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

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

Design and Application of Electrical Machines

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

Publications of the Jet Propulsion Laboratory, July 1961 through June 1962

Jpl bibliography on space science, 1961-196

Electrical effects in winding of large electrical ac machines application to advanced large size DFIM

To meet the electrical grid's demand on pump power variation, GE Renewable Energy develops since 10 years variable speed machines (also called Doubly Fed Induction Generators or DFIG). Within turbogenerators, the phenomenon of circulating currents in Roebel bars is well known, while is it has not yet been studied for DFIGs. The main goal of this study is to calculate the circulating currents in the stator and rotor bars of DFIG under different operating points with a theoretical and practical precision of around 1\%. This study starts with an overview of the current situation in circulating current calculation and presentation of the characteristic circulating current curves for a hydrogenerator, study that led to a patent application. After a presentation of the possible calculation methods and models based on a deep and broad literature review, this study performs with a deep review of the slot inductance model analysing its precision and limitations. Based on these finds, two novel analytical models are proposed to enhance the taking into account of the strand dimensions. Only the last slot inductance model developed, based on a slot differential inductance model, permits to take the strand dimensions and the saturation into account. This model is validated experimentally using a small-scale slot/strand-model, while all slots models are compared to each other to highlight their differences. The winding overhang model and novel analytical expressions are presented in a later chapter as well as the analytical treatment of the rotor overhang made of non-linear steel. The winding overhang model uses analytical expressions to determine the magnetic field and vector potential in the winding overhang, which have the advantage of additional knowledge compared to the results of a finite-element computation. \In another chapter, novel exact transient current and torques expressions are derived for a DFIG experiencing a 3-phase and a 2-phase short-circuit. Then the winding overhang force computation and the circulating current calculation results are presented in two crowing chapters. In these chapters, the influence of the approximation and boundary on the end winding forces as well as the origin of the end winding forces are shown. The last result chapter is dedicated to the circulating current calculation, where several original results are presented to detail the circulating current losses reduction potential and the impact of well-known classical special transitions on the circulating currents in the case of a DFIG. The influence of the operating point and the boundary are also shown for the stator and the rotor. This study presents many original contributions on several domains. It presented a novel slot inductance model, which was validated using a specially designed small-scale model of a slot. This small-scale model concept can certainly be extended to other parts of an electrical machine, which could help to study these effects in a laboratory instead of a power plant. This study could quantify the circulating current losses in the stator winding of a DFIG, losses that can easily be reduced to increase the efficiency of this machine. This study also presented several original fundamental contributions in the field of analytical expressions for the transient expression of current and torque in the case of a 3-phase and 2-phase short-circuit

Development and evaluation of the elastic recovery concept for expandable space structures

Elastic recovery of expandable space structure

High speed high power electrical machines

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

Energy: A continuing bibliography with indexes

This bibliography lists 335 reports, articles, and other documents introduced into the NASA scientific and technical information system from October 1, 1974 through December 31, 1974

Finite-element analysis of eddy currents in the form-wound multi-conductor windings of electrical machines

The aim of this research was to develop comprehensive numerical models for considering eddy currents and circulating currents in the form-wound multi-conductor windings of electrical machines and to study the effects of eddy currents and circulating currents. Time-harmonic and time-discretised finite-element methods were developed. The methods were applied to the stator winding of a 1250-kW cage induction motor and in both the stator and rotor windings of a 1.7-MW doubly-fed induction generator (DFIG). The series and parallel connections of the winding were taken into account. The Newton-Raphson iteration method was used to solve the system of non-linear equations. In time-harmonic FEM, the system of equations was solved iteratively just once for the steady-state solution. In time-discretised FEM, the system of equations was solved iteratively at every time step. The backward Euler method was used for the time discretisation. The radial distance of the stator bars from the air gap has a remarkable effect on losses and was found to be an important design parameter. A significant amount of stator-winding eddy-current loss can be reduced by considering this design parameter. A transposition of the conductors was implemented to reduce the circulating currents between the parallel stator conductors. The eddy-current effects in the form-wound multi-conductor windings of electrical machines were studied for both a sinusoidal and non-sinusoidal supply. A pulse-width-modulated (PWM) voltage supply was achieved by sinus triangle comparison and used as a non-sinusoidal supply for the machine. A PWM supply produced a significant amount of additional eddy-current losses in the form-wound stator winding of the cage induction motor when compared to the sinusoidal supply. The fundamental harmonic voltages of the sinusoidal and PWM supplies were equal for comparing the results. Similar sinusoidal and PWM voltages were used to supply the rotor winding of the DFIG as well. The additional eddy-current losses in the form-wound rotor winding as a result of the PWM supply were small

Energy: A continuing bibliography with indexes, February 1975

Reports, articles, and other documents introduced into the NASA scientific and technical information system from July 1, 1974 through September 30, 1974 are cited. Regional, national, and international energy systems; research and development on fuels and other sources of energy; energy conversion, transport, transmission, distribution, and storage, with emphasis on the use of hydrogen and solar energy are included along with methods of locating or using new energy resources. Emphasis is placed on energy for heating, lighting, and powering aircraft, surface vehicles, or other machinery