PWM Drive Related Bearing Film

The phenomenon of motor shaft voltages producing circulating shaft currents has been recognized since the 1920s. When a motor is operated by sinusoidal power, shaft voltages are caused by alternating flux linkages with the shaft. The linkages are associated with flux unbalance caused by: □ rotor static or dynamic eccentricity □ rotor and stator slotting □ axial cooling holes in the stator and/or rotor laminations □ shaft keyways □ rotor core support arms □ joints between segmental laminations □ directional properties of magnetic materials □ supply unbalance □ transient conditions [1].