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EMC and leakage currents
3.1.3 Power supply harmonics
The drive unit 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.
The differences between harmonics and RF noises are indicated below:
Suppression technique
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 maker's equipment specifications
Suppression example Provide reactor. Increase distance.
The harmonic current generated from the drive unit
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.
NOTE
The power factor improving capacitor and surge suppressor on the drive unit output side may be overheated or
damaged by the harmonic components of the drive unit output. Also, since an excessive current flows in the drive unit
to activate overcurrent protection, do not provide a capacitor and surge suppressor on the drive unit output side when
the motor is driven by the drive unit. For power factor improvement, install a reactor on the drive unit input side or in
the DC circuit.
AC reactor
(FR-HAL)
DC reactor
(FR-HEL)
Do not insert
power factor improving
capacitor.
MCCB MC
Drive
unit
Power
supply
R
S
TZ
Y
X
U
V
W
R/L1
S/L2
T/L3
P/+P1
M