It is well known that multiphase machines exhibit the better performance (efficiency, torque density, fault tolerance, etc.) than three-phase machines. From the manufacturing point of view, it is interesting to have the possibility of improving a machine design by just conducting minor changes in the production process. In this regard, six-phase machines emerge as the natural choice to improve a design without modifying the active parts. This article presents an optimal procedure to shift from a three-phase to a six-phase induction motor design by just rearranging the coil connections. By starting from a three-phase winding design, different six-phase winding arrangements are analyzed. A methodology to define all the possible six-phase winding arrangements is presented. Discard criteria based on balanced radial forces and impedances are defined. Afterward, selected winding candidates are compared in terms of analytical calculations and later on, based on finite element (FE) simulations for a 690 V, 1-MW induction machine design. Different possible configurations are evaluated in terms of stator Joule losses, torque ripple, power factor, and electromagnetic efficiency both under healthy and faulted inverter conditions. Finally, a six-phase machine prototype is tested in order to verify the improvement in machine characteristics, thus validating the proposed method.

This study presents the electromagnetic, thermal and mechanical analysis of a 750 kW, 1200 rpm, 690 V surface permanent magnet motor aimed at marine propulsion (azimuth thruster). Based on a preliminary machine design, key electromagnetic design aspects including magnet demagnetisation and magnet loss reduction by tangential and axial segmentation are assessed. Then, three different cooling solutions are evaluated via computational fluid dynamics simulations combining the use of a water-jacket surrounding the stator, wafters attached to the rotor structure and the addition of an inner fan. Subsequently, the dynamic design analysis method is applied in order to check the machine's response to shock loadings due to underwater explosions. Finally, a machine prototype is successfully manufactured and tested, showing the proper fulfilment of the design requirements.

A computational fluid dynamics (CFD) model representing the effect of wafters in a totally enclosed electric machine is presented, introducing the most relevant theoretical assumptions and simplifications. The validation of the model is conducted through experimental measurements. From the CFD simulation data, a second-order response surface is developed using statistical tools, from which the wafters' influence on the convective heat transfer from the stator end windings is predicted. Wafter design criteria are obtained from the response surface information. Finally, a specific case is analysed, showing through CFD simulations that temperatures in the machine are reduced by including wafters in the design.

An analytical thermal model of an IC71W Induction Machine (IM) is presented, introducing the most relevant theoretical assumptions and equations. The validation of this model is conducted through experimental measurements. Some criteria for design of the most critical parts of the cooling system are provided using both a model based on Computational Fluid Dynamics (CFD) techniques and the analytical thermal model. First, the design of the water jacket and its main parameters are broadly analysed and some correlations for the design of the cooling ducts are presented. The influence of wafters on this cooling arrangement is also discussed.

Efficient cooling is needed, for example, in traction motors which face regularly high torque peaks and generate high stator Joule losses. This paper studies the feasibility of the direct liquid cooling in the thermal management of a low-power low-voltage permanent-magnet machine. A tooth-coil axial-flux permanent-magnet double-stator-single-rotor test machine was first equipped with indirect liquid cooling using water cooling jackets and then with direct winding cooling. The winding material used is a hybrid conductor comprising a stainless steel coolant conduit tightly wrapped with stranded Litz wire. The performance of the motor is examined at various power levels using oil or water as the cooling fluid. The results confirm that the proposed direct coolingmethod is practical also in small machines, and furthermore, it offers significant improvements in the machine thermal management, especially, in cases where stator Joule losses dominate.

Prediction of the thermal behavior of electric motors in the early design stage is crucial in any design process. The most popular prediction methods are analytical, and based on the lumped parameter model approach. These methods require experimental data in order to obtain accurate results, but this data is often not available. This paper deals with the problem of the lack of experimental data for an Open Self-Ventilated (OSV) Induction motor and reviews some of the most controversial parameters in thermal modeling, such as the bearings model and the axial conductivity of the lamination stack. Due to the nature of the OSV machine, through ventilation is also investigated, and a hydraulic model with improvements focused on rotational effects observation is presented. Moreover, the heat transfer in end spaces and ducts is studied, using dimensionless analysis correlations, along with focusing on new hydraulic phenomena, such as the development of the flow and the roughness effect. An implementation of a thermal circuit for an OSV machine that has good agreement with reference results is used to compare heat transfer coefficients used regularly for Totally Enclosed Fan Cooled (TEFC) enclosures. Finally, a sensitivity analysis is carried out on some parameters to determine their importance.

The prediction of the thermal behaviour of electric motors in the early stages of their design is a critical factor for reducing time and cost in the design process. In complex machine topologies such as open self-ventilated machines, there are several phenomenas to take into account in order to predict the correct thermal behaviour of the machine. In this study, a thermal model coupled with a hydraulic model is presented. These models provide information of the thermal behaviour of the machine. First, the complete thermal circuit is described, with some emphasis in the specially modelled parts. Then, the heat transfer coefficients for each surface inside the machine are presented, by the use of dimensionless correlations that avoids the need of previous knowledge. Moreover, the hydraulic model of the machine is studied, and also the coupling methodology between the two models is described for both steady state and transient calculations. Finally, the results from the model are validated using the data from two experimental runs, the first one with constant torque and speed, and the other with variable power, in a standardised service cycle, with a difference in the rotor bars and the stator winding below +/- 10 degrees C.

This paper describes an algebraic model for predicting the air flow-rate in the cooling system of an open self-ventilated machine. The method is easily applicable to any type of air-cooled electrical machine. The air flow-rates in different areas of the machine as well as the head losses of the hydraulic system were obtained, and the results were compared with a more detailed model developed with Computational Fluid Dynamic (CFD) techniques. Moreover, a sensitivity analysis was carried out in order to compare the different topologies of the machine studied