Permissible Cable Length Between Frequency Converter and Motor
Because the voltage waveform output by the frequency converter is similar to a sine wave, but not a true sine wave, it contains a large number of harmonic components. High-order harmonics, in particular, can increase the output current of the frequency converter, causing motor winding heating, vibration and noise, accelerating insulation aging, and even potentially damaging the motor. At the same time, harmonics of various frequencies will emit varying degrees of radio interference into the surrounding space, which may lead to malfunctions in other electromechanical equipment.
Therefore, when installing a frequency converter, it is necessary to consider the distance between the central control room, the frequency converter, and the motor to minimize the impact of harmonics and improve control stability.
(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) Industrial Application Scenarios:
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, but the carrier frequency of the frequency converter needs to be adjusted to reduce harmonics and interference;
3. Long distance: The frequency converter and the motor can be directly connected, but in addition to adjusting the carrier frequency of the frequency converter to reduce harmonics and interference, an output AC reactor is also required.
(III) In Highly Automated Factories:
In highly automated factories, all equipment needs to be monitored and controlled from a central control room. Therefore, the signals of the frequency converter system also need to be sent to the central control room.
1. Short distance: If the frequency converter is installed in the central control room, the control console and the frequency converter can be directly connected, controlled by 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 signals. Therefore, it is not necessarily ideal to place the frequency converter in the central control room. 2. Intermediate distance: If the distance between the frequency converter and the central control room is relatively far, a 4-20mA current signal and some digital I/O signals can be used for control connection; if the distance is even greater, an RS485 serial communication method can be used for connection.
3. Long distance: If the distance between the frequency converter and the central control room is greater than 100m, a communication relay can be used to extend the distance to 1km; for even longer distances, fiber optic connectors are required, allowing for distances up to 23km.
Using communication cables allows for the convenient construction of multi-level drive control systems, thus achieving requirements such as master/slave and synchronous control. Connecting with currently popular fieldbus systems will greatly increase the data transfer rate. Extending the distance between the central control room and the frequency converter cabinet helps to shorten the distance between the frequency converter and the motor, allowing for a more reasonable layout and improved system performance.