Analytical 2-D slot model for predicting AC losses in bar-wound machine windings due to armature reaction

A 2-D analytical closed-form model of bar-wound ac machine stator slots is presented for calculating ac winding losses attributable to armature reaction effects. The proposed model is capable of predicting the ac winding losses in the slots of bar-wound stators for arbitrary numbers of bar conductor layers excited with currents of variable amplitude, frequency, and phase angle. Finite element (FE) analysis has been used to raise confidence in the accuracy of the analytical model. The analytical model has been used to explore the impact of several key design variables on the ac winding losses including slot depth, winding depth, number of conductors per slot, and phase conductor slot order. These results show that skin and proximity effects can have a significant impact on the ac winding losses at elevated excitation frequencies, making it important to carefully consider the number of bars in each slot, their dimensions, and placement in the slot in order to minimize losses.

I. Introduction

Bar-wound windings have experienced rising popularity in traction machine applications for a variety of reasons including the opportunities opened by this winding type for achieving high machine power density values. However, a bar-wound winding has large conductor cross-sectional dimensions compared to strand-wound windings, raising questions about the vulnerability of bar-wound windings to elevated losses due to eddy currents and proximity effects caused by high-frequency excitation during typical driving cycles.