High temperature superconductors (HTS), with a capability of carrying current more than 100 times of copper, can be used to develop very powerful, compact and efficient electric machines. The superconductors in HTS machines are under complex time-varying magnetic field, which triggers dynamic loss even there is only DC current in the superconductors. Such time-varying magnetic field usually exists in the form of AC field with a DC field background. Dynamic loss under such complex field is not well understood.

This paper is presenting a comprehensive analysis of the dynamic loss in HTS electric machines, particularly the loss under both solo AC field and a mixture of AC field with DC field background. We developed a numerical model to study the loss, as well as the distributions of electric currents and magnetic fields, which are essential to enable us to understand how this loss occurs and changes. Furthermore, the knowledge developed is very useful for the loss reduction of HTS electric machines.

Keywords: Dynamic loss, high temperature superconductor, electric machine