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Online ISSN 1751-8830 Print ISSN 1751-8822

IET Science, Measurement & Technology

Volume 5, Issue 1, January 2011

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Volume 5, Issue 1

January 2011

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    • Fast monostatic radar cross section computation using Maehly approximation
      • Author(s): J. Ling ; S.-X. Gong ; W.-T. Wang ; X. Wang ; Y.-J. Zhang
      • Source: IET Science, Measurement & Technology, Volume 5, Issue 1, p. 1 –4
      • DOI:  10.1049/iet-smt.2009.0096
      • Type: Article
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      • p. 1 –4 (4)
        The method of moments (MoM) in conjunction with the best uniform rational approximation is applied to predict monostatic radar cross section (RCS) pattern from a few pattern value calculations. Numerical results for three-dimensional arbitrarily shaped perfectly electric conductor objects are considered. Good agreement between the proposed technique and the exact solution is observed. Compared with the asymptotic waveform evaluation (AWE) technique, the proposed technique is accurate in much broader angular domains.
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      Calibration of on-line partial discharge measuring system using Rogowski coil in covered-conductor overhead distribution networks
      • Author(s): G.M. Hashmi ; M. Lehtonen ; M. Nordman
      • Source: IET Science, Measurement & Technology, Volume 5, Issue 1, p. 5 –13
      • DOI:  10.1049/iet-smt.2009.0124
      • Type: Article
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      • p. 5 –13 (9)
        Partial discharge (PD) detection has been regarded as one of the most effective on-line predictive maintenance test and diagnostic tool for the condition monitoring of high voltage (HV) equipment. In this study, a methodology for detecting on-line PDs produced because of falling trees on the covered-conductor (CC) overhead distribution lines is introduced and calibration of PD measuring system is carried-out. The Rogowski coil is used as a PD sensor which is non-intrusive and superior to the conventional PD detectors. The experimental set-up was arranged in the HV laboratory for real-time analysis and a pulse calibrator was used to calibrate the PD measuring system. Few real-life PD measurements have been taken and it is revealed that PD magnitudes and signals bandwidth may vary under various circumstances. The calibrated on-line PD measuring system can be used to detect and measure the amount of PDs produced because of falling trees on CC lines, thus improving the reliability and safety of the distribution networks as well as reducing visual inspection work after storms.
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      Estimation of uncertainty regarding soil breakdown parameters
      • Author(s): F.E. Asimakopoulou ; I.F. Gonos ; I.A. Stathopulos
      • Source: IET Science, Measurement & Technology, Volume 5, Issue 1, p. 14 –20
      • DOI:  10.1049/iet-smt.2010.0021
      • Type: Article
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      • p. 14 –20 (7)
        The behaviour of a grounding system under fault currents differs from its steady-state behaviour. It has been observed that, when a high impulse current is injected into the grounding system, its impulse impedance drops because of the ionisation phenomenon. The critical parameter for the ionisation phenomenon is the soil critical electric field, which corresponds to the electric field threshold above which the soil ionisation occurs. In bibliography various attempts have been made aiming at its estimation. However, a physical quantity is determined not only by its value, but also by an estimation of the uncertainty. The aim of this work is the analysis of the components of uncertainty and the estimation of the uncertainty regarding the determination of the breakdown voltage associated with the soil critical electric field. Therefore a series of measurements has been conducted by subjecting dry and wet soil samples to impulse voltages, while recording the voltage and the current. Based on these measurements the random uncertainty is calculated while an estimation of the systematic uncertainty is given taking into account the measuring equipment.
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      Arbitrary-shaped single-layer coil self-inductance using shape functions
      • Author(s): K. Ishida ; T. Itaya ; A. Tanaka ; N. Takehira ; T. Miki
      • Source: IET Science, Measurement & Technology, Volume 5, Issue 1, p. 21 –27
      • DOI:  10.1049/iet-smt.2010.0035
      • Type: Article
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      • p. 21 –27 (7)
        Coils of various shapes are used in various applications such as sensing and magnetic energy storage. Successful practical application of coils requires knowledge about their self-inductance, which is one of their fundamental properties. In the past, approximation analyses have been performed on coils of various shapes by means of theoretical analysis methods and finite element methods. In this paper, we propose a theory for determining the self-inductances of arbitrary-shaped single-layer coils: this theory is based on the novel concept of adopting a shape function for a coil of a particular shape to determine the coil's self-inductance. We used the double Fourier transform method to derive equations for determining the self-conductance of coils of various shapes. Then, to determine the validity of the proposed theory, we experimentally measured the self-inductances of coils and compared the measured self-inductance values with those calculated theoretically using the proposed theory of shape functions. The comparison results showed that the calculated and measured values were in good agreement, which confirms the validity of our proposed theory. Therefore, we conclude that by using shape functions, it is possible to perform a unified and highly detailed theoretical analysis of magnetic fields in arbitrary-shaped coils and determine their self inductances.
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