Influence of the Preformed Coil Design on the Thermal Behavior of Electric Traction Machines

Benedikt Groschup,Florian Pauli,Kay Hameyer

doi:10.3390/en14040959

Abstract

Preformed coils are used in electrical machines to improve the copper slot fill factor. A higher utilization of the machine can be realized. The improvement is a result of both, low copper losses due to the increased slot fill factor and an improved heat transition out of the slot. In this study, the influence of these two aspects on the operational improvement of the machine is studied. Detailed simulation models allow a separation of the two effects. A preform wound winding in comparison to a round wire winding is studied. Full machine prototypes as well as motorettes of the two designs are built up. Thermal finite element models of the stator slot are developed and parameterized with the help of motorette microsections. The resulting thermal lumped parameter model is enlarged to represent the entire electric machine. Electromagnetic finite element models for loss calculation and the thermal lumped parameter models are parameterized using test bench measurements. The developed models show very good agreement in comparison to the test bench evaluation. The study indicates that both, the improvements in the heat transition path and the advantages of the reduced losses in the slot contribute to the improved operational range in dependency of the studied operational point.

Highlights

To further increase the thermal operational limits of high torque low speed electrical machines, high slot fill factors are required
In the machine are crucial for the thermal modeling, a short review is given
A detailed comparison of the conventional round wire design and the innovative preformed coil design is performed in this study

Summary

Introduction

To further increase the thermal operational limits of high torque low speed electrical machines, high slot fill factors are required. The theoretical maximum copper fill factor using round-wire-windings without insulation is given by the value of an orthocyclic winding with 90.7%. This theoretical value is reduced by the wire insulation and a nonperfect arrangement of the conductors within the notch. Several studies focus to approach high slot fill factors with round wires. Rectangular conductor designs are a well-known approach to increase the copper slot fill factor in comparison to a round wire design. A state-of-the-art approach is using parallel slot designs with rectangular conductors of the same size in a so called hairpin winding design [2,3,4,5,6,7]. A widely studied field is the loss calculation of ac-copper losses within the winding in two dimensional [5] or three dimensional [4]

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Conclusion