Effect of Load on Impedance Characteristics of High Frequency Circulating Bearing Current Path in Stator Laminations for an Inverter Fed AC Machine

High frequency switching in an inverter fed AC electrical machine can cause high frequency circulating bearing currents which flow through a zigzag path in the stator laminations due to skin effects. This paper presents both analytical calculation and finite element analysis of the zigzag impedance. The finite element methods with frozen permeability technique can account for the load effect which is usually neglected in literature. It is shown that the zigzag impedance is lower at full load than that at light load and varies with the rotor position angle. The impedance results can be used for further prediction of circulating bearing currents.