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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.
1

Use of naturally occurring system disturbances to estimate the fault current contribution of induction motors

Williamson, G. E. January 1995 (has links)
The contribution of induction motor loads to short circuit currents can be significant and so must be considered when evaluating system fault levels. Standard procedures for calculating short circuit currents of induction motors require detailed machine data which may not be available. An algorithm has been developed to estimate the fault contribution of induction motor loads. The estimation technique is based on an analysis of load responses to naturally occurring disturbances. Neither disruptive staged tests or detailed information of the load or the network are required. The algorithm has been applied in practice by using the Fault Level Monitor, which records system disturbances. The fault infeed estimation algorithm has been examined using simulation studies and field tests. Results are presented which show good agreement between the values obtained from the algorithm and from conventional techniques.
2

A three-dimensional singular model of a magnetic perpendicular recording head with applications to inter-track interference

Jermey, P. M. January 2008 (has links)
Two-dimensional models of the read head are not suitable for simulating the replay of the extremely high density data that is expected to be achieved in hard drives using perpendicular recording. By matching a singular function approximation to the Fourier solution at the air-bearing surface (ABS), a three-dimensional analytic model of a shielded giant magnetoresistive head, with side shields, for perpendicular replay is derived in this thesis. An explicit expression for the potential in the ABS is presented and parameters in that expression are accurately estimated for a range of practical head dimensions. Using only a few terms of this singular potential model, the vertical field is accurate to within 2% of the sensor potential in the region of the medium for the majority of head dimensions suitable for magnetic recording. The expected increase in areal density in hard drives using perpendicular technology will require very narrow t racks which normally suffer from large inter-track interference (ITI) or crosstalk. This interference can corrupt the read data and reduce t he signal strength. Here, the effects of ITI across three tracks in a three-head system are modelled by applying the three-dimensional singular function model of the head field. The magnetisation patterns which cause the worst ITI are identified so that these codes can be prohibited. A coding constraints scheme, in which ITI is exploited to read from tracks which have widths that are just 70% of the width of the head, is presented.
3

Permanent magnet synchronous machines with fractional slot and concentrated winding configurations

Fei, Wei-Zhong January 2011 (has links)
The permanent magnet synchronous machines with fractional slot and concentrated winding configuration have been steadily gaining traction in various applications in recent times. This is mainly driven by several advantages offered by this configuration such as high-torque density, outstanding efficiency, and easy and low-cost fabrication. The main focus of this thesis is dedicated to the investigation of three main topologies of fractional-slot and concentratedwinding permanent magnet synchronous machines specifically suited for particular applications. Additionally, the cogging torque and torque ripple reduction technique based on a novel axial pole pairing scheme in two different radial-flux permanent magnet synchronous machines with fractional-slot and concentratedwinding configuration are investigated. First, an axial flux permanent magnet segmented-armature-torus machine with laminated stator is proposed for in-wheel direct drive application. Both simplified analytical method and three-dimensional finite element analysis model accounting for anisotropic property of lamination are developed to analyze the machine performance. The predicted and experimental results are in good agreement and indicate that the proposed machine could deliver exciting and excellent performance. The impact of magnet segmentation on magnet eddy current losses in the prototype is carried out by the proposed three-dimensional finite element analysis model. The results show that the eddy current losses in the magnet could be effectively reduced by either circumferentially or radially segmenting the magnets. Furthermore, a magnet shaping scheme is employed and investigated to reduce the cogging torque and torque ripple of the prototype. This is validated using the three-dimensional finite element analysis model as well. Second, a coreless axial flux permanent magnet machine with circular magnets and coils is proposed as a generator for man-portable power platform. Approximate analytical and three-dimensional finite element analysis models are developed to analyze and optimize the electromagnetic performance of the machine. Comprehensive mechanical stress analysis has been carried out by threedimensional structural finite element analysis, which would ensure the rotor integrity at expected high rotational speed. The results from both three-dimensional finite element analysis and experiments have validated that the proposed prototype is a compact and efficient high speed generator with very simple and robust structure. Additionally, this structure offers simplified assembly and manufacturing processes utilizing off-the-shelf magnets. Third, a novel radial flux outer rotor permanent magnet flux switching machine is proposed for urban electric vehicle propulsion. Initial design based on the analytical sizing equations would lead to severe saturation and excessive magnet volumes in the machine and subsequently poor efficiency. An improved design is accomplished by optimizing the geometric parameters, which can significantly improve the machine efficiency and effectively reduce the overall magnet volumes. Magnet segmentations can be employed to further improve the machine performance. Finally, a novel axial pole pairing technique is proposed to reduce the cogging torque and torque ripple in radial flux fractional-slot and concentrated-winding permanent magnet synchronous machines. The implementation of the technique in outer rotor surface mounted permanent magnet synchronous machine shows that the cogging torque and torque ripple can be reduced very effectively with different magnet pairs. However, careful pair selection is of particular importance for compromise between cogging torque and torque ripple minimizations during the machine design stage. This technique is also employed to minimize the cogging torque in a permanent magnet flux switching integrated-stator-generator and it is compared with rotor step skewed technique. The estimated and experimental results show that the axial pole pairing technique can not mitigate the torque ripple of the machine as effectively as rotor step skewed approach although both the techniques could reduce the cogging torque to the same level.
4

Surface engineered polymer bonded magnets

Sidambe, Alfred Twala January 2004 (has links)
No description available.
5

Quench propagation in conduction cooled HTS pancake coils

Johnstone, Adam Paul January 2005 (has links)
No description available.
6

Magnetic properties and microstructure of intermediate and low rare earth content Nd₂Fe₁₄B-based nanocomposite magnets

Harrison, Nicola January 2007 (has links)
No description available.
7

Magnetic micro electro-mechanical systems

Dean, Julian Sebastian January 2007 (has links)
No description available.
8

Development and application of low-field mobile NMR devices

Routley, Nathan Richard January 2003 (has links)
No description available.
9

Corrosion of soft magnetic recording head alloys and the effect of magnetic fields on corrosion

Tang, Yee Chin January 2004 (has links)
No description available.
10

Production of sintered permanent magnets based on (Nd/Pr)Fe-B alloys

Corfield, Martin Richard January 2003 (has links)
No description available.

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