Influencing Parameters on Discharge Bearing Currents in Inverter-Fed Induction Motors

This article investigates discharge bearing currents in inverter-fed electric motors. Industrial reports indicate that among prevalent bearing failures, bearing currents are one of the influent drivers leading to a variety of tribological issues and premature wear in bearings. While the root-causes of bearing currents have been extensively reported over the years, the response of bearing under voltage stress and the factors that influence bearing endangerment through electric discharges have been far less studied. An online measurement of the bearing voltage is proposed on a motor test-bench to estimate both the discharge activity and the energy of the discharges. The designed test bed allows reproduction of representative bearing currents leading to electrical micropitting. This paper presents extensive measurements results that highlight the critical operating conditions and parameters that worsen the discharge phenomenon inside bearings. Testing protocols are performed to quantify the influence of each parameter separately. While the bearing voltage magnitude play a significant role in the discharge phenomenon, other parameters such as successive startups, bearing temperature, and type of grease deserve appropriate investigations to avoid or mitigate the well-known shortened bearing life under inverter operation.