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Dielectric properties of pole insulation oftTraction motors under ageing with thermal cycling

Chronopoulos Dimitrios

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Summary

This diploma thesis investigates the dielectric properties of pole insulation in traction motors subjected to aging through thermal cycling. It is a part of the TEAMstress project at the Technical University of Crete, which aims to understand the degradation processes of insulating materials in traction motor poles. The project encompasses the development of quality testing procedures, model design, and analysis of various aging mechanisms, with a particular focus on thermal cycling stress in this thesis. Impedance spectroscopy serves as the monitoring technique utilized throughout the project to generate results. The initial section of the thesis provides a concise overview of electric vehicles and their traction motors. It also examines the permanent magnet synchronous motor utilizing the YASA topology, characterized by axial flux pathing between two external rotors and an internal stator, which is the specific traction motor under investigation. Following this, the thesis outlines the typical faults that electric motors may encounter. It delves into fault generation, focusing on prevalent sequences such as inter-turn short circuits, eccentricity, and demagnetization. Additionally, it discusses the widely employed diagnostic methods aimed at early fault detection. Subsequently, the thesis delves into pole insulation monitoring and thermal aging. It describes the insulation system, diagnostic tests to assess insulation condition, and analyzes the thermal cycling mechanism, along with relevant literature on thermal cycling testing. During the experimental process, impedance spectroscopy is the primary method for monitoring pole insulation condition. The thesis outlines the FRAX analyzer instrument and the procedure for conducting experimental tests. The section on performed work begins with the development of a complex equivalent circuit for the pole specimen. It then explores thermal cycling stress and analyzes results using impedance spectroscopy plots, Nyquist diagrams and breakdown voltage distributions. The thesis also investigates fixed thermal degradation to understand the absence of thermomechanical effects and examines multi-stress mechanisms, including electromechanical stress, using an in-house designed mechanical accelerator. In summary, this thesis provides insights into thermal cycling stress and other degradation mechanisms while examining impedance spectroscopy as a monitoring technique for assessing pole insulation condition.

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