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Noise and leakage currents
3.1.3 Power supply harmonics
The inverter may generate power supply harmonics from its converter circuit to affect the power generator, power
capacitor etc. Power supply harmonics are different from noise and leakage currents in source, frequency band and
transmission path. Take the following countermeasure suppression techniques.
zThe differences between harmonics and noises are indicated below:
z
Measures
Item Harmonics Noise
Frequency
Normally number 40 to 50 max.
(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
Depending on the current fluctuation ratio (larger as
switching is faster)
Affected equipment immunity Specified in standard per equipment
Different depending on maker's equipment
specifications
Suppression example Provide reactor. Increase distance.
The harmonic current generated from the inverter
to the input side differs according to various
conditions such as the wiring impedance, whether
a reactor is used or not, and 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
high frequency 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.
For power factor improvement, install a reactor on the inverter input side or in the DC circuit.
AC reactor
(FR-HAL)
DC reactor
(FR-HEL)
Do not insert power
factor improving capacitor.
MCCB MC
Inverter
Power supply
R
S
TZ
Y
X
U
V
W
P1
R/L1
S/L2
T/L3
P/+
IM
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