A methodology for predicting the thermal behaviour of modular-wound electrical machines

A methodology is proposed whereby performing a series of tests on a stator/winding subassembly can estimate the thermal envelope of a modular-wound single-layer machine topology. Concentrated windings offer many advantages, such as reduced manufacturing costs, improved thermal performance and readily lend themselves to fault-tolerant designs. Single-layer modular windings have inherent magnetic, thermal and physical isolation, which means they are applicable to a segmented stator design, which further reduces the manufacturing cost. Commonly used design methods rely on prototyping and testing a complete machine to inform decisions on how the next revision is to be improved. Such an approach can provide valuable insight into machine design nuances; however, it can be costly and time consuming. A benefit of modular single-layer wound machines is that the overall winding loss can be extrapolated from testing a single stator/winding module/section. The experimental approach has been supplemented with two- and three-dimensional (2D and 3D) finite element analyses (FEAs). The FEAs have been used to predict both the electromagnetic and thermal performance of representative stator/winding variants. The methodology has been employed to give some insight into the thermal behaviour of a fractional-slot, high-speed traction motor. Initial results have confirmed that the interface thermal resistance between stator/winding/housing sub-regions is the main limiting factor for the conductive heat dissipation. Furthermore, impact of conductor placement within the stator slot on the winding loss at ac operation is investigated. Two winding variants are considered: `standard' and `slot-wedge' showing that the later winding design provides improved machine performance over entire torque-speed envelope. The theoretical findings have been validated experimentally showing good correlation.