Mechanism behind high-frequency circulating bearing currents in view of motor structures

Frequency converter feeds can cause high-frequency current pulses through motor bearings. Consequently, the lifetime of bearings may decrease remarkably. A study of the effect of motor structures on these currents may offer a way out of the problem. The conditions under which circuit analysis can be applied in a model taking into account the electric and magnetic fields inside the motor are reviewed. This investigation is applied to the mechanism behind the circulating type bearing current. This leads to a comparison of a modified model with a previously utilised one. Results indicate that the present models are somewhat oversimplified.