The prevalent motor bearing premature failures due to the high frequency electric current passage

• A hypothesis of bearing current skin effect has been proposed.
• The theory can explain the common bearing symptoms in the contemporary motors.
• The analyses of the brown deposit support the hypothesis.
• The serial features of the microcraters have been discovered.
• The discovery in nature of fluting pattern disproved some of the previous theories.

Bearing premature failures are prevalent in VFD (Variable Frequency Drives) motors. The three common symptoms of the modern bearing current appeared on the bearings of a group of pump motors. The bearing failure mechanisms have been studied from the tribological point of view. The natures of the three common symptoms have been uncovered. A hypothesis of the skin effect has been proposed to explain the three common symptoms. The discovery of the serial microcraters reveals the discharge with Fourier series features. The nature of the fluting patterns excluded the theories of both EDM (Electrical Discharge Machining) and discharge corrugation. VA (Vibration Analysis) detected the harmonics of the BPOR (Ball Pass Outer Ring) frequency which associated with the fluting on the outer raceway. This discovery may be applied to detect fluting in condition monitoring.