Motor bearing currents due to inverter PWM output voltage lead to a shorter lifetime of bearings. The cause is the common mode voltage of the inverters. How common mode inverter output filters can eliminate the bearing currents will be shown. Measurements show that using only a small common mode choke is not sufficient to eliminate the bearing currents, but an LC-Filter circuit. Also the other beneficial effects of common mode filters like leakage current reduction, conducted and radiated EMI reduction will be shown. RCD tripping and shielded motor cable can be avoided with such filters in many cases.
BLOCK Transformatoren-Elektronik GmbH namens Elincom electronics – Bernd Eilers