Evaluation of combined star-δ connections for hairpin windings considering MMF and current displacement

Abstract:
This paper investigates the combined star-δ winding, which is known to improve the performance of electrical machines with wire windings, under the constraints of hairpin windings, i. e. limited choice of the numbers of turns per phase and strong current displacement. The analysis of the mmf of feasible windings shows improved fundamental winding factors and harmonic leakage coefficients. Current displacement is problematic especially for third order circulating currents in the δ sub-winding. As Finite Element analyses show, the circulating currents may be comparatively high in permanent magnet synchronous machines, which nullifies the above mentioned advantages. Finally, combined star-δ hairpin windings are not recommended.