High-specific-power electrical machines for transportation applications require effective thermal management to enable elevated power density and efficiency. Hollow-conductor windings offer direct internal cooling, reducing temperature rise and increasing allowable current density. This paper investigates the thermal performance of copper hollow-conductor windings fabricated using additive manufacturing (AM) and evaluated via reduced-complexity motorette demonstrators. The windings were produced using a filament-copper AM process, enabling continuous hollow channels along the full conductor length. Experiments demonstrate winding-to-coolant heat transfer exceeding 2000 W/m2K, corresponding to a 0.7l/min corresponding to a 37 × increase in allowable winding power loss relative to a baseline design employing conventional round copper conductors with liquid-cooled housing. Complementary theoretical analysis of complete machine variants shows that hollow-conductor cooling can significantly enhance machine operating envelope and efficiency, extending high-efficiency regions and torque-speed capability. The findings illustrate that direct cooling of hollow-conductor windings, enabled by AM, provides a viable route to higher specific output and improved thermal robustness in propulsion-relevant electrical machines. Practical considerations for integrating hollow-conductor windings into full machine assemblies are also discussed, including manufacturing, assembly, and thermal design implications.

This paper describes a methodology for experimentally deriving thermal parameters in the design of electrical machines, with a focus on, but not limited to, short-duty transient operation. Here, all key stator-winding thermal resistances and capacitances, which can be directly derived from thermal tests, are considered. The proposed approach is based on the transient thermal step-change response for a specimen /mottorete under test, where the heat transfer is well-defined and limited to a single path, e.g. a heat source (stator-winding body) to a heat sink (machine housing). Any imperfections like the heat flux leakage from the motorette body/test rig are considered and experimentally compensated for. A detailed description of the underpinning assumptions, test procedure, required instrumentation, and measured data post-processing is provided and supplemented with several examples from hardware tests. Applicability and limitations of the methodology are also discussed. The presented approach provides a novel standardised testing method, where the measured data can be simply shared across different electrical machine designs to bring a means for an accurate, time- and resource-effective design/assessment process. This expanded work elaborates more on the existing figures of merit, highlighting their deficiencies when thermally sizing electrical machines. Further to this, a more detailed discussion of the methodology, supplemented with new examples, is provided.

This paper presents an experimental methodology developed to accurately measure the thermal conductivity of composite materials like impregnated electrical windings. The proposed approach utilises a custom-built heat flow metering system to analyse cuboidal material samples, which allow for the material thermal anisotropy to be derived. Validation and accuracy assessment are conducted by comparing the proposed method with the commercially available transient plane source method. The paper comprehensively discusses both the theoretical foundations and experimental results obtained from tests on several material samples, highlighting the efficiency of the proposed technique. Furthermore, the work includes a comparative analysis of various resins and conductor types, suggesting that the rectangular profile conductors with Epoxylite resin impregnation exhibits superior thermal conductivity both in transverse and longitudinal directions. The experimental findings have shown that the proposed method allows for more accurate measurements. For materials with high thermal conductivities (e.g., 180W/m.K), a measurement deviation as low as 1.81% is achieved, while materials with low thermal conductivity (e.g., 0.2W/m.K) are more susceptible to an increased method error, as theoretically shown through numerical simulations. Additionally, the study illustrates an impact of accuracy of the thermal conductivity data on the temperature predictions within an electrical machine demonstrator. The case study theoretical results revealed an increased thermal resistance between the winding and housing of up to 17%. The effect is particularly prominent when considering more conventional electrical insulation systems with poorer thermal properties.

This paper presents a comparative study of alternative liquid cooling methods applicable to high specific output electric machines. The research aims to identify the cooling system that best balances the thermal/electromagnetic trade-offs inherent in the machine design for high power applications through simulation and experimental validation. The computational fluid dynamics (CFD) analysis is employed to compare three different liquid cooling techniques: stator housing cooling jacket, winding axial and end cooling channels. The research focus has been placed on thermal performance and overall efficacy of the analysed thermal management system. A case study permanent magnet (PM) machine demonstrator has been used to illustrate an impact of the enhanced heat transfer on the motor generic performance metrics Both theoretical findings from CFD and experimental data from tests on a set of custom built motorettes are discussed in the paper showing that the winding integrated axial cooling channels offers similar heat removal capability, as the more conventional liquid cooled cold plate. The end winding cooling offers the lowest performance gains among the analysed cases. The results also show that using a combination of two active cooling techniques, e.g. winding embedded features and cooling jacket housing) significantly improves the over motor performance when compared to stand alone cooling methods considered in this investigation. Further performance gains can be achieved by introducing better (thermally) materials or finely tuning the cooling channel design, e.g. introduction of microfeatures.

W obliczu zagrożeń bezpieczeństwa powszechnego i zagrożeń powiązanych (np. zagrożeń bezpieczeństwa militarnego wywołujących zagrożenia bezpieczeństwa powszechnego) o zdolnościach do efektywnego przeciwstawienia się zagrożeniu i jego następstwom świadczy potencjał ochrony ludności. W nawiązaniu do standardów międzynarodowych potencjał ochrony ludności można utożsamiać ze zdolnością do radzenia sobie w obliczu sytuacji zagrożenia. Tę z kolei można zdefiniować jako zdolność ludzi, organizacji i systemów do działań prowadzonych w sytuacji zagrożenia z wykorzystaniem dostępnych zasobów i sposobów działania. Wymaga ciągłej świadomości sytuacyjnej w odniesieniu czynników zewnętrznych i wewnętrznych podmiotu kształtującego tę świadomość, zasobów będących w dyspozycji tego podmiotu, a także dobrego zarządzania. Potencjał ochrony ludności to pochodna zasobów i sposobów ich wykorzystania. Kształtowanie potencjału ochrony ludności powinno odpowiadać stanom funkcjonowania państwa, gdyż to ich uwarunkowania będą zasadniczo determinowały konieczność i specyfikę odpowiedzi na zróżnicowane zagrożenia (w tym zagrożenia rozwijające się zgodnie z zasadami efektu kaskadowego). Powinno także wyrażać specyfikę szczebla systemu bezpieczeństwa, na którym to kształtowanie się odbywa. Każdy z takich szczebli cechuje się właściwymi sobie uwarunkowaniami (m.in. podatnością na zagrożenia operacyjne, a także uwarunkowaniami formalnoprawnymi, organizacyjnymi i oczekiwaniami). W przypadku ochrony ludności działania z jej zakresu można rozpatrywać na szczeblu międzynarodowym, szczeblu centralnym, szczeblu województwa, szczeblu powiatu, szczeblu gminy i szczeblu lokalnym.

Szkolenia i ćwiczenia z zakresu ochrony ludności i obrony cywilnej stanowią sposoby podnoszenia odporności społecznej i przygotowania struktur państwowych na wystąpienie zróżnicowanych rodzajów zagrożeń rzutujących na najważniejsze wartości utylitarne. W obu przypadkach (szkoleń i ćwiczeń) mogą być traktowane jako formy kształcenia. W odniesieniu do szkoleń jest to naturalna konsekwencja ich specyfiki. Natomiast w przypadku ćwiczeń uwidacznia możliwość wykorzystania czynności praktycznych nie tylko do weryfikacji stopnia ich opanowania, ale również do celów podnoszenia wiedzy i umiejętności, a także kształtowania kompetencji społecznych.

This paper describes key aspects of the development process of an ultra-lightweight electrical motor for solar-powered high-altitude (20 km) platform applications (HAPSs). A radial-flux permanent magnet (PM) machine topology with outer rotor and integrated direct air-cooling is considered here. The mission profile of the analysed solar-powered aircraft calls for a high-torque overload (x2.5) at take-off and a high-efficiency (>95%) at high-altitude cruise operation. Consequently, a fine balance between both operating points needs to be seen when sizing the motor. Effective thermal management of the motor at take-off is critical for achieving a compact motor design. Further to these, the motor design should enable a simple and cost-effective manufacturing and sassembly process, which makes use of the lightweight composite materials for all structural elements of the motor assembly. In this work, a careful integration between both active and structural subassemblies of the motor resulted in a significant weight reduction, with contribution of all structural components less than 5% of the overall motor weight. The theoretical and experimental results discussed in the paper confirm the key design targets of the motor are met, with a motor torque density of 10Nm/kg (take-off operation) and 94% efficiency (cruise operation). Further to the motor development process, a comprehensive insight into the existing state of the art HAPS solar-powered aircrafts with focus on the commercial electrical motor technology and motor to aircraft integration is provided to highlight some of the application driven engineering challenges.

This paper presents a theoretical study of alternative thermal management systems in application to electrical machines. A case study permanent magnet (PM) motor for propulsion has been selected as a platform for comparing an array of cooling methods. Starting from commonly used techniques like air- or -liquid cooling via the motor housing and finishing with less conventional concepts, with integrated or embedded winding cooling including alternative coolants, e.g., deionised water, oil, or liquid metal. The single motor platform offers a unique insight into the key performance measures when comparing the alternative thermal management systems. Here, the commonly used figures of merit like winding/conductor current density and electric loading is supplemented with thermal resistance between the heat source (winding) and reference heat sink (coolant). Such approach provides more insight into the heat transfer effects, which would otherwise be difficult to deduce. The initial theoretical finings suggests that the integrated or embedded motor (winding) cooling offers clear performance benefits, i.e., significantly improved heat removal path. However, this is not very clear when comparing the current density or electrical loading data. E.g., liquid cooled hollow conductors and liquid cooled housing offer here similar current density and electric loading ratings, but significantly higher winding to coolant thermal resistance is found for the latter cooling variant. This highlights the importance of more in-depth data analysis when comparing alternative thermal designs of electrical machines, where multitude of design and manufacturing factors need to be accounted for.

This paper describes key aspects of the development process of an ultra-lightweight electrical motor for solar-powered high-altitude (20km) platform applications. A radial-flux permanent magnet (PM) machine topology with outer rotor and integrated air-cooling is considered here. The mission profile of the analysed solar-powered aircraft calls for a high-torque overload (x2.5) at take-off and a high-efficiency (> 95%) at high altitude cruise operation. Consequently, a fine balance between both operating points needs to be seen when sizing the motor. Here, effective thermal management of the motor at take-off is critical for achieving a compact/lightweight motor design. Further to these, the motor design should enable a simple/cost-effective manufacturing and assembly process, which makes use of the lightweight composite materials for all structural subassemblies. In this work, a careful integration between both active and structural subassemblies of the motor resulted in a significant weight reduction, with contribution of all structural components less than 5% of the overall motor weight. The theoretical and initial experimental results discussed in the paper confirm that the developed motor meets the key design targets. Further evaluation will include the mission specific and aircraft integration aspects, i.e. high-altitude tests, aerodynamic tests and flight tests.

This paper quantifies the environmental impacts of a range of electrical machines to demonstrate some of the challenges associated with such an evaluation. Emissions across the supply and value chain of machines are considered, which include the raw material supplies, manufacturing and processing, in-application use and maintenance, and reuse, recycling and final disposal. In this study, a set of cordless power tools (combi drills) was selected as a platform for the comparison. The drills were outsourced from a single manufacturer across a broad price range, i.e. budget, mid-range and premium drills including both brushed and brushless motor technology. The study highlights the complexity of the problem, where a fine balance amongst a multitude of factors needs to be found to achieve specific environmental targets over the lifetime of an electrical machine. The limited availability of life cycle inventory (LCI) data specific to the electrical machines, together with relatively low resolution (granularity) of the LCI data related to materials extraction, product manufacturing and recycling processes are some of the key obstacles in providing a more insightful LCA. Clearly, some of the findings are specific to the analysed machines, however some issues related to an accurate (representative) LCA are more generic and are applicable to a variety of electrical machines and their applications.

This paper investigates innovative methods for enhancing heat transfer efficiency in high-power permanent magnet electrical machines. The objectives are to quantify the effects of increasing the air speed, increasing the turbulence intensity, and introducing the spacing between windings on cooling performance. The cooling of stator windings is studied through experimental wind tunnel testing and Computational Fluid Dynamics (CFD) modelling. The CFD model is validated against wind tunnel measurements to within 4 Kelvin (K). The results demonstrate that each enhancement method significantly improves the cooling capability. Increasing the air speed from 10 m/s to 40 m/s reduces the winding hotspot temperature by 34%. Introducing a high turbulence intensity of 40% leads to a 21% lower hotspot temperature compared to 0.5% turbulence intensity. Creating a 1.5 mm spacing between coils also substantially improves convection and conduction heat transfer. Overall, combining these optimised design parameters yields over a 40% reduction in hotspot temperature compared to the original design. This research provides practical guidance for maximising heat transfer efficiency in high-power permanent magnet machines, without increasing complexity. The findings will lead to higher machine efficiency, reliability, and longevity for aerospace and other applications.

Heat pipes have played a large part in the thermal management market for the past five decades and have contributed to the development and optimisation of countless components in a wide range of high-level applications, most notably in the aerospace, electronics, automotive and power generation industries. These thermal management systems span a wide range of temperatures, which in turn requires the heat pipe fluid and casing material to be specially selected to meet the application requirements. Recently, there has been an increasing demand for heat pipes which can operate in the 300-600 degrees C temperature range - a range which is still under-developed in the heat pipe marketplace due to the lack of conventional fluids which can adequately operate at these temperatures. This range is referred to as the 'medium' or 'intermediate' temperature range. The analysis and exploration of novel fluids, which could potentially be used in this range, will cater for a huge market potential. Although there has been mild development in this temperature range with the aim of testing particular fluid/metal combinations which may be suitable, there appears to currently be a severe lack of continuity in the work with little progression towards a definitive solution and no central reference catalogue of successful and unsuccessful tests. Previous works on the topic tends to follow a 'patchwork' process, often with overlaps in testing and with a focus only on long-term compatibility tests with a limited analytical approach which often lead to incompatible results. This paper intends to summarise all major and stand out efforts in developing medium temperature heat pipes and highlight the most promising fluids and wall materials which have been tested to date. To summarise the content, this review will explore (a) current applications which could benefit from the use of medium temperature heat pipes, (b) the work that has been done on investigating medium temperature fluids, (c) highlight some of the principles behind heat pipe performance prediction, fluid analysis, fluid/metal compatibility and fluid selection and (d) suggest the potential future direction of research in this area, particularly focusing on the development of novel heat pipe fluids. Additionally, a standardised fluid assessment framework is also proposed aiming to aid the identification and analysis of both existing and newly developed heat pipe fluids.

This paper describes a methodology for experimentally deriving thermal parameters in design of electrical machines, with focus on, but not limited to short-duty transient operation. Here, all key stator-winding thermal resistances and capacitances, which can be directly derived from thermal tests, are considered. The proposed approach is based on the transient thermal step-change response for a test specimen/mottorete under test, where the heat transfer is well-defined and limited to a single path, e.g. a heat source (stator-winding body) to a heat sink (machine housing). Any imperfections like the heat flux leakage from the motorette body/test rig are considered and experimentally compensated for. A detailed description of the underpinning assumptions, test procedure, required instrumentation, measured data post-processing is provided and supplemented with several examples from hardware tests. Applicability and limitations of the methodology are also discussed. The presented work provides a novel standardised testing approach, where the measured data can be simply shared across different electrical machine designs, to provide a mean for accurate, time and resource effective design /assessment process.

This paper explores alternative thermal management techniques of a rotor assembly of a high-speed salient-pole wound-field synchronous motor for traction applications. In general, the rotor assembly of an electrical machine is very chal-lenging in terms of effective heat removal. This is due to nature of the rotary part with a limited thermal path for extracting the generated heat. Further to this, factors like system integration and additional mechanical power loss need to be carefully considered for a well-balanced thermal management/electrical machine design. In this work, the authors investigate several selected cooling techniques, which involves passing a fluid (air and/or oil-based coolant) through the rotor assembly. To aid the analysis, a number of design tools have been developed/used including a simplified correlation-based thermal equivalent-circuit (TEC), a finite element (FE) method and a finite volume computational fluid dynamics (CFD). The proposed methodology offers a computationally efficient approach, with the TEC used for initial trade-off study, and high-fidelity detailed CFD employed at later stage of the development process. A case study motor design is used here, to demonstrate the methodology. The initial theoretical predictions suggest that the active rotor cooling offers clear performance gains, as compared with the baseline rotor design with passive heat removal. Both convective heat transfer coefficient (HTC) and rotor power loss handling are discussed in the context of the overall motor performance/torque-speed envelope. Moreover, comments regarding the thermal management and motor system integration, and additional mechanical power loss are provided.

This paper presents analysis of eddy-current power loss in heat pipes (HPs) for integrated thermal management of electrical machines. Here, a close integration of HPs with winding body is considered. Such an arrangement is particularly attractive, as it targets the main heat source within the machine assembly. However, there are several challenges associated with the subsystem compatibility, which include electromagnetic, thermal, and mechanical design aspects. The HP’s power loss, which is generated as a results of the time varying stator and/or rotor slot magnetic flux leakage, requires careful considerations. Although, the HP-enabled thermal management of electrical machines (electrical windings) has been previously investigated, the additional HP generated power loss has had a very little attention. In this work, the author proposes alternative techniques for accurate predictions of HP generated power loss accounting for the HP’s wick structure. Three alternative custom-built HP constructions Copper-Water and Titanium-Water with sintered and mesh wicks have been investigated in this analysis. Both theoretical finite element (FE) electromagnetic and experimental methods are discussed in detail. The results show that the proposed experiment informed FE model of HP with an equivalent electrical resistivity wick region provides an accurate HP representation useful in design of electrical machines. Further to these, the proposed approach is demonstrated on an example custom vapor chamber (VC) highlighting the importance of accurate power loss predictions in HPs and VCs.

This paper presents an experimental approach for accurate derivation of equivalent thermal conductivity of anisotropic impregnated electrical windings. The proposed method employs a custom-built heat flow metering system for the analysis of cuboidal materials samples, which allow for the material anisotropic properties to be experimentally derived. Both theoretical fundamentals and experimental data from tests on 8 differing materials samples are discussed in the paper demonstrating the effectiveness of the proposed method. A comparison between various resins and winding geometries is made concluding that a rectangular winding with Epoxylite resin demonstrates the highest equivalent thermal conductivity in all planes. For sample planes with high thermal conductivities (i.e., 180W/m.K) a measured accuracy down to 1.81% was achieved. As predicted by numerical methods, sample planes with low thermal conductivity (i.e., 0.2W/m.K) had a much higher propensity for error. Further to these, an impact of accuracy of the thermal conductivity data on the winding temperature distribution is illustrated for a case study electrical machine demonstrator. The theoretical predictions show a significant effect, i.e., here, an increased winding to housing thermal resistance up to 17% when using measured thermal conductivity data for the proposed test setup.

This article presents design considerations for a short-operating-duty, fault-tolerant actuator for aerospace applications, with the research focus placed on thermal management. A fully enclosed and naturally ventilated permanent magnet (PM) synchronous machine with a dual-lane modular stator-winding topology is analysed. The aim is to assess alternative solutions for satisfying both sufficient heat removal and simple and robust machine construction design targets. The thermal management is particularly challenging because there are limited means for an effective heat removal from the machine body. Selected design choices impacting the machine's thermal behaviour, including alternative electrical insulation systems, winding impregnation quality, thermal contact interfaces and different winding and housing configurations are investigated. A three-dimensional (3D) transient finite element (FE) analysis has been carried out alongside an experiment informed low-order thermal network sensitivity evaluation. The theoretical body of work has been supplemented with thermal tests on an array of motorettes fabricated using alternative electrical insulation systems. The theoretical and experimental findings suggest that the winding impregnation quality has a dominant impact on the actuator's thermal behaviour, where both heat removal path (thermal resistance) and heat storage (thermal capacitance) need to be well balanced for the short-duty transient operation under a faulted condition.

The continuous drive towards electrified propulsion systems has been imposing ever more demanding performance and cost targets for the future power electronics, machines and drives (PEMDs). This is particularly evident when exploring various technology road mapping documents both for automotive and aerospace industries, e.g. Advanced Propulsion Centre (APC) UK, Aerospace Technology Institute (ATI) UK, National Aeronautics and Space Administration (NASA) USA and others. In that context, a significant improvement of the specific performance and cost measures, e.g. power density increase by a factor of 10 or more and/or cost per power unit reduction by 50% or better, is forecasted for the next 5 to 15 years. However, the existing PEMD solutions are already at their technological limits to some degree. Consequently, meeting the performance and cost step change would require a considerable development effort. This paper is focused on electrical machines and their thermal management, which has been recognised as one of key enabling factors for delivering high specific output solutions. The challenges associated with heat removal in electrical machines are discussed in detail, alongside with new concepts of thermal management systems. Several examples from the available literature are presented. These include manufacturing techniques, new materials and novel integrated designs in application to electrical machines.