Non-Circulating Bearing Currents in Drum-Winding Machine: Threat Level and Role of End Windings

Bearing currents are a significant challenge in electric machines, particularly in variable speed drives with modern fast-switching frequency converters. This study focuses on non-circulating bearing currents in drum-winding machine, a specialized machine type characterized by unique stator winding configurations. The study centers on a 27 kW, 100 krpm axially laminated synchronous reluctance machine, optimized for high power density and compactness through a drum-winding configuration. While bearing currents are a known challenge in conventional electric machines, the unique electrostatic characteristics of drum-wound designs introduce new considerations. This paper investigates the winding-to-rotor capacitance, the distribution of parasitic capacitances between core and end-winding regions, and their potential impact on non-circulating bearing currents. The findings aim to deepen the understanding of electrostatic phenomena in drum-winding machines and evaluate the threat level for circulating bearing currents in the machines with specific design features like large distance from winding to rotor and deep narrow stator slots.