Influence of system parameters in variable speed AC-induction motor drives on parasitic electric bearing currents

High frequency bearing currents are a parasitic phenomenon that affects inverter-fed induction machines, causing damage and wear to the mechanical bearings, which might lead to unexpected failures, increase of the machine downtime and reduction of its lifespan. This paper describes how the bearing currents are affected by changes in the components of the electrical circuit that feeds the induction machine. The referred system consists of: Two-level voltage source inverter, different passive filters (a) common-mode ring filter, b) common-mode ring filter with small phase-to-ground capacitances, c) differential mode filter, d) dual-mode filter and e) du/dt-filter), different motor supply cables (shielded vs. unshielded cables with lengths of 50 m, 150 m or 300 m) and the two different induction motors (rated power of 11 kW and 15 kW, respectively). So, in total sixty system arrangements were tested. The highest reduction of bearing currents was measured with the dual-mode filter in all cable configurations.