Development of a non-contact measurement setup for the evaluation of bearing voltages

The damage resulting from bearing voltages is a major cause of premature machine failures. The necessary measurements at system level and installed conditions can be difficult to perform with conventional measurement systems. This leads to a significant risk for the development of electrical vehicles. The main requirement for implementing a suitable measurement application on systems level is the limited installation space, considering the need to retain the machine’s original design as well as the significance of the measured values. Depending on the used measurement system, different types of parasitic currents and voltages can be detected. This paper presents a novel sensor concept for bearing voltage measurement in electrical machines. The proposed measurement technique is based on a capacitive arrangement, which allows the non-contact measurement of voltages on the rotating shaft. The arrangement is based on a cylindrical capacitor consisting of the motor shaft and an isolating attachment with a conductive inlay. The measuring principle is developed by simulation and validated on an electrical machine in the lower power range at different speeds. It can estimate the electrical stress on the motor’s bearings caused by electrical discharge machining (EDM) currents. The proposed sensor can be customized easily and used in a real application environment. The presented measuring setup enables simple mounting by attaching the sensor to the housing. Only the stress caused by EDM currents is rated, using the Index of potential EDM damage. The obtained data includes the required information to analyse for the intensity and frequency of EDM currents.