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Science, Measurement & Technology, IET

Popular Articles (December 2014)

Includes the top 50 most frequently downloaded documents for this publication according to the most recent monthly usage statistics.
  • 1. Intelligent controller for managing power flow within standalone hybrid power systems

    Page(s): 191 - 200
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1101 KB)  

    This study presents a novel adaptive management strategy for power flow in standalone hybrid power systems. The method introduces an on-line energy management by using a hierarchical controller between three energy sources: photovoltaic (PV) panels, battery storage and proton exchange membrane fuel cell. The proposed method includes a feed-forward, back-propagation neural network controller in the first layer, which is added in order to achieve the maximum power point for the different types of PV panels. In the second layer, a fuzzy logic controller has been developed to optimise performance by distributing the power inside the hybrid system and by managing the charge and discharge of the current flow. Finally, and in the third layer, local controllers are presented to regulate the fuel cell/battery set points in order to reach to best performance. Moreover, perturb and observe algorithm with two different controller techniques - the linear proportional-integral (PI) and the non-linear passivity-based controller - are provided for a comparison with the proposed maximum power point tracking controller system. The comparison revealed the robustness of the proposed PV control system for solar irradiance and load resistance changes. Real-time measured parameters and practical load profiles are used as inputs for the developed management system. The proposed model and its control strategy offer a proper tool for optimising the hybrid power system performance, such as the one used in smart-house applications. View full abstract»

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  • 2. Nonlinear fillers in electrical insulating materials

    Page(s): 96 - 102
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (423 KB)  

    Nonlinear composite dielectric materials can be formed through the inclusion of appropriate fillers in polymers. Depending on the type of filler used, the composite material can then possess either an electrical field-dependent conductivity (FDC) or an electrical field-dependent permittivity (FDP). These nonlinear properties can then be used for the purposes of electrical stress relief in insulation systems with divergent electric fields, reducing the intensity of highly stressed regions. FDC polymer composites are formed through the inclusion of narrow-band gap semiconductive fillers in a polymer matrix and can be used for electrical stress relief in both AC and DC applications. FDP materials on the other hand use ferroelectric fillers in polymers; however, the stress-relieving properties of these materials are only realisable under AC fields. The paper reports on the electrical characterisation of both of these stress-relieving materials, with the criteria required for them to function. The materials that have been studied in these investigations take the form of zinc oxide in epoxy resin and barium titanate in an acrylic resin, respectively. Improvements in thermal conductivity are also reported as a consequence of the introduction of these fillers View full abstract»

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  • 3. Experimental investigation of the effect of the design parameters of pressboard in mineral oil on creepage discharge propagation

    Page(s): 23 - 31
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1020 KB)  

    One of the vital causes of the failure of oil transformers is considered as the creepage discharge propagation on pressboard. The authors performed an experimental investigation under an AC step test voltage to analyse the effects of the structure, distance and gluing direction of pressboard on creepage propagation. Flat, ribbed and grooved test specimens were prepared. Further, breakdown experiments were conducted for two gluing directions, parallel and vertical with respect to the electric field. For parallel gluing, the average breakdown voltage (VBD) of the ribbed and grooved types was 1.2-1.33 times that of the flat type. For vertical gluing, the VBD of the flat type was 1.28-1.66 times that of the same type with parallel gluing, whereas the values for the ribbed and grooved types were 1.02-1.11 times the corresponding values for parallel gluing. The rib height and groove depth do not seem to contribute greatly to the breakdown strength because most of the flashover propagation appeared not on the pressboard's surface but at the glued interface. The results of this preliminary investigation may be useful for improving the dielectric creepage strength of solid insulation systems using pressboard as radial spacers, and high-voltage winding lead support parts. View full abstract»

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  • 4. A multifunctional real-time power quality monitoring system using Stockwell transform

    Page(s): 155 - 169
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (2352 KB)  

    The proliferation of power electronic devices in the power sector has intensified the power quality (PQ) issues. Identification of these PQ issues is one of the most important steps for their effective elimination. Hence, development of a real-time (hardware) PQ monitoring system is of great research interest. This study proposes a multifunctional real-time (hardware) PQ monitoring system using Stockwell transform (S-transform). The proposed system is designed and implemented in LabVIEW environment, which can display the real-time fast Fourier transform plots, root-mean-square values, harmonic components, values of total harmonic distortion and three-dimensional plots of S-transform of the three-phase voltages. Main contribution of this study is the real-time detection and classification of different PQ disturbances which even a layman can understand through visual displays to ascertain the quality of supply, unlike other PQ analysers available commercially that require some technical expertise. View full abstract»

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  • 5. Detection and classification of power quality disturbances using discrete wavelet transform and wavelet networks

    Page(s): 193 - 205
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (503 KB)  

    A novel approach for detection and classification of power quality (PQ) disturbances is proposed. The distorted waveforms (PQ events) are generated based on the IEEE 1159 standard, captured with a sampling rate of 20 kHz and de-noised using discrete wavelet transform (DWT) to obtain signals with higher signal-to-noise ratio. The DWT is also used to decompose the signal of PQ events and to extract its useful information. Proper feature vectors are selected and applied in training the wavelet network classifier. The effectiveness of the proposed method is tested using a wide spectrum of PQ disturbances including dc offset, harmonics, flicker, interrupt, sag, swell, notching, transient and combinations of these events. Comparison of test results with those generated by other existing methods shows enhanced performance with a classification accuracy of 98.18. The main contribution of the paper is an accurate (because of proper selection of feature vectors), fast (e.g. a new de-noising approach with proposed identification criterion) and robust (at different signal-to-noise ratios) wavelet network-based algorithm (as compared to the conventional wavelet-based algorithms) for detection/classification of individual, as well as combined PQ disturbances. View full abstract»

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  • 6. Wavelet-based switching faults detection in direct torque control induction motor drives

    Page(s): 303 - 310
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (785 KB)  

    This study describes a method of detection and identification of IGBT-based drive open-circuit faults in direct torque control (DTC) induction motor drives. The detection mechanism is based on wavelet decomposition. The Symlet2 wavelet was selected as the wavelet base to perform stator current analysis during transients. In this method, the stator currents will be used as an input to the system. The MATLAB program was used to process discreet wavelet transform (DWT) of the signals. The stator current was used for the detection of the fault. When an open-circuit fault appears in an inverter IGBT, the signal fault information is included in each frequency region. There are spikes in the sixth level detail for incipient faults. The time of the spikes in the DWT is correlated with the time of fault. As a result of time domain studies, a faulty system can be easily discriminated from a healthy one. In this study the analysis of electrical transients arising during switch open-circuit faults in a three-phase power inverter feeding DTC induction motor drives was decomposed using the wavelet transform. The results demonstrate that the proposed fault detection and diagnosis system has very good capabilities. View full abstract»

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  • 7. Influence of nano-fillers on electrical treeing in epoxy insulation

    Page(s): 21 - 28
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1010 KB)  

    This paper presents the results of a study on the effect of alumina nano-fillers on electrical tree growth in epoxy insulation. Treeing experiments were conducted at a fixed ac voltage of 15 kV, 50 Hz on unfilled epoxy samples as well as epoxy nanocomposites with different loadings of alumina nano-fillers. Time for tree inception as well as tree growth patterns were studied. The results show that there is a significant improvement in tree initiation time with the increase in nano-filler loading. Different tree growth patterns as well as slower tree growth with increasing filler loadings were observed in epoxy nanocomposites. The nature of the tree channel and the elemental composition of the material on the inner lining of the tree channels have been studied using SEM imaging and EDAX analysis respectively of the cut section of the tree channels. It has been shown that the type of bonding at the interface has an influence on the electrical tree growth pattern. The nature of the bonding at the interface between the epoxy and the nano-filler has been studied using FTIR spectrometry. Finally the influence of the interface on tree growth phenomena in nanocomposites has been explained by a physical model. View full abstract»

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  • 8. Feature extraction of partial discharge signals using the wavelet packet transform and classification with a probabilistic neural network

    Page(s): 177 - 192
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (594 KB)  

    Partial discharge (PD) classification in power cable accessories and high voltage equipment in general is essential in evaluating the severity of the damage in the insulation. In this article, the PD classification was realised as a two-fold process. Firstly, measurements taken from a high-frequency current transformer (HFCT) sensor were represented as features by means of a transformation to the classifier and secondly, the probabilistic neural network (PNN) classifier itself was capable of effectively recognising features coming from different types of discharges. The feature that was used as a fingerprint for PD characterisation was extracted from the moments of the probability density function (PDF) of the wavelet coefficients at various scales, obtained through the wavelet packets transformation. The PNN classifier was used to classify the PDs and assess the suitability of this feature vector in PD classification. Four types of artificial PDs were created in a high voltage laboratory, namely corona discharge in air, floating discharge in oil, internal discharge in oil and surface discharge in air, at different applied voltages, and were used to train the PNN algorithm. The results obtained here (97.49, 91.9, 100 and 99.8% for the corona, the floating, the internal and the surface discharges, respectively) are very encouraging for the use of PNN in PD classification with this particular feature vector. This article suggests a feature extraction and classification algorithm for PD classification, which when combined together reduced the dimensionality of the feature space to a manageable dimension, and achieved very high levels of classification. View full abstract»

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  • 9. Precision irrigation based on wireless sensor network

    Page(s): 98 - 106
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (706 KB)  

    The main purpose of this study is to present a complete irrigation solution for the farmer based on wireless sensor network. The challenge is to create an automated irrigation system which can reduce in the same time the water's waste and is cost effective. Different parameters are important to measure in order to calculate the efficient quantity of water needed by plants. In this study, the proposed solution is the use of low-cost sensor nodes having reduced power consumption able to realise necessary requirements. The system is composed of different types of nodes. Each node consists of a TelosB mote and adequate sensors or actuators. Soil nodes are used to detect the level of moisture and temperature in soil. Weather nodes monitor the climatic changes. Other nodes are connected to actuators which are able to control the opening of the irrigation valve if necessary. View full abstract»

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  • 10. Profit-based unit commitment with security constraints and fair allocation of cost saving in industrial microgrids

    Page(s): 315 - 325
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (379 KB)  

    Unit commitment (UC) in industrial microgrids (IMGs) is an important issue which has not received much attention in the literature. IMGs consist of many factories with distributed energy resources (DERs) and electric loads that heavily rely on combined heat and power systems. This study illustrates that UC in an IMG is not solely a profit-based UC or a security constrained UC (SCUC) problem. Therefore a new profit-based SCUC (PB-SCUC) formulation is proposed for IMGs that includes both microgrid (MG) security and factories constraints while utilising the generators waste heat to fulfill thermal requirements. The MG controller will solve the PB-SCUC problem to minimise the final production cost through maximisation of the profit by selling electricity to the upstream network. As each DER and boiler may have an individual owner, an approach based on game theory is also implemented to fairly allocate cost saving among factories participating in the generation process. Detailed simulation results are presented for an IMG consisting of 12 factories and analysed to show the effectiveness of the proposed approaches. View full abstract»

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  • 11. Remote monitoring of partial discharge data from insulated power cables

    Page(s): 319 - 326
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1094 KB)  

    Partial discharge (PD) diagnostics is one of the most widely used tool to assess the insulation condition of insulated power cables and which facilitates informed maintenance planning leading to the extension of the service life of such ageing assets. PD occurs with varying intensity due to circuit loading and weather conditions. Proven systems based on off-line PD diagnostics find limited application, since this method requires a circuit outage. In this study, remote controlled PC based PD monitoring system using client server technology is proposed. Continuous monitoring of cable network using the proposed system can capture sudden or gradual changes in PD activity which is often difficult in conventional PD monitoring systems which are based on spot measurement. In this system, the remote control capability using internet has been implemented to reduce the frequency of site visits which in turn reduces the cost of manpower. Relational database management system is used as a back-end server for data storage, data analysis and data management. This would help the utility to maintain insulation integrity history database which can be used for cable renewal program in the longer term. System design, testing, implementation and field measurements are discussed. View full abstract»

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  • 12. Strapdown inertial navigation system alignment based on marginalised unscented kalman filter

    Page(s): 128 - 138
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (528 KB)  

    This study concerns the strapdown inertial navigation system (SINS) initial alignment under marine mooring condition with large initial error. The ten-dimensional state initial alignment error functions of the SINS with inclusion of non-linear characteristics have been derived. It is pointed out for the first time that the non-linear functions are applied to only a subset of the elements of the state vector, that is, the velocities error and the misalignment angles. Then a computationally efficient refinement of the unscented transformation (UT) called marginalised UT (MUT) is investigated in these special non-linear systems with a linear substructure. A performance comparison between the extended Kalman filter (EKF), the UT-based Kalman filter (UKF) and the MUT-based Kalman filter (MUKF) demonstrates that both the UKF and the MUKF can outperform the EKF and the MUKF and can achieve, if not better, at least a comparable performance to the UKF, at a significantly lower expense. View full abstract»

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  • 13. Measurement of the resistive leakage current in surge arresters under artificial rain test and impulse voltage subjection

    Page(s): 256 - 262
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (369 KB)  

    Surge arresters are installed on transmission and distribution lines and in substations between phase and earth in order to improve the lightning performance and reduce the failure rates. High-energy stresses and housing deterioration are the main factors of degradation and damage of surge arresters. Thus, there is need for testing and monitoring the electrical network's arresters, in order to verify their good condition and their ability to effectively protect the lines. The most common method used, is the measurement of the arresters' total leakage current (with the isolation of the resistive part), which is an indicator of the arrester's condition, since every change, deterioration or damage leads to an increase of the resistive leakage current. In the current work, the total leakage current of two 20 kV ZnO surge arresters without gaps is measured and the resistive component for three different cases (brand new arresters, measurements under artificial rain and measurements after impulse voltage subjection) is computed. The analysis of the produced results can be useful in correct diagnosis of arresters' condition and in more effective schedule maintenance, since any recorded high-resistive currents do not necessarily result arrester's repair or replacement. View full abstract»

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  • 14. Simulation and energy management of an experimental solar system through adaptive neural networks

    Page(s): 427 - 431
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (245 KB)  

    In this study, the authors consider a solar system which consists of a solar trainer that contains a photovoltaic panel, a DC centrifugal pump, flat plate collectors, storage tank, a flowmeter for measuring the water mass flow rate, pipes, pyranometer for measuring the solar intensity, thermocouples for measuring various system temperatures and wind speed meter. The various efficiencies of the solar system have been predicted by an artificial neural network (ANN) which was trained with historical data. The ANN fails to predict the efficiencies accurately over the long-time horizon because of system parts degradation, environmental variations, date changes within the year from the modelling date and presence of modelling errors. Therefore the ANN is adapted using the error between the ANN-predicted efficiency and the efficiency measurement from the appropriately selected sensors and efficiency laws to update the network's parameters recursively. The adaptation scheme can be performed online or occasionally and is based on the Kaczmarz's algorithm. The adaptive ANN capability is demonstrated through computer simulation. View full abstract»

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  • 15. Application of the Hilbert-Huang transform with fractal feature enhancement on partial discharge recognition of power cable joints

    Page(s): 440 - 448
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1000 KB)  

    This study proposes a novel method of partial discharge (PD) pattern recognition based on the Hilbert-Huang transform (HHT) with fractal feature enhancement. First, this study establishes three common defect types with one blank sample of 25 kV cross-linked polyethylene (XLPE) power cable joints and uses a commercial acoustic emission sensor to measure the acoustic signals caused by the PD phenomenon. The HHT can represent instantaneous frequency components through empirical mode decomposition, and then transform to a 3D Hilbert energy spectrum. Finally, this study extracts the fractal theory feature parameters from the 3D energy spectrum by using a neural network for PD recognition. To demonstrate the effectiveness of the proposed method, this study investigates its identification ability using 120 sets of field-tested PD patterns generated by XLPE power cable joints. Unlike the fractal features extracted from traditional 3D PD images, the proposed method can separate different defect types easily and shows good tolerance to random noise. View full abstract»

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  • 16. Modelling of metal oxide arrester for very fast transients

    Page(s): 140 - 146
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (273 KB)  

    At present metal oxide arresters find limited applications against very fast transient overvoltages (VFTOs). To enable these arresters to function effectively against VFTOs, it becomes necessary to study its design aspects and improve it. With this in view, modelling of arrester under VFTO has been performed. Experimental studies have been conducted to determine the behaviour of one 12 kV arrester assembly under VFTO. It is observed that there is a delay in the initial response of the arrester, which increases with steepness of the current surge because of stray capacitance effect. Based on this study, an innovative arrester model (198 kV) with distributed parameters for VFTO is proposed by incorporating the block and stray capacitance values, which are calculated using finite element method (FEM). The dynamic performance of arrester is successfully obtained using electromagnetic transient program (EMTP) for current surges of different front times. A dynamic hysteresis curve is constructed using proposed arrester model to verify the relative delays between the residual voltage and current surge. A few modifications in the arrester have been suggested to improve the dynamic performance and also for the new testing procedure of arrester under VFTO. View full abstract»

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  • 17. Efficient multi-stage load modulation radio frequency power amplifier for green radio frequency front end

    Page(s): 117 - 124
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (527 KB)  

    The road towards the reduction in the carbon footprint associated with power-hungry wireless communication devices will require a holistic design approach to ensure that energy saving can be achieved throughout the entire system. The information and communication technology today accounted for 3 and 2% global power consumption and global CO2 emissions, respectively, where a significant portion is a result of the power consumption in the radio frequency (RF) power amplifier device. Moreover, tomorrow amplifiers will need to be reconfigurable and host a plethora of modulated signals to support effective signal processing. Therefore performance metrics such as linearity, power efficiency and their trade-off should be at the forefront of the RF power amplifier design. This study proposes an energy-efficient power amplifier design based on the Doherty configuration as part of a green RF front end for mobile WiMAX. The authors extend the classical Doherty to incorporate a three-stage load modulation design with a proposed new output power combiner. The performance of the three-stage load modulation RF power amplifier is compared with the legacy two-stage load modulation technique. The experimental results show that 30 dBm output power can be achieved with 67 power-added efficiency, which represents a 14 improvement over the current state-of-the-art system while meeting the power output requirements for mobile WiMAX. View full abstract»

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  • 18. Empirical mode decomposition of acoustic signals for diagnosis of faults in gears and rolling element bearings

    Page(s): 279 - 287
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (614 KB)  

    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. View full abstract»

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  • 19. Energy-harvesting system design through Bluetooth environment for smart phone

    Page(s): 201 - 205
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (405 KB)  

    Recent mobile handhelds, for example, smart-phone, can be charged wirelessly using the traditional wireless communication technologies as well as a new energy-harvesting circuit. In particular, Bluetooth with a charging circuit enables a short-range wireless charging of a mobile handheld. This study presents an overview of power-charging structures and proposes a new charging and harvesting circuit based on schottky diode with a real commercial film-type antenna on mobile terminal. The authors' new circuit improves the charging efficiency approximately by 160%, that is, 0.45 mA rather than 5 mA for a current Smartphone in the consumer market. View full abstract»

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  • 20. A dielectric frequency response model to evaluate the moisture content within an oil impregnated paper condenser bushing

    Page(s): 223 - 231
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (570 KB)  

    Increased moisture content within an oil-paper insulation system can significantly reduce its life expectancy, and for oil impregnated paper condenser type bushings, it is the most common cause of failure. Distinction between moisture contents using traditional power frequency tests of dissipation factor and capacitance can be difficult, particularly at ambient temperatures. Dielectric frequency response is becoming an established technique to measure the dissipation factor and capacitance of a bushing, but to date an accurate model to evaluate the condenser moisture content has not been presented using this technique. In this study, a dielectric frequency response bushing model is proposed and finite element method software is used to simulate the variation in dissipation factor and capacitance of a bushing with varying moisture content, as a function of frequency and temperature. The modelled results are compared with measurements reported in the literature and from the authors' own field measurements, where a good agreement is demonstrated. It is shown that the distinction in dissipation factor between moisture contents at frequencies <;0.1 Hz is in excess of ten times greater than at 50 Hz. The proposed model can be used by practitioners to evaluate moisture content within the condenser insulation and distinguish between moisture contents ranging from 0.2 to 4.0%. View full abstract»

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  • 21. Intelligent stochastic framework to solve the reconfiguration problem from the reliability view

    Page(s): 245 - 259
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (831 KB)  

    This study proposes a new method to employ the distribution feeder reconfiguration as a reinforcement strategy to enhance the reliability of the distribution systems. Also, several wind power sources are considered to assess their effects on the reliability indices. In order to make the final results more dependable, a stochastic framework based on the probabilistic power flow is utilised to consider the uncertainty of forecast/measurement error of the active and reactive loads, failure rate, repair rate and output generation of wind units, concurrently. The objective functions to be investigated are (i) system average interruption frequency index, (ii) average energy not supplied, (iii) active power losses and (iv) total cost. Moreover, a new modified optimisation method based on harmony search algorithm is proposed to improve the total ability of the algorithm to explore the problem search space globally. The effectiveness and efficiency of the proposed method are examined through two radial distribution test systems. View full abstract»

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  • 22. Photovoltaic power forecasting using statistical methods: impact of weather data

    Page(s): 90 - 97
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (623 KB)  

    An important issue for the growth and management of grid-connected photovoltaic (PV) systems is the possibility to forecast the power output over different horizons. In this work, statistical methods based on multiregression analysis and the Elmann artificial neural network (ANN) have been developed in order to predict power production of a 960 kWP grid-connected PV plant installed in Italy. Different combinations of the time series of produced PV power and measured meteorological variables were used as inputs of the ANN. Several statistical error measures are evaluated to estimate the accuracy of the forecasting methods. A decomposition of the standard deviation error has been carried out to identify the amplitude and phase error. The skewness and kurtosis parameters allow a detailed analysis of the distribution error. View full abstract»

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  • 23. Improved FEM model for defect-shape construction from MFL signal by using genetic algorithm

    Page(s): 196 - 200
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (213 KB)  

    In-line inspection of ferromagnetic gas or oil pipe lines having pipe wall defects is typically accomplished using magnetic flux leakage (MFL) technique. An efficient modelling and computational scheme for forward model, during the process of solving inverse problems in magnetostatic non-destructive evaluation using finite-element method is presented. The shape, size and place of defect are determined considering the nonlinearity of the pipe material using genetic algorithm as the optimisation technique. It is shown that the reduced model improves the FE computations significantly. The methodology for construction of defect shapes from particular MFL signals has been explained View full abstract»

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  • 24. On-line partial discharge monitoring in medium voltage underground cables

    Page(s): 354 - 363
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (799 KB)  

    For many years incipient partial discharge (PD) faults in power cables have been identified through off-line investigation techniques. More recently, in an effort to allow pro-active asset management of the medium-voltage (MV) cable network to be carried out, continuous on-line monitoring systems are being installed with the aim of reducing unexpected failures. This study presents work on the analysis and handling of acquired data, from the point of view of asset management and the PD activities observed in an on-line cable monitoring systems. Initially, a review of on-line against off-line cable PD monitoring is presented, in terms of their setups and their respective advantages and disadvantages. The study then presents the authorspsila experience of applying wavelet-based denoising techniques [both the discrete wavelet transform (DWT) and the second generation wavelet transform (SGWT)] to PD data denoising. Results of a study on the on-line PD-based monitoring of MV underground cables that are presented in the following section demonstrate that PD activity which is observed in on-line monitoring also has an associated high level of electrical noise that must be removed to allow proper identification of the PD signals and the denoised PD activity is seen to vary with time. Finally, the necessity of developing a means by which knowledge rules can automatically be acquired from on-line condition monitoring data, to reduce reliance on human expertise, is discussed. View full abstract»

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  • 25. Application of numerical evaluation techniques for interpreting frequency response measurements in power transformers

    Page(s): 275 - 285
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (566 KB)  

    Frequency response analysis (FRA) is an emerging, powerful non-intrusive condition monitoring and diagnostic tool for verifying the mechanical integrity of power transformers. FRA results are graphical in nature and require trained experts to interpret test results. The work reported discusses numerical-criteria- based evaluation techniques. Persons not familiar with interpreting the FRA results can apply the evaluation criteria. The various criteria help in deriving proper conclusions. By evaluating correlation coefficient (CC), standard deviation and absolute sum of logarithmic error (ASLE) techniques, it is possible to discriminate between defective and non-defective windings. Experimental studies were conducted on two test transformers for axial and radial displacements, and additionally two sets of identical substation transformers. The techniques mentioned above are useful for interpreting frequency responses even in situations when a reference fingerprint was not available. However, it was concluded that if original fingerprints are available, the method gives very reliable indication for diagnosing the faulty winding. In addition, the severity of displacement/deformation can also be concluded from the amount of variation of the parameters from the suggested critical values. View full abstract»

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  • 26. Unbalanced three-phase distribution system frequency estimation using least mean squares method and positive voltage sequence

    Page(s): 30 - 38
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1154 KB)  

    The subject of this study is a frequency estimation algorithm suitable for grid-connected power converters placed at a weak coupling point of a three-phase electrical distribution system. An upgraded version of the widely used complex least mean squares (CLMS) algorithm for frequency estimation is introduced to cope with different voltage amplitude unbalance and harmonic distortion levels, both frequently present in power system at distribution level. First, it is suggested that the CLMS algorithm uses only a positive phase-sequence component of voltage vector, the component that is inherently symmetrical and by cancelling the phase unbalance preserves the circular vector trajectory in a two-phase αβ-plane. This study shows that it is even possible to use the positive voltage phase-sequence vector extracted using a constant delay block, thus avoiding potential instability issues in the case of signal frequency feedback loop. Second, possible high signal harmonics and signal measurement noise are both removed using low-pass filters prior to CLMS algorithm deployment. Computer simulations and experiments are performed under a variety of conditions to validate the effectiveness of the proposed technique. Experimental results are achieved using the dataset sampled from the actual three-phase grid voltage at distributed level and with data processing done in the LabVIEW software environment. View full abstract»

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  • 27. Tracking algorithm with radar and infrared sensors using a novel adaptive grid interacting multiple model

    Page(s): 270 - 276
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (280 KB)  

    This study presents a novel adaptive grid interacting multiple model based on modified iterated extended Kalman filter (AGIMM-MIEKF) for tracking a manoeuvreing target using radar/infrared (IR) heterogeneous sensors. This tracking algorithm is developed by aligning observation data of radar/IR sensors in time, and fusing the synthesised data before applying to AGIMM-MIEKF algorithm. Under the architecture of the proposed algorithm, the AGIMM deals with the model switching, whereas the MIEKF accounts for non-linearity in the dynamic system models. A new measurement update equation and an iterated termination criterion are derived and applied to radar/IR tracking system. The simulation results show that the presented AGIMM-MIEKF has higher tracking precision than the traditional algorithms. View full abstract»

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  • 28. Effect of Ar pressure on grain size of magnetron sputter-deposited Cu thin films

    Page(s): 87 - 90
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (211 KB)  

    Copper (Cu) thin films with thicknesses ranging from 300 to 425 nm were prepared at various argon (Ar) pressures on p-type silicon substrates by direct current magnetron sputtering deposition. X-ray diffraction (XRD) and Karl Suss four-point probe were employed to study the film crystallinity and conductivity, respectively, as a function of Ar pressure in the deposition process. Detailed analysis on the XRD patterns shows that low Ar pressure enhances the Cu film crystallinity with larger grain size, which was deduced using Scherrer's formula. The behaviour of the electrical property of the Cu films complies with the trend of the grain size with Ar pressure, in which the film conductivity decreases with increasing Ar pressure. The authors attribute these phenomena to the degraded surface diffusion mechanism of the adatom on the growing surface, with increasing Ar pressure during the sputtering deposition process View full abstract»

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  • 29. Partial discharge within a spherical cavity in a dielectric material as a function of cavity size and material temperature

    Page(s): 52 - 62
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (915 KB)  

    For high-voltage components, the measurement of partial discharge (PD) is a useful tool for performance assessment of electrical insulation. In this study, experimental measurements of PD activity for different spherical cavity sizes and material temperatures have been performed. A simulation model representing PD behaviour within spherical cavities in homogeneous dielectric materials has also been developed. The model has been used to study the influence of cavity size and material temperature on PD activity. Comparison of measurement and simulation results has been undertaken. The model uses a finite element analysis (FEA) method along with MATLAB code. It has been found that certain parameters in the model are both cavity size and temperature dependent. Thus, critical parameters influencing PD behaviour for different cavity sizes within the material and material temperatures can be identified; these are the charge decay time constant, cavity surface conductivity, electron generation rate (EGR), PD inception and extinction fields and the cavity temperature decay time constant. View full abstract»

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  • 30. N-way planar high-power combiner design for RF power amplifiers

    Page(s): 61 - 67
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (475 KB)  

    The complete design using a novel technique for an N-way planar high-power combiner is introduced for radio-frequency (RF) power amplifiers (PAs) at high-frequency (HF) range for the first time. On the basis of this design technique, a three-way planar combiner is simulated, designed and built on a ceramic-based material that allowed a surface-mount application. Design charts for a thermally reliable operation under high-power conditions are given. The simulated and measured results are compared and found to be very close. The design technique for planar combiners introduced here can be used for RF PAs to obtain power level in the several-kilowatt range in HF communication for industrial and military applications. View full abstract»

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  • 31. Calibration of on-line partial discharge measuring system using Rogowski coil in covered-conductor overhead distribution networks

    Page(s): 5 - 13
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (663 KB)  

    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. View full abstract»

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  • 32. Dynamic voltage restorer control using bi-objective optimisation to improve power quality's indices

    Page(s): 203 - 213
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1140 KB)  

    Dynamic voltage restorer (DVR) is one of the custom power devices for compensating power quality indices which is used. The main function of DVR that is discussed in many studies is to compensate voltage sag at times when faults occur. For the first time, a new control structure is presented for considering the voltage sag as the main objective and voltage total harmonic distortion (THD) as the second objective of DVR controller. In this strategy, a new and powerful optimisation algorithm (known as chaotic accelerated particle swarm optimisation (CAPSO)) which is an improved version of particle swarm optimisation algorithm is used for determining the coefficients of the proportional-integral controller of DVR. These coefficients are determined in a way that voltage sag is considered as the main objective of optimisation algorithm and voltage THD is considered as its second objective. By fuzzifying the objectives, an appropriate objective function is proposed for the optimisation process. Results obtained from simulation and a comparison made between these results and those of other controllers show that the proposed strategy outperforms other strategies. View full abstract»

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  • 33. Novel designs of wideband Rogowski coils for high pulsed current measurement

    Page(s): 9 - 16
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (743 KB)  

    This study presents design, calibration and testing of six novel flat-spiral self-integrating Rogowski coils wound in two layers. These coils are two varnished-wire wound coils with air and ferrite cores (RC1 and RC2, respectively), two flat-twin wire wound coils with air and ferrite cores (RC3 and RC4, respectively) and two coaxial-cable wound coils with and without the insulating jacket and with ferrite core and RC5 and RC6, respectively. All coil parameters are calculated and good agreement is found between these values and the corresponding measured ones. Coil sensitivity decreases as coil-to-wire separation increases and so does mutual inductance between the coil and the current-carrying wire. Linearity of all coil sensitivities are checked for different separations and waveforms, and good agreement is found. Designed coils with ferrite core give better response than those with air core because the low cutoff frequency decreases. On the contrary, the droop effect is slightly observed for coils wound on wooden core, where RC4 and RC6 give the best response. Finally, the frequency response analysis for all coils shows that the percentage relative errors of the measured and the calculated coil sensitivities are within ±0.1%. View full abstract»

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  • 34. Resonant frequency and Q factor extraction from temporal responses of ultra-high Q optical resonators

    Page(s): 277 - 284
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (610 KB)  

    Resonant frequency extraction from time signal simulations of optical resonators is often required to resolve closely spaced resonances in addition to estimating high Q factors. Traditional Fourier transform-based fitting methods thus require very long time signals, limiting their usage. Complex exponential fitting-based methods such as matrix pencil, modified Prony and harmonic inversion provide better accuracy, but each has its own advantages as well as disadvantages. In this study, it is shown that the matrix pencil method is limited by the number of time samples, but provides accurate results, whereas the harmonic inversion method provides less accurate results with high efficiency. The difference formulation of the modified Prony method implemented with multiple precision, while providing the best accuracy, is the least efficient approach and requires careful adjustment of its parameters to obtain a solution. View full abstract»

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  • 35. Response of metal oxide arrester in gas-insulated substation and methods to improve its dynamic characteristics

    Page(s): 222 - 228
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (400 KB)  

    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 s. However, there is a deviation in it when front time is less than 1 s, 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. View full abstract»

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  • 36. Two-step optimal filter design for the low-cost attitude and heading reference systems

    Page(s): 240 - 248
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (451 KB)  

    This study presents a novel sensing methodology with two optimal condition-based fusion algorithms for attitude estimation, using low-cost micro-machined gyroscopes, accelerometers and magnetometers. The proposed methodology named two-step optimal filter is composed of an optimal filter and fast determination algorithm. The filter is designed as sensor-based Kalman filter, which is augmented by a fuzzy rule to adjust the parameters on line to yield optimal measurements of accelerometers and magnetometers. Then, the fast second estimator of the optimal quaternion algorithm is described to determine the orientations. Meanwhile, adaptation architecture is implemented to yield robust performance, even when the vehicle is subject to strong accelerations or ferromagnetic disturbed. The new construction of attitude estimation algorithm is easy to be implemented, the precise, robustness and efficient are compared with the common methodology. Experimental results are provided for a remotely operational vehicle test and the performance of the proposed filter is evaluated against the output from a conventional filter. View full abstract»

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  • 38. Model for power consumption of wireless access networks

    Page(s): 155 - 161
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (203 KB)  

    The power consumption of wireless access networks will become an important issue in the coming years. In this study, the power consumption of base stations for mobile WiMAX (Worldwide Interoperability for Microwave Access), fixed WiMAX, UMTS (Universal Mobile Telecommunications System), HSPA (High-Speed Packet Access) and LTE (Long-Term Evolution) is modelled and related to the coverage. A new metric, the power consumption per covered area PCarea, is introduced, to compare the energy efficiency of the considered technologies for a basic reference configuration and a future extended configuration, which makes use of novel Multiple Input Multiple Output (MIMO) technology. The introduction of MIMO has a positive influence on the energy efficiency: for example, for a 4×4 MIMO system, PCarea decreases with 63% for mobile WiMAX and with 50% for HSPA and LTE, compared to a Single Input Single Ouptut (SISO) system. However, a higher MIMO array size (i.e. a higher number of transmitting and receiving antennas) does not always result in a higher energy efficiency gain. View full abstract»

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  • 39. Partial discharge identification system for highvoltage power transformers using fractal featurebased extension method

    Page(s): 77 - 84
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (632 KB)  

    Partial discharge (PD) pattern identification is an important tool in high-voltage (HV) insulation diagnosis of power systems. Based on an extension method, a PD identification system for HV power transformers is proposed in this paper. A PD detector is used to measure the raw three-dimensional (3D) PD patterns of epoxy resin power transformers using an L sensor, according to which two fractal features (the fractal dimension and the lacunarity) and the mean discharge are extracted as critical PD features that form the cluster domains of defect types. The matter-element models of the PD defect types are then built according to the PD features derived from practical experimental results. The PD defect type can be directly identified by the correlation degrees between a tested pattern and the matter-element models. To demonstrate the effectiveness of the PD features extraction and the extension method, the identification ability is investigated on 144 sets of field-test PD patterns of epoxy resin power transformers. Compared with a multilayer neural network and K-means methods, the results show that a high accuracy together with a high tolerance in the presence of noise interference is reached by use of the extension method. View full abstract»

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  • 40. Development of multi-band ultra-high-frequency sensor for partial discharge monitoring based on the meandering technique

    Page(s): 327 - 335
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (809 KB)  

    To design high-sensitivity sensors is one of the critical issues to be solved for ultra-high-frequency (UHF) partial discharge (PD) detection in substations. Commonly-used UHF sensors usually use ultra-wideband antennas for the frequency bands ranging from 300 MHz to 1.5 GHz. To avoid interference in the frequency bands, such as signals generated from mobile phones, a new multi-band UHF sensor is proposed based on the loop antenna theory and meandering technique, which reduces the sensor size, provides high sensitivity and exhibits omnidirectional performance. The sensor works in the bandwidth ranges of 480-520, 800-850 and 1100-1200 MHz, and has sensitivity of more than 10 mm. The PD detection platform was set up, three typical insulation defects, such as corona discharge, surface discharge and free metal particle discharge, were designed, and then the tests were performed to compare the performance of the multi-band sensor and broadband sensor. The results show that the multi-band sensor's bandwidth covers the main spectra of PD signals, thereby can be used for detecting most kinds of PD signals. The sensor's sensitivity is higher than that of the broadband sensor with its size occupying only 5% of the latter, meeting the requirements for detection of PD sources in substations. View full abstract»

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  • 41. Fuzzy sliding mode control scheme for a class of non-linear uncertain chaotic systems

    Page(s): 249 - 255
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (397 KB)  

    This study deals with the problem of controlling class of uncertain non-linear systems in the presence of external disturbances. To achieve this goal, a robust fuzzy sliding mode (RFSM) controller is introduced. First known dynamics of the system are eliminated through feedback linearisation and then fuzzy sliding mode controller is designed using Takagi-Sugeno (TS) method, based on the Lyapunov method which is capable of handling uncertainties. There is no sign of the undesired chattering phenomenon in the proposed method. The globally asymptotic stability of the closed-loop system is mathematically proved. In order to evaluate the performance of the proposed controller, the results are compared with those obtained by optimal H adaptive proportional integral derivative controller and an optimal Type-2 fuzzy proportional integral derivative, which are the latest researches in the problem in hand. Simulation results show the effectiveness of the RFSM controller. View full abstract»

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  • 42. Multimedia data delivery table and improving transfer time on mobile handhelds

    Page(s): 54 - 59
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (442 KB)  

    This study presents an enhanced method to improve the transfer time of the audio/video file delivery table employed in a mobile handheld, terrestrial-data multimedia broadcasting. The authors analysed the factors responsible for the delay in the dynamic carousel which is transmitted on broadcasting channels. They improved the transfer time and verified using comparison methods and other approaches. In this study, they measured the mobile handheld transmission delay time by analysing and comparing the transmission speed and by showing its characteristics. Proposed method which boosts up time for the mobile handheld data updating can be achieved approximately 20.5% performance improvement. View full abstract»

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  • 43. Adaptive complex unscented Kalman filter for frequency estimation of time-varying signals

    Page(s): 93 - 103
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (881 KB)  

    A simple and robust non-linear filter algorithm has been proposed in this study for estimating the frequency of a time-varying sinusoidal signal under high noise conditions. The real signal is first converted to an analytical signal and its complex state-space model is derived. An unscented complex Kalman filter (CUKF) is then obtained using the complex signal model and the error covariances along with the Kalman gain are updated iteratively. Also, the stability and the convergence characteristics of the proposed filter are presented for a single sinusoid embedded in noise. It has been shown that the proposed algorithm works efficiently for the estimation of abrupt changes in signal frequency under high noise conditions. To evaluate the performance of the proposed algorithm several computer simulation results of real-time and synthetic signals are presented. Further to improve the performance of the proposed filter in the presence of significant noise and distortions, the covariance matrices are tuned iteratively. View full abstract»

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  • 44. Prediction of magnetising current waveform in a single-phase power transformer under DC bias

    Page(s): 2 - 5
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (253 KB)  

    Direct current (DC) flowing through the earthed neutrals of transformer windings causes a DC component in the magnetising current. Owing to non-linearity, the waveform of this current is strongly distorted. A method based on the finite element analysis of a transformer is presented that is capable of predicting the waveform of the magnetising current with the voltage of the winding as well as the magnitude of the DC bias given. The relationship between the flux linkage of the winding and the value of the magnetising current is determined, with static conditions assumed. With the aid of this flux-current curve, the dependence of the waveform and thus of the DC component of the magnetising current upon the bias flux is established. Hence, the flux bias yielding the given DC component is obtained by suitable iterative techniques, arriving at the waveform of the magnetising current with the prescribed DC value. Measurement of the current waveform at various voltages and DC bias has been carried out on a single phase transformer. The computed waveforms agree well with the measured ones View full abstract»

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  • 45. Stability analysis of an hydropower generator subjected to unbalanced magnetic pull

    Page(s): 231 - 243
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (886 KB)  

    Eccentricity leading to unbalanced magnetic pull (UMP) in electrical machines is a significant concern in industry. The UMP is known to be composed of two components: A radial component and a tangential one. Models that are used in industry currently tend to include the radial component alone. In this study, a Jeffcott rotor model together with a new UMP model that incorporates both the radial and tangential UMP constituents is studied for an industrial hydropower generator. Characterising the UMP as springs permits the proposed model to inherit UMP stiffness contribution. It is shown firstly that the new UMP model is sensitive to forcing frequency in the rotor movements and secondly, that this sensitivity to forcing frequency increases with decreasing rotor system stiffness. Moreover, quasi-periodic motion in the rotor displacements is observed for some forcing frequencies and system stiffnesses. Eigenvalue-based stability analysis is performed and shows that damping and stiffness of the rotor and of the bearings are important when non-synchronous whirling of the rotor comes into play. Accounting for both UMP components is an important cornerstone in the generation of better rotor designs which can help to curb rotor-stator malfunction and can contribute in the design of long lasting rotors. View full abstract»

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  • 46. Temperature measurement of high-density winding coils of electromagnets

    Page(s): 1 - 5
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (407 KB)  

    In this study, the temperature of high-density winding coils of electromagnets is measured without using any temperature measurement probe. In fact, the probe cannot get access to the interior of the coil. Infrared radiometry can measure only the coil surface temperature which can be very different from the interior temperature. In the present measurement technique, the copper winding wire itself is used as the temperature-sensitive element. The current against voltage (I-V) of the coil is first measured. The electrical resistance of the coil is then obtained and plotted against dissipation power. Using the thermal coefficient of the electrical conductivity of copper at ambient temperature (20°C), the coil temperature is deduced and plotted against dissipation power. The resulting temperature is the temperature along the wire averaged over the entire wire length. This is the average interior temperature rather than surface temperature. The case temperature is measured by a precision thermometer. The difference between coil temperature and case temperature is calculated and divided by dissipation power to attain the thermal resistance from the coil to the case. For the electromagnet studied, the thermal resistance is 1.1°C/W. Electromagnets are components that are used in numerous electrical machines and electronic products. Coil temperature measurement is of critical importance because the insulating coating of the winding wire has finite temperature ratings beyond which the coating may deteriorate and get damaged. By using the pulsed mode, the technique presented here can be implemented to measure the coil temperature even while the electromagnets are in operating conditions. It should be valuable to the electricity and motor industries. View full abstract»

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  • 47. Effect of a micro dielectric barrier discharge plasma actuator on quiescent flow

    Page(s): 135 - 142
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (677 KB)  

    A dielectric barrier discharge plasma actuator (PA) was designed and manufactured with microscale dimensions using photolithographic process on fibre glass substrate. AC operation under sinusoidal voltage was investigated experimentally by means of electrical characterisation, smoke flow visualisations and particle image velocimetry. The performances of the micro PA were evaluated and compared with the ones of a macro PA found in this literature. The velocity induced by the micro PA was comparable with the macro PA one, but with lower applied voltage, electrical power dissipation and actuator size. This is particularly interesting for potential applications in turbomachinery. View full abstract»

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  • 48. Investigation of partial discharge activity of single conducting particle in transformer oil under DC voltages using UHF technique

    Page(s): 325 - 333
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (592 KB)  

    Converter transformers play an important role in the high-voltage DC power transmission system. The insulation of these transformers is stressed by both AC and DC voltages. Particle contamination is one of the major problems in insulation structures, as they generate partial discharges. A methodical experimental study was carried out to understand the partial discharge formation because of single macroscopic conducting particle movement in transformer oil at different temperatures under DC voltages using ultra-high-frequency (UHF) technique. It is observed that the single particle moves in the vertical electrode gap under the DC voltage, and generates UHF signal in the range of 1-3 GHz. At high electric fields, the levitated particle sometime floats in the oil medium and as and when the applied voltage is removed, the particle slowly drops down. When it comes in contact with ground electrode, it generates UHF signals with the frequency content lying in the range of 1-3 GHz. Oil breakdown tests were carried out (without any particle in the oil electrode gap) under DC voltages and fast Fourier transform (FFT) analysis of the signal generated by the UHF sensor because of breakdown indicates that the frequency content of the UHF sensor signal lies up to 1 GHz. View full abstract»

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  • 49. Quasi-balanced bridge method for the measurements of the impedances

    Page(s): 403 - 409
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (431 KB)  

    A measurement method called `a quasi-balanced bridge` is described in this study. It can be applied for the determination of the value of the active and reactive impedance parameters separately, as well as the module and the phase of the electric circuit. This can be possible by using a false balancing bridge state, called a quasi-balanced state. This method gives the possibility of measuring the inductance, capacitance, resistance, quality factor, and dissipation factor of a component`s impedance, without caring of the frequency influence. The quasi-balance corresponds to the phase quadrature between two arms of the bridge. The detection of the quadrature is given by using a synchronous detector. The automation of the bridge consists of conceiving a control system that acts in one of the bridge parameters to obtain the required state. The analyses illustrate that an accuracy better than 0.08% is possible using a simple configuration of a quasi-balanced bridge method. Experimental results are included to demonstrate its performances. The automation of the quasi-balanced bridge is made through an interface board of the type CIGAL exploiting a multiplier digital to analogue converter (MDAC) of the type (AD7542), which functions as a virtual potentiometer. View full abstract»

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  • 50. Performance of time-difference-of-arrival ultra wideband indoor localisation

    Page(s): 46 - 53
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (505 KB)  

    Ultra wideband (UWB) is a good candidate for indoor positioning, thanks to its ability to resolve multipath and penetrate through walls. This study investigates the performance of UWB-based time difference of arrival (TDOA) positioning for indoor environment, where one or more blind nodes are to be localised with the aid of a number of anchor nodes. The positions of the blind nodes are estimated using the previously proposed iterative localisation method. The achievable positioning accuracy is analysed in terms of Cramer-Rao lower bound (CRLB), which is a theoretical lower bound on the variance of the positions of blind nodes. The range errors are modelled as distance independent (DI) and distance dependent (DD) for line-of-sight (LOS) and non-line-of-sight (NLOS) cases. Closed-form expressions of CRLB for TDOA localisation are derived and the theoretical analyses have been verified by experimental results. View full abstract»

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IET Science, Measurement & Technology publishes papers in science, engineering and technology underpinning electronic and electrical engineering, nanotechnology and medical instrumentation.

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