The impact of the distance between VFD (Variable-frequency Drive) and motor on the system and preventive measures

In industrial use sites, the installation distance between the VFD (Variable-frequency Drive) and the motor can be roughly divided into three situations: long distance, medium distance and short distance. Within 20m is short distance, 20-100m is medium distance, and more than 100m is long distance.

Since the voltage waveform output by the VFD (Variable-frequency Drive) is not sinusoidal, the waveform contains a large number of harmonic components. High-order harmonics will increase the output current of the VFD (Variable-frequency Drive), causing the motor windings to heat up and produce vibrations. and noise, accelerate insulation aging, and may damage the motor; at the same time, harmonics of various frequencies will emit radio interference of different programs into space, and may also cause other equipment to malfunction. Therefore, it is hoped that the VFD (Variable-frequency Drive) will be placed near the controlled motor. However, due to space limitations at the production site, there is often a certain distance between the VFD (Variable-frequency Drive) and the motor. If the short distance between the VFD (Variable-frequency Drive) and the motor is within 20m, it can be directly connected to the VFD (Variable-frequency Drive); for the medium distance between the VFD (Variable-frequency Drive) and the motor, it is 20m to 100m. For connection, the carrier frequency of the VFD (Variable-frequency Drive) needs to be adjusted to reduce harmonics and interference; for long-distance connections of more than 100m between the VFD (Variable-frequency Drive) and the motor, not only the carrier frequency must be moderately reduced, but also An output AC reactor must be installed.

In a highly automated factory, all control equipment can be monitored in the central control room. The signal of the VFD (Variable-frequency Drive) system must also be sent to the central control room. If the position of the VFD (Variable-frequency Drive) is controlled in the center, the total The console and VFD (Variable-frequency Drive) 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 VFD (Variable-frequency Drive) will cause some interference to the weak current control signal, so it does not have to be beautiful and neat. The VFD (Variable-frequency Drive) is placed in the central control room. If the VFD (Variable-frequency Drive) is far away from the central control room, a 4-20mA current signal and some switching values can be used for control connection; if the distance is further, RS485 serial communication can be used to connect; if necessary To extend the distance, communication intermediate relays can be used to reach a distance of 1km; if optical fiber connectors are used, a distance of 23km can be achieved. Using communication cables to connect, a multi-drive control system can be easily formed to achieve master/slave and synchronous control requirements. Connecting with the current popular fieldbus system will greatly increase the data conversion rate. The extension of the distance between the central control room and the VFD (Variable-frequency Drive) cabinet is conducive to shortening the distance between the VFD (Variable-frequency Drive) and the motor, so as to improve system performance with a more reasonable layout.

In short, when installing a VFD (Variable-frequency Drive), it is necessary to comprehensively consider the distance between the central control room, the VFD (Variable-frequency Drive), and the motor to minimize the impact of harmonics and improve the stability of the control.