2 Design
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High-function General-purpose Inverter 3G3RX-V1 User’s Manual (I578-E1)
Measures against radio noise
Besides the I/O wires, radio noise is radiated from the inverter itself. This radio noise can be reduced
by installing noise filters on both the input and output sides of the inverter and by installing and
shielding the inverter body in a grounded iron enclosure etc.
Keep the cables between the inverter and the motor as short as possible.
Cable length between inverter and motor
If the length of the cables between the inverter and the motor is long, consider how to address the
following problems.
• Voltage drop in output cables
As the cable length between the inverter and the motor increases, the resistance in the cables
becomes higher and accordingly the amount of voltage drop in the inverter output voltage
becomes larger. This causes a decrease in the voltage that is to the motor, which results in a low
output torque.
If the cables is long, take measures to reduce the resistance, for example, by selecting cables
whose wire diameter is larger than specified.
• Surge in long cables
If the cable length exceeds 20 m, a surge voltage (approximately 1200 V maximum for 400-V
class) may be generated at the motor terminal depending on the stray capacitance or inductance
of the cable, which may result in motor burnout.
In particular, when using a 400-V class inverter with a cable length of over 20 m, it is
recommended to use a dedicated inverter motor. Dedicated inverter motors are designed to
support the above surge voltage level.
• Leakage current from output cables
As the cable length between the inverter and the motor increases, stray capacitance increases
between the inverter output and the ground. The increase in the stray capacitance on the output
side of the inverter causes an increase of the high-frequency leakage current.
This high-frequency leakage current may negatively affect on the current detector in the inverter
output section or peripheral equipment. It is recommended to keep the wiring distance between
the inverter and the motor at 100 m or shorter.
If your system configuration requires the wiring distance of over 100 m, take measures to
decrease the stray capacitance. The applicable measures are such as not wiring in a metal duct
and using a separate cable for each phase.
In addition, set a carrier frequency appropriate for the wiring distance between the inverter and the
motor according to the table below.
Wiring distance between inverter and motor 50 m max. 100 m max. Over 100 m
Carrier frequency 10 kHz max. 5 kHz max. 2.5 kHz
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