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Volume 152
Issue 4
IEE Proceedings - Science, Measurement and Technology
Volume 152, Issue 4, July 2005
Volumes & issues:
Volume 152, Issue 4
July 2005
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- Author(s): G.Y. Tian ; A. Sophian ; D. Taylor ; J. Rudlin
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 152, Issue 4, p. 141 –148
- DOI: 10.1049/ip-smt:20045011
- Type: Article
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p.
141
–148
(8)
A new approach for defect classification and quantification by using pulsed eddy current sensors and integration of principal component analysis and wavelet transform for feature based signal interpretation is presented. After reviewing the limitation of current parameters of peak value and its arrival time from pulsed eddy current signals, a two-step framework for defect classification and quantification is proposed by using adopted features from principal component analysis and wavelet analysis. For defect classification and quantification, different features have been extracted from the pulsed eddy current signals. Experimental tests have been undertaken for ferrous and non-ferrous metal samples with manufactured defects. The results have illustrated the new approach has better performance than the current approaches for surface and sub-surface defect classification. The defect quantification performance, which is difficult by using current approaches, is impressive. - Author(s): J.F. Borges da Silva and V. Maló Machado
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 152, Issue 4, p. 149 –154
- DOI: 10.1049/ip-smt:20045003
- Type: Article
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p.
149
–154
(6)
The need to evaluate electric and magnetic fields arises frequently in the design of electrical equipment. Analysis by the finite element method (FEM) is usually employed for this purpose, being most efficiently carried out by solving first for the node potentials, thus obtaining a vector of approximate potential values on a discrete finite set of field points. In this paper it is shown how a linear operator may be set up to yield, at each node, an estimate for the potential function derivative along a prescribed direction in space. The operation consists in taking, for each node, a weighed average of the previously calculated potential values at its neighbouring nodes. The possibility of achieving high accuracy with a simple method, is attributed to its taking advantage of potential function properties inherent in their being solutions of certain field equations. The method is applicable, in principle, to 2-D and 3-D problems and is developed explicitly here for the plane 2-D and axisymmetric cases, using triangular elements with linear basis functions. Results for a typical axisymmetric magnetic field having a known analytic solution are presented and compared with exact values. - Author(s): D.E. Gourgoulis ; P.N. Mikropoulos ; C.A. Stassinopoulos ; C.G. Yakinthos
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 152, Issue 4, p. 155 –160
- DOI: 10.1049/ip-smt:20045006
- Type: Article
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p.
155
–160
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The positive impulse breakdown behaviour of conductor-rod gaps 50 cm in length is investigated while negative DC voltages pre-stress the gap. Breakdown voltage and time to breakdown variations are discussed in terms of the parameters influencing the discharge mechanism such as the gap geometry, the amplitude of the pre-stress negative DC voltage applied at the rod, the waveshape of the applied impulse voltage at the conductor and the variation of absolute humidity. It is shown that pre-stressing, by producing sufficient DC coronas at both electrodes, results in a significant increase in the breakdown voltage. There is a threshold value of the pre-stress DC voltage above which the gap factor against breakdown may double its value. Both absolute humidity and pre-stressing affect, in a combined way, the dielectric strength of the gaps. - Author(s): W. Manners and B. Gholami
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 152, Issue 4, p. 161 –168
- DOI: 10.1049/ip-smt:20045034
- Type: Article
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p.
161
–168
(8)
Material surfaces tend to show roughness that has fractal characteristics, and this affects the nature of contacts between surfaces. In particular, as smaller and smaller scales of roughness are added to a model, the areas in contact break up to form larger numbers of smaller contacts. The total area in contact diminishes towards zero. What this means for the constriction resistance is examined, and using the ‘Cantor Dust’ fractal model, it is shown that, in realistic situations, it tends towards a finite limit. If however, the contact area reduces fast enough as the scale is reduced, an infinite limit is possible. The effect is dependent on the clustering of the contacts determined by the largest scales. In the absence of such clustering, the resistance can tend to zero. - Author(s): P.N. Mikropoulos and C.A. Stassinopoulos
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 152, Issue 4, p. 169 –174
- DOI: 10.1049/ip-smt:20045030
- Type: Article
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p.
169
–174
(6)
The sparkover behaviour of sphere-rod gaps under standard impulse voltages is investigated by assessing the influence of gap spacing, impulse voltage waveshape and polarity, and atmospheric conditions on the distribution of the sparkover voltage. At sparkover the growth of streamers of both polarities can be estimated since a value of 2 MV/m is found to be characteristic for the average negative streamer gradient. The IEC atmospheric conditions correction is discussed and compared with a new optimised correction procedure. The feasibility of using the sphere-rod gap as substandard for measuring impulse voltages, replacing the conventional more expensive sphere gap, is examined. - Author(s): S. Yuferev and N. Ida
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 152, Issue 4, p. 175 –185
- DOI: 10.1049/ip-smt:20049050
- Type: Article
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p.
175
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The surface impedance boundary conditions (SIBCs) for the tangential component of the electric field and normal component of the magnetic field on the smooth curved surface of a homogeneous non-magnetic conductor are derived in time- and frequency-domain. Scale factors for the basic variables are introduced in such a way that, a small parameter, equal to the ratio of the penetration depth and the body's characteristic size, appears in the dimensionless Maxwell's equations for the conducting region. The perturbation method is then used to represent the SIBCs in the form of power series in this small parameter and the first four terms of the expansions are derived. The zero-order, first-order, second-order and third-order terms of the expansions are the solution of the problem in the perfect electrical conductor limit, the Leontovich approximation, the Mitzner approximation and in the high order approximation (referred to as Rytov's approximation), respectively. Therefore, the accuracy of the proposed conditions exceeds the accuracy of the SIBC for planar surfaces (Leontovich's approximation) that are usually used in the time-domain analysis, by two orders of magnitude. In Part II of this paper, the formulation of the SIBCs developed here in conjunction with a boundary element method is demonstrated and applied to the problem of transient skin and proximity effect problems in cylindrical conductors. - Author(s): A.P. Robinson ; P.L. Lewin ; S.G. Swingler ; S.J. Sutton
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 152, Issue 4, p. 187 –195
- DOI: 10.1049/ip-smt:20045017
- Type: Article
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p.
187
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High voltage polymeric cables can be insulated using an automated extrusion process to a predefined standard up to a maximum continuous length. For longer cables, lengths are joined together manually. Consequently, the manufacturing quality of the cable joint is likely to be lower than that of the cable; therefore joints must be assessed prior to energisation. One method of manually inspecting joints uses conventional X-ray techniques. This could be automated using digital technology and image processing techniques. One possible sensor that could be used to replace the film would be a CCD camera coupled to a scintillating screen. Two post-processing algorithms for inspection of the digital images produced have been implemented; these are a statistical approach using mean, variance, skewness and kurtosis, and a method that equates pixels to Newtonian bodies. In order to verify that digital X-raying of cable joints is a feasible inspection procedure, CCD camera and film images have been taken of three test pieces. The film-based images were converted into a digital format using a high resolution scanner. Both sets of images were processed using the algorithms. The results of this test show that images generated by the camera are more distinct than film. - Author(s): T. Devolder ; C. Maufront ; J.-V. Kim ; H.W. Schumacher ; C. Chappert ; R. Fournel
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 152, Issue 4, p. 196 –200
- DOI: 10.1049/ip-smt:20049037
- Type: Article
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p.
196
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Precessional switching of the magnetisation is a convenient way to ensure sub-ns, reliable, energy cost efficient writing of an MRAM cell. In this technique, a controlled pulse of magnetic field is applied perpendicular to the easy magnetisation axis of the MRAM cell free layer, which switches the magnetisation from one direction to its reverse. Bit selection and fast direct overwrite can be obtained by superimposing another field pulse along the easy magnetisation axis. It is proposed to change the cell shape while reducing its size to postpone the onset of superparamagnetism. Based on the Landau-Lifshitz-Gilbert equation an analytical theory of this precessional switching process has been developed. This allows the understanding of the minimal switching field and accountingly for the bit selection scheme. A study of how the writing parameter window is affected by a distribution of cell parameters in a array and by the intercell dipolar coupling has been made. A high-pass encoding, and a balanced encoding algorithm are proposed to reduce the maximum intercell dipolar field.
Wavelet-based PCA defect classification and quantification for pulsed eddy current NDT
Accurate gradient field evaluation using node potential values obtained by the finite element method
Effects of negative DC pre-stressing on positive impulse breakdown characteristics of conductor-rod gaps
Constriction resistance between materials with fractal patterns of contact
Impulse sparkover characteristics of sphere-rod gaps
Time domain surface impedance concept for low frequency electromagnetic problems—Part I: Derivation of high order surface impedance boundary conditions in the time domain
X-ray image processing for high voltage cable inspection
Bit selection scheme and dipolar interactions in high density precessional MRAM
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