Effect of Parasitic Capacitances in Drum-Winding Machine

Most electric machines utilize lap-type or wave-type winding. For those machines, the parasitic capacitances and bearing current phenomena are well studied. However, there are cases where drum winding is favourable, such as when minimizing overall machine dimensions or increasing power output. Of particular interest are the parasitic capacitances that arise with this arrangement of the stator windings. This paper presents the impact of parasitic capacitances in drum-winding machines through a case study of a 27 kW 100 krpm drum-wound axially laminated synchronous reluctance machine. The electric machine is designed for a micro-gas turbine application. To improve specially the rotordynamic performance of the system, drum winding is selected. In this configuration, the winding consists of both in-slot and outer-wound sections around the stator core. In comparison with traditional winding arrangement, where only in-slot winding is presented, this structure increases the parasitic capacitance of the machine, leading to a higher probability of circulating bearing currents. This potential issue must be addressed at the design stage, and additional countermeasures should be explored to mitigate parasitic capacitance effects.