VLT ® 2000 Series I Radio interference in general (emission) Use of screened motor cable increases the leakage current. This is because screened cables have higher capacitance to earth than unscreened cables. If the leakage current is not filtered, it will cause greater interference on the mains in the radio leakage range under approx. 5 MHz. Since the leakage current is carried back to units through the screen, in principle this will give only a small electromagnetic field from the screened motor cable. The screen reduces the radiated interference, but increases the low frequency interference on the mains.
Special conditions Electrical interference from the cable network, cable- borne interference, 150 kHz-30 MHz, and airborne interference from the drive system, 30 MHz-1 GHz, is produced in particular by the inverter, the motor cable and the motor system for frequencies under approx. 50 MHz. As the sketch below shows, capacitive currents in the motor cable together with high du/dt from the motor voltage will produce interference. With regard to installation, it is generally less complicated to use unscreened cables than screened cables.
For VLT 2000 an RFI and motor filter as well as a LC and RFI filter have been developed making it possible to observe the EMC emission requirements when unscreened motor cables are used. The motor filter reduces the leak current I 1 (see figure below). VLT 2000 frequency converters with built-in RFI filter and without motor coils fulfil the EMC emission requirements. In order to reduce the interference level from the sy- stem overall (unit + installation) as far as possible, it is important to make motor and brake cables as short as possible. Cables with a sensitive signal level may not be led together with motor and brake cables.
Radio interference higher than 50 MHz (airborne) will particularly affect the control electronics. Section 1 Section 2 Section 3 MG.20.B6.02 – VLT is a registered Danfoss trademark 89