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Design, Taking into Account the Partial Discharges Phenomena, of the Electrical Insulation System (EIS) of High Power Electrical Motors for Hybrid Electric Propulsion of Future Regional Aircrafts

par Laurence Laffont - publié le , mis à jour le

Philippe COLLIN’s thesis defense, intitled "Design, taking into account the partial discharges phenomena, of the Electrical Insulation System (EIS) of high power electrical motors for hybrid electric propulsion of future regional aircrafts", will be taking place on Tuesday, November 3rd 2020, at 10 am in the Amphithéâtre 2 de la Maison de la Recherche et de la Valorisation (MRV) on the Paul SABATIER University campus.

The thesis has been supervized by Mr David MALEC et Mr Yvan LEFEVRE.

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Abstract :

Reducing CO2 emissions is a major challenge for Europe in the years to come. Nowadays, transportation is the source of 24% of global CO2 emissions. Aviation accounts for only 2% of global CO2 emissions. However, air traffic is booming and many concerns are emerging. For instance, CO2 emissions from air traffic have increased by 61% in Sweden since the 1990s. This explains the emergence of the "Flygskam" movement which is spreading in more and more European countries.

In this context, the European Union has launched in September 2016 the Hybrid Aircraft Academic research on Thermal and Electrical Components and Systems (HASTECS) project. The consortium brings together Airbus and different laboratories. This project is part of the “Clean Sky 2” program, which aims to develop a greener aviation. Its ambitious goal is to reduce CO2 emissions as well as the noise produced by aircraft by 20% by 2025. In order to do so, the consortium is studying a serial hybrid architecture. Propulsion is provided by electric motors. Two targets are being defined. By 2025, the engines must reach a power density of 5kW/kg, including the cooling system. By 2035, the engines’ power density will be doubled in order to reach 10kW/kg. To reach these targets, the voltage level will be considerably increased, beyond one kilovolt. The risk of electric discharges in the stators of electric motors is considerably increased. The objective of this thesis is to develop a tool to assist in the design of the primary Electrical Insulation System (EIS) of the stator of an electric motor controlled by a converter. It is organized in 5 parts.

The first part begins by clarifying the issues and challenges of a greener aviation. The electric motor stator EIS is developed. Finally, the constraints that apply to the EIS in the aeronautical environment are identified.

The second part presents the different types of electric discharges that can be found. The main risk comes from Partial Discharges (PD) which gradually deteriorate the EIS. The main mechanism for explaining the appearance of PD is the electronic avalanche. The Paschen criterion makes it possible to evaluate the Partial Discharge Inception Voltage (PDIV). Different techniques are used to detect and measure the activity of PD. Numerical models are used to evaluate the PDIV.

The third part presents an original method for determining the electric field lines in an electrostatic problem. It only uses a scalar potential formulation.

The fourth part presents an experimental study to establish a correction of the Paschen criterion. An electric motor winding is very far from the hypotheses in which this criterion was originally defined.

Finally, the fifth part is devoted to the development of the SIE design aid tool. Graphs are generated to provide recommendations on the sizing of the various insulators in a stator slot. A reduction in the PDIV due to a combined variation in temperature and pressure is taken into account.

Keywords : Partial discharges, Paschen, Modeling, Finite elements, Electric field, Sizing, Dielectrics, Electrical insulation, PDIV.