Bearing current prevention of converter-fed AC machines with a conductive shielding in stator slots

The paper analyses a shielding method against circulating-type bearing currents in converter-fed AC machines. These currents are induced by the high-frequency flux components that are generated by the common-mode current penetrating the stator core. A conductive shield is placed in the stator slots between the winding and the core, providing a low-impedance path for high-frequency common-mode currents. The shielding effectiveness is analysed using a circuit model, and the fundamental-frequency losses in the shield are analysed by a two-dimensional finite element method and an analytical formulation. The analysis shows that the current penetrating the stator core is attenuated very effectively. The losses in the shield can be reduced to an acceptable level by proper shield thickness selection or by splitting the shield into axial strips.