Brushless Doubly-Fed Machines have potential benefits in variable speed generation and adjustable speed drive applications by combining a robust machine structure with a reduced power converter rating. While recent work has demonstrated feasibility, steady-state performance has not been optimized. The nature of doubly-fed operation causes rotor currents of varying, relatively high frequency. Moreover, the rotor structure deviates from conventional squirrel cages. Consequently, induction machine rotor bar geometries need to be carefully examined and refined for applicability in the doubly-fed system. The present thesis uses finite element analysis to investigate alternative rotor bar design. Two-dimensional finite element analysis is used to investigate basic rotor bar characteristics. Interface with a detailed simulation program enables investigation of assembled rotors, otherwise a three-dimensional analysis problem. Rotor bar geometries for a high speed alternator are investigated. Bar shapes are kept simple to allow manufacturing of the rotor in the absence of the-casting equipment. Rotor prototypes are constructed using custom, laser-cut laminations and experimental results for the alternator verify improved line-to-shaft efficiencies over conventional rotor geometries as well as off-the-shelf alternators. / Graduation date: 1994

The proliferation of electric machines has drastically increased in recent years and is likely to increase into the future. This interest in the production of advanced, high power density electrical machines that are small in size has heightened the need for flexible manufacturing processes to produce their laminated components during short batch and prototyping production runs. A means of cost effective, accelerated prototyping of these machines will have a substantial impact on their design and optimization, reducing time requirements to produce and test a given design. A review of the current manufacturing methods for prototyping electric machines was conducted. In particular, laser cutting, electric discharge machining, and abrasive waterjet (AWJ) machining were researched as competitive processes. Each of these methods exhibits marked advantages and disadvantages that present the opportunity for a new process to compete. This work investigates the applicability of high throughput profile milling (HTPM) for the prototyping of advanced electric machines, specifically, the process parameter space for milling of electrical steels. The material response will be determined by characterizing its specific cutting energy and utilizing this to develop a model to predict cutting forces during the milling process. Optimal process parameters will be investigated to obtain maximum productivity and minimal burr formation. Finally, the impact of HTPM processing on the magnetic properties of electrical steels will be compared to that of a leading prototyping technology, AWJ machining.

Advances in electrical machinery with high efficiencies could significantly reduce the cost of industrial and residential energy systems, thereby reducing fossil fuel needs and emissions. Electrical machine design is a comprehensive process based on several factors, including economic factors, material limitations, specifications and special application-dependent factors. At the same time, machine design is a multi-physics task comprising of electric design, magnetic design, insulation design, thermal design and mechanical design. However, the out-of-date conventional machine design can neither reflect the advances in the past 30 years, nor exploit the trade-offs between design factors from the multi-physics nature of the electrical machine. This work focus on the development a fast and efficient method for the design and optimization of Surface Mount Permanent Magnet (SMPM) machines and induction machines, as influenced by the energy source, mechanical loads, thermal effects, and the up-to-date developments in materials and manufacturing capabilities. A new analytical design method is developed for the electromagnetic design of SMPM machines. Both distributed and concentrated winding types of SMPM machines are considered and compared. Based on the proposed electromagnetic analytical design method and a generic thermo-mechanical machine design model [1], an innovative and computationally efficient electromagnetic-thermo-mechanical integrated design method is developed for SMPM machines. Particle Swarm Optimization (PSO) is applied in a novel way based on this integrated design method for the multi-objective design optimization of SMPM machines. With the proposed method, the thermal and mechanical design is no longer treated separately and heuristically as in the traditional design, but has been systemically integrated with the electromagnetic design; the effect of power source, cooling capability, thermal limits, and up-to-date material capabilities are also reflected in the design and optimization. Superior designs compared to traditional designs can be achieved with PSO based multi-objective optimization. The proposed integrated design approach also has the merit of good computational efficiency and provides a significant time reduction of the design cycle compared to finite element analysis. A novel electromagnetic analytical design method of induction machines has been developed, which needs only six prime design variables but is able to design induction machines in fine details. The advantage over the traditional and other existing design method is that this proposed method does not have the heuristic selection of the design variables and does not need manual design iterations. The computing time is almost negligible and the design cycle is significantly reduced compared to the tradition machine design.

Thesis (M. Phil.)--University of Hong Kong, 1989.

published_or_final_version / Electrical Engineering / Master / Master of Philosophy

No description available.

No description available.

No description available.

The stator inter-turn faults can result in catastrophic failure of the electric machines leading to extended downtime of the equipment, increased cost of repair and heavy financial losses in the industries. In the recent trends, online fault diagnosis of the electric machines that arc employed in critical applications has been considered very important since frequent outage of the machines for the purpose of testing cannot he recommended. In this work. diagnostic tools have been developed to unambiguously detect the early stages of these limits in the salient-pole synchronous machines. both reluctance synchronous machine and synchronous machine with DC excitation. Motor current signature analysis. a very useful tool in the condition monitoring of electrical machines. has been primarily used for this purpose. This study mainly consists of development of theoretical background for the diagnostic schemes followed by the implementation of these schemes on both simulated and experimental machines. For this purpose. detailed mathematical models of the synchronous machines have been developed that can include stator inter-turn faults with desired fault severity. The developed models can also accommodate some structural asymmetries of the machines. These models have been instrumental in testing the proposed diagnostic schemes under ideal conditions. Also. reversible stator inter-turn faults have been carefully created in the experimental machines to test the feasibility of the diagnostic schemes under practical conditions. In order to ensure unambiguous fault detection. a detailed analysis has been performed under various possible abnormal operating conditions of the machines such as supply unbalance. time harmonics and internal asymmetries of the machines. Initially. certain drawbacks have been identified in a diagnostic scheme based on negative sequence quantities of the machine and critical improvements have been suggested to enhance its sensitivity. However, the modified method fails to detect faults involving one turn short. Hence a frequency domain approach has been considered to detect these faults. As a first step in this direction, it has been demonstrated that the triplen harmonics in the line current of synchronous machines cannot detect these faults unambiguously. Subsequently, owing to the stored magnetic energy in the machine after supply disconnection, it has been observed that the triplen harmonics in the terminal voltages of RSM can be useful for unambiguous detection of stator inter-turn faults. A new and very effective technique of online fault detection. based on the monitoring of some specific frequency components in the field current. has been developed for the synchronous machines with DC excitation. This scheme uses the structural asymmetries of the field winding. Similar results have also been realized using a rotor-mounted search-coil with very high sensitivity. In this work, an instrument has also been devised to implement fault diagnosis on machines using the computational capabilities of digital signal processors.

Thesis (PhDEng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: The advent of new high energy product permanent magnet materials has opened great opportunities for novel electrical machine topologies with advantageous features such as high efficiency and high power/weight ratio. Amongst others, axial field permanent magnet (AFPM) machines with ironless stators are increasingly being used in power generation applications. Because of the absence of the core losses, a generator with this type of design can operate at a substantially high efficiency. Besides, the high compactness and disc-shaped profile make this type of machine particularly suitable for compact integrated power generation systems. Due to construction problems, the generator application of this type of machine has been limited to quite a low power range. There is a need to investigate the performance capability of this type of AFPM machine in the upper medium power level. The focus of this thesis is on the design optimisation of the air-cooled AFPM generator with an ironless stator. A design approach that directly incorporates the finite element field solution in a multi-dimensional optimisation procedure is developed and applied to the design optimisation of a 300 kW (at unity power factor) AFPM generator. To enable an overall design optimisation of the machine, different design aspects, such as the cooling capacity, the mechanical strength and eddy loss, are also studied in this research. To enable the free movement of the rotor mesh with respect to the stator mesh, the air-gap element originally proposed by Razek et. al. is derived for Cartesian coordinate systems. For minimising the large computation overhead associated with this macro element, a number of existing time-saving schemes have been utilised together with the derived Cartesian air-gap element. The developed finite element time-step model is applied to calculating the steadystate performance of the AFPM machine. Since the flux distribution in an AFPM machine is three dimensional by nature, calculating the eddy current loss by merely using a simple analytical method may be subject to a significant error. To overcome this problem, the two dimensional finite element field modelling is introduced to perform accurate field analysis. To exploit the full advantages of the twodimensional finite element modelling, a multi-layer approach is proposed, which takes into account the variation of the air-gap flux density in the conductors with regard to their relative positions in the air-gap. To account for the radial variation of the field, a multi-slice finite element modelling scheme is devised. The thermal analysis is an important aspect of the design optimisation of AFPM machines. From a design point of view, it is preferable to have a simple but effective method for cooling analysis and design, which can easily be adapted to a wide range of AFPM machines. In this thesis a thermofluid model of the AFPM machine is developed. The fluid flow model is needed for calculating the air flow rate, which is then used to find the convective heat transfer coefficients. These are important parameters in the subsequent thermal calculations. Experimental investigations have been carried out to verify each of the above-mentioned models/methods. With these models implemented, the design optimisation of an air-cooled ironless stator 300 kW (at unity power factor) AFPM generator is carried out. The performance measurements done on the fabricated prototype are compared in this thesis with predicted results. The study shows that the proposed design approach can be applied with success to optimise the design of the AFPM machine. The advantages of high power density, high efficiency, no cogging torque and good voltage regulation make this type of AFPM machine very suitable for power generator applications. The optimum steady-state performance of the AFPM machine shows that this machine with an ironless stator is an excellent candidate for high speed power generator applications, even in the upper medium power level. The good cooling capacity of this type of machine holds the promise of its being a self-cooled generator at high power ratings. / AFRIKAANSE OPSOMMING: Die uitvinding van nuwe hoë energiedigtheid permanent magneet materiale het groot geleenthede vir nuwe elektriese masjien topologië laat ontstaan met voordelige eienskappe soos hoë benuttingsgraad en hoë drywing/gewig verhouding. Onder andere word die aksiaalveld permanente magneet (AVPM) masjiene met kernlose stators toenemend gebruik vir elektriese generator toepassings. As gevolg van die afwesigheid van kernverliese kan 'n generator met hierdie tipe ontwerp teen 'n aansienlik hoë benuttingsgraad werk. Daarbenewens maak die hoë kompaktheid en skyfvorm-profiel die masjien in besonder geskik vir die ontwikkeling van kompak geïntegreerde drywing generator stelsels. As gevolg van konstruksie probleme is die toepassing van hierdie tipe masjien as generator beperk tot redelik lae drywingsgebiede. Dit is nodig om die werkverrigtingsvermoë van hierdie tipe AVPM masjien in die boonste medium drywingsgebied te ondersoek. Die fokus van hierdie tesis is op die ontwerp-optimering van 'n lugverkoelde AVPM generator met 'n kernlose stator. 'n Ontwerpsbenadering wat die eindige element veldoplossing in 'n multi-dimensionele optimeringsprosedure insluit, is ontwikkel en toegepas op die ontwerpsoptimering van 'n 300 kW (by eenheidsarbeidsfaktor) AVPM generator. Om 'n globale ontwerpsoptimering van die masjien te kan doen is verskillende ontwerpsaspekte soos die verkoelingskapasiteit, meganiese sterkte en werwelverliese ook in hierdie navorsing bestudeer. Om die vrye beweging van die rotormaas ten opsigte van die statormaas te verseker is die lugspleet-element, soos oorspronklik deur Razek et al voorgestel, afgelei vir Cartesiaanse koórdinaat stelsels. Om die lang berekeningstyd geassosieer met hierdie makro-element te minimaliseer is 'n aantal bestaande tydbesparende metodes saam met die ontwikkelde Cartesiaanse lugspleet-element gebruik. Die ontwikkelde eindige element tydstapmodel is toegepas om die bestendige werkverrigting van die AVPM masjien te bereken. Aangesien die vloedverspreiding in 'n AVPM masjien van nature drie-dimensioneel is, kan die berekening van die werwelstroomverliese tot aansienlike foute lei as eenvoudige analitiese metodes gebruik word. Om hierdie probleem te oorkom is twee-dimensionele eindige element modellering gebruik om akkurate veld-analise te doen. Om die volle voordele van die twee- dimensionele eindige element modellering te eksploiteer is 'n multi-laag benadering voorgestel wat die variasie van die lugspleetvloeddigtheid in die geleiers met betrekking tot hulle relatiewe lugspleetposisies in ag neem. Om voorsiening te maak vir die radiale variasie van die veld, is 'n multi-skyf eindige element modelleringstegniek ontwikkel. Die termiese analise is 'n belangrike aspek van die ontwerpsoptimering van AVPM masjiene. Vanuit 'n ontwerpsoogpunt is dit verkieslik om 'n eenvoudige maar tog effektiewe metode van verkoelingsanalise en -ontwerp te hê wat maklik toegepas kan word op 'n wye reeks van AVPM masjiene. In hierdie tesis word 'n termovloeimodel van die AVPM masjien ontwikkel. Hierdie vloeimodel is nodig vir die berekening van die lugvloeitempo, wat op sy beurt weer nodig is om die konveksie hitte-oordrag koëffisiënte te bepaal. Hierdie is belangrike parameters in die opvolgende termiese berekeninge. Eksperimentele ondersoek is uitgevoer om elkeen van die bogenoemde modelle en metodes te verifieer. Nadat hierdie modelle geïmplimenteer is, is die ontwerpsoptimering van 'n 300 kW (by eenheidsarbeidsfaktor) lugverkoelde kernlose stator AVPM generator uitgevoer. Die werkverrigtingmetings gedoen op 'n vervaardigde prototipe masjien, word in hierdie tesis vergelyk met voorspelde resultate. Daar word getoon dat die voorgestelde ontwerpsbenadering met sukses toegepas kan word om die ontwerp van die AVPM masjien te optimeer. Die voordele van hoë drywingsdigtheid, hoë benuttingsgraad, geen vertandingsdraaimomente en goeie spanningsregulasie maak hierdie masjien baie aantreklik vir generator toepassings. Die optimum bestendige werkverrigting van die AVPM masjien toon dat hierdie masjien met 'n kernlose stator 'n goeie kandidaat is vir hoë spoed generator toepassings, selfs in die boonste medium drywingsgebied. Die goeie verkoelingskapasiteit van hierdie tipe masjien hou die belofte in van'n selfverkoelde generator by hoë drywing aanslae.