In double bearing machines, why should the antifriction bearing be electrically insulated?
In double bearing machines, a potential difference between the rotor shaft and frame – caused by harmonics in the rotor supply, for example – could result in an electrical circuit from the shaft through the DE bearing, frame, and NDE bearing, back to the shaft. This potential difference will create currents, and if the currents flow through the bearings, damage will be caused to the bearings.In this situation two solutions are available to prevent bearing damage from occurring: insulate the bearing (i.e. break the circuit and prevent the currents from flowing) or earth the shaft. Use of an insulated bearing is typically the easier option due to the rotation of the shaft and problems associated with wear in earthing brushes.
