Fuji Electric FRENIC-HVAC User Manual page 731

(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 available in these types--the simplified type such as a capacitive filter to
be connected in parallel to the power supply line and an inductive filter to be connected
in series to the power supply line and the orthodox type such as an LC filter to meet
radio noise regulations. Use them according to the targeted effect for reducing noise.
Power supply transformers include common insulated transformers, shielded
transformers, and noise-cutting transformers. These transformers have different
effectiveness in blocking noise propagation.
Capacitive filter
(a)
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.
Inductive filter
(b)
(zero-phase reactor)
A-8
LC filter
(c)