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Online ISSN 1751-8830 Print ISSN 1751-8822

IET Science, Measurement & Technology

Volume 6, Issue 4, July 2012

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Volume 6, Issue 4

July 2012

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    • Estimation of time-varying power quality indices with an adaptive window-based fast generalised S-transform
      • Author(s): M. Biswal  and  P.K. Dash
      • Source: IET Science, Measurement & Technology, Volume 6, Issue 4, p. 189 –197
      • DOI:  10.1049/iet-smt.2011.0202
      • Type: Article
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      • p. 189 –197 (9)
        The S-transform (ST) finds widespread application in non-stationary signal analysis. However, the relatively high computational complexity of the ST remains as a challenge. Further, the optimum choice of the window function and the discretisation side effects of the ST need to be addressed for accurate time–frequency localisation. This study proposes a fast adaptive discrete generalised ST (FDGST) algorithm based on a new frequency scaling named selective frequency scaling, window cropping and an adaptive window function. The proposed algorithm optimises the shape of the window function for each analysis frequency to improve the energy concentration of the time–frequency distribution, and applies folded window functions to minimise aliasing affect owing to discretisation. Further, the algorithm is applied for analysis and measurement of parameters in various types of power quality waveforms. Standard transient and steady-state indices calculation from the FDGST analysis is also illustrated. The improved performance of the proposed algorithm is supported by simulations using synthetic as well as practical signals.
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      Partial discharge recognition based on SF6 decomposition products and support vector machine
      • Author(s): J. Tang ; F. Liu ; X. Zhang ; X. Liang ; Q. Fan
      • Source: IET Science, Measurement & Technology, Volume 6, Issue 4, p. 198 –204
      • DOI:  10.1049/iet-smt.2011.0163
      • Type: Article
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      • p. 198 –204 (7)
        Partial discharge (PD) is usually aroused before the failure of gas-insulated switchgear (GIS) caused by insulation defects, which results in the decomposition of SF6 used as insulation gas. Concentrations of decomposition products of SF6 under different kinds of PDs are disparate. Thus, SF6 decomposition products can be used for PD recognition. In this study, a gas chamber and four defect models were designed to simulate four kinds of typical PDs in GIS. SF6 decomposition experiments were conducted under the four kinds of PDs. Four kinds of decomposition products, that is, SO2F2, SOF2, CO2 and CF4, were selected as feature components. Their concentrations were detected under each experiment. Three concentration ratios, that is, c(SO2F2)/c(SOF2), c(CF4)/c(CO2) and c(CO2+CF4)/c(SOF2+SO2F2), were proposed as feature parameters for PD recognition. Their physical significances were also analysed. Then, a support vector machine (SVM) was employed as classifier to recognise the four kinds of PDs. The parameters of the SVM were optimised using particle swarm optimisation algorithm. Results show that the recognition method based on SF6 decomposition products and SVM performs well in PD recognition.
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      Comparison of methods for measuring ultrasonic velocity variations during ageing or fermentation of food materials
      • Author(s): D. Novoa-Díaz ; J. García-Álvarez ; J.A. Chávez ; A. Turó ; M.J. García-Hernández ; J. Salazar
      • Source: IET Science, Measurement & Technology, Volume 6, Issue 4, p. 205 –212
      • DOI:  10.1049/iet-smt.2011.0178
      • Type: Article
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      • p. 205 –212 (8)
        A comparison of methods for measuring time-of-flight (TOF) variations of ultrasonic waves travelling through food materials is presented. Six commonly used methods for the TOF determination were taken into account, four in the time domain and two in the frequency domain. First, methods were briefly described and then tested using simulated ultrasonic waves. Factors such as signal-to-noise ratio (SNR), attenuation and delay between signals are taken into consideration, whereas the root mean-squared error (RMSE) and execution time are used as parameters for comparison. Of the six methods, the one operating on the basis of phase shift proved to be the most robust and provided excellent levels of resolution and optimum performance across a wide range of SNR values. Experiments were subsequently conducted in a real process, which corroborated the results obtained during the theoretical study. The ability to accurately measure TOF variations of ultrasonic waves makes it possible to detect more precisely velocity variations, which is the most commonly used parameter to determine and acoustic monitor physicochemical changes and properties of food materials.
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      Improving the efficiency of high power piezoelectric transducers for industrial applications
      • Author(s): P. Davari ; N. Ghasemi ; F. Zare ; P. O'Shea ; A. Ghosh
      • Source: IET Science, Measurement & Technology, Volume 6, Issue 4, p. 213 –221
      • DOI:  10.1049/iet-smt.2011.0209
      • Type: Article
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      • p. 213 –221 (9)
        Most high-power ultrasound applications are driven by two-level inverters. However, the broad spectral content of the two-level pulse results in undesired harmonics that can decrease the performance of the system significantly. On the other hand, it is crucial to excite the piezoelectric devices at their main resonant frequency in order to have maximum energy conversion. Therefore a high-quality, low-distorted power signal is needed to excite the high-power piezoelectric transducer at its resonant frequency. This study proposes an efficient approach to develop the performance of high-power ultrasonic applications using multilevel inverters along with a frequency estimation algorithm. In this method, the resonant frequencies are estimated based on relative minimums of the piezoelectric impedance frequency response. The algorithm follows the resonant frequency variation and adapts the multilevel inverter reference frequency to drive an ultrasound transducer at high power. Extensive simulation and experimental results indicate the effectiveness of the proposed approach.
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      Response of metal oxide arrester in gas-insulated substation and methods to improve its dynamic characteristics
      • Author(s): P. Valsalal ; S. Usa ; K. Udayakumar
      • Source: IET Science, Measurement & Technology, Volume 6, Issue 4, p. 222 –228
      • DOI:  10.1049/iet-smt.2011.0051
      • Type: Article
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      • p. 222 –228 (7)
        It is well known that the metal oxide arrester (MOA) has the inability to operate against very fast transient overvoltage (VFTO). The aim of this paper is to study the dynamic performance of MOA in gas-insulated substation (GIS). A 230 kV GIS is taken from a local utility and the system is modelled for very fast transients. The dynamic performance of arrester is analysed for current surges of different front times, varying from microsecond to nanosecond using electromagnetic transient program. The dynamic characteristics can be obtained for front time, more than 1 µs. However, there is a deviation in it when front time is less than 1 µs, showing failure of arrester conduction because of delay in its initial response, especially under VFTO. The dynamic characteristic is improved by making modifications in the system as well as in the arrester. A dynamic hysteresis curve is constructed to confirm the delay between the residual voltage and current surge. By decreasing the delay, it is possible to improve the dynamic characteristics of the arrester so that the effective utilisation of MOA can be enhanced in VFTO applications.
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      Methodology for developing a low-pressure discharge lamp model with electron density variation and ambipolar diffusion
      • Author(s): D. Lin ; W. Yan ; G. Zissis ; S.Y.R. Hui
      • Source: IET Science, Measurement & Technology, Volume 6, Issue 4, p. 229 –237
      • DOI:  10.1049/iet-smt.2011.0146
      • Type: Article
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      • p. 229 –237 (9)
        In this study, the procedure for developing a low-pressure discharge lamp model incorporating novel features of the electron density variation and the ambipolar diffusion process is introduced. The model can accurately predict not only the lamp electrical terminal characteristic but also the electron density and electron temperature inside the fluorescent lamp. The results are comparable with the outcome from the complicated plasma models. The lamp model can accurately predict the lamp characteristics at both high- and low-operating frequencies, and the voltage spikes caused by arc re-ignition at each half-cycle when the lamp is operated at mains frequency. This model can be easily implemented into MATLAB/Simulink as a simple, accurate and user-friendly CAD lamp model. The detailed genetic algorithm schemes used to determine the model parameters are included in this study.
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      Rigorous electromagnetic model of an induction cooking system
      • Author(s): V. Mariani Primiani ; S. Kovyryalov ; G. Cerri
      • Source: IET Science, Measurement & Technology, Volume 6, Issue 4, p. 238 –246
      • DOI:  10.1049/iet-smt.2011.0145
      • Type: Article
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      • p. 238 –246 (9)
        An electromagnetic model of an induction cooking system and its numerical solution are proposed. The analytical approach for the whole system is based on a field theory concept. Currents in each part of the system, as well as the electric and magnetic fields generated by these currents are defined and composed into a system representing the material constitutive equations. A numerical solution of the electromagnetic problem that provides all the electric and magnetic currents of the system is achieved by application of the moment method. Finally, the proposed model has been validated experimentally by measuring the input impedance at the feeding port and comparing it with the calculated values.
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      Automated region-based hybrid compression for digital imaging and communications in medicine magnetic resonance imaging images for telemedicine applications
      • Author(s): V.K. Bairagi  and  A.M. Sapkal
      • Source: IET Science, Measurement & Technology, Volume 6, Issue 4, p. 247 –253
      • DOI:  10.1049/iet-smt.2011.0152
      • Type: Article
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      • p. 247 –253 (7)
        Many classes of images contains spatial regions which are more important than other regions. Compression methods which are capable of delivering higher reconstruction quality are attractive in this situation for the important parts. For the medical images, only a small portion of the image might be diagnostically useful, but the cost of a wrong interpretation is high. Hence, Region Based Coding (RBC) technique is significant for medical image compression and transmission. Lossless compression in these ‘regions’ and lossy compression for rest of image can helps to achieve high efficiency and performance in telemedicine applications. This paper proposes an automated, efficient and low complexity, lossless, scalable RBC for Digital Imaging and Communications in Medicine (DICOM) images. The advantages of RBC are exploited in this paper, segmenting the region into various regions of importance and subjecting varying bit-rates for optimal performance. Moreover, the combined effects of Integer Wavelet Transform (IWT) and bit-rate limiting compression technique for lesser important regions helps reconstruct the image, reversibly, up to a desired quality. The overall compression thus reaches a satisfactory level to be able to safely transmit the image in limited bandwidth over a telemedicine network and reconstruct diagnostic details for treatment, most faithfully.
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      Electromagnetic interference detection method to increase the immunity of a microcontroller-based system in a complex electromagnetic environment
      • Author(s): F. Wan ; F. Duval ; X. Savatier ; A. Louis ; B. Mazari
      • Source: IET Science, Measurement & Technology, Volume 6, Issue 4, p. 254 –260
      • DOI:  10.1049/iet-smt.2011.0087
      • Type: Article
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      • p. 254 –260 (7)
        This study introduces an electromagnetic interference detection technique to increase the immunity of a microcontroller-based system in a complex electromagnetic environment (EME). The detection method is explained. First, the interference in the power supply and at the input port of the microcontroller is detected. The simulation results are achieved in both time domain and frequency domain. The measurement results are obtained to verify the correctness of the detection method and the application of the detection method in the automotive field is presented. The final objective of the work is to ensure that the microcontroller-based system works fast in a normal EME and correctly in a complex EME without adding too much cost.
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      Ultrasonic signal compressive detection using improved random equivalent sampling
      • Author(s): Y.-J. Zhao ; X.-Y. Zhuang ; H.-J. Wang ; Z.-J. Dai
      • Source: IET Science, Measurement & Technology, Volume 6, Issue 4, p. 261 –266
      • DOI:  10.1049/iet-smt.2011.0168
      • Type: Article
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      • p. 261 –266 (6)
        An improved random equivalent sampling (RES) approach based on compressed sensing (CS) for repetitive ultrasonic signal detection is presented. The proposed system considers recovering ultrasonic signal with high equivalent sampling frequency from samples captured using analogue-to-digital converter (ADC) clocked at a rate much lower than Nyquist rate. A basis function is constructed to realise the ultrasonic signal sparse representation, which paves the way for applying CS theory to ultrasonic signal sub-Nyquist sampling. A sampling architecture is developed, which is applicable for ultrasonic compressive detection. The CS measurement matrix is constructed in the context of RES. Experimental results indicate that, with this sampling system, an ultrasonic signal sampled at ultra-low rate, but still can be recovered with overwhelming probability.
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      Coordinated aggregated-based particle swarm optimisation algorithm for congestion management in restructured power market by placement and sizing of unified power flow controller
      • Author(s): S. Hajforoosh ; S.M.H. Nabavi ; M.A.S. Masoum
      • Source: IET Science, Measurement & Technology, Volume 6, Issue 4, p. 267 –278
      • DOI:  10.1049/iet-smt.2011.0143
      • Type: Article
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      • p. 267 –278 (12)
        This study presents a particle swarm optimisation (PSO)-based algorithm to perform congestion management by proper placement and sizing of one unified power flow controller (UPFC) device in a market-based power systems. The algorithm uses quadratic smooth curves for generators’ costs. A typical load duration curve (LDC) is used to improve the accuracy of the model by incorporating the impacts of load variation on the optimisation problem. The proposed approach makes use of the PSO algorithm to allocate the near-optimal GenCos as well as the optimal location and size of UPFC whereas the Newton–Raphson solution minimises the mismatch of the power flow equations. Simulation results (without/with the line flow constraints, before and after the compensation) are used to analyse the impact of UPFC on the congestion levels of the reliability test system (RTS) 24-bus test system. Simulation results by the proposed PSO algorithm are also compared with solutions obtained by the conventional sequential quadratic programming (SQP) approach.
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      Empirical mode decomposition of acoustic signals for diagnosis of faults in gears and rolling element bearings
      • Author(s): M. Amarnath  and  I.R. Praveen Krishna
      • Source: IET Science, Measurement & Technology, Volume 6, Issue 4, p. 279 –287
      • DOI:  10.1049/iet-smt.2011.0082
      • Type: Article
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      • p. 279 –287 (9)
        Rolling element bearings and gears are the most important components of rotating machines. One of the major causes of machine down time is because of the failure of these elements. Down time of rotating machines can be reduced by monitoring vibration and acoustic behaviour of machine elements. This study describes the application of the empirical mode decomposition (EMD) method to diagnose the faults in rolling element bearings and helical gears. By using EMD, a complicated signal can be decomposed into a number of intrinsic mode functions (IMFs) based on the local characteristic timescale of the signal. The IMFs reveal the intrinsic oscillation modes embedded in the signal. Acoustic signals acquired from the bearings and gears have been decomposed and kurtosis values are extracted from these IMFs to quantify various faults. Results demonstrate the advantages of EMD method to detect the faults in the early stage.
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      Variable leaky least mean-square algorithm-based power system frequency estimation
      • Author(s): B. Subudhi ; P.K. Ray ; S. Ghosh
      • Source: IET Science, Measurement & Technology, Volume 6, Issue 4, p. 288 –297
      • DOI:  10.1049/iet-smt.2011.0103
      • Type: Article
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      • p. 288 –297 (10)
        Dynamic variation in power system frequency is required to be estimated in order to implement correcting measures. This study presents power system frequency estimation by using a leaky least mean-square algorithm. The proposed approach uses a variable leak adjustment technique to avoid drifting of the weights involved in the estimation mechanism. A variable adaptation step size is also incorporated in the algorithm to attain faster convergence. The performance of the proposed algorithm is studied through simulations for several critical cases that often arise in a power system. These studies show that the present algorithm is superior over the existing ones in estimating power system frequency. Studies made on experimental data also support the superiority.
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      Electromagnetic fields generated by arbitrarily shaped current loops
      Multi-band weakly ground-coupled balanced antenna design for portable devices
      • Author(s): D. Zhou ; R.A. Abd-Alhameed ; A.G. Alhaddad ; C.H. See ; J.M. Noras ; P.S. Excell ; S. Gao
      • Source: IET Science, Measurement & Technology, Volume 6, Issue 4, p. 306 –310
      • DOI:  10.1049/iet-smt.2011.0151
      • Type: Article
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      • p. 306 –310 (5)
        A balanced antenna for wireless portable devices applications with multiple band operational performance is investigated and discussed. The designed antenna is weakly ground-couple, although can be considered as an energy-efficient radiator. The antenna structure is a thin-strip planar dipole with a dual-folded structure on each arm. The performance of the proposed antenna is analysed and optimised for WLAN and WiMAX applications over the relevant frequency bands, including the 2.4 and 5.2 GHz WLAN bands and the 2.5 and 3.5 WiMAX bands. For validation, the antenna prototype was fabricated and tested. The performance of this balanced antenna was verified and characterised in terms of the return loss, radiation pattern and power gain. The predicted and measured results show acceptable agreement and the results also confirm good impedance bandwidth characteristics with excellent dual-band operation.
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