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Since the voltage waveform output by a frequency converter is similar to a sine wave, but not a true sine wave at all. The waveform contains a large number of harmonic components. In particular, high - order harmonics will increase the output current of the frequency converter, causing the motor winding to heat up, generating vibration and noise, accelerating insulation aging, and may even damage the motor. At the same time, harmonics of various frequencies will emit radio interference of different degrees into space. Therefore, it may lead to the malfunction of other electromechanical equipment.

Therefore, when installing a frequency converter, it is necessary to comprehensively consider the distances among the central control room, the frequency converter, and the motor so as to minimize the influence of harmonics and improve the stability of control.

  I) Definition of Distance:

  1.Short Distance: The distance between the frequency converter and the motor is ≤20m;

  2.Medium Distance: The distance between the frequency converter and the motor is > 20m and ≤100m;

  3.Long Distance: The distance between the frequency converter and the motor is > 100m;

  (II) Situations in Industrial Use Sites:

  1.Short Distance: The frequency converter and the motor can be directly connected.

  2.Medium Distance: The frequency converter and the motor can be directly connected. However, it is necessary to adjust the carrier frequency of the frequency converter to reduce harmonics and interference.

  3.Long Distance: The frequency converter and the motor can be directly connected. Not only is it necessary to adjust the carrier frequency of the frequency converter to reduce harmonics and interference, but also an output AC reactor needs to be installed. [Frequency converter - Associated Equipment]

  (III) In a Highly - Automated Factory:

  In a highly - automated factory, all equipment needs to be monitored and controlled in the central control room. Therefore, the signals of the frequency - converter system also need to be transmitted to the central control room.

  1.Short Distance: If the frequency converter is installed in the central control room. The console and the frequency converter can be directly connected and controlled through 0 - 5/10V voltage signals and some switching signals. However, the electromagnetic radiation of the high frequency switching signal of the frequency converter will cause some interference to the weak current control signal. Therefore, it is not necessary to place the frequency converter in the central control room just for the sake of a neat appearance.

  2.Medium Distance: The frequency converter is a little farther from the central control room. 4 - 20mA current signal and some switching signals can be used for control connection; if the distance is farther, the RS485 serial communication method can be used for connection.

  3.Long Distance: The distance between the frequency converter and the central control room is more than 100m. At this time, a communication intermediate relay can be used to reach a distance of 1km; if it is even farther, a fiber - optic connector is needed, and the maximum distance that can be reached is 23km.

  Connected by communication cables, it can conveniently form a multi-stage drive control system, thus fulfilling requirements such as master/slave and synchronous control. Connecting with the currently popular fieldbus systems will greatly increase the data transmission rate. The extension of the distance between the central control room and the frequency converter cabinets is conducive to shortening the distance between the frequency converter and the motor, so that the system performance can be improved with a more reasonable layout.