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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Fault diagnosis of rotating machinery

Edwards, S. January 1999 (has links)
In this thesis, topics of importance to the fault diagnosis of rotating machinery in the power generation industry have been addressed, including a review of the relevant literature and an overview of the associated rotordynamics modelling and analysis techniques. For faults involving rotor-stator interaction it has been shown that the inclusion of torsion in mathematical models used for rotor-stator contract analyses can have a significant influence on the dynamic behaviour of the system. A 3 degrees-of-freedom model based on the Jeffcott rotor was developed and, for physically realistic systems, it was shown that very different results were obtained when including torsion, compared to when torsion was neglected, as has generally been the case in the past. An identification method for estimating both the excitation and flexible support parameters of a rotor-bearings-foundations system has been presented. Excitation due to both mass unbalance and a bent rotor were included in the analysis, which has been verified both in simulation and experimentally. The method has great practical potential, since it allows balancing to be performed using data obtained from just a single run-up or run-down, which has obvious benefits for field balancing. Using this single-shot balancing technique in experiment, vibration levels were successfully reduced by as much as 92% of their original levels. A bent rotor has been accurately identified in both simulation and experiment. It was also shown that including bend identification in those cases where only unbalance forcing was present in no way detracted from the accuracy of the estimated unbalance or foundation parameters. The identification of the flexible foundation parameters was generally successful, with measured and estimated parameters matching very closely in most cases. The identification method was tested for a wide range of conditions and proved suitably robust to changes in the system configuration, noisy data and modelling error.

Probabilistic modelling of load and harmonic distortion in an A.C. traction system using an object-oriented approach

Hewings, D. B. January 1995 (has links)
As a means of reducing over-design and gaining greater insight into the operation of dynamic systems, probabilistic methods have evolved as a extremely important design tool. This has been true of power system design in general over the past thirty years, and probabilistic methods are now used in the design of overhead line supports, fault-clearing plant and the assessment of load demands. However, the application of probabilistic methods to the design and analysis of traction power systems has been relatively limited. These systems involve not only the electrical characteristics of the power system, but also the mechanical aspects of an electric railway, and produce moving, frequently changing electrical loads. The electrical system itself is not easily analysed, since modern locomotives incorporate power electronic switching drives, conventionally analysed in the time domain, whilst the supply is analysed in the frequency domain. This study details the development of an object-oriented traction system model, which can incorporate both the time and frequency representations into a single integrated model. This integrated model is then used as the basis of investigation into the probabilistic characteristics of the electrical load and harmonic distortion produced by the traction system. The study shows that an object-oriented approach may be applied to switching-circuit analysis, and that a combined frequency- and time- domain analysis may be easily implemented with this type of system. The probabilistic simulations show for the first time that the load and harmonic characteristics of an a.c. traction system do not fit known parametric models, and are in fact highly dependent upon the operational characteristics of the traction system, e.g. route profile and timetable.

Real-time sliding mode control of a brushless DC motor

Anagren, Y. N. F. January 1998 (has links)
Conventional DC-brush motors have been used extensively as variable speed drive systems due to their linear characteristics, which result in easy speed control. However, AC drives become an attractive alternative to their DC counterparts in various industrial applications. This is due to the recent developments in both power electronics and microelectronics technology. Brushless permanent magnet motors combine the advantages of brush-DC motors and AC motors. Therefore, a tremendous effort is carried out to utilise this type of electrical drive in high performance industrial applications. A robust control design, having the feature of insensitivity to parameter variations and load torque disturbances, is highly demanded in many modern variable drive systems. The recent advancements in producing fast microprocessors and high switching power devices enable the digital implementation of advanced control schemes. One of these schemes is the sliding mode control technique, which has been implemented successfully in a wide variety of industrial applications. A real-time high performance low cost speed control of brushless DC motor drive is developed in this thesis. The controller design is based on the theory of sliding mode control. The developed drive system is further improved by including a 'chattering reduction' in the controller design. The developed speed control system is assessed through both simulation and practical studies. The practical implementation is achieved using the Intel 80C196KC single chip microcontroller and all the required tasks are carried out solely through software, which has the flexibility for future development. Extensive results at different operating conditions are given throughout the thesis to prove the validity of the developed scheme.

Sensorless Control of High Power Induction Motors Using Multilevel Converters

Saleh, Kamel Subhi January 2010 (has links)
No description available.

The Application of Simulated Annealing for Condition Monitoring in Induction Motors

Zakaria, Khairul Parman January 2009 (has links)
No description available.

High-speed drives for consumer products

Leaver, Mark Edward January 2010 (has links)
The aesthetic design and thus market appeal of consumer products is limited by the size and weight of the universal or brushed DC motors that they typically employ. As many similar products are displayed for sale side-by-side, it is the aim of any manufacturer to ensure that their product stands out from the rest either in terms of performance, features, aesthetics or ergonomics. This thesis presents the research, design, development and product deployment of two high-speed brushless machines that remove the limitations and restrictions on machine design imposed by mechanical commutation and demonstrates the significant advantages to product design and performance that can be gained by moving away from traditional brushed motor technology. The first machine design is a 3-phase 100,000rpm permanent magnet machine which has been coupled with a high-ratio gearbox to provide a unique drive system for use within a 700W mains-powered electric drill. The research shows that for a given power rating, an optimal motor speed exists for size minimisation of a motor/gearbox transmission system when the design of the corresponding gearbox is also considered. Following the presented optimisation method, a new drive system has been designed that is half the size and 80% lighter than the existing drive, leading to an easy-to use tool that fits within the housing of a much smaller cordless drill product. The second machine is a single-phase, bifilar-wound, 32,000rpm permanent magnet machine for directly driving the impeller of a 200W cordless vacuum cleaner. This lowcost machine demonstrates that a bifilar winding with simple two-switch drive can be successfully applied at this power rating. When compared to the original machine, the presented design shows an axial length reduction from 59mm to 20mm and a 29% reduction in mass. The high speed of the new motor increases the vacuum performance of the product by 70% when using the existing vacuum impeller.

Speed Sensorless Induction Motor Drives : A Comparison

Smith, Andrew Neil January 2009 (has links)
No description available.

Electromagnetic losses in brushless permanent magnet machines

Ng, Kong January 1998 (has links)
No description available.

High voltage partial discharge measurements - improving their significance

Reeves, John Howard January 1979 (has links)
No description available.

Development of a 3-D x-ray system

Evans, James Paul Owain January 1993 (has links)
No description available.

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