To see the other types of publications on this topic, follow the link: Electrical machines.
Dissertations / Theses on the topic 'Electrical machines'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Electrical machines.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Cooke, Glynn. "Magnetically geared electrical machines." Thesis, University of Sheffield, 2018. http://etheses.whiterose.ac.uk/20710/.
Full textAbstract:
Considerable research efforts are being carried out worldwide to develop technologies which meet the increasing demand for the efficient utilisation of energy resources. Modern applications, such as renewable energy and electrical vehicles, place a premium on electro-mechanical energy conversion in a power dense and high efficiency manner. Magnetic gears (MG) and magnetically geared machines, offer an attractive alternative to existing systems which may favour the combination of a high speed electrical machine with a mechanical gearbox. This has led to the opportunity to use Pseudo Direct Drives (PDDs) and MGs to be developed for use on an industrial scale. Therefore, in this thesis techniques for facilitating the manufacture and robustness of PDDs are presented, for both radial and axial field topologies. This includes use of alternative windings and soft magnetic composites. PDDs and MGs has so far mainly been developed in the radial topology and little attention has been given to axial topologies. The pole piece (PP) rotor required for MG operation, represents the main difference between PDD/MG and a conventional electrical machine. As such the PP shape and supporting structures have been investigated both in terms of electromagnetic and mechanical performance. Furthermore, detailed electromagnetic and thermal design and analysis of an axial field PDD (AFPDD) with improved robustness was undertaken, and a prototype was manufactured to demonstrate the operation of the AFPDD and validate the predictions.
2
Muhit, M. S. "Magnetic and Electric Characterization of Materials for Electrical Machines." Thesis, KTH, Elektrisk energiomvandling, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-53689.
Full textAbstract:
This thesis aims to characterize materials for electrical machines. Electromagnetic properties (b-hcurves) and electrical resistivity were the main properties investigated in the project work. Two types of samples are considered: stator lamination sheet and rings made of steel used for structural pieces in large AC machines. To facilitate magnetic characterization experiments, an existing test setup was upgraded. Sensors and amplifiers have been developed. The control system has been upgraded and developed SIMULINK modules have been adapted to dSPACE GUI. The retrieved ‘B’ and ‘H’ signals are processed offline to obtain the results. The lamination sheet has been tested for frequencies in the range [0.1-150 Hz] and flux density levels up to 1.5 T. The obtained results depict characteristics hysteresis curves and measured loss figures. The ring samples (structural steel) are characterized to explore the B-H curves at frequencies in the range [0.1-250 Hz] and field intensity up to 900 A/m. For resistivity measurements of the lamination sheets and ring samples, standard resistivity measurement techniques have been implemented.
3
Gerada, David. "High speed electrical machines for the more-electric engine." Thesis, University of Nottingham, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.659206.
Full textAbstract:
With the increasingly stringent emissions legislation as well as the hiking fuel prices, engine electrification is currently a prime path for automotive companies to meet the environmental and efficiency targets, thus placing the need for high-performance automotive electrical machines. This research looks at developing high-speed electrical machines for an electrically-assisted turbocharger to be used within Cummins' heavy duty diesel engines. While the potential benefits of such a system are high, integrating a high speed, high power-density electrical machine within the aggressive turbocharger environment is challenging. In this work detailed system multi-domain models which include the electromagnetic, thermal and mechanical aspects are developed. Using these models, together with knowledge of electrical machine material properties, the capabilities and limitations of different types of electrical machines for use in electrically-assisted turbo-charging are determined. The field weakening properties, robustness and relatively low-cost make the Induction Machine the preferred technology for the application. This work provides a set of design guidelines for maximising the power density of high speed Induction Machines. In particular moving away from the conventionally used round rotor-bar and tailoring the split-ratio together with tailoring the machine IS electrical and magnetic loadings are shown to be important aspects in increasing the power density. An algorithm for increasing the power-density of high-speed induction machines is presented. Design recommendations are also presented for PM machines where tailoring the air-gap length is identified and shown to be important in optimising the distribution of losses. A computationally-efficient PEA-based technique is developed for the analysis of closed rotor-slot IMs. The optimized 9.5kW, 50000rpm IM design is prototyped and experimental results compared to those predicted from analysis.
4
Downes, David. "Interactive models of electrical machines." Thesis, Nottingham Trent University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.273777.
Full text
5
Panda, Goutam Kumar. "Nonlinear phenomenon in electrical machines." Thesis, University of North Bengal, 2002. http://hdl.handle.net/123456789/1033.
Full text
6
Smith, Daniel James Bernard. "High speed high power electrical machines." Thesis, University of Newcastle upon Tyne, 2014. http://hdl.handle.net/10443/2645.
Full textAbstract:
High Speed High Power (HSHP) electrical machines push the limits of electromagnetics, material capabilities and construction techniques. In doing so they are able to match the power performance of high speed turbomachinery such as gas turbines, compressors and expanders. This makes them attractive options for direct coupling to such machinery as either a power source or as a generator; eliminating the need for gearboxes and achieving a smaller system size and greater reliability. The design of HSHP machines is a challenging, iterative process. Mechanical, electromagnetic and thermal constraints are all placed on the machine shape, topology, operating point and materials. The designer must balance all of these constraints to find a workable solution that is mechanically stable, can work within the available electrical supply and will not overheat. This thesis researches the fundamental origins and interaction of the mechanical, electromagnetic and thermal constraints on electrical machines. Particular attention was paid to improving the accuracy of traditional mechanical rotor design processes, and improving loss estimation in inverter fed machines. The issues of selecting an appropriate electric loading for low voltage machines and choosing effective, economic cooling strategies were explored in detail. An analytical iterative design process that combines mechanical, electromagnetic and thermal design is proposed; this process balances the need for speed versus accuracy for the initial design of a machine, with Finite Element Analysis used only for final validation of performance and losses. The design process was tested on the design and manufacture of a 1.1MW 30,000rpm PM dynamometer used in an industrial test stand. The machine operating point was chosen to meet a gap in the industrial machines market and exceed the capabilities of other commercially available machines of the same speed. The resulting machine was successfully tested and comfortably meets the performance criteria used in the design process.
7
Anpalahan, Peethamparam. "Design and analysis of permanent magnet electrical machines for hybrid electric vehicles." Thesis, Imperial College London, 2007. http://hdl.handle.net/10044/1/7605.
Full text
8
Shahaj, Annabel. "Mitigation of vibration in large electrical machines." Thesis, University of Nottingham, 2010. http://eprints.nottingham.ac.uk/11337/.
Full textAbstract:
In this study two new technologies are investigated with a view to improving the efficiency and reducing the vibrations of large electrical machines. These machines are used for high powered industrial applications. Individually controlled conductors are part of an active stator project that Converteam Ltd are developing. This involves individual conductors located in each stator slot that can be controlled separately. These replace traditional polyphase windings in order to provide a high level of control over the operation of the machine. A linear magneto-mechanical finite element model has been used here to show that this control method can enable a 44% reduction in the copper loss from the machine compared to a sinusoidal supply whilst maintaining the same operational torque. This method introduces extra Fourier harmonics into the excitation pattern supplied to the machine that are not present in the supply current to traditional polyphase windings. These extra harmonics utilize saliency advantageously to produce torque. However, they also increase the vibration of the stator and may increase hysteresis loss in the iron. The bimorph concept is an idea that is unique to this thesis. This concept involves individually controlled conductors positioned through the root of each stator tooth. On application of a relatively small power input to these conductors a magnetic field is created in the stator which distorts the existing magnetic field. Under certain conditions, the magnetostriction phenomenon causes the teeth to act as a vibration absorber. The effect of this method on the Maxwell forces in the air gap is small. This enables the cancellation of components of vibration of the stator whilst the machine torque is maintained. This is a vibration control method suited to high frequency vibrations where the deformed shape of the stator includes a rocking motion of the teeth and where the resultant stator vibrations lead to tonal noise emission from the machine. This thesis investigates the two technologies mentioned above with a magnetomechanical finite element model and two experimental investigations. The thesis also contains background information relevant to this study including an introduction to electrical machines and power electronics, noise radiation and sources of noise in electrical machines, finite element modelling, vibrations of electrical machines and vibration absorbers.
9
Kampisios, Konstantinos T. "Electrical machines parameter identification using genetic algorithms." Thesis, University of Nottingham, 2010. http://eprints.nottingham.ac.uk/14005/.
Full textAbstract:
In Indirect Field Orientation (IFO) of induction motors, the interest for parameters identification has increased rapidly due to the great demand for high performance drives and more sophisticated control systems that have been made possible by the development of very powerful processors, such as floating point DSPs. Accurate knowledge of the machine electrical parameters is also required to ensure correct alignment of the stator current vector relative to the rotor flux vector, to decouple the flux - and torque - producing currents and to tune the current control loops. The accuracy and general robustness of the machine is dependant on this model. Artificial intelligent technologies have been tested in the field of electro mechanics like neural networks, fuzzy logic, simulated annealing and genetic algorithms. These methods are increasingly being utilised in solving electric machine problems. This thesis addresses a novel non - intrusive approach for identifying induction motor equivalent circuit parameters based on experimental transient measurements from a vector controlled Induction Motor (I.M.) drive and using an off line Genetic Algorithm (GA) routine with a linear machine model. The evaluation of the electrical motor parameters at rated flux operation is achieved by minimising the error between experimental responses (speed or current) measured on a motor drive and the respective ones obtained by a simulation model based on the same control structure as the experimental rig. An accurate and fast estimation of the electrical motor parameters is so achieved. Results are verified through a comparison of speed, torque and line current responses between the experimental IM drive and a Matlab - Simulink model. The second part of the research work introduces a new approach based on heuristic optimisation for identifying induction motor electrical parameters under different operating conditions such as different load and flux levels. Results show via interpolation test the effect of the most important electrical parameters, the magnetising inductance Lm and rotor resistance Rr, at each different operating condition.
10
Rönnberg, Kristian. "Heat-transfer simulations applied to electrical machines." Licentiate thesis, KTH, Teknisk mekanik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-286686.
Full textAbstract:
Electrification and energy efficiency are two important aspects in present scenarios describing a sustainable future. Electric motors constitute a large fractionof industry’s electricity demand today, and it is expected to remain high inthe future. Electrification of the transport sector is expected in a sustainabledevelopment scenario, leading to a large increase in electric vehicles. Theirpropulsion systems will contain one or several motors.Development of new energy efficient motors and generators requires highresolution methods for studying and describing heat transfer phenomena. Thissince temperature level affects a motors efficiency and effective and efficientcooling allows for using less active material in the motor.In this work simulations of temperature distribution in a motor for tractionapplications are performed with different specifications of the loss distributionand distribution of coolant flow. Simulation results are compared to measuredvalues. The comparison shows how the simulation results differ in comparisonto the measurements. It can be concluded that attention needs to be paid tohow the simulation is defined when comparing to measured data.In establishing high resolution simulation approaches, the heat transfersystem constituting of an impinging jet on a flat plate is considered as aprototype problem. A Large-Eddy Simulation (LES) approach is employed tostudy the heat transfer and gather heat transfer data. Statistical analysis ofsampled heat transfer data shows behavior which is previously unpublished.The application of Proper Orthogonal Decomposition (POD), on the heattransfer field, and Extended Proper Orthogonal Decomposition (EPOD), linkingheat transfer modes with fluid flow modes, regarding the impinging jet systemis performed for the first time. The results show a clear correlation betweenstructures in the heat transfer field and structures in the fluid flow field.The investigated simulation methods and approaches can be employed instudies of heat transfer in electric machines.
11
KöÅ, er Hür 1976. "Development of magnetic induction machines for micro turbo machinery." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/8119.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2002.Includes bibliographical references.
This thesis presents the nonlinear analysis, design, fabrication, and testing of an axial-gap magnetic induction micro machine, which is a two-phase planar motor in which the rotor is suspended above the stator via mechanical springs, or tethers. The micro motor is fabricated from thick layers of electroplated NiFe and copper, by our collaborators at Georgia Institute of Technology. The rotor and the stator cores are 4 mm in diameter each, and the entire motor is about 2 mm thick. During fabrication, SU-8 epoxy is used as a structural mold material for the electroplated cores. The tethers are designed to be compliant in the azimuthal direction, while preventing axial deflections and maintaining a constant air gap. This enables accurate measurements of deflections within the rotor plane via a computer microvision system. The small scale of the magnetic induction micro machine, in conjunction with the good thermal contact between its electroplated stator layers, ensures an isothermal device which can be cooled very effectively. Current densities over 109 A/m2 simultaneously through each phase is repeatedly achieved during experiments; this density is over two orders of magnitude larger than what can be achieved in conventional macro-scale machines. More than 5 Nm of torque is obtained for an air gap of about 5 zm, making this micro motor the highest torque density micro-scale magnetic machine to date. About 0.3 buNm for the large air gap of 70 m is also achieved in systematic tests that reveal the influence of strong eddy-currents and associated nonlinear saturation within the micro motor.
(cont.) Eddy-current effects are modeled using a finite-difference vector potential formulation. Its results demonstrate the presence of flux crowding on the stator surface, which leads to heavy saturation. To capture saturation effects, a fully nonlinear finite-difference time-domain simulation is developed to solve Maxwell's Equations within the computational space of the micro machine. To mitigate the inherent stiffness in the partial differential equations, the speed of light is artificially reduced by five orders of magnitude, taking special care that assumptions of magnetoquasistatic behavior are still met. The results from this model are in very good agreement with experimental data from the tethered magnetic induction micro motor.
by Hür KöÅer.
Ph.D.
12
MINERVINI, MARCELLO. "Multi-sensor analysis and machine learning classification approach for diagnostics of electrical machines." Doctoral thesis, Università degli studi di Pavia, 2022. http://hdl.handle.net/11571/1464785.
Full text
13
Bourchas, Konstantinos. "Manufacturing Effects on Iron Losses in Electrical Machines." Thesis, KTH, Elektrisk energiomvandling, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-172373.
Full textAbstract:
In this master thesis, the magnetic properties of SiFe laminations after cutting and welding are studied. The permeability and the iron loss density are investigated since they are critical characteristics for the performance of electrical machines. The magnetic measurements are conducted on an Epstein frame for sinusoidal variations of the magnetic ux density at frequencies of 50, 100 and 200 Hz, according to IEC 404-2. Mechanical cutting with guillotine and cutting by means of ber and CO2 laser are performed. The inuence of the ber laser settings is also investigated. Especially the assisting gas pressure and the power, speed and frequency of the laser beam are considered. In order to increase the cutting e ect, the specimens include Epstein strips with 1, 2 and 3 additional cutting edges along their length. It is found that mechanical cutting degrades the magnetic properties of the material less than laser cutting. For 1.8% Si laminations, mechanical cutting causes up to 35% higher iron loss density and 63% lower permeability, compared to standard Epstein strips (30 mm wide). The corresponding degradation for laser cut laminations is 65% iron loss density increase and 65% permeability drop. Material of lower thickness but with the same Si-content shows lower magnetic deterioration. Additionally, laser cutting with high-power/high-speed characteristics leads to the best magnetic characteristics among 15 laser settings. High speed settings have positive impact on productivity, since the cutting time decreases. The inuence of welding is investigated by means of Epstein measurements. The test specimens include strips with 1, 3, 5 and 10 welding points. Experiments show an iron loss increase up to 50% with a corresponding 62% reduction in the permeability. A model that incorporates the cutting e ect is developed and implemented in a FEMbased motor design software. Simulations are made for a reference induction motor. The results indicate a 30% increase in the iron losses compared to a model that does not consider the cutting e ect. In case of laser cut core laminations, this increase reaches 50%. The degradation prole considers also the deteriorated magnetizing properties. This leads to increased nominal current up to 1.7% for mechanically cut laminations and 3.4% for laser cut laI detta examensarbete studeras hur de magnetiska egenskaperna hos SiFe-plat paverkas av skarning och svetsning. Permeabilitet och jarnforlustdensitet undersoks eftersom de ar kritiska variabler for elektriska maskiners prestanda. De magnetiska matningarna genomfordes pa en Epstein ram med en odesfrekvens pa 50, 100 och 200 Hz, enligt IEC 404-2. E ekterna av mekanisk skarning med giljotin samt skarning med ber- och CO2-laser studerades. Inverkan av olika berlaserinstallningar undersoktes ocksa genom att variera gastrycket, skarhastigheten samt frekvensen och e ekten av laserstralen. For att oka skare ekten inkluderades Epsteinremsor med ytterligare 1, 2 och 3 langsgaende skarsnitt. Det visas att mekanisk skarning har en mindre paverkan pa de magnetiska egenskaperna hos materialet an vad laserskarning har. Matningar pa plat med 1.8% Si visar att da prov med tre extra langsgaende giljotinklipp anvands kan permeabiliteten reduceras med upp till 63% och jarnforlusterna kan oka med upp till 35%. Motsvarande resultat for laserskurna platar visar en permeabilitetsreduktion pa upp till 65% och en jarnforlustokning pa upp till 65%. Ur studien av de tva studerade skarprocesserna framkommer aven att tunnare plat paverkas mindre negativt an tjockare plat. Ett antal olika installningar har provats for att utreda hur olika parametrar paverkar e ekterna av laserskarning. Studien indikerar att skarning med hog e ekt och hog hastighet ger den minsta paverkan pa materialets magnetiska egenskaper. Vilket aven har en positiv inverkan pa produktiviteten vid laserskarning. Epsteinprover har aven utforts for att undersoka vilka e ekter som introduceras da SiFe-plat svetsas. Provstyckena bestod av remsor med en, tre, fem och 10 svetspunkter. Experimenten visar en jarnforlustokning med upp till 50% samt en permeabilitetsreduktion upp till 62% da platarna svetsats samman tva och tva. En modell for att studera e ekterna av de forandrade materialegenskaperna vid skarning pa en induktionsmotor utvecklas och implementeras i en FEM-baserad mjukvara. Resultaten tyder pa en jarnforlustokning med 30% da skare ekten orsakad av giljotin beaktas. Vid simulering av laserskuren plat kan denna okning vara sa stor som 50%. Det framkommer aven att laserskarningen kan reducera e ektfaktorn sa mycket som 2.6%.
14
Dickinson, Phillip George. "Application of soft magnetic composites in electrical machines." Thesis, University of Newcastle Upon Tyne, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.405084.
Full text
15
Amrani, Mustapha. "Development of small electrical machines utilising permanent magnets." Thesis, University of Manchester, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329764.
Full text
16
Camilleri, Robert. "Heat transfer in high current density electrical machines." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:2541b67a-bea8-4496-8410-ca1e88bf56e2.
Full textAbstract:
The aim of this research is to increase the current density of electrical machines by improving the heat transfer from the stator. Hence, this research investigates key heat transfer parameters that limit convective and conductive heat transfer. The current density is interdependent on temperature and parameters governing heat transfer. Therefore, thermal analysis of electrical machines is important to design high current density electrical machines. This research starts by investigating the role air-cooled axial flux machines in the context of electric transportation. These are found to suffer from thermal limitations, forcing the propulsive power to be distributed among several wheels. The machine topology is found to play an important role in the heat transfer limits. The internal rotor topology suffers from heat transfer limits from the casing while the internal stator topology suffers from heat transfer in the rotor-stator gap. Addressing the latter is more challenging. This research does this by investigating a novel evaporative cooling mechanism to transport heat from the machine's internal stator to the outer rotor. A proof of concept was experimentally established and the challenges for adopting this mechanism to an electrical machine are investigated. The research focus is turned to direct oil-cooled machines. These do not suffer from the same thermal limits as they use an external radiator to expel heat. However, direct liquid cooled machines suffer from a non-uniform flow distribution, which affects the stator temperature distribution. To investigate this problem, an efficient thermo-fluid model was developed to predict the flow and temperature distribution in an oil-cooled stator. This was compared to CFD models and validated to within 6% of experimental results. The stator temperature distribution is improved by carefully controlling the flow distribution. The hot spot temperature is reduced by 13 K, doubling the insulation lifetime, or for the same hot spot temperature increasing the current density by 7%. The heat transfer coefficient an oil-cooled machine was measured by adapting the double layer thin film heat flux gauge technique. Correlations for the heat transfer coefficient on the pole piece surfaces are established and compared with analytical and CFD predictions. Finally the focus is turned to conductive heat transfer in concentrated windings. These are shown to suffer from a severe temperature gradient. Heat is transferred from one winding layer to the next and a hotspot is formed on the layer with the longest thermal path. The hotspot limits the current density of the machine. A lumped parameter thermal model was developed to predict the value and location of the hotspot in concentrated windings. To shorten the thermal path of the windings, a heat sink was interleaved between the windings. The new construction offers a reduction in hotspot temperature by up to 70 K. For the same maximum temperature the current density is increased by 30%. This thesis revisits flat windings and addresses their manufacturing challenges. Lastly, the relevance of thermal contact resistances is broadened to the general thermal design of electrical machines. This research shows that modeling the thermal resistance at the interface of concentric geometry by a constant parameter is an oversimplification. This was experimentally demonstrates to change with heat flux, contact pressure and material properties.
17
Spagnol, Marco. "Maintenance of electrical machines: Instantaneous Angular Speed analysis." Doctoral thesis, Università degli studi di Trieste, 2015. http://hdl.handle.net/10077/11102.
Full textAbstract:
2013/2014This research is focused on the condition monitoring of electrical machines and its long term purpose is to monitor electrical and mechanical faults at the same time, in non-stationary conditions (variable load and speed), with a single piece of hardware. The Instantaneous Angular Speed (IAS) measurement of an electrical machine is proposed and analysed in order to detect the fault development inside it. Chapter 1 introduces some basic principles about the maintenance of an electrical machine. Machine unscheduled downtimes are frequently caused by bearing faults, and rotor/stator faults. Monitoring systems are needed when the machine is very important for the plant (cost, safety). In this chapter, the electrical machine’s behaviour is also examined. Induction electrical machines have been chosen for this research. A review of the excitation frequencies is reported in the chapter. In the last section, characteristic fault frequencies (from mechanical and electrical sources) are collected. Chapter 2 presents the IAS measurement and its signal processing. The IAS is the measurement of the shaft rotating speed in order to visualize what’s happening during a single or in multiple turns. There are many measurement methods which are based either analogical to digital conversion or which use counters. Analogical to digital methods use a standard data acquisition board. Counter methods have to use specific hardware that is more expensive, but with less data to store. In this research, the counter method is used, combined with the Elapsed Time (ET) counting technique. Chapter 3 describes the encoder system. Its output signal is acquired with an oscilloscope and with the counter board. The signal’s differences are highlighted. In this chapter, the measurement’s source of errors are listed: the encoder’s geometrical error, the counter’s quantization error, the clock stability and the general electrical noise. Chapter 4 collects all the experimental tests done during the PhD research. Three experimental test rigs are shown and two measurements at Nidec ASI S.p.A. are reported. Note that the experimental test rigs were designed and built at the Università degli Studi di Trieste during the three years of the PhD. Experimental Test Rig 1 (ETR1) is used to understand the electrical motor’s behaviour with varying speed, the difference between the IAS and the speed acquired with the Torsional Laser Vibrometer, the difference between the IAS and the acceleration signal measured with an accelerometer located on the motor’s stator, the effect of the unbalance in the IAS measurement. Experimental Test Rig 2 (ETR2) allows to examine the load effect on the IAS measurement, the magneto-motive force harmonics, the slip and the rotor effects. Experimental Test Rig 3 (ETR3) is designed in order to detect the Inner Race Bearing Fault (Ball Pass Frequency Inner - BPFI) with varying load. The acceleration, the voltage and the current are compared with the Instantaneous Angular Speed. The motor is also tested with an unbalanced power supply. The two measurements at Nidec ASI S.p.A show how the IAS measurement could be implemented in an industrial machine larger than the one tested in the laboratory. This research presents the pros and cons of the IAS measurement, highlighting the capability of detecting BPFI bearing fault, feeling the load variations owing to the brake system (a synchronous generator), measuring the Fundamental Train Frequency of an healthy bearing, detecting unbalance in the rotor and other special features. The author would like to thank the Fondo Sociale Europeo, the Regione Friuli Venezia Giulia and Nidec ASI S.p.A (an electrical motor company) for the sponsorship and the collaboration during the three PhD years covered by the SHARM project ”Manutenzione Preventiva Integrata”.
Questo studio è focalizzato al monitoraggio dello stato di salute delle macchine elettriche con l'obbiettivo finale di monitorare danni meccanici ed elettrici, in condizioni non stazionarie (carico e velocità variabili), con un singolo sistema hardware. Viene quindi proposta ed analizzata la misura della Velocità Angolare Istantanea (Instantaneous Angular Speed - IAS) di una macchina elettrica allo scopo di prevedere l'insorgere di guasti al suo interno. Il Capitolo 1 introduce i principi base relativi alla manutenzione di macchine elettriche. Di frequente, le fermate non programmate sono conseguenti a danni su cuscinetti e su rotore/statore. I sistemi di monitoraggio sono indispensabili quando la macchina è molto importante nel contesto dell'impianto, considerazione esaminata sia dal punto di vista del costo che della sicurezza. In questo capitolo, viene analizzato anche il funzionamento della macchina elettrica. Dopo un'attenta valutazione, per lo sviluppo di questa ricerca sono state selezionate le macchine ad induzione asincrone. Nel capitolo è riportata anche un'analisi bibliografica sulle frequenze caratteristiche delle forzanti elettromagnetiche presenti. Nell'ultima sezione vengono elencate le frequenze tipiche dei danni rilevabili in misure di tipo vibrazionale ed elettrico. Il Capitolo 2 presenta la misura IAS. Questa rappresenta la misurazione della velocità di rotazione dell'albero e viene analizzata con accuratezza, individuando la relazione tra velocità di rotazione e le caratteristiche dell'encoder; inoltre vengono descritti i vari processamenti del segnale. Tale sistema permette di visualizzare ciò che sta accadendo alla macchina durante il suo funzionamento, in una o più rotazioni. Esistono metodi di misura basati o sulla conversione analogico-digitale o che prevedono l’impiego di contatori. I primi si servono di una scheda di acquisizione dati standard, mentre i secondi richiedono l'utilizzo di un hardware specifico, che alle volte può risultare più costoso, ma permette di acquisire i dati occupando una quantità inferiore di memoria. In questa tesi si è scelto di utilizzare un contatore per eseguire la misura IAS, sfruttando il conteggio Elapsed Time (ET). Il Capitolo 3 descrive l'encoder. Il segnale in uscita dal dispositivo viene acquisito con una scheda contatore e con un oscilloscopio in modo da confrontare ed analizzare le differenze presenti. In questo capitolo vengono elencate le tipologie di errore presenti nel sistema encoder: l'errore geometrico, l'errore di quantizzazione, l'errore dovuto alla stabilità del clock interno e l'errore dovuto a fonti esterni di rumore elettrico. Il Capitolo 4 raccoglie tutti i test sperimentali condotti durante il dottorato. Sono stati progettati e costruiti tre setup allo scopo di evidenziare particolari aspetti e problematiche; sono riportate anche due misure eseguite presso la sala prove dell'azienda Nidec ASI S.p.A. Il setup Experimental Test Rig 1 (ETR1) è stato utilizzato per conseguire le seguenti finalità: capire il funzionamento del motore elettrico con velocità variabile, analizzare la differenza della velocità acquisita con un torsiometro laser ed una scheda contatore, confrontare una misura vibrazionale (accelerometro posizionato sullo statore del motore) e la misura IAS, analizzare l'effetto dello sbilanciamento sulla misura IAS. Il setup Experimental Test Rig 2 (ETR2) permette di esaminare l'effetto del carico sulla misura IAS, le armoniche della forza elettromotrice, l'effetto dello slip e del rotore. Il setup Experimental Test Rig 3 (ETR3) è progettato in modo da evidenziare un difetto sulla guida interna di un cuscinetto, considerando anche un carico variabile. L'accelerazione, il voltaggio e la corrente sono confrontate con la Velocità Angolare Istantanea. Il motore viene testato anche applicando una tensione di alimentazione sbilanciata. Le due misure rilevate in Nidec ASI S.p.A dimostrano che la misura IAS può essere implementata in macchine industriali di grandi dimensioni e non solo nei setup di laboratorio. Questa ricerca espone gli aspetti positivi e negativi della misura IAS, evidenziando le capacità di individuare un danno sulla guida interna di un cuscinetto, captare le variazioni di carico prodotte dal freno (un generatore sincrono), misurare la Fundamental Train Frequency di un cuscinetto in buona salute, individuare uno sbilanciamento ed altre funzionalità. L'autore vuole ringraziare il Fondo Sociale Europeo, la Regione Friuli Venezia Giulia e l'azienda Nidec ASI S.p.A (produttore di macchine elettriche di medio-grandi dimensioni) per la sponsorizzazione e la collaborazione durante i tre anni di dottorato previsti dal progetto SHARM ”Manutenzione Preventiva Integrata”.
XXVII Ciclo
1983
18
Nategh, Shafigh. "Thermal Analysis and Management of High-Performance Electrical Machines." Doctoral thesis, KTH, Elektrisk energiomvandling, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-122695.
Full textAbstract:
This thesis deals with thermal management aspects of electric machinery used in high-performance applications with particular focus put on electric machines designed for hybrid electric vehicle applications. In the first part of this thesis, new thermal models of liquid (water and oil) cooled electric machines are proposed. The proposed thermal models are based on a combination of lumped parameter (LP) and numerical methods. As a first case study, a permanent-magnet assisted synchronous reluctance machine (PMaSRM) equipped with a housing water jacket is considered. Particular focus is put on the stator winding and a thermal model is proposed that divides the stator slot into a number of elliptical copper and impregna- tion layers. Additionally, an analysis, using results from a proposed simplified thermal finite element (FE) model representing only a single slot of the sta- tor and its corresponding end winding, is presented in which the number of layers and the proper connection between the parts of the LP thermal model representing the end winding and the active part of winding are determined. The approach is attractive due to its simplicity and the fact that it closely models the actual temperature distribution for common slot geometries. An oil-cooled induction machine where the oil is in direct contact with the stator laminations is also considered. Here, a multi-segment structure is proposed that divides the stator, winding and cooling system into a number of an- gular segments. Thereby, the circumferential temperature variation due to the nonuniform distribution of the coolant in the cooling channels can be predicted. In the second part of this thesis, the thermal impact of using different winding impregnation and steel lamination materials is studied. Conven- tional varnish, epoxy and a silicone based thermally conductive impregnation material are investigated and the resulting temperature distributions in three small induction machines are compared. The thermal impact of using different steel lamination materials is investigated by simulations using the developed thermal model of the water cooled PMaSRM. The differences in alloy con- tents and steel lamination thickness are studied separately and a comparison between the produced iron losses and the resulting hot-spot temperatures is presented. Finally, FE-based approaches for estimating the induced magnet eddycurrent losses in the rotor of the considered PMaSRM are reviewed and compared in the form of a case study based on simulations. A simplified three-dimensional FE model and an analytical model, both combined with time-domain 2D FE analysis, are shown to predict the induced eddy current losses with a relatively good accuracy compared to a complete 3D FE based model. Hence, the two simplified approaches are promising which motivates a possible future experimental verification.QC 20130528
19
ShaÌneÌŒl, Martin. "Investigation of rotor cooling in salient pole electrical machines." Thesis, University of Nottingham, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.412119.
Full text
20
Lui, Zheng. "Stray magnetic field based health monitoring of electrical machines." Thesis, University of Newcastle upon Tyne, 2018. http://hdl.handle.net/10443/4105.
Full textAbstract:
Electrical machines are widely used in industrial and transportation applications which are essential to industrial processes. However, the lack of reliability and unpredictable life cycles of these machines still present opportunities and challenges for condition monitoring research. The breakdown of an electrical machine leads to expensive repairs and high losses due to downtime. The motivation of this research is to improve the reliability of electrical machines and to classify different kinds of failures via non-intrusive methods for condition-based maintenance and early warning of failure. Major potential failure types in electrical machines are winding and mechanical failures, which are caused by dynamic load state, component ageing and harsh working environments. To monitor and characterise these abnormal situations in the early stages, this thesis proposes stray magnetic field-based condition monitoring allowing fault diagnosis with the help of finite element models and advanced signal processing technology. By investigating the interaction between stray flux variations and machine failure, different kinds of faults can be classified and distinguished via numerical and experimental studies. A non-intrusive stray flux monitoring system has been developed and can provide both static and transient stray flux information and imaging. The designed monitoring system is based on a giant magnetoresistance (GMR) sensor used to capture low stray flux fields outside the electrical machine's frame. Compared with other monitoring systems, its small size, low cost, non-inventive and ease of setting up make the designed system more attractive for in many long-term monitoring applications. Additionally, integration with the wireless sensor network (WSN) means that the latter's unique characteristics makes the proposed system suitable for electrical machine monitoring in industrial applications replacing existing expensive wired systems. The proposed system can achieve real-time data collection and on-line monitoring with the help of spectrogram and independent component analysis. Three cases studies are conducted to validate the proposed system with different failures and loading states, using load fatigue, winding short-circuit failure and mechanical testing. In these case studies, electrical and mechanical failures and dynamic loads are investigated, collecting stray flux information with different kinds and sizes of electrical machines using both simulation and experimental approaches. Stray flux information is collected for different situations of winding failure, unbalanced load and bearing failures. Comprehensive transient feature extraction using spectrogram is implemented with respect to multiple failures and load variations. Spectrograms of stray flux can provide time-frequency information allowing the discrimination of different failures and load states. Different faults can be distinguished through independent component analysis of stray flux data. Compared with traditional and current detection strategies, stray flux-based monitoring can not only provide failure indicator and better resolution but also gives location information. Additionally, by applying different feature extraction methods, different failure types can be separated based on stray flux information, which is likely to be difficult to achieve using traditional monitoring approaches. However, stray flux monitoring systems suffer from issue of noise and instability, and more case studies and investigations are needed for further refinement.
21
Ridley, G. K. "Application of EL CID to salient-pole electrical machines." Thesis, University of Warwick, 2017. http://wrap.warwick.ac.uk/107783/.
Full textAbstract:
Sutton introduced EL CID in the 1970's. This thesis records the development of EL CID theory, with particular reference to its application to large, salient-pole, water-turbine driven, electrical machines, known as hydrogenerators. Factors are identified and clarified which otherwise may cause misunderstanding of hydrogenerator stator core interlamination insulation condition. Features discussed, with reference to their impact upon the detected EL CID signal, are alternative forms of excitation winding of the stator core, its constructional features, including core build bars (or key bars), core segmentation, proximity of ferrous components, plus ancillary matters such as the location of brake/jack units, the degree of machine assembly, whether in or out of the operational situation, the extent of the machine enclosure, and the presence of the stator winding and rotor-mounted salient poles. Although satisfactory application of EL CID to turbogenerators was achieved in the 1970's, anomalies arose when applied to salient-pole machines, due to shorter stator winding end-overhang, its multi-parallel circuits, and also the disincentive of realignment of the rotor if removed, making access to the stator bore and accurate location of the excitation cable more difficult. When present, joints in very large hydrogenerator stator frames and cores, for transportation, made analysis of EL CID results particularly difficult. The problem presented by core joints arose in the initial factory demonstration of application of EL CID to hydrogenerators. The solution recognises the interdependence of the two orthogonal EL CID signal components, which indicate EL CID as analogous to a transformer, with two short-circuited secondary windings; one for interlamination fault current (designated "delta"), the other being the stator winding, when present. In order to draw the phasor diagram with reference to the secondary side of the analogous transformer, the direction of the excitation phasor is reversed, since the fault current is detected in a secondary circuit. Application of standard transformer theory produces an appropriate EL CID phasor diagram, in various forms, depending upon the particular test circumstance. In this context, the significant concept of a line for which interlamination fault current (delta) is zero (i.e. a zero delta line) was introduced. The two orthogonal EL CID signals, designated PHASE and QUAD, are plotted on equal scales; unless related appropriately by a technique described, which takes the difference into account, to ensure the highest accuracy. Evaluation of delta indicates the effectiveness of core repairs, which supports the usefulness of the EL CID technique when applied to hydrogenerators, as well as turbogenerators. At core joints, the detected maximum fault current (deltamax) is usually appreciably greater than the traditional acceptance criterion of 100 mA. This is discussed, and the conclusion drawn that the distribution of delta along the core length provides an adequate indication of any weak region of interlamination insulation. The practise of routinely resetting the Phase Reference for an EL CID test is examined, and found to be not acceptable, unless the results are subsequently referred back to the basic reference. As a final demonstration of the EL CID technique usefulness, the analysis of results from a core joint, where there was an imposed artificial fault, identifies the location concerned.
22
Gerber, Stiaan. "A finite element based optimisation tool for electrical machines." Thesis, Stellenbosch : University of Stellenbosch, 2011. http://hdl.handle.net/10019.1/6635.
Full textAbstract:
Thesis (MSc (Electrical and Electronic Engineering))--University of Stellenbosch, 2011.ENGLISH ABSTRACT: Knowledge of the magnetic fields in the domain of electrical machines is required in order to model machines accurately. It is difficult to solve these fields analytically because of the complex geometries of electrical machines and the non-linear characteristics of the materials used to build them. Thus, finite element analysis, which can be used to solve the magnetic field accurately, plays an important part in the design of electrical machines. When designing electrical machines, the task of finding an optimal design is not simple because the performance of the machine has a non-linear dependence on many variables. In these circumstances, numerical optimisation using finite element analysis is the most powerful method of finding optimal designs. In this thesis, the work of improving an existing finite element simulation package, formerly known as the Cambridge package among its users, and the use of this package in the optimisation of electrical machine designs, is presented. The work involved restructuring the original package, expanding its capabilities and coupling it to numerical optimisers. The developed finite element package has been dubbed SEMFEM: the Stellenbosch Electrical Machines Finite Element Method. The Cambridge package employed the air-gap element method, first proposed by Razek et. al. [2], to solve the magnetic field for different positions of the moving component in a time-stepped finite element simulation. Because many new machine topologies have more than one air-gap, the ability to model machines with multiple air-gaps is important. The Cambridge package was not capable of this, but during the course of this work, the ability to model machines with multiple air-gaps using the air-gap element method was implemented. Many linear electrical machines have tubular, axisymmetric topologies. The functionality to simulate these machines was newly implemented because the original program was not capable of analysing these machines. Amongst other things, this involved the derivation of the coefficients of an axisymmetric air-gap element’s stiffness matrix. This derivation, along with the original air-gap element derived by Razek et. al. [2] and the extension of the method to the Cartesian coordinate system by Wang et. al. [29, 30], completes the derivation of all two-dimensional air-gap elements. In order to speed the numerical optimisation process, which is computationally expensive, parallelisation was introduced in two areas: at the level of the finite element simulation and at the level of the optimisation program. The final product is a more powerful, more usable package, geared for the optimisation of electrical machines.
AFRIKAANSE OPSOMMING: Kennis van die magnetiese velde in die gebied van elektriese masjiene word benodig om masjiene akkuraat te modelleer. Dit is moeilik om hierdie velde analities op te los as gevolg die komplekse geometrieë van elektriese masjiene en die nie-lineêre karakteristieke van die materiale wat gebruik word om hulle te bou. Dus speel eindige element analise ’n belangrike rol in die ontwerp van elektriese masjiene omdat dit gebruik kan word om die magnetiese veld akkuraat te bepaal. Wanneer elektriese masjiene ontwerp word, is dit nie ’n eenvoudige taak om ’n optimale ontwerp te vind nie omdat die werkverrigting van die masjien nie-lineêr afhanklik is van baie veranderlikes. Onder hierdie omstandighede is numeriese optimering, tesame met eindige element analise, die kragtigste metode om optimale ontwerpe te vind. In hierdie tesis word die verbetering van ’n bestaande eindige element simulasie pakket, wat onder gebruikers van die pakket as die Cambridge pakket bekend staan, en die gebruik van hierdie pakket vir die optimering van elektriese masjiene, voorgelê. Die werk het die herstrukturering van die oorspronklike pakket, die uitbreiding van die pakket se vermoëns en die koppeling van die pakket aan numeriese optimeerders behels. Die ontwikkelde eindige element pakket word SEMFEM genoem: die Stellenbosch Elektriese Masjiene Finite Element Method. Die Cambridge pakket het van die lugspleet element metode, soos oorspronlik deur Razek et. al. [2] voorgestel, gebruik gemaak om die magnetiese veld vir verskillende posisies van die bewegende komponent in ’n tyd-stapsgewyse eindige element simulasie op te los. Omdat baie nuwe masjien topologieë meer as een lugspleet het, is die vermoë om masjiene met meer as een lugspleet te kan modelleer belangrik. Die Cambridge pakket was nie hier toe in staat nie, maar die vermoë om masjiene met meervoudige lugsplete te modelleer is gedurende hierdie werk geïmplementeer. Baie lineêre masjiene het tubulêre, assimmetriese topologieë. Die funksionaliteit om hierdie masjiene te simuleer is nuut geïmplementeer omdat die oorspronlike program nie in staat was om hierdie masjiene te analiseer nie. Dit het onder andere behels dat die koeffisiënte van ’n assimmetriese lugspleetelement se styfheidsmatriks afgelei moes word. Hierdie afleiding, tesame met die oorspronlike lugspleetelement afgelei deur Razek et. al. [2] en die uitbreiding na die Cartesiese koördinaatstelsel deur Wang et. al. [29, 30], voltooi die afleiding van alle twee-dimensionele lugspleet elemente. Om die numeriese optimeringsproses, wat tipies tydsgewys duur is, te versnel, is parallellisering op twee vlakke ingebring: op die vlak van die eindige element simulasie en op die vlak van die optimeringsprogram. Die finale produk is ’n kragtiger, meer bruikbare pakket, goed aangepas vir die optimering van elektriese masjiene.
23
Guardado, J. L. "Computer models for representing electrical machines during switching transients." Thesis, University of Manchester, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.521481.
Full textAbstract:
Switching transients produce steep fronted waves (prestrikes or restrikes) which reach the machine terminals producing severe dielectric stresses in the winding insulation. The object of this study is to develop computer models for calculating the surge distribution in the winding during switching transients as well as to obtain a machine terminal representation. Beginning with a very simple model valid for very short periods of time, the computer models are extended and finally a full machine winding model is presented. The computer models developed cover a broad time and frequency range and they are based on multiconductor transmission line theory. Several phenomena like the flux penetration into the iron and the stator inter-coil coupling are studied and incorporated into the solutions. The thesis also describes several application studies using the computer models developed. The studies include a sensitivity analysis from which guidelines for reducing the dielectric stresses in the winding insulation are suggested. Using convolution techniques and measurements on machine terminals, a technique for a better assessment of the dielectric stresses in the coils during real switching transients is presented. Finally, the computer results are supported by a comprehensive set of measurements carried out on a 6.6 KV. 1690 KW. machine winding
24
Afinowi, Ibrahim A. A. "Novel doubly salient stator slot permanent magnet electrical machines." Thesis, University of Sheffield, 2015. http://etheses.whiterose.ac.uk/11626/.
Full textAbstract:
It is well known that the torque density in electrical machines is limited by magnetic saturation and thermal constraints on the winding insulation and permanent magnets (PMs). In particular, doubly salient electrically-excited machines with the armature and DC windings on the stator, for example, the variable-flux machine (VFM), have (a) limited stator slot area for both windings, (b) severe magnetic saturation due to the DC excitation, and (c) negligible reluctance torque, and may exhibit high copper loss and high magnetic saturation. A novel method to alleviate magnetic saturation in the stator of VFMs is proposed. It is achieved by pre-magnetizing the stator core using PMs placed in the stator slots. The PM effects and performance improvements are analyzed by the finite element method based on the frozen permeability (FP) method. The developed novel VFM with PMs is a hybrid excited stator slot PM (HSSPM) machine. The basic operation principle and the electromagnetic performance with different stator and rotor pole combinations having double (all pole wound concentrated windings) and single layer (alternate pole wound concentrated windings) windings are investigated. HSSPM machines have improved electromagnetic performance and also retain the good flux regulation capability of VFMs. They can also be operated without the DC excitation, i.e. only with the armature and PM excitation. Thus, a new machine configuration – stator slot PM machine (SSPM) is further developed and investigated in terms of the influence of stator/rotor pole combinations and double and single layer windings. The newly developed SSPM machine also has the potential for fail-safe capability in the event of drive faults, and in addition, the requirements on the DC inverter and controller can be eliminated. The finite element predicted electromagnetic performances of HSSPM and SSPM machines are experimentally validated. Finally, the PM- and iron losses in HSSPM and SSPM machines having different stator/rotor pole combinations with single and double layer windings and their demagnetization ratio are analyzed. The influence of leading design parameters on their machine losses and efficiency is further investigated and their electromagnetic performance compared.
25
Romanazzi, Pietro. "Fast and accurate hot-spot estimation in electrical machines." Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:099cea22-d184-4b2f-a648-23ae8c061f52.
Full textAbstract:
Temperature is one of the parameters that limits the output torque and reduces the lifespan of electrical machines. Models that can provide accurate estimation of the temperature field in the most critical components (e.g. windings) at lower computational effort can be useful to improve the design process and reduce the time to market. Depending on the application, engineers usually rely on hi-fidelity models, e.g. based on the finite elements method (FEM), or lower order models, e.g. thermal equivalent circuits (TECs). The aim of the present work is to provide new tools and methodologies to obtain the temperature distribution within the windings using reduced order hi-fidelity models or improved TEC that could account for any working condition, including AC effects. A new methodology, based on the multiple scales method (MSM), is introduced which homogenises the complex windings domain and allows for the estimation of its effective thermal properties. The homogenisation through the MSM is performed solving a single elementary cell. The MSM also allows for the reconstruction of the actual thermal field. Extensive numerical and experimental validation is provided, in particular for the case of electrical windings encapsulated with epoxy. The thermal homogenisation is then combined with an electromagnetic homogenisation technique to estimate winding losses including AC effects, such as proximity and skin effects. The coupled analysis is validated numerically on reference test problems, and experimentally, on a suitably built "motorette". The method is proven to correctly predict losses including thermal effects and to estimate magnitude and location of the temperature hotspot within the winding domain. This work also introduces a new approach for building thermal equivalent circuits that represents the most commonly employed modelling technique for electrical machine thermal analysis. Here the TEC approaches are thoroughly analysed, highlighting limitations. The proposed new technique extends the range of numerical accuracy, accounting for high Biot numbers (up to Bi = 2) and internal heat generation. The result of this approach is higher spatial resolution about the temperature field within the winding domain and thus enables improved information on hotspot location and magnitude. The method is experimentally validated and also applied to model an electrical machine for full-electric in-wheel vehicle propulsion.
26
Sciascera, Claudio. "Design of short time duty permanent magnet electrical machines." Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/48112/.
Full textAbstract:
Recent progresses of the aviation industry toward the More Electric Aircraft have increased the demand for high performance Electro-Mechanical Actuators. In this context, extensive research is being conducted for the design of high torque density electrical machines able to meet the high reliability standards required. For low-rate duty applications (e.g. landing gear extension, retraction and steering; flight control surfaces), this can be achieved also by exploiting the characteristic that the motor does not reach a thermal equilibrium. In this work, the principal aim is to investigate the main limits in the design of low-rate duty, high torque density electrical machines and to propose methods for the improvement of the performance and reliability of such machines. This is achieved through detailed analysis of the motor design issues, of its thermal performance, as well as of the most critical ageing phenomena during operations. A structured design procedure for surface mounted permanent magnet machines is presented. A novel thermal model which features high accuracy and low computational cost is presented. A novel winding insulation lifetime consumption model which relates the winding time to failure to its temperature profile during operations is proposed. As vessel to address the thesis’ objectives, a fault tolerant electrical machine, which is an integral part of an actuator for the extension and retraction of a helicopter landing gear, is designed, built and experimentally tested. The tests are aimed at validating the design procedure and the thermal model accuracy. A series of accelerated ageing tests is conducted on samples of the motor windings, which serve to analyse the insulation degradation processes under different stress levels and to validate the proposed lifetime consumption model.
27
Rodrigues, Leon. "High temperature embedded electrical machines for aerospace turbine applications." Thesis, University of Sheffield, 2013. http://etheses.whiterose.ac.uk/4392/.
Full textAbstract:
This thesis describes research contributions in the field of electrical machines for operation at elevated temperatures. High temperature operation of electrical machines is considered critical for the realisation of the 'more-electric aircraft' concept, which involves electrical machines embedded directly on to the shafts of the aircraft gas turbine. The particular machine of interest for this thesis is a switched reluctance machine for operation on the high pressure shaft. The hostile environment, mainly due to the high temperatures (~350°C ambient) introduces several challenges in the modelling, design and manufacture of electrical machines. In order to aid selection of materials and collect necessary data for the machine design, detailed analysis of the published magnetic and electrical data for key materials at high temperatures has been carried out. Further measurements on the high strength 50% Cobalt Iron materials were also conducted, which supplement the understanding of the materials behaviour at high temperatures, specifically in terms of the effects of the long term thermal ageing on the individual loss mechanisms in the material. The design optimisation of an SR machine for 350°C operation is also described in detail. The design procedure illustrates how the high temperature material properties influence machine performance and achievable power densities. In order to more reliably predict the performance of machines at elevated temperatures several modelling techniques have been developed. A method to calculate instantaneous core loss was introduced, which was formulated such that it could be used in circuit simulations to ensure power balance. Extensive validation of this model has also been carried out.
28
Chong, Yew Chuan. "Thermal analysis and air flow modelling of electrical machines." Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/10466.
Full textAbstract:
Thermal analysis is an important topic that can affect the electrical machine performance, reliability, lifetime and efficiency. In order to predict the electrical machine thermal performance accurately, thermal analysis of electrical machines must include fluid flow modelling. One of the technologies which may be used to estimate the flow distribution and pressure losses in throughflow ventilated machines is flow network analysis, but suitable correlations that can be used to estimate the pressure losses in rotor ducts due to fluid shock is not available. The aim of this work is to investigate how the rotation affects the pressure losses in rotor ducts by performing a dimensional analysis. Apart from the additional friction loss due to the effects of rotation, other rotational pressure losses that appear in a rotor-stator system are: duct entrance loss due to fluid shock and combining flow loss at the exit of the rotor-stator gap. These losses are analysed using computational fluid dynamics (CFD) methods. The CFD simulations use the Reynolds-averaged Navier Stokes (RANS) approach. An experimental test rig is built to validate the CFD findings. The investigation showed that the CFD results are consistent with the experimental results and the rotational pressure losses correlate well with the rotation ratio (a dimensionless parameter). It shows that the rotational pressure loss generally increases with the increase in the rotation ratio. At certain operating conditions, the rotational pressure loss can contribute over 50 % of the total system loss. The investigation leads to an original set of correlations for the pressure losses in air ducts in the rotor due to fluid shock which are more suitable to be applied to fluid flow modelling of throughflow ventilated machines. Such correlations provide a significant contribution to the field of thermal modelling of electrical machines. They are incorporated into the air flow modelling tool that has been programmed in Portunus by the present author. The modelling tool can be integrated with the existing thermal modelling method, lumped-parameter thermal network (LPTN) to form a complete analytical thermal-fluid modelling method.
29
Powell, David James. "Modelling of high power density electrical machines for aerospace." Thesis, University of Sheffield, 2004. http://etheses.whiterose.ac.uk/15158/.
Full textAbstract:
This thesis is concerned with the electrical, thermal and mechanical modelling of electrical machines for the 'more-electric' aircraft. Two specific applications are considered viz. a permanent magnet brush less DC (BLDC) machine for an electrohydraulic actuator for a primary flight control surface, and a switched reluctance (SR) starter/generator for the HP spool of a large civil aero-engine. As a consequence of the highly variable and often hostile ambient environment and constrained available space envelope, these electrical machines can rarely be designed in isolation, with thermal and mechanical constraints often having a significant influence on the design. In view of these considerations, a transient lumped parameter thermal model has been developed for the BLDC machine, and validated by experimental measurements on a prototype machine at various stages of manufacture. Since the rotor cavity of the BLDC machine is flooded with hydraulic fluid leaking from the pump, fluid friction losses have been modelled, and validated by tests on a prototype machine. Optimisation of the BLDC machine airgap has also been investigated using analytical electromagneticlfluiddynamic modelling. Detailed investigation of the mechanical stresses in the rotor of the HP spool machine have led to the development of a novel rotor structure for SR machines which is shown to have comparable electromagnetic performance with a conventional SR machine. A specific design of SR machine is analysed in detail in terms of dynamic current waveforms and the subsequent iron losses, and its thermal performance is modelled in a representative aero-engine environment.
30
Duan, Yao. "Method for design and optimization of surface mount permanent magnet machines and induction machines." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37280.
Full textAbstract:
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.
31
Sitsha, Lizo M. M. "Design of tapered and straight stator pole switched reluctance machines." Thesis, Stellenbosch : Stellenbosch University, 2000. http://hdl.handle.net/10019.1/51678.
Full textAbstract:
Thesis (MEng)--University of Stellenbosch, 2000.ENGLISH ABSTRACT: This thesis deals with the design and optimisation of medium power traction switched reluctance machines with tapered and straight stator poles. Only the prototype of the tapered stator pole machine is constructed and evaluated in this study. A non-commercial finite element package is used in the design and optimisation of the machines. The finite element method is applied directly in the optimisation procedure to optimise the design of the machines in multi-dimensions. The lumped circuit analysis method is used only for the purpose of verifying some of the finite element calculated. It is not used in the optimisation procedure. The performance characteristics of the tapered and straight stator pole machines are compared and discussed and the tapered stator pole machine is found to have better torque performance. Also the calculated and measured static torque versus rotor position characteristics of the tapered stator pole machine are compared and discussed.
AFRIKAANSE OPSOMMING: Die tesis beskryf die ontwerp en optimering van medium drywing trekkrag geskakelde reluktansie masjiene met tapse en reguit stator pole. Slegs 'n prototipe van die tapse stator pool masjien is gebou en geëvalueer. Die masjiene is ontwerp en geoptimeer met behulp van 'n nie-kommersiële eindige element metode pakket. Die eindige element metode is direk in die optimerings algoritme gebruik vir die optimering van die masjiene in multi-dimensies. Die gekonsentreede parameter stroombaananalise is slegs gebruik om sommige van die eindige element berekenings te verifeer. Die vermoës van die tapse en reguit stator pool masjiene is vergelyk en bespreek. Die resultate toon dat die tapse stator pool masjien se draaimoment vermoë beter is as die van die reguit stator pool masjien. Die berekende en gemete statiese draaimoment teenoor rotorposisie van die tapse stator pool masjien is ook vergelyk en bespreek.
32
Wang, Rong-Jie. "Design aspects and optimisation of an axial field permanent magnet machine with an ironless stator." Thesis, Stellenbosch : Stellenbosch University, 2003. http://hdl.handle.net/10019.1/53351.
Full textAbstract:
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.
33
Vélez-Reyes, Miguel. "Speed and parameter estimation for induction machines." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/14761.
Full text
34
Herndler, Barbara Linda. "Non-intrusive efficiency estimation of induction machines." Master's thesis, University of Cape Town, 2010. http://hdl.handle.net/11427/11423.
Full textAbstract:
Includes abstract.Includes bibliographical references (leaves 189-194).
Determining the efficiency of an in-service motor requires the motor to be decoupled from its load or the use of highly specialised equipment which is often unavailable on site. In order to assess the efficiency of an induction machine, it is subjected to numerous testing procedures established by recognised international testing standards. These procedures are considered to be time consuming, manually intensive and disruptive to the machine’s operation. Also, the efficiency of the machine quoted after these laboratory tests often does not reflect the motor’s efficiency under operating conditions. This thesis aims to address the aforementioned concerns by implementing a non-intrusive efficiency estimation technique that is applicable to induction motors in industry.
35
Micallef, Christopher. "End winding cooling in electric machines." Thesis, University of Nottingham, 2006. http://eprints.nottingham.ac.uk/10260/.
Full textAbstract:
The fluid flow field and temperature distribution within the end region of a Totally Enclosed Fan Cooled (TEFC) induction motor have been investigated both experimentally and using Computational Fluid Dynamics (CFD) techniques, in order to improve the thermal performance. The flow field and the distribution of heat transfer coefficients over the end windings and internal surfaces (mainly frame and end shield) are characterised for a typical end region configuration. This is then used as a base case in order to investigate the impact configuration changes have on the fluid flow field and heat transfer characteristics in the end region of TEFC induction motors. Common parameters governing the flow field inside the end region are varied, allowing recommendations for improved design and further research recommendations to be made. CFD techniques are successfully applied to model the end region, including the copper where the heat generated is a function of temperature. Through these numerical techniques a good understanding of the flow field was made possible which enabled the author to propose and test configuration changes which improve the heat transfer characteristics in the region. These changes were validated experimentally.
36
Pagonis, Meletios. "Electrical power aspects of distributed propulsion systems in turbo-electric powered aircraft." Thesis, Cranfield University, 2015. http://dspace.lib.cranfield.ac.uk/handle/1826/9873.
Full textAbstract:
The aerospace industry is currently looking at options for fulfilling the technological development targets set for the next aircraft generations. Conventional engines and aircraft architectures are now at a maturity level which makes the realisation of these targets extremely problematic. Radical solutions seem to be necessary and Electric Distributed Propulsion is the most promising concept for future aviation. Several studies showed that the viability of this novel concept depends on the implementation of a superconducting power network. The particularities of a superconducting power network are described in this study where novel components and new design conditions of these networks are highlighted. Simulink models to estimate the weight of fully superconducting machines have been developed in this research work producing a relatively conservative prediction model compared to the NASA figures which are the only reference available in the literature. A conceptual aircraft design architecture implementing a superconducting secondary electrical power system is also proposed. Depending on the size of the aircraft, and hence the electric load demand, the proposed superconducting architecture proved to be up to three times lighter than the current more electric configurations. The selection of such a configuration will also align with the general tendency towards a superconducting network for the proposed electric distributed propulsion concept. In addition, the hybrid nature of these configurations has also been explored and the potential enhanced role of energy storage mechanisms has been further investigated leading to almost weight neutral but far more flexible aircraft solutions. For the forecast timeframe battery technology seems the only viable choice in terms of energy storage options. The anticipated weight of the Lithium sulphur technology is the most promising for the proposed architectures and for the timeframe under investigation. The whole study is based on products and technologies which are expected to be available on the 2035 timeframe. However, future radical changes in energy storage technologies may be possible but the approach used in this study can be readily adapted to meet such changes.
37
Ganapathiraju, Aravind. "Support Vector Machines for Speech Recognition." MSSTATE, 2002. http://sun.library.msstate.edu/ETD-db/theses/available/etd-02202002-111027/.
Full textAbstract:
Hidden Markov models (HMM) with Gaussian mixture observation densities are the dominant approach in speech recognition. These systems typically use a representational model for acoustic modeling which can often be prone to overfitting and does not translate to improved discrimination. We propose a new paradigm centered on principles of structural risk minimization using a discriminative framework for speech recognition based on support vector machines (SVMs). SVMs have the ability to simultaneously optimize the representational and discriminative ability of the acoustic classifiers. We have developed the first SVM-based large vocabulary speech recognition system that improves performance over traditional HMM-based systems. This hybrid system achieves a state-of-the-art word error rate of 10.6% on a continuous alphadigit task ? a 10% improvement relative to an HMM system. On SWITCHBOARD, a large vocabulary task, the system improves performance over a traditional HMM system from 41.6% word error rate to 40.6%. This dissertation discusses several practical issues that arise when SVMs are incorporated into the hybrid system.
38
Shen, Gang 1968. "Hierarchical control for finite state machines." Thesis, McGill University, 1999. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=36708.
Full textAbstract:
We base the notion of state aggregation for finite state machines (FSM) on the dynamical consistency (DC) relation ([17]) between the blocks of states in any given state space partition pi. In this framework, we present the new notion of ST dynamical consistency (ST-DC) for source-target (ST) FSMs where there is a preferred sense of flow from a set of source states (S) to a set of target states (T). It is proven that if a partition pi is ST in-block controllable (ST-IBC), the partition machine of an ST FSM M based on pi, Mpi (i.e. high level abstraction of M based on pi), is controllable if and only if M itself is controllable. We also prove that all ST-IBC partition machines of M form a lattice and any chain from the top to the bottom of this lattice provides a hierarchical feedback control structure.This methodology is next extended to optimal control problems for discrete event systems (DES) modelled by finite state machines. A partition machines based scheme called hierarchically accelerated dynamic programming (HADP) is introduced which significantly speeds up the standard dynamic programming procedure (up to several orders of magnitude) at the cost of a certain degree of sub-optimality. We present necessary and sufficient conditions for the HADP procedure to generate globally optimal solutions and, further, give bounds on the degree of sub-optimality. An example called the Broken Manhattan Grid (BMG) system is used to illustrate the implementation of HADP, and flexible and generalisable code for this example is described.
Many complex systems appear in the form of the product of multiple interacting sub-systems. A formulation of multi-agent systems is presented where the dynamics of the agents are described by default specifications, of a sets of forbidden state-event relational pairs, denoted R . Such systems are called relational multi-agent product systems (MA( R )). The application of the HADP methodology to relational multi-agent product systems is analysed. A multi-machine system consisting of a time counter and agents called a timed multi-agent relational product (TMA( R )) is formulated.
To apply hierarchical control to the routing problem for networks, we consider two conceptual classes of networks: first, link network systems (LN), and, second, buffer network systems (BN). The notions of dynamical costs and network states are introduced. In particular, the notion of throughput-independent ST-IBC (TI-ST-IBC) partitions is used to formulate the incremental HADP ( IHADP) methodology. For the multiple objective optimisation problem of LNs, a notion of (vector) network state is introduced to carry the information describing the available transmission capacity of each link. For buffer network systems, the notion of (matrix) network states is given.
39
Hall, Ross. "The design of high temperature electrical machines for aerospace applications." Thesis, University of Newcastle Upon Tyne, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.420033.
Full text
40
Gundogdu, Tayfun. "Advanced non-overlapping winding induction machines for electrical vehicle applications." Thesis, University of Sheffield, 2018. http://etheses.whiterose.ac.uk/20728/.
Full textAbstract:
This thesis presents an investigation into advanced squirrel-cage induction machines (IMs), with a particular reference to the reduction of the total axial length without sacrificing the torque and efficiency characteristics and analysis of recently found non-sinusoidal bar current phenomenon, which occurs under some certain design and operating conditions, and affects the overall performance characteristics of the IMs. As a first step, the most convenient method is determined by utilizing a fractional-slot concentrated winding (FSCW) technique, which has advantages such as non-overlapping windings, high slot filling factor, and simple structure. After implementing this technique, it is found that due to the highly distorted magnetomotive forces (MMFs) created by the FSCWs, significant high rotor bar copper loss occurs. In order to reduce the MMF harmonics without increasing the size of the machine, a new technique titled “adapted non-overlapping winding” is developed. This technique consists of the combination of the auxiliary tooth and phase shifting techniques, resulting in a stator with concentrated windings of two-slot coil pitches but without overlapping the end-windings. Thanks to this method a large number of the MMF harmonics are cancelled. Thus, a low copper loss IM with significantly reduced total axial length is obtained. Influence of design parameters; such as stator slot, rotor slot, and pole numbers, number of turns, stack length, stator and rotor geometric parameters, etc. on the performance characteristics of the advanced IM is investigated and a comprehensive comparison of advanced and conventional IMs is presented. This thesis also covers an in-depth investigation on the non-sinusoidal bar current phenomenon. It is observed that the rotor bar current waveform, usually presumed to be sinusoidal, becomes non-sinusoidal in some operation and design conditions, such as high speed operation close to synchronous speed, or fairly high electrical loading operation, or in the IMs whose air-gap length is considerably small, etc. Influences of design and operating parameters and magnetic saturation on the rotor bar current waveform and the performance characteristics of squirrel-cage IMs are investigated. The levels of iron saturation, depending on the design and operating parameters, in different machine parts are examined and their influences are also investigated, whilst the dominant part causing the non-sinusoidal rotor bar current waveform is identified. It is revealed that the magnetic saturation, particularly in the rotor tooth, has a significant effect on the bar current waveform.
41
Liu, Xiaojun Zhang. "Transformations and stability of electrical machines in nearly ideal operation." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/14543.
Full text
42
Miersch, Sören, Ralph Schubert, Thomas Schuhmann, Uwe Schuffenhauer, Markus Buddenbohm, Markus Beyreuther, Jeannette Kuhn, Mathias Lindner, Bernd Cebulski, and Jakob Jung. "Ceramic-like Composite Systems for Winding Insulation of Electrical Machines." IEEE, 2020. https://htw-dresden.qucosa.de/id/qucosa%3A74384.
Full textAbstract:
Insulating sheets, impregnants and encapsulation materials commonly used for winding insulation offer low thermal conductivities. This leads to an increased heating of the winding of electrical machines and to the existence of hotspots. The electromagnetical utilization of the machine has to be reduced with respect to the allowed maximum winding temperature. In this paper, the development and experimental investigation of novel polysiloxane composites with ceramic fillers are presented. The materials are tested by means of impregnated and encapsulated samples of a round-wire winding as well as the main insulation of electrical steel sheets and laminated cores. Numerical models are implemented for determining the equivalent thermal conductivity of the winding compound comprising the enameled wire and the impregnant. Based on the example of a permanent-magnet synchronous machine with outer-rotor in modular construction, the potential for increasing the electromagnetical utilization is shown.
43
Buckley, Gary. "Fault detection and tolerance of electrical machines in automotive applications." Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/41992/.
Full textAbstract:
This project explores the drive for further electrification in the automotive industry and the challenges that this brings. Specifically this thesis focuses on the demands of safety and reliability; highlighting the subtle difference between the two concepts, explaining how legislation is forcing designers to consider the ways in which a system could fail and requiring them to create methods to detect and safely handle these failures, many of which can never be completely eliminated by design. With this motive in mind, the research within this thesis is focused on fault detection and condition monitoring. A novel method of rotor magnet condition monitoring is developed, an investigation into the effects of stator impedance variation is carried out to identify opportunities to develop diagnostic algorithms and sensorless control is considered as a back-up control method should a traditional position sensor fail. This thesis shows how current research and new techniques could be applied in the modern automotive industry; highlighting the demand for ever safer electronic systems as the world strives for greater levels of autonomy on the roads.
44
BORTOLOZZI, MAURO. "Modeling and analysis of special electrical machines for distributed generation." Doctoral thesis, Università degli Studi di Trieste, 2017. http://hdl.handle.net/11368/2908185.
Full textAbstract:
Nowadays, the pollution caused by the massive use of fossil fuel is a well-known critical issue makes the design of the electrical machines a crucial task because the vast majority of the industrial or household applications are integrated with this kind of technology; hence improving the efficiency of electric motors is expected to result in an extraordinary benefit in terms of energy saving. On the other side, the increasing use of renewable energies (like wind energy, hydropower, tidal energy), combined with the distributed generation concept, call for new electric machine technology and for modern design approaches.
This doctoral thesis has been mainly focused on finding analytical procedures to model and analyze some types of electrical machines which are of interest for renewable and distributed generation. The use of analytical approaches is, in some cases, fundamental because numerical methods, mostly based on Finite Element Analysis (FEA), are very inefficient in terms of required time and computation resources.
The types of electrical machines considered in this work are various. The attention is first placed on the slotless surface permanent magnet (SPM) topology (with different types of rotor magnetization). Wound-field synchronous generators with both three phase or multiphase stator are then considered. For the various kinds of the machines taken into account, some modeling, design and analysis studies have been conducted in the attempt to fill some gaps in the existing technical literature.
In the first part of the thesis the purely analytical modeling of slotless SPM machines is addressed. In the work, it has been considered how the stator slotless design can be combined with different surface permanent magnet rotor topologies. The main efforts of the study have been addressed to the purpose of finding an explicit analytical expression to compute slotless machine torque and no-load back-EMF, covering all the SPM rotor topologies of interest.
The subsequent part of the thesis, is about the analytical computation of end-coil leakage inductance in concentric windings. For a good dynamic modeling of machines equipping this kind of winding, it is useful that their mathematical model is implemented and that model parameters are identified with good accuracy. The proposed technique shows a very good accordance compared with a 3D FEA simulation and is also validated though tests conducted on a dedicated experimental set-up.
Multiphase machines are attractive for many energy-saving fault-tolerant applications thanks to their higher efficiency and intrinsic resilience to faults. A challenging task in the modeling of multiphase machines for design and simulation is identifying the self and mutual inductances due to leakage fluxes. In this thesis is also presented a novel approach for the leakage inductance determination in multiphase machines based on routine tests combined with very simple 2D magnetostatic FEA simulations.
The subsequent part of the thesis is about the design of wound-field synchronous generators specifically required to operate in a distributed generation system where significant fluctuations are known to frequently occur in both voltage and frequency. Design provisions are investigated to improve the generator resilience to these grid disturbances.
In the last part of this thesis the attention is focused on multiphase alternators interfaced to DC distribution systems through multiple rectifiers. As a new finding presented as a part of this investigation, it is shown that a short circuit fault occurring on AC/DC rectifier terminals generates a strongly oscillatory behavior with much larger current peaks than could be predicted with conventional models regarding short circuit transients in DC networks.
45
Poskovic, Emir. "Innovative magnetic materials for the new applications in electrical machines." Doctoral thesis, Università degli studi di Padova, 2019. http://hdl.handle.net/11577/3424784.
Full textAbstract:
Permanent magnets play a key role as a component in a wide range of devices utilised by many industries; they are widely used in several electromechanical applications to convert energy, including actuators, motors and sensors, home appliances, office automation equipment, speakers, aerospace, wind generators and more.
Traditionally the adopted PMs were obtained from Rare Earth components, such as NdFeB, with high magnetic performance, but expensive. The research of alternative permanent magnets, in many cases has brought to choose the ferrites, mainly due to their low cost, but sometimes with significant design modifications of the final circuit, and possible increment of the weight.
Permanent magnets can roughly be divided into two categories: sintered (metallic) and bonded, these last representing a valid alternative to the first. Bonded magnets consist of two components: a hard magnetic powder and a non-magnetic binder; the powder may be hard ferrite, NdFeB, SmCo, and is mixed with binders for compression or injection moulding. The benefits lie in the adoption of polymeric binders to prepare the magnetic mixture: the resulting magnetic characteristic can be then “tuned” by adopting different percentages of the plastic binder. Moreover, the realisation process is simpler and cheaper than that of sintered materials, and no special protective treatment is needed.
The majority of the magnetic circuits are made with soft magnetic materials. Commonly laminated steels are adopted but recently the use of Soft Magnetic Composite (SMC) materials has increased representing a new solution to design the electrical machines with respect to traditional electrical steels.
SMC materials are realized with pure Iron grains coated and insulated by means of a layer that should be organic or inorganic. With respect to traditional laminated steel, these materials present different advantages: the capability to lead the magnetic flux in all directions, the volume reduction, the possibility to realize components with new complex shapes and geometries, and the reduction of iron losses, mainly the eddy currents, at medium and high frequency. On the other hand, the mechanical performances, in terms of strength, are in general weak.
Furthermore, a new material typology is introduced: the Hybrid Magnetic Composites (HMC), which are obtained with a combination of soft and hard magnetic materials mixed with a binder. The basic idea is that such materials should reflect the performance of AlNiCo magnets, low coercivity and adequate remanence, typically used in sensors applications.
Prototypes of traditional and unconventional rotating machines, such as assisted reluctance motors, brushless DC motors, axial flux machines and electromechanical frequency converters, have been studied in own laboratories and tested to evaluate the results coming from the adoption of the proposed materials in substitution of the commonly adopted (and expensive) Rare Earth sintered magnets. Different type of electrical machines can adopt innovative magnetic materials with the aim to improve their performance.
Induction motors are very useful and robust machines; on the other hand, such type of machines does not have a high dynamic behaviour. The DC motors can be easily controlled, but the presence of the brushes causes limitations on the efficiency, thermal restrictions and reduced life. The axial flux motors (AFM) have high efficiencies but the construction of the machines is very complex. The synchronous reluctance machines (SRM) have a lower cost compared to brushless ones.
In general, the reluctance electrical machines don’t use permanent magnets. In this way, they have a reduction in the costs and allow a high overload capability. On the other hand, the lower power factor and power density, compared to PM synchronous motor (PMSM), are the main disadvantages. The filling of flux barriers with the permanent magnets allows the overcoming of these drawbacks. However, the regular ferrite and NdFeB sintered magnets cannot fill the flux barriers with complex geometries. For this reason, the use of bonded magnets can be a solution for a better utilization and design of flux barriers.
Therefore different prototypes have been prepared and analyzed in our laboratories using SMC materials. Several experiments have been performed using dedicated test benches, where magnetic, energetic and mechanical aspects have been considered.
On the other hand, with regard to HMCs, various magnets have been made in our laboratories, and different properties have been investigated: the effect of Iron content in the material and, also the binder content effect has been analysed.
46
Tekgun, Burak. "Analysis, Measurement and Estimation of the Core Losses in Electrical Machines." University of Akron / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1481047992739036.
Full text
47
de, Santiago Ochoa Juan. "FEM Analysis Applied to Electric Machines for Electric Vehicles." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-157879.
Full textAbstract:
Electric vehicle technology is an interdisciplinary field in continuous development. It appears to be a margin for improvements. The Division for Electricity at Uppsala University is doing significant research in the field. The present thesis investigates electric machines for vehicular applications, both in the driveline and in the traction motor. Section 1 presents a driveline with two galvanically isolated voltage levels. A low power side is operated at the optimum voltage of the batteries, while a high power side is operated at a higher voltage leading to higher efficiencies in the traction motor. Both sides are coupled through a flywheel that stabilizes the power transients inherent to a drive cycle. A review of electric machine topologies for electric vehicles is presented in Section 2. The permanent magnet excited machine is the most suitable technology for an electric driveline. Section 3 is devoted to numerical models applied to electric machines. The equivalent circuit of a motor/generator with two sets of windings is first presented. This machine couples both sides of the driveline and drives the rotor of the flywheel. The electric parameters are calculated with custom FEM models. A discussion on slotless machines concludes with a simple model to analyze the magnetic field from one static 3D simulation. The tooth ripple losses in solid salient poles are also analyzed with a novel FEM approach. A complete description of the losses in electric machines gives a proper background for further discussion on efficiency. Section 4 presents the experimental work constructed to validate the theoretical models. The experiments include an axial flux, single wounded prototype, an axial flux, double wound prototype and a planed radial flux coreless prototype. Section 5 focuses on traction motors for electric vehicles. A simulated prototype illustrates a design and calculation process. The loss theory and the numerical methods presented in Section 3 are applied.
48
Sitzia, A. "Torque in elementary variable-reluctance machines." Thesis, University of Leeds, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376518.
Full text
49
Cohen, Sharon B. "Auditing technology for electronic voting machines." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/33119.
Full textAbstract:
Thesis (M. Eng. and S.B.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.Includes bibliographical references (leaf 63).
Direct Recording Electronic (DRE) voting machine security has been a significant topic of contention ever since Diebold voting machine code turned up on a public Internet site in 2003 and computer scientists at Johns Hopkins University declared the machine "unsuitable for use in a general election." Since then, many people from computer scientists to politicians have begun to insist that DREs be equipped with a paper trail. A paper trail provides a paper printout for the voter to approve at the end of each voting session. Although there have been strong political efforts to place paper trails on DRE machines, there have not been any scientific studies to indicate that paper trails are effective audits. This work describes a user study done to compare paper trails to audio audits, a new proposal for DRE auditing. Participants in the study completed four elections on a voting machine with a paper trail and four elections on a machine with an audio trail. There were purposeful mistakes inserted into the audits on some of the machines. Results from the study indicated that participants were able to find almost 10 times as many errors in the audio audit then they were able to find in the paper trail. Voters' attitudes towards the paper audit were extremely apathetic, and voters did not spend much time reviewing their paper record. When asked which type of audit voters would prefer for their own county elections, almost all voters preferred the VVPAT. These results indicate that newer alternative audit technology holds great promise in delivering a safe and accurate audit and further that paper trails have some significant design obstacles that need to be overcome before they will be effective audits.
by Sharon B. Cohen.
M.Eng.and S.B.
50
Swenson, Shane Michael 1979. "Spatial instruction scheduling for raw machines." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/28620.
Full textAbstract:
Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2002.Includes bibliographical references (leaves 89-91).
Instruction scheduling on software exposed architectures, such as Raw, must be performed in both time and space. The complexity and variance of application scheduling regions dictates that the space-time scheduling task be divided into phases. Unfortunately, the interaction of phases presents a phase ordering problem. In this thesis, the structure of program scheduling regions is studied. The scheduling regions are shown to have varying characteristics that are too diverse for a single simple algorithm to cover. A new scheduling technique is proposed to cope with this diversity and minimize the phase ordering problem. First, rather than maintaining exact mappings of instructions to time and space, the internal state of the scheduler maintains probabilities for different assignments of instructions to time and space resources. Second, a set of small scheduling heuristics cooperatively iterate over the probabilistic assignments many times in order to minimize the effects of phase ordering. A simple spatial instruction scheduler for Raw machines based on this technique is implemented and shown to outperform existing spatial scheduling systems on average.
by Shane Michael Swenson.
M.Eng.