What motor cable to use in combination with frequency inverters
Frequency inverters cause electromagnetic interference (EMI) or so-called electromagnetic noise. This is typical for frequency inverters and is caused by the built-in IGBTs (electronic switches) that switch the relatively high voltage (500 to 1000 VDC) on and off at a very high speed. The advantage of this switching technique is that it results in a very nice motor signal, which benefits the life of the motor. To prevent these EMI interference signals from interfering with the proper operation of other devices, extra attention must be paid to the cable between the electric motor and the frequency inverter.
One of the measures that can be taken to counter electromagnetic radiation is the use of the correct type of shielded motor cable between frequency converter and motor. The cable shield allows the EMI generated by the frequency converter to flow along the cable sheath through the motor chassis and back to the frequency converter where it is reduced to an acceptable level in a purpose-built circuit. Otherwise it can be fed back to the grid and cause noise on your electrical installation. It is therefore important, if possible, to use a cable with sufficient shielding and to correctly connect the cable at both ends to the PE earth terminals. Both on the motor side and on the frequency converter side. This is the only way to absorb as much EMI as possible. Special EMC cable glands are available from the electrical wholesaler with which the cable can be correctly assembled. They enclose the cable shield. Due to their capacitive properties, shielded cables must be kept shorter than unshielded cables. If longer cable lengths are required in combination with unshielded cables, take other measures against electromagnetic noise. Tables with cable length and diameter can be found in the installation manual of the frequency converters on our website.
All frequency inverters offered by Sentera are equipped with an EMC filter as standard. This EMC filter reduces the electromagnetic noise between drive and the power grid. EMC filters do have the property of causing leakage current. In exceptional cases, they can activate the RCD or leakage current circuit breaker in your electrical circuit. If that is the case, it is best to disconnect the EMC filter. With the IP20 models, this can be done by loosening the EMC screw on the left side of the device (it does not have to be removed). On the IP66 models, the EMC screw is located next to the terminal block for the motor connection. In addition, it is also recommended to connect the Incoming Ground (PE) terminal of the frequency converter directly to the building ground circuit. So looping from one frequency converter to the next is strongly discouraged. Fact: With our frequency converters, the switching speed of the IGBTs can be set between 4 and 32 kHz. The IGBTs therefore switch up to 32.000 times per second. By default they are set to 8 kHz.