Measuring Electric Contact in an Axial Ball Bearing at DC Current Flow

Bearing currents induced in electrical motors, driven with fast switching power electronic inverters, can lead to bearing surface damages on the raceway. In this paper the electrical contact in the bearing is studied. The influence of surface oxidation in the electric contact is described. The bearing voltage and the bearing current of the axial ball bearing, type 51208, are investigated under influence of injected DC bearing currents. The contact radius of the electric contact spots (
a-
spots) are estimated based on the measured bearing resistance. Measured voltage-current characteristics of the bearing are presented for rotational speeds
${\boldsymbol{n}} = 0, 100, 1000 \mathbf{mi}{\mathbf{n}}^{ - 1}$
, bearing forces
${{\boldsymbol{F}}}_{\mathbf{b}} = 100 \mathbf{N}$
and
$1000 \mathbf{N}$
, DC bearing currents between
${{\boldsymbol{I}}}_{\mathbf{b}} = 10 \mathbf{mA}$
and
$9.5 \mathbf{A}$
, without and with lubrication and without and with the oxide-cleaning agent, citric acid. This paper is for better understanding of the bearing electrical behavior.