Calculation of parasitic capacitances of an electrical machine by finite element method and estimation of bearing current threat

Abstract

Electrical machines and drives have a long history of developing, apply in many industry fields such as power systems, power electronics, thermodynamics, electrical vehicles. In the modern days, induction motors supplied by converters are the most popular electrical drives system. However, usage of high switching frequencies in modern converters leads to the phenomenon of bearing currents. This parasitic current wears down bearings and reduces life expectancy of electrical machines, affect performance and efficiency of the whole drive system. This thesis focuses on non-circulating bearing currents in induction motors by introducing the theoretical background of bearing current phenomena and their effects on machine operation. The relevant parasitic capacitances are defined, and the bearing current risk is estimated using the bearing voltage ratio (BVR). Furthermore, a step-by-step finite element method (FEM)–based workflow for capacitance extraction is presented, followed by analysis and discussion of the obtained results.