How long is the distance between inverter and motor allowed?

Since the voltage waveform output by the inverter is similar to a sine wave, it is by no means a real sine wave. The waveform contains a lot of harmonic components, especially the high-order harmonics will increase the output current of the inverter, cause the motor winding to heat up, generate vibration and noise, accelerate insulation aging, and may even damage the motor. At the same time, the harmonics of various frequencies will emit different degrees of radio interference into the space, therefore, it may cause the malfunction of other electromechanical equipment.

Therefore, when installing the inverter, it is necessary to comprehensively consider the distance between the central control room, the inverter, and the motor in order to minimize the influence of harmonics and improve the stability of the control.

1. The distance between industrial VFD and motor

• Close distance: the distance between the inverter and the motor is ≤20m;

• Middle distance: The distance between the inverter and the motor is >20m, and ≤100m;

• Long distance: The distance between the inverter and the motor is >100m.

2. VFD in industrial site

• Close distance: The inverter and the motor can be directly connected;

• Middle distance: The inverter and the motor can be directly connected, but the carrier frequency of the inverter needs to be adjusted to reduce harmonics and interference;

• Long distance: The inverter and the motor can be directly connected, not only need to adjust the carrier frequency of the inverter to reduce harmonics and interference, but also need to install an output AC reactor.

3. Frequency inverters in automated factories

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

• Close distance: that is, if the inverter is installed in the central control room. The console and the inverter can be directly connected and controlled by 0-5/10V voltage signal and some switching signals. However, the electromagnetic radiation of the high-frequency switching signal of the inverter will cause some interference to the weak current control signal, so it does not have to be beautiful and neat, and the inverter should be placed in the central control room;

• Mid-distance: that is, the distance between the inverter and the central control room is farther, and the 4-20mA current signal and some switches can be used for control connection; if the distance is longer, RS485 serial communication can be used to connect;

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

With communication cable connection, a multi-level drive control system can be easily formed, so as to realize the requirements of master/slave and synchronous control. Connecting with the current popular field bus system will greatly increase the data conversion rate. The extension of the distance between the central control room and the inverter cabinet is beneficial to shorten the distance between the inverter and the motor, so as to improve the system performance with a more reasonable layout.