Design and performances of a high temperature superconducting axial flux generator

Abstract

An important quality index of electric machine is the power density: it is known that axial flux machine tends to have a higher power density than the radial machines. As a result they are becoming more and more used in applications where the power density is a critical issues. However, the best way to enhance the power density is to increase the value of the airgap field and this could be achieved by using a superconducting excitation. Many projects have been developed in the world in order to develop both superconducting generator and superconducting motor, but in most of these programs the geometry of the machine has been based on radial machines [1]. All of these approaches show the feasibility of a superconducting generator but some drawbacks, that are eventually linked to the fact that the low temperature area must be guaranteed in the moving part of the machine, have been evidenced In this paper, a high temperature axial flux (HTSAF) generator is presented. In this generator the excitation is obtained by using some high temperature superconducting magnets (HTSPM). The magnets are installed in the stationary part of the machine inside a thermal vessel which contains the coolant and reduces the thermal losses. This vessel is linked to the cooling system through two ducts. The winding is located on the rotating part of the generator and are linked to the power electronics section of the generator trough a slip and ring system. Due to the fact that this machine has been built in order to work at a maximum field of 2T, a ferromagnetic yoke has been installed. The structure of the stator consists of a disk containing 8 HTSPMs. The rotor has a double sided structure. The windings are made of copper. The rotor runs at room temperature. The pole shoes and the yoke are made of laminated steel. In the paper, preliminarily, an analytical magnetic analysis of the structure of the machine is performed. Then, the analytical analysis is validated through numerical technique. Finally, the electrical and mechanical output parameters of the machine are computed. The power density ratio is calculated and it is shown that is much higher than a traditional machine