
Power factor
improving DC
reactor
Motor
Do not insert power factor
improving capacitor
Power factor
improving AC
reactor
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, when an overcurrent flows in the inverter,
the overcurrent protection is activated, Hence, when the motor is driven by the inverter, do not install
a capacitor or surge suppressor on the inverter’s output. To improve the power factor, insert a power
factor improving reactor in the inverter’s input or DC circuit.
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