Reduction of Inverter-Induced Shaft Voltages Using Electrostatic Shielding

The simple three-phase inverter topology that is most widely used in electrical machine drive systems produces a large, high-frequency common-mode voltage. Through capacitive coupling, a fraction of this common-mode voltage typically appears on the machine's shaft relative to ground. The shaft voltage can discharge through the bearings of the machine, causing damage and eventually resulting in premature bearing failure compared with equivalent line-fed machines. As a first step in the investigation of mitigation techniques for this problem, this paper evaluates the use of simple aluminium foil shielding applied to a standard 4-pole induction machine with a rated power of 11 kW for mitigation of bearing currents.