Innovative Insulation and Grounding Solutions against electrical Erosion

Dr. Jens Dörner

Value for the audience

- Introducing new opportunities to avoid electrical erosion

- High degree of design freedrom for motor designers and makers

- New results which have not been released yet

Summary

Battery Electric Vehicles drives show a trend towards high voltages of at least 800V. This trend results in demand for countermeasures against electrical leakage, which causes damages to bearings and other machine elements such as fluting. Given the necessity of countermeasures for motor designers, insulating as well as conductive solutions can be considered depending on the type of bearing current occurring. To facilitate countermeasures, NSK developed two designs of injection overmolded bearings as well as a conductive grounding element which properly functions even under oil lubrication conditions. Often conductive brushes are used but have limitations in oil lubrication condition since as insulating oilfilm can be formed which again would cause the current flowing through the bearing, different to the intention to guide the current to the housing.

This article introduces the benefits of each overmolded bearing design solution together with a guideline for customers when to use which design. Depending on requirements such as fit conditions, tolerances, costs, avoiding bearing creeping and further, this article will suggest the best possible solution for preventing against circulating bearing currents. On the other hand, the mentioned conductive brush shows good performance when tackling electric discharge machining (EDM) bearing currents. Both solutions also work nicely in parallel and give plenty of design options for motor designers. All three developments will be introduced together with test and simulation data to confirm the functions and are contributors to cost savings comparing hybrid bearings using ceramic rolling elements.

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