Investigation of the Static Breakdown Voltage of the Lubricating Film in a Mechanical Ball Bearing

In this paper, the current pulse (discharge) activity in a small bearing is investigated when current-limited DC voltages of different levels are applied to the shaft under varying rotational speeds and mechanical loads. The measurements show that the inception voltage of discharges in the bearing is higher than the extinction voltage. However, when the discharge activity has been intense the bearing exhibits difficulties to recover its insulating properties when the voltage is decreased to a low voltage level and thus the discharge activity continues. The measurements also show that at low voltages the bearing acts as an insulator but if the voltage is increased the bearing starts to act as a conductor. This transition occurs during a narrow voltage interval. The time interval between two consecutive current pulses decreases significantly with increasing shaft voltage