The supplier of inverter equipment reminds you: because the output voltage waveform of frequency converter is similar to sine wave, it is not the real sine wave. Its waveform contains a large number of harmonic components, especially high-order harmonics, which will increase the output current of frequency converter, cause motor winding heating, generate vibration and noise, accelerate insulation aging, and even damage the motor; at the same time, harmonics of various frequencies will emit radio interference of different procedures to space, so it may lead to misoperation of other electromechanical equipment.

Therefore, when installing the frequency converter, the distance between the central control room, frequency converter and motor should be considered comprehensively, so as to minimize the influence of harmonic and improve the stability of control.

（1） Definition of distance:

1. Close distance: the distance between frequency converter and motor ≤ 20m;

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

3. Long distance: the distance between inverter and motor > 100m;

（2） Occasions of industrial use site:

1. Close distance: the inverter and motor can be directly connected;

2. Medium distance: the inverter and the motor can be directly connected, but the carrier frequency of the inverter needs to be adjusted to reduce harmonic and interference;

3. Long distance: the inverter and motor can be directly connected, not only need to adjust the frequency converter carrier frequency to reduce harmonic and interference, but also need to install output AC reactor.

（3） In highly automated factories:

In a highly automated factory, all equipment needs to be monitored and controlled in the central control room. Therefore, the signal of frequency converter system should also be sent to the central control room.

1. Close distance: if the frequency converter is installed in the central control room. The control panel and the frequency converter can be directly connected and controlled by 0-5 / 10V voltage signal and some switch signal. However, the electromagnetic radiation of high-frequency switch signal of frequency converter will produce some interference to weak current control signal, so it is not necessary to be beautiful and tidy. Put the frequency converter in the central control room.

2. Medium distance: the inverter is far away from the central control room, 4-20mA current signal and some switching values can be used for control connection; if the distance is longer, RS485 serial communication mode can be used to connect;

3. Long distance: the distance between frequency converter and central control room is greater than 100m. At this time, the communication intermediate relay can be used to achieve a distance of 1km; if it is further away, optical fiber connector is needed, and the maximum distance can reach 23km.

The multi-level drive control system can be easily constructed by using communication cable connection, so as to realize master / slave and synchronous control requirements. Connecting with the current popular fieldbus system will greatly improve the data conversion rate. The extension of the distance between the central control room and the inverter cabinet is conducive to shortening the distance between the inverter and the motor, so as to improve the system performance with a more reasonable layout.