In the field of application, the installation distance between the frequency converter and the motor can be divided into three categories: long distance, medium distance, and short distance. A distance of over 100m is considered long distance, 20-100m is medium distance, and less than 20m is short distance.
Longer cables can significantly impact motor performance due to their distributed capacitance and voltage drop. It is recommended to add a reactor on the output side. However, even with a reactor and a reduced-capacity inverter to match the motor, the problem may not be solved if the cable length exceeds 100 meters.
The distance between the frequency converter and the motor should generally not exceed 100 meters. If the line is long, the cable diameter can be increased. The carrier frequency of the frequency converter should be set to the minimum (in order to reduce the impact of capacitive leakage current).
Because the output voltage of the frequency converter is a high-voltage pulse series, its frequency is equal to the carrier frequency, and its peak value is equal to the DC circuit voltage (513V), when the connecting line between the frequency converter and the motor is long, the distributed inductance and capacitance between the wires become significant. When the distance between the motor and the frequency converter is large, the distributed capacitance between the wires and the leakage inductance of the motor may approach the resonance point, leading to an excessively high input voltage for the motor. This can easily damage the motor or cause vibration during operation.
Because different frequency converters use different internal processing methods (such as the dead time setting when the upper and lower transistors are alternately conducting), the specified distances also vary. Please refer to the frequency converter's instruction manual for details.
Industrial application scenarios:
Short distance: The frequency converter and the motor can be directly connected.
Medium distance: The inverter and the motor can be directly connected; however, 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 is it necessary to adjust the carrier frequency of the inverter to reduce harmonics and interference, but it is also necessary to install an output AC reactor.
In highly automated factories:
In highly automated factories, all equipment needs to be monitored and controlled in a central control room. Therefore, the signals from the frequency converter system also need to be sent to the central control room.
Close proximity: This refers to the inverter being installed in the central control room. The control panel and the inverter can be directly connected, controlled via 0-5/10V voltage signals and some switching signals. However, the electromagnetic radiation from the inverter's high-frequency switching signals can interfere with low-voltage control signals, so placing the inverter in the central control room is not necessarily aesthetically pleasing.
Medium distance: This refers to a distance between the frequency converter and the central control room. A 4-20mA current signal and some switching signals can be used for control connections. If the distance is even greater, RS485 serial communication can be used for connection.
Long distance: This refers to a distance greater than 100m between the frequency converter and the central control room. In this case, a communication intermediate relay can be used to achieve a distance of 1km; if the distance is even greater, fiber optic connectors are required, with a maximum range of 23km.
Using communication cables for connection, multi-level drive control systems can be easily constructed to meet requirements such as master/slave and synchronous control. Connecting to currently popular fieldbus systems will significantly improve data conversion rates. Extending the distance between the central control room and the inverter cabinet helps to shorten the distance between the inverter and the motor, allowing for a more rational layout to improve system performance.
