The voltage waveform output by the frequency converter is only similar to a sine wave, but not a real sine wave. Its waveform contains a large number of harmonic components.
It is well known that higher harmonics will increase the output current of frequency converter, cause motor winding heating, 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 programs into space, which may cause misoperation of other electromechanical equipment.
Therefore, when installing the frequency converter, the distance between the central control room, the frequency converter and the motor should be considered comprehensively to minimize the impact of harmonics and improve the stability of control.
Definition of distance
1. Near distance: the distance between frequency converter and motor is ≤ 20m;
2. Medium distance: the distance between the frequency converter and the motor is>20m and ≤ 100m;
3. Remote distance: the distance between frequency converter and motor is more than 100m;
Situations at industrial use site
1. Near distance: the frequency converter and the motor can be directly connected;
2. Medium distance: the frequency converter and the motor can be directly connected, but the carrier frequency of the frequency converter needs to be adjusted to reduce harmonics and interference;
3. Remote distance: the frequency converter and the motor can be directly connected. It is not only necessary to adjust the carrier frequency of the frequency converter to reduce harmonics and interference, but also necessary to install an output AC reactor.
In a highly automated factory all equipment needs to be monitored and controlled in the central control room. Therefore, the signal of the converter system should also be sent to the central control room.
1. Close distance: that is, if the frequency converter is installed in the central control room. The console can be directly connected with the frequency converter and controlled by 0-5/10V voltage signal and some switching signals. However, the electromagnetic radiation of the high-frequency switch signal of the frequency converter will cause some interference to the weak current control signal, so it is not necessary to put the frequency converter in the central control room;
2. Medium distance: that is, the distance between the frequency converter and the central control room is a little farther, and 4-20mA current signal and some switching values can be used for control connection; If the distance is longer, RS485 serial communication can be used to connect;
3. Remote distance: that is, the distance between the frequency converter and the central control room is more than 100m. At this time, the communication intermediate relay can be used to reach a distance of 1 km; If it is further away, optical fiber connector shall be used, and the maximum distance can reach 23km.
The multi-level drive control system can be easily formed by using communication cable connection, so as to realize the requirements of master/slave and synchronous control. 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 converter cabinet is conducive to shortening the distance between the converter and the motor, so as to improve the system performance with a more reasonable layout.
Post time: Feb-20-2023