Parasitic effects caused by static frequency converters, like electromagnetic interference (EMI), may endanger the reliable operation of electrical machines up to 500 MVA. They can cause shaft voltages up to 300 Vpp, if a non optimized converter design is chosen. Shaft voltages occur in converter fed drives due to different effects [7.1-7.9]. With the application of power electronic devices, new types of shaft voltage sources occur [7.1, 7.2, 7.8, 7.9]. In general shaft voltages due to power electronics are either capacitive or inductive.