Selection of main circuit cable of inverter

(1) The cable must be capable of handling the rated current of the frequency converter.

(2) During continuous operation of the inverter, the cable should endure temperatures up to 70°C.

(3) The cable’s rated durability must be at least 1kV.

(4) For motors with a power rating exceeding 30 kW, it's advisable to use the symmetrical shielded cable depicted in the image. For motors below 30 kW, a standard four-core power cable is sufficient. Please refer to the diagram below for the cable structure:

Figure: Symmetrically shielded cable structure

When choosing the main circuit wires, take into account the current-carrying capacity, overcurrent protection, voltage drop across the line, and the impact of temperature rise on capacity. If the specifications aren't explicitly provided, it's best to increase the wire gauge slightly based on the standard selection method for similar-capacity conventional motors.

When the distance between the inverter and the motor is extensive, the voltage drop along the line increases as well. This issue becomes particularly noticeable at lower output frequencies of the inverter, where the motor may experience insufficient torque due to the reduced voltage. Thus, the maximum recommended distance between the inverter and the motor should not exceed 50 meters. If this limit is exceeded, increasing the wire diameter and adding a line filter becomes necessary to ensure proper performance.

Moreover, it’s essential to note that the shielding function of the cable plays a critical role in reducing electromagnetic interference. Properly grounded shielding ensures that the inverter operates smoothly without interference from external electromagnetic fields. Additionally, regular checks of the cable’s insulation and connections are crucial to prevent potential failures or overheating issues.

In summary, selecting the appropriate cables for connecting an inverter to a motor requires careful consideration of multiple factors, including current capacity, temperature tolerance, voltage drop, and shielding effectiveness. By adhering to these guidelines, you can ensure reliable and efficient operation of your system.