A Higher Resolution, Local Thermal Analysis of an AC Armature Winding of a High Temperature Superconductor Motor

The armature of high performance synchronous motors with High Temperature Superconductor (HTS) field is an AC copper winding, mounted in an iron-less stator – a so-called "air winding". Its thermal design poses difficult problems because while the armature works at ambient temperatures it is siege of higher than usual power dissipation by Joule and variable magnetic field effects. Considering that air windings are not common in classical electrical machines design, novel cooling solutions need to be considered. The standard, design class lumped thermal circuit analysis may not suffice, and it has to be complemented with a finer resolution investigation of the regions with increased structural and heat transfer complexity. As a detailed, field analysis of the entire armature is not practical a local analysis is both desirable and feasible. This paper reports a mathematical model for the heat flow in a critical part of the air-winding armature of a forced convection air-cooled HTS motor. The heat transfer mechanisms and paths, the thermal load structure unveiled by numerical simulation are then used to produce a high resolution lumped thermal circuit that conveniently complements the design class schemes used for sizing models and prototypes.