6.3 EMC Precautions in Wiring
EMC stands for Electromagnetic Compatibility, which refers to the ability of a device or system to work
normally in its electromagnetic environment without constituting anything in the environment that cannot
withstand electromagnetic disturbance. The two properties that judge it good or bad are:
1. The level of electromagnetic noise generated when the equipment is working;
2. The ability level of operating equipment to resist electromagnetic noise from the surroundings.
The working principle of the frequency converter determines that it will generate a certain amount of
electromagnetic interference noise, which will affect the equipment and nearby instruments and meters. At the
same time, in order to ensure that the frequency converter can work reliably in a certain electromagnetic
environment, it must have A certain ability to resist electromagnetic interference. Correctly installing the inverter
can reduce the electromagnetic noise of the equipment and improve the anti-interference ability of the
equipment itself. In order to ensure the long-term normal operation of the power system, please refer to the
following introduction to install the inverter.
6.3.1 On-site wiring
Power wiring: In different control systems, the power supply line is independently powered from the power
transformer, generally using 4-core lines (3 of which are the main circuit power line, and 1 is the ground line).
The ground line is at the near end of the inverter Ground, and the other side is connected to the motor casing.
Equipment classification: Generally, there are different electrical equipment in the same control cabinet,
such as inverters, filters, PLCs, testing instruments, etc., which are divided into strong noise equipment and noise
sensitive equipment according to the ability to emit electromagnetic noise and withstand noise. Install similar
equipment in the same area,
Keep a distance of more than 20cm between different types of equipment, and it is best to separate
different areas with metal shells or ground partitions in the cabinet.
Wiring in the control cabinet: There are generally main circuit power lines (strong current) and signal lines
(weak current) in the control cabinet. The signal lines are easily interfered by the main circuit power line and
cause equipment malfunction. When wiring, the signal line and the main circuit power line should be distributed
in different areas. The cables in different areas should not be placed in the same cable tray. The two cannot be
tied together. If the signal cable must cross the power line, the angle between the two should be kept at 90
degrees. The incoming and outgoing wires of the main circuit power lines cannot be staggered or bundled
together.
6.3.2 Noise suppression and grounding
The frequency converter must be grounded safely and reliably when it is working. Grounding is not only
for equipment and personal safety, but also the simplest, most effective, and lowest-cost method to solve EMC
problems. It should be given priority.
All inverter control terminal connection wires use shielded wires, and the shielded wires connect the
shielding layer to the nearest ground at the entrance of the inverter, and the grounding uses cable clips to form
a 360-degree ring connection.
It is strictly forbidden to twist the shielding layer into a pigtail and then connect it to the inverter ground,
which will greatly reduce or even lose the shielding effect. The connecting wire (motor wire) between the inverter
and the motor adopts a shielded wire or an independent wiring trough, and the shielding layer of the motor
wire or the metal of the wiring trough
One end of the casing is connected to the ground of the frequency converter, and the other end is
connected to the motor casing.
The ground wire should be as short and thick as possible to minimize ground impedance.
Arrange the grounding cable away from the input and output wiring of noise-sensitive equipment.
6.3.3 Leakage current suppression
Leakage current includes leakage current between lines and leakage current to ground. Its size depends on
the distributed capacitance of the system wiring and the carrier frequency of the inverter. Reducing the carrier
frequency and selecting the shortest motor cable can effectively reduce the leakage current; when the motor
cable is long (more than 100m), an AC reactor or a sine wave filter should be installed on the output side of the
inverter; when the motor cable is longer , a reactor should be installed at intervals. The two classifications of
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NVF2G-S Series Inverter User's Guide
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