High-Frequency Соmmоn-Mode Voltage as a Cause of Damage to the Bearings of Traction Motors

The analysis of processes occurring in the power electric circuits of the traction drive of a dc electric train with induction motors has shown that the highest values of common-mode voltage arise when the induction traction motor of an electric train is started. In this mode, the bearing currents and their frequency can reach maximum values and cause damage to the bearings of traction motors. By means of a mathematical-simulation experiment, the factors causing damage to the bearings of traction motors when exposed to common-mode voltage have been determined. It is shown that the use of motor-armature bearings with a protective dielectric coating is an efficient method to reduce bearing damage owing to capacitive resistance and thereby for the reduction of bearing currents. However, the main means for reducing high-frequency currents is an appropriate grounding system. It is necessary to reduce the active resistance and the inductance of the grounding wire by grounding the frame of the traction motor to the axle of the wheelset driven by the motor. In addition, the clutch that transmits torque from the traction motor to the gearbox is worthwhile to make of electrically nonconductive materials.