Prevention of harmful EDM currents in inverter-fed AC machines by use of electrostatic shields in the stator winding overhang

In this paper, an inexpensive mitigation technique is used for prevention of harmful EDM currents in small power inverter-fed AC machines. An electrostatic shield is mounted close to the stator winding overhang to eliminate the capacitive coupling between the stator end winding and the rotor surface. The bearing voltage that is caused by the common mode voltage at the motor terminals via the machine capacitances is reduced and the harmful EDM currents are eliminated. A 3D finite element method (FEM) is proposed for the calculation of the machine capacitances. The results are verified by analytical calculation, 2D FEM calculation and measurements.