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Hairpin windings are gaining increasing popularity in recent years due to their advantages in improving electrical machine performance while reducing manufacturing time and costs. Their geometrical features introduce new challenges and opportunities on thermal management. In particular, spray cooling is increasingly being used, since hairpin windings open up regular and accurately defined gaps in the end-windings compared to the traditional random windings. To date, technical literature on the effectiveness of spray cooling with hairpin windings is lacking, with no practical guidelines available to researchers. In this article, taking an existing hairpin-wound stator, a test rig is developed to investigate the cooling ability of different spray cooling setups on the end-windings. Three types of commercial spray nozzles are chosen to carry out a series of experiments, varying the oil flow rate, pressure, outlet velocity, and number of nozzles. The winding temperature and heat transfer coefficients are presented and discussed. Furthermore, the efficiency of spray cooling is reviewed based on the experimental results. Finally, suggestions on designing similar cooling setups and increasing the cooling efficiency are also provided. [ABSTRACT FROM AUTHOR]

Thermal analysis is a key aspect in electrical machine design and for those operating with severe duty where a high-reliability thermal analysis is required. This paper presents a comprehensive analysis of techniques for calibrating generic thermal model of electrical machines. The proposed approach combines two existing experimental methods commonly used in thermal testing of electrical devices. The first method uses a short-duty transient excitation to derive the winding thermal parameters, whereas the second method uses a steady-state excitation to estimate the thermal parameters related to the heat transfer from the winding. Both experimental methods are based on a well-defined heat source provided by a constant current (dc) excitation. For reference, alternative existing methods for calibrating thermal models, are usually combining the winding thermal data predictions and a set of experimentally derived temperatures from dc tests. Such approach, however, might be inadequate if not supported by extensive experimental data. This frequently leads to a significant rate of inaccuracy, thus having a significant impact on the reliability of temperature predictions. The main advantage of newly proposed approach is the reducing of the number of variable parameters and a more systematic calibration process. Additionally, a detailed test procedure for generic thermal model calibration is presented and discussed. [ABSTRACT FROM AUTHOR]

This paper presents various solutions for the power traction motors of electrical vehicles. Equivalent designs to those commercially available on the roads are investigated. Potential simple modifications of the winding configurations and cooling system are studied: 1) flat wire (hairpin) winding versus stranded round wire in induction, synchronous permanent magnet, and wound field machine topologies, 2) winding material grades effect—copper versus aluminum, and 3) cooling systems—water jacket versus spray, fluid properties, and flow rate. [ABSTRACT FROM PUBLISHER]

The thermal conductivity between winding and lamination is one of the most critical parameters in electrical machine thermal analysis. Its value depends on the insulation material and on the manufacturing process of the winding system, and for this reason cannot be computed using analytical equations. In this paper, a practical investigation of equivalent thermal conductivity of electrical machines stator winding is presented and discussed. The fully experimental approach is based on a fast transient thermal test to evaluate the winding equivalent thermal conductivity. The test campaign is carried out on two sets of Total Enclosed Fan Cooled (TEFC) industrial induction motors produced by two different manufacturers; the rated power of the devices under test ranges from 1.5 to 55 kW. [ABSTRACT FROM PUBLISHER]

This paper presents a review of modern cooling system employed for the thermal management of power traction machines. Various solutions for heat extractions are described: high thermal conductivity insulation materials, spray cooling, high thermal conductivity fluids, combined liquid and air forced convection, and loss mitigation techniques. [ABSTRACT FROM AUTHOR]

A new technique for coupling the electromagnetic, thermal, and airflow analysis is proposed particularly for electric machines that exhibit reduced dependence of core losses with temperature and load and have low rotor losses. Within the overall iterative loop, another inner loop that cycles only the thermal calculations and employs a simplified model to estimate losses is introduced. The thermal and airflow analysis models the conduction, radiation, and convection heat transfer and is based on equivalent circuit networks. A computationally efficient finite-element (FE) technique is employed for the electromagnetic field analysis. The combination of algorithms results in ultrafast processing as the number of outer loop iterations, which include electromagnetic FE analysis, is minimized. The overall computational time is significantly reduced in comparison with the conventional method, such that the new technique is highly suitable for large-scale optimization studies. Example simulation studies and measurements from an integral horsepower interior permanent-magnet motor are included to support validation. [ABSTRACT FROM PUBLISHER]

This paper investigates the effect of the inlet configuration on cooling for an air-cooled axial-flux permanent-magnet (AFPM) machine. Temperature rises in the stator were measured and compared with results predicted using computational fluid dynamic (CFD) methods linked to a detailed machine loss characterization. It is found that an improved inlet design can significantly reduce the stator temperature rises. Comparison between the validated CFD model results and the values obtained from heat transfer correlations addresses the suitability of those correlations proposed specifically for AFPM machines. [ABSTRACT FROM PUBLISHER]

This paper compares four analytical models for predicting the cogging torque in surface-mounted permanent-magnet machines, viz., lateral force (LF), complex permeance (CP), and exact subdomain (SD) models, together with an SD model based on a single slot/pole. The models are evaluated for the air-gap flux density, cogging torque, back electromotive force (EMF), electromagnetic torque, saturation effect, and computational complexity, with particular focus on the influence of design parameters, such as the slot-depth-to-slot-opening ratio and the optimal pole-arc-to-pole-pitch and slot-opening-to-slot-pitch ratios, on the cogging torque. It shows that all studied analytical models have similar high accuracy for the fundamental back EMF and average torque. However, their predictions are quite different for the ripples in the back EMF, cogging torque, and electromagnetic torque waveforms. Overall, the SD models have high accuracy, while the exact SD model is the most accurate among the studied models by accounting for mutual influence between slots, albeit with high computational complexity. The computation of the SD models is slower than that of the LF model but can be quicker than that of the CP model. The comparison is validated by the finite-element and experimental results. [ABSTRACT FROM PUBLISHER]

This paper reviews many design issues and analysis techniques for the brushless permanent-magnet machine. It reviews the basic requirements for the use of both ac and dc machines and issues concerning the selection of pole number, winding layout, rotor topology, drive strategy, field weakening, and cooling. These are key issues in the design of a motor. Leading-edge design techniques are illustrated. This paper is aimed as a tutor for motor designers who may be unfamiliar with this particular type of machine. [ABSTRACT FROM AUTHOR]

In this paper, the determination of the end space induction motor heat transfer coefficients is presented, and the methodologies used are examined closely. Two "ad hoc" prototypes have been built and a test bench completed. This paper reports the setup of the test procedures and results obtained in detail. As the end windings are the hottest points of the motor, particular care has been devoted to the determination of the heat transfer coefficient concerning the end-winding structure. The results obtained are of fundamental importance for the determination of the thermal resistances between end windings and end caps. These can then be used in thermal networks usually adopted in thermal model analysis. [ABSTRACT FROM AUTHOR]

In this paper, the authors present an extended survey on the evolution and the modern approaches in the thermal analysis of electrical machines. The improvements and the new techniques proposed in the last decade are analyzed in depth and compared in order to highlight the qualities and defects of each. In particular, thermal analysis based on lumped-parameter thermal network, finite-element analysis, and computational fluid dynamics are considered in this paper. In addition, an overview of the problems linked to the thermal parameter determination and computation is proposed and discussed. Taking into account the aims of this paper, a detailed list of books and papers is reported in the references to help researchers interested in these topics. [ABSTRACT FROM AUTHOR]

This paper deals with the formulations used to predict convection cooling and flow in electric machines. Empirical dimensionless analysis formulations are used to calculate convection heat transfer. The particular formulation used is selected to match the geometry of the surface under consideration and the cooling type used. Flow network analysis, which is used to study the ventilation inside the machine, is also presented. In order to focus the discussion using examples, a commercial software package dedicated to motor cooling optimization (Motor-CAD) is considered. This paper provides guidelines for choosing suitable thermal and flow network formulations and setting any calibration parameters used. It may also be considered a reference paper that brings together useful heat transfer and flow formulations that can be successfully applied to thermal analysis of electrical machines. [ABSTRACT FROM AUTHOR]

In this paper, the authors discuss the problem concerning the determination of some thermal parameters which are very complex to compute. These parameters play an important role in thermal networks usually adopted for electrical machine thermal analysis. In particular, in this paper, the following thermal parameters are analyzed: equivalent thermal resistance between external frame and ambient, equivalent thermal conductivity between winding and lamination, forced convection heat transfer coefficient between end winding and end-caps, radiation heat transfer coefficient between external frame and ambient, interface gap between lamination and external frame, air cooling speed, and the bearings effective thermal resistance. While the information given in this paper is mainly related to induction motors, it is also of general use for the designers of other types of machine. The reported results have been validated using induction motors with power ranges from a few kilowatts up to 1 MW. [ABSTRACT FROM AUTHOR]

In this paper, the thermal behavior of two induction motors (2.2 and 4 kW, four poles) and two synchronous reluctance motors [(SynRMs) transverse-laminated] are investigated and compared. Both motor types use the same stator but have different rotors. Using a lumped-parameter simulation program, a thermal analysis has been also carried out, and the obtained results have been compared with the experimental ones. A direct comparison of the thermal behavior of the two motor types has thus been made for constant load and constant average copper temperature conditions. Inasmuch as the SynRM has negligible rotor losses compared with the induction motor, it is capable of a larger rated torque, from 10% to more than 20%, depending on the relative size of end connections and motor length. [ABSTRACT FROM AUTHOR]

With the increasing pressures on electric motor man ufacturers to develop smaller and more efficient electric motors, there is a trend to carry out more thermal analysis in parallel with the traditional electromagnetic design. It has been found that attention to thermal design can be rewarded by major improvements in the overall performance. Thus, there is a requirement for accurate and reliable thermal analysis models that can be easily incorporated into motor design software. In this paper, emphasis is given to thermal sensitivity analysis of totally enclosed fanooled induction motors. In particular, thermal parameters are modified and their effects on the temperature rise shown. The results are useful for identifying the most important thermal parameters and enable robust designs to be developed that are insensitive to manufacturing tolerances. [ABSTRACT FROM AUTHOR]

Describes a method for predicting the effect of skew on torque ripple in permanent-magnet machines. Comparison of calculated electromagnetic torque ripple for the spoke-type motor without skew and with a skew of one slot pitch; Experimental validation; Quantitative analysis of calculated trajectory.