Application of a novel measurement principle for high frequency bearing currents in electric machines and drive systems

Abstract This paper presents and validates a novel method for measuring bearing currents in an electric drive system. As with any current measurement, a defined path must first be established through which the bearing currents flow. To achieve this, the bearings are insulated from the housing using plastic sleeves and then reconnected via printed circuit board assemblies (PCBAs). To ensure that the drive system undergoes minimal alteration in order to maintain validity, the bearing currents are ascertained by measuring the voltage across a large number of parallel-connected shunts that are circumferentially distributed on the PCBAs. Once the measurement principle has been presented in detail, a methodology is introduced that explains how to accurately determine bearing currents from the voltage drop across the shunts. In the following, the measurement principle is validated by displaying example measurement results of bearing currents in a real drive system. Finally, potential measurement errors and their effects on the bearing current determination are discussed.