(3) Anti-noise devices
To reduce the noise propagated through the electrical circuits and the noise radiated from the main circuit wiring to
the air, a line filter and power supply transformer should be used (refer to Figure A-10).
Line filters are classified into simple-type filters including capacitive filters to be connected in parallel to a power
line and inductive filters to be connected in series to a power line and authentic filters (LC filters) to address radio
noise restrictions. They are used selectively used to meet the target noise reduction effect. Power transformers
include generally used insulation transformers, shield transformers and noise-cut transformers, which have
different effects to block propagation of noise.
(a) Capacitive filter (b) Inductive filter
(zero-phase reactor)
(c) LC filter
Figure A-10 Various Filters and their Connection
(4) Noise prevention measures at the receiving side
It is important to strengthen the noise immunity of those electronic devices installed in the same control panel as
the inverter or located near an inverter. Line filters and shielded or twisted shielded wires are used to block the
penetration of noise in the signal lines of these devices. The following treatments are also implemented.
1) Lower the circuit impedance by connecting capacitors or resistors to the input and output terminals of the
signal circuit in parallel.
2) Increase the circuit impedance for noise by inserting choke coils in series in the signal circuit or passing
signal lines through ferrite core beads. It is also effective to widen the signal base lines (0 V line) or grounding
lines.
(5) Other
The level of generating/propagating noise will change with the carrier frequency of the inverter. The higher the
carrier frequency, the higher the noise level.
In an inverter whose carrier frequency can be changed, lowering the carrier frequency can reduce the generation
of electrical noise and result in a good balance with the audible noise of the motor under driving conditions.
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