19 research outputs found

    Studies in Electrical Machines & Wind Turbines associated with developing Reliable Power Generation

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    The publications listed in date order in this document are offered for the Degree of Doctor of Science in Durham University and have been selected from the author’s full publication list. The papers in this thesis constitute a continuum of original work in fundamental and applied electrical science, spanning 30 years, deployed on real industrial problems, making a significant contribution to conventional and renewable energy power generation. This is the basis of a claim of high distinction, constituting an original and substantial contribution to engineering science

    Investigation into high-speed thermal instability testing of synchronous turbo-generator rotors

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    A thesis submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 2017The research presented in this thesis conclusively shows that the most effective method to perform synchronous turbo-generator rotor Thermal Instability Testing is by utilising the current injection method of condition assessment. Analysis of the experiences of a local utility for well over a decade has uncovered a high number of rotors failing thermal instability testing in recent years. This trend has brought the current testing methodology into question. Two different assessment modes of testing have been found to be utilised internationally without preference, namely, current injection and friction/windage. By determining the method that is best suited to detect a thermally sensitive rotor a service provider can benefit by improved rotor reliability as well as cost saving. The evaluation is accomplished by utilising a scaled down experimental setup based on the model of a local testing facility as well as a 600 MW turbo-generator rotor. A direct thermal mapping technique has been devised utilising infrared thermography to capture the thermal distribution of the rotor surface under different test conditions. The results obtained have shown that the methods differ substantially with the friction method exhibiting a uniform surface distribution and the current-injection method exhibiting areas of higher temperature concentration around the rotor pole faces. However, weaknesses do exist in present-day testing techniques in the form of inaccurate temperature measurements during testing as well as little consideration given to external factors such as the interaction between the slip-ring and brush-gear that have the potential to influence test outcomes. A presented augmented method of performing thermal sensitivity testing taking advantage of infrared thermography is found to improve testing accuracy and aid in fault detection and location. Current thermal instability testing coupled with the direct thermal mapping method has been demonstrated to be the most effective means for performing rotor thermal sensitivity testing.MT201

    Design and Application of Electrical Machines

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    Electrical machines are one of the most important components of the industrial world. They are at the heart of the new industrial revolution, brought forth by the development of electromobility and renewable energy systems. Electric motors must meet the most stringent requirements of reliability, availability, and high efficiency in order, among other things, to match the useful lifetime of power electronics in complex system applications and compete in the market under ever-increasing pressure to deliver the highest performance criteria. Today, thanks to the application of highly efficient numerical algorithms running on high-performance computers, it is possible to design electric machines and very complex drive systems faster and at a lower cost. At the same time, progress in the field of material science and technology enables the development of increasingly complex motor designs and topologies. The purpose of this Special Issue is to contribute to this development of electric machines. The publication of this collection of scientific articles, dedicated to the topic of electric machine design and application, contributes to the dissemination of the above information among professionals dealing with electrical machines

    Loss Reduction in Axial Flux Machines using Magnetic Shielding

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    PhD ThesisAbstract– The introduction of compacted insulated iron powder in electrical machines design makes their manufacturing process easy together with high rates of production and the machine parts made from it are stable dimensionally compared to conventional laminated steel. The research work presented in this thesis was carried out with the main aim to improve the overall performance of a three-phase Axial Flux Machine (AFM) using Soft Magnetic Composite (SMC). To realise it, the machine was redesigned in a way to benefit from the unique properties of the material such as low eddy current loss at high frequency, isotropic magnetic properties and simple manufacturing process. Due to the three-dimensional (3D) nature of the SMC material and AFM structure, 3D Finite Element Analysis (FEA) was carried out for accurate prediction of performance and extensive simulation results were provided. Higher fill factor up to 70% was achieve by compacting the pre-formed coils on a bobbin before sliding onto the tooth for final assembly, which offered a significant improvement in performance. AC winding loss analysis was performed due to open-slot stator winding configuration and the higher frequency of operation resulting in skin-depths of the same order of size as the typical conductor diameters. A method of AC winding loss reduction was introduced using a single steel lamination sheet to shield the windings from stray fields due to the open-slot stator construction which encourage an elevated AC loss at AC operation. Moreover, this approach is easy to implement for this machine topology and does not require the use of more complex twisted and Litz type conductors. To validate the 3D FEA, a prototype machine was built which ultimately resulted in 6 machines being tested without and with steel lamination sheet during this PhD. The measured result which includes the back EMF, full load voltage, torque, power and losses are thoroughly presented and agreed with the 3D FEA very well. Depending on lamination type, it is shown that the AC winding loss reduced by up to 48.0%, total loss reduced by up to 31.7%, this method has disadvantages of minor reduction of up to 3.5%, 5.8% and 2.8% in the peak back EMF, torque and output power respectively. The efficiency has increased by up to 10.3%. The research studies signify the viability of designing and producing a highly efficient AFM with SMC and has the potential for mass production, this thesis makes significant contribution by implementing a simple novel method for AC winding loss reduction using steel lamination sheet to shield the stray flux due to open-slot stator winding construction.The Petroleum Technology Development Fund (PTDF) Nigeria and NASRDA-CBS

    High speed high power electrical machines

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    DEng ThesisHigh 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

    Fault tolerant drives for safety critical applications

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    PhD ThesisThe correct operation of adjustable speed drives, which form part of a larger system, is often essential to the operation of the system as a whole. In certain applications the failure of such a drive could result in a threat to human safety and these applications are termed 'safety critical'. The chance of a component failure resulting in non-operation of the drive can be dramatically reduced by adopting a fault tolerant design. A fault tolerant drive must continue to operate throughout the occurrence of any single point failure without undue disturbance to the power output. Thereafter the drive must be capable of producing rated output indefinitely in the presence of the fault. The work presented in this thesis shows that fault tolerance can be achieved without severe penalties in terms of cost or power to mass ratio. The design of a novel permanent magnet drive is presented and a 'proof of concept' demonstrator has been built, based on a 20 kW, 13000 RPM aircraft fuel pump specffication. A novel current controller with near optimal transient performance is developed to enable precise shaping of the phase currents at high shaft speeds. The best operating regime for the machine is investigated to optimise the power to mass ratio of the drive. A list of the most likely electrical faults is considered. Some faults result in large fault currents and require rapid detection to prevent fault propagation. Several novel fault sensors are discussed. Fault detection and identification schemes are developed, including new schemes for rapid detection of turn to turn faults and power device short circuit faults. Post fault control schemes are described which enable the drive to continue to operate indefinitely in the presence of each fault. Finally, results show the initially healthy drive operating up to, through and beyond the introduction of each of the most serious faults.EPSR

    Coordination of Generator Protection and Control in the Over and Under Excited Regions

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    This thesis deals with the coordination of protection and control functions associated with the synchronous generators. The excitation control functions are a key component in maintaining the stability of machines and the network. The overall objective of coordination is simple; to allow excitation control functions, the automatic recovery from excursions beyond normal limits, and only take protective action as a last resort. This thesis focuses on four areas of generator control and protection : a) Loss of excitation protection, b) Dynamic underexcitation coordination, c) Dynamic Overexcitation coordination, and d) a generic protective relay development platform for hardware and software development. Loss of excitation (LOE) is a condition in the underexcited region that presents a risk of severe damage to a generator. The state of the art in the detection of a loss of excitation condition is based on the principle that, for a zero Thevenin voltage, the generator becomes a reactance as seen from the power system. The difficulty in detecting a loss of excitation is that several other disturbances may temporarily present a similar behavior, for instance a fault followed by a power swing. In this part of the work, a new algorithm for the detection of a loss of excitation condition is proposed by using the Support Vector Machine (SVM) classification method and a careful design of the necessary feature vectors. The proposed method is robust to changes in conditions including initial load, fault types, line impedance, as well as generator parameter inaccuracies. Coordination in the underexcited region presents difficulties due to the commonly used static characteristics instead of dynamic simulation. The underexcited limit presents an overload characteristic that is not normally known or used. Once the limit is exceeded, the limiting control action is a control loop that presents a dynamic behavior not typically represented in studies in the current industry practice. It is also important to properly model and include dynamic performance of protection functions. An important consideration not typically taken into account is the actual stability limit, which depends on the characteristics and the mode of excitation control used. This thesis includes all the above considerations necessary to achieve the required coordination using the more accurate dynamic simulations. Specific scenarios that present risk to the machine or the system are included to assess the coordination achieved. A real generator from the Alberta power system is used as a case study to demonstrate the proposed coordination methodology. Coordination in the overexcited region again presents practical difficulties due to static characteristics instead of dynamic simulation of conditions that exercise the overexcitation limits. The problems observed relate to coordination methodology and modeling methods for both protection and control limits. Once the limit boundary characteristic is exceeded, the limiting action is a control loop that presents dynamic behavior that needs to be represented. Similar considerations need to be made with the protection function protecting against rotor overload. Current modeling methods mostly use low bandwidth simulations, i.e., transient stability studies. A modeling methodology as well as specific model improvements to the IEEE ST1A excitation control model are proposed to achieve the required coordination. The ST1A type is one model that can represent a wide variety of system models from different manufacturers. The proposed modeling methodology applies to high bandwidth simulations such as electromagnetic simulations. Specific important scenarios, such as severe temporary reactive overload or severe power swing conditions, where the protection and control are required to coordinate but that present risk to the machine or the system are proposed as part of the coordination considerations. The detection of LOE conditions by the proposed SVM method and by traditional methods was implemented in hardware by using a digital signal processor (DSP) platform and tested using real time power system simulations. A new platform for real time protective relay development was designed and used for the purpose of implementation. In the proposed platform, a processor independent code is used so that development can be performed using native host computer development tools. By using the proposed platform-independent code, off line testing can be performed either interactively or in batch mode for evaluating multiple cases

    SIRM 2017

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    This volume contains selected papers presented at the 12th International Conference on vibrations in rotating machines, SIRM, which took place February 15-17, 2017 at the campus of the Graz University of Technology. By all meaningful measures, SIRM was a great success, attracting about 120 participants (ranging from senior colleagues to graduate students) from 14 countries. Latest trends in theoretical research, development, design and machine maintenance have been discussed between machine manufacturers, machine operators and scientific representatives in the field of rotor dynamics. SIRM 2017 included thematic sessions on the following topics: Rotordynamics, Stability, Friction, Monitoring, Electrical Machines, Torsional Vibrations, Blade Vibrations, Balancing, Parametric Excitation, and Bearings. The papers struck an admirable balance between theory, analysis, computation and experiment, thus contributing a richly diverse set of perspectives and methods to the audience of the conference

    Selected Papers Compiled from Presentations - Leningrad Task Force Meeting, May 24-29, 1982, Leningrad, USSR

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    In line with the selected methodology, the Management and Technology area at IIASA decided to have the Innovation Management Task concentrate on sectors in an attempt to analyze the situation at this level of the economy before making any aggregations or conclusions relevant to management. In order to properly cover industry, it was suggested that branches that are at differing stages or that display different kinds of development be chosen for the study. Electrotechnology or power electrical engineering was one of the branches selected being an example of mature industry. The task force meeting held in Leningrad from May 24-29, 1982, was the first attempt LO scan problems in this branch and gain some kind of understanding as to the research that has been performed. The event was a multiobjective undertaking intended to identify the interest in this field. potential collaborators, and relevant issues. Due to the unique opportunity of becoming acquainted with the work of Soviet scientists, the papers presented were not only by researchers and scholars in this field, but also by decision makers on the different levels of management. For the first time, several issues are exposed for the English speaker, thus, rendering a service to the English speaking community of researchers, and enhancing the contacts with collaborators in socialist countries. The papers are arranged into four sections, each devoted to issues that can be viewed as interesting topics for further research. The discussion, found in the back of the proceedings as Appendix A, reflects the character of the productive and creative environment at the meeting. The reader must bear in mind that this is only an attempt to reflect the "milieu" as accurately as possible. It almost seems impossible to express the true working atmosphere created by the participants. The task force meeting was also the first attempt to see if IIASA could prepare a program of interest to representatives of industrial enterprises. Many questions were raised and discused. The reactions expressed by the participants at the meeting and later on significantly prove that the answer is generally positive

    Advanced Knowledge Application in Practice

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    The integration and interdependency of the world economy leads towards the creation of a global market that offers more opportunities, but is also more complex and competitive than ever before. Therefore widespread research activity is necessary if one is to remain successful on the market. This book is the result of research and development activities from a number of researchers worldwide, covering concrete fields of research
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