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.

This article describes the underpinning research, development, construction, and testing of a 4-MW multithree phase generator designed for a hybrid-electric aircraft propulsion system demonstrator. The aim of the work is to demonstrate gravimetric power densities around 20 kW/kg, as required for multi-MW aircraft propulsion systems. The key design choices, development procedures, and tradeoffs, together with the experimental testing of this electrical machine connected to an active rectifier, are presented. A time-efficient analytical approach to the downselection of various machine configurations, geometrical variables, different active and passive materials, and different thermal management options is first presented. A detailed design approach based on the 3-D finite element analysis (FEA) is then presented for the final design. Reduced power tests are carried out on a full-scale 4-MW machine prototype, validating the proposed design. The experimental results are in good agreement with simulation and show significant progress in the field of high-power-density electrical machines at the targeted power rating.

More-electric aircraft (MEA) has become a dominant trend for modern aircraft. On-board MEA, many functions, which are conventionally driven by pneumatic and hydraulic power, are replaced with electrical subsystems. Starting aircraft engines with an electrical motor instead of using pneumatic power from the auxiliary power unit (APU) is one of the major characteristics of future aircraft. This paper presents the development of a novel electric starter-generator system for aircraft applications. The paper describes the main achievements of the project within the key areas including electric machines, power electronic converters, thermal management and overall system control design. The developed prototype has been tested successfully and the test results are presented in this paper.

While the electromagnetic aspects of hairpin windings are actively being investigated and discussed in recent literature, including the design rules together with the loss calculation and reduction techniques, the thermal performance and modeling aspects have received less attention to date. In hairpin windings, the conductors (pins) are comparatively larger and arranged as separate components in parallel within the slot. In contrast, conductors randomly overlap and contact each other for traditional random windings. The differences in the aforementioned winding physical characteristics result in a different methodology to develop the thermal network. This article presents a 3-D lumped parameter thermal network (LPTN) approach for an oil-spray cooled hairpin winding, which includes the slot thermal model configuration, the end-winding connections, together with different methodologies of analyzing the end-winding sprayed oil characteristics. The aforesaid thermal model captures unique features related to the winding technology and cooling mechanism, such as the nonuniform end-winding temperature caused by the uneven oil-spray cooling effects. Finally, taking an existing propulsion drive hairpin stator and a bespoke-designed test setup, the presented steady-state thermal modeling approach is experimentally validated covering various experimental tests, including different spray conditions.

This paper describes the design process of a 10 kW 19 000 r/min high power density surface mounted permanent magnet synchronous machine for a directly coupled pump application. In order to meet the required specifications, a compact machine with cooling channels inside the slots and flooded airgap has been designed through finite element (FE) optimization. For high power density, high-speed machines, an accurate evaluation of the power losses, and the electromechanical performance is always extremely challenging. In this case, the completely flooded application adds to the general complexity. Therefore, this paper deals with a detailed losses analysis (copper, core, eddy current, and mechanical losses) considering several operating conditions. The experimental measurements of ac copper losses, as well as the material properties (BH curve and specific core losses) including the manufacturing process effect on the stator core, are presented. Accurate 3-D FE models and computational fluid dynamics analysis have been used to determine the eddy current losses in the rotor and windage losses, respectively. Based on these detailed analysis, the no-load and full-load performance are evaluated. The experimental results on the manufactured prototype are finally presented to validate the machine design.