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Peripheral Devices
1
INSTALLATION AND WIRING
1.10.6 Power harmonics
The inverter may generate power harmonics from its converter circuit to affect the
power generator, power capacitor, etc. Power harmonics are different from noise and
leakage currents in source, frequency band and transmission path. Take the following
suppression techniques.
!
!!
!The following table indicates differences between harmonics and noise:
Item Harmonics Noise
Frequency
Normally 40th to 50th
degrees or less (up to 3kHz or
less)
High frequency (several 10kHz to 1GHz
order)
Environment
To-electric channel, power
impedance
To-space, distance, wiring path
Quantitative
understanding
Theoretical calculation
possible
Random occurrence, quantitative grasping
difficult
Generated
amount
Nearly proportional to load
capacity
Change with current variation ratio (larger as
switching speed increases)
Affected
equipment
immunity
Specified in standard per
equipment
Different depending on manufacturer's
equipment specifications
Suppression
example
Provide reactor Increase distance
!
!!
!Suppression technique
Harmonic currents produced on the
power supply side by the inverter
change with such conditions as
whether there are wiring impedances
and a power factor improving reactor
and the magnitudes of output
frequency and output current on the
load side.
For the output frequency and output
current, we understand that they
should be calculated in the conditions
under the rated load at the maximum
operating frequency.
CAUTION
The power factor improving capacitor and surge suppressor on the inverter
output side may be overheated or damaged by the harmonic components 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 in the inverter's primary
side or DC circuit. For more detailed information, refer to page 27.
NFB
IM
Inverter
Power factor
improving
DC reactor
Motor
Power factor
improving
AC reactor
Do not provide power
factor improving capacitor.