Axial-flux electrical machines are ideal candidates as in-wheel motors for electrical vehicles (EVs). Due to their characteristics of high power density and compact structure, thermal management is vital for them. Lowering the temperature of the stator windings can protect the insulation material from rapid degradation and reduce the extra copper losses by decreasing their electrical resistance. Contrary to the widely reported axial-flux permanent magnet synchronous machines, thermal modeling methods of axial-flux induction machines are rarely seen in previous literature. Hence, the present work aims at investigating their thermal response based on both the finite element method (FEM) and computational fluid dynamics (CFD) techniques. In addition, a test rig is built to validate the computed results of these two thermal models with the experimental measurement. The CFD conjugate heat transfer analysis is found to be more accurate than the FEM thermal analysis in predicting the temperature distribution of different components in the machine and the temperature rise of the airflow, with lower than 5 ∘C average errors deviating from the corresponding measured data at three rotation speeds. Additionally, the CFD simulation is able to capture the backflow occurring near the outlets of the casing that has been found during the experiments.

In recent years, hairpin windings are becoming a common choice being used for the high power density electric machines in Electrical Vehicles (EVs), e.g., Toyota Prius, owing to their high slot-fill factor, the compactness of their end windings, and their reduced manufacturing time and cost. Direct liquid cooling techniques are often utilised for the thermal management of the hairpin windings, such as oil spray cooling. The present paper aims at researching its heat removal performance via the Computational Fluid Dynamics (CFD) approach. Parameters that cannot be conveniently altered in experiments, such as the injection direction and the spray angles of the spray nozzles, are systematically varied to investigate their influence on the overall heat transfer performance. The mesh-less Moving Particle Simulation (MPS), which is a deterministic Lagrangian method discretizing the Navier-Stokes equations into particles and solving them, is adopted here as it has been proven to be particularly suitable when dealing with the free surface flow, like the atomization of jets and the splashing of droplets. Moreover, thanks to its capability of easily handling complex geometries, the hairpin windings can be modeled without simplifications or extensive pre-processing, making the simulation more realistic and affordable simultaneously. The simulation results indicate the heat transfer performance of spray cooling increases with increasing the spray angle or adopting the rotating axial or hollow shaft configurations.

The demand for larger power density and torque for the power traction motors used in electrified transportation puts forward a requirement for better thermal management methods. Spray cooling is a promising direct liquid cooling technique that has been proved to possess high heat removal capability in previous research. This paper investigates the heat transfer characteristics of spray cooling on endwindings of electric machines via numerical simulation through an Eulerian–Lagrangian approach. The utilized numerical models and calculated results are validated with experimentally measured data. The influence of different parameters and options involved in the simulation settings on the final results, like the stream numbers for the spray injector, the constant heat flux versus constant temperature thermal boundary condition, the influence of splashing, the effect of heat conduction in the endwindings and the Saffman lift force, only solving the energy equation for the air after its flow field reaches a steady-state, are evaluated. Parameter analyses are also conducted for operation conditions, configuration of the spray nozzles, and material properties of the coolant liquid. It is found that larger flow rate, smaller droplet size, lower spray height, more nozzle numbers, larger thermal conductivity and smaller viscosity of the coolant liquid tend to increase the overall heat transfer performance.

Induction machines are the working horses in a lot of industries. Inter-turn short-circuit (ITSC) fault is one of the most common failure modes taking place in them. It can generate large fault currents that lead to a local temperature rise in the faulty stator slot, which deteriorates the working performance of the machine or even cascades to a complete machine breakdown. This article focuses on developing transient thermal models for an induction machine under ITSC faults. The aim of these thermal models is to understand the thermal behaviour of the induction machine at different ITSC fault propagation stages. The first thermal model is based on finite element method (FEM) simulation that includes a physics-based model for the thermal contact resistance. The second thermal model is a lumped parameter thermal network that models the stator as inter-connected slot-number parts. They are both capable of modelling the characteristic of non-uniform temperature along the circumferential direction for the induction machine operating under ITSC fault conditions. After area-weighted averaging the results of the FEM simulation, it is found they are quantitatively consistent, with an average relative error magnitude of 5%, as well.

As the working horse in the industrial world, induction motors are widely applied in many important areas. Hence, it is crucial to investigate the fault operation conditions that would cause their deterioration of working performance or even failures, such as the inter-turn short-circuit (ITSC) fault. This study aims at analyzing the extra generated loss and induced thermal response in an 11kW induction motor under such a fault scenario. Specifically, a new finite element model with separated conductors in the stator slot is built, which characterizes the physics of ITSC fault propagation at different stages by varying the numbers of shorted conductors. In addition, the ITSC fault is implemented in different positions of the stator slots and the consequent motor temperature distributions are analyzed as well.