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Science, Measurement and Technology, IEE Proceedings -

Popular Articles (March 2015)

Includes the top 50 most frequently downloaded documents for this publication according to the most recent monthly usage statistics.
  • 1. Optimal battery energy storage system (BESS) charge scheduling with dynamic programming

    Publication Year: 1995 , Page(s): 453 - 458
    Cited by:  Papers (18)  |  Patents (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (628 KB)  

    A dynamic programming algorithm for the optimal charge/discharge scheduling of BESS energy storage is presented. It ensures the minimisation of the electricity bill for a given battery capacity, while reducing stress on the battery and prolonging battery life. Optimal scheduling of the battery charge state is in itself unique; the methods of multipass dynamic programming are used to accomplish this. Maximum payoff for load redistribution and peak load shaving is determined while accounting for charging rate, battery voltage fluctuation and internal losses as a function of charge state. The optimal charging curve is significantly different from the curve conventionally published for BESS View full abstract»

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  • 2. Design theory of thermoelectric modules for electrical power generation

    Publication Year: 1996 , Page(s): 351 - 356
    Cited by:  Papers (12)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (580 KB)  

    One of the main requirements in the design of a thermoelectric module is to determine the optimum module geometry, based upon available thermoelectric material and manufacturing technology, which meets the given application specifications. In order to assist in determining the appropriate module geometry for thermoelectric generation, its relationship to the power output and conversion efficiency is examined. A practical procedure for optimising module geometry guided by the “economic factor” is described, together with formulae and graphs which form the foundations of thermoelectric module design View full abstract»

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  • 3. Review of chemical indicators of degradation of cellulosic electrical paper insulation in oil-filled transformers

    Publication Year: 1994 , Page(s): 324 - 334
    Cited by:  Papers (70)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (840 KB)  

    Chemical and thermal degradation of electrical insulation in oil-filled transformers, mechanisms of failure and methods of condition monitoring and of life prediction are reviewed. An insulation life prediction model is developed and estimates of insulation life are presented under a variety of oil/paper conditions. Systematic measurements of the concentration of chemical indicators in transformer oil are used to demonstrate that furaldehyde and related products can be used to detect high rates of paper degradation. Similarly, phenol and related products indicate electrical degradation in phenol-formaldehyde resins View full abstract»

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  • 4. Electromagnetic compatibility of radio telecommunications equipment

    Publication Year: 1994 , Page(s): 244 - 247
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (356 KB)  

    The paper gives an overview of the application of the electromagnetic compatibility directive to radiocommunications equipment, the interaction with the telecommunications terminal equipment and satellite Earth station equipment directives and some changes to the European regulation of EMC. It also describes the main features of the UK implementation of the EMC directive, with special reference to the procedures for EC-type examination in the UK, and summarises the position on the production of harmonised standards for radio equipment View full abstract»

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  • 5. Broadband couplers for UHF detection of partial discharge in gas-insulated substations

    Publication Year: 1995 , Page(s): 237 - 243
    Cited by:  Papers (13)  |  Patents (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (476 KB)  

    The paper describes investigations of the UHF performance of a disc coupler designed for continuous monitoring of partial discharge in gas-insulated substations and indicates how the UHF sensitivity can be improved. Resonant frequencies of the disc are calculated, and the coupler is shown to be most sensitive at these frequencies. The bandwidth of the coupler can be extended by coupling the UHF signal from the edge of the disc, allowing detection of a greater number of the possible resonant modes of the disc, including the dominant, lowest frequency mode. Sensitivity to the UHF signals generated by partial discharge can be further improved by various means. The disc can be earthed at certain points while still retaining the coupling function. A novel nonresonant experimental coupler design is also presented, based on the design techniques used for broadband log-spiral antennas. The frequency response of the spiral coupler is much flatter than that of a comparable disc coupler View full abstract»

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  • 6. Degradation of cellulosic insulation in power transformers. Part 3: effects of oxygen and water on ageing in oil

    Publication Year: 2000 , Page(s): 115 - 119
    Cited by:  Papers (40)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (336 KB)  

    Heat, water and oxygen accelerate the degradation of cellulose insulation in electrical transformers. Their effects on insulation have been studied over a number of years using degree of polymerisation (DP) of the paper as a measure of ageing. Results are reported of a systemic study to measure the relative effectiveness of each component individually and in combination, on ageing in oil in a three-parameter two-level, partial factorial experiment. Ageing was measured in terms of change of degree of polymerisation of the paper and analysed according to recently developed models. In addition, the concentrations of furfural-based degradation products in the oil were measured. Water and temperature are most effective in accelerating ageing, with oxygen about one-third as efficient. There is a strong synergistic effect between temperature and water, a weaker synergism between temperature and oxygen, but, importantly, an apparent antagonistic effect between water and oxygen, at low water levels. If correct, the antagonism implies that the effectiveness of water, as an accelerator of ageing, decreases with increasing levels of oxygen in the oil at low water levels, which could explain why the insulation in scrapped transformers is sometimes found to be in very good condition View full abstract»

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  • 7. Towards a piezoelectric vibration-powered microgenerator

    Publication Year: 2001 , Page(s): 68 - 72
    Cited by:  Papers (40)  |  Patents (10)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (500 KB)  

    As MEMS and Smart Material technologies advance, embedded and remote applications are becoming more widespread. Powering these systems can be a significant engineering problem, as traditional solutions such as batteries are not always appropriate. An inertial generator is developed that uses thick-film piezoelectric technologies to produce electrical power from vibrations in the environment of the device. The device validates the concept, and produces an output of 3 μW. Predictions show that orders of magnitude increase in power output are possible View full abstract»

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  • 8. Review of radio frequency microelectromechanical systems technology

    Publication Year: 2004 , Page(s): 93 - 103
    Cited by:  Papers (27)  |  Patents (15)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (498 KB)  

    A review of radio frequency microelectromechanical systems (RF MEMS) technology, from the perspective of its enabling technologies (e.g. fabrication, RF micromachined components and actuation mechanisms) is presented. A unique roadmap is given that shows how enabling technologies, RF MEMS components, RF MEMS circuits and RF microsystems packaging are linked together; leading towards enhanced integrated subsystems. An overview of the associated fabrication technologies is given, in order to distinguish between the two distinct classes of RF microsystems' component technologies; non-MEMS micromachined and true MEMS. An extensive literature survey has been undertaken and key papers have been cited; from these, the motivations behind different RF MEMS technologies are highlighted. The importance of understanding the limitations for realising new and innovative ideas in RF MEMS is discussed. Finally, conclusions are drawn as to where future RF MEMS technology may lead. It is likely that the switch will continue to be the most important RF MEMS component, with future work investigating its enhanced functionality, subsystem integration and volume production. The focus of RF MEMS circuits will shift from the digital phase shifter to high-Q tuneable filters. View full abstract»

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  • 9. Degradation of cellulosic insulation in power transformers. Part 2: formation of furan products in insulating oil

    Publication Year: 2000 , Page(s): 110 - 114
    Cited by:  Papers (22)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (372 KB)  

    The analysis of furan degradation products in transformer oil provides a complementary technique to dissolved gas analysis for monitoring transformer condition. The main products of the ageing are 2-furfuryl alcohol, 2-furaldehyde (furfural), 2-acetylfuran and 5-methylfurfural and are formed from wood-based paper (containing lignin and hemicellulose), cotton-based paper and pure cotton linters in accelerated, laboratory experiments. Also, 5-hydroxy-methyl-cellulose was seen in the early stages of some experiments. The concentration of 2-furaldehyde (furfural) was found to be highest of all the products and the concentrations of all products increased exponentially with time to a maximum value and then decreased. The concentration of most products increased rapidly as the paper approached the end of its useful life, indicating that furfural analysis could provide a sensitive trouble-shooting tool for rapid ageing. All the furan products apart from 2-furfuryl alcohol are relatively stable in the oil, at temperatures up to 140°C View full abstract»

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  • 10. Modelling partial discharge excitation of UHF signals in waveguide structures using Green's functions

    Publication Year: 1996 , Page(s): 63 - 70
    Cited by:  Papers (9)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (716 KB)  

    A model describing the excitation of UHF signals by current pulses in a waveguide is developed using dyadic Green's functions. This model relates to UHF signals used for the detection of partial discharge (PD) caused by defects in gas-insulated substations (GIS). Application of the theory is demonstrated by comparison with experimental results for a cavity excited by a PD source. A technique for the injection of calibrated current pulses for PD simulation is also presented View full abstract»

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  • 11. Space charge measurement in polymer insulated power cables using flat ground electrode PEA system

    Publication Year: 2003 , Page(s): 89 - 96
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (624 KB)  

    Data processing methods used to accurately determine the space charge and electric stress distributions in DC power cables using the pulsed electroacoustic (PEA) system are described. Due to the coaxial geometry and the thick-walled insulation of high-voltage cables, factors such as divergence, attenuation and dispersion of the propagated acoustic pressure wave in the PEA can strongly influence the resultant measurements. These factors are taken into account ensuring accurate measurements to be made. Most importantly, a method is presented to determine the electric stress profile across the insulation due to both the divergent applied field and that as a consequence of trapped charge in the bulk of the insulating material. Results of space-charge measurements and the corresponding derived electric stress distributions in XLPE DC cables are presented. View full abstract»

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  • 12. New AC-based capacitance tomography system

    Publication Year: 1999 , Page(s): 47 - 53
    Cited by:  Papers (55)  |  Patents (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (512 KB)  

    Electrical capacitance tomography (ECT) is a new technology that is used to visualise the internal behaviour of industrial processes comprising dielectric components. A particular difficulty with capacitance measurement for tomography is that the stray capacitance to earth of an ECT sensor is large (~150 pF) compared with the interelectrode capacitance to be measured (usually <0.5 pF), and the measurement range is wide (0.01-2 pF). The authors present a highly sensitive AC-based capacitance measuring circuit, which has been specially designed for this purpose, and a PC-based ECT system with this circuit. Experimental results show that this ECT system can measure as small as 0.01 pF capacitance with 0.0002 pF error, and could collect tomographic image data at more than 100 frames per second View full abstract»

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  • 13. Degradation of cellulosic insulation in power transformers .4. Effects of ageing on the tensile strength of paper

    Publication Year: 2000 , Page(s): 285 - 290
    Cited by:  Papers (23)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (500 KB)  

    For pt.3 see ibid., vol.147, no.3, p.115-19, 2000. Evidence for transformer failures related to insulation failure indicates that the primary cause is normally mechanical failure/loss of integrity due to loss of mechanical strength as a result of degradation. The paper investigates the primary causes of loss of strength of paper during ageing under accelerated conditions in insulating oil. The latest mathematical models are used to relate change of tensile strength to ageing time and to degree of polymerisation (DP). Comparison of measurements using wide-span and zero-span tensometers suggests that the primary loss of strength results from loss of fibre strength, but that failure ultimately occurs due to loss of inter-fibre strength. This remains constant until a DP of about 200, then rapidly falls to zero, at the same time as the furan levels in the oil increase. It is suggested that a better understanding of the statistical probability of loss of inter-fibre strength would provide a better end-of-life criterion for predicting insulation life than those currently used View full abstract»

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  • 14. Electric field breakdown at micrometre separations in air and nitrogen at atmospheric pressure

    Publication Year: 2000 , Page(s): 261 - 265
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (812 KB)  

    For efficient operation, micromotors and microactuators, such as those employed in microsystems, are required to operate with high electric fields at electrode separations of the order of micrometres. An apparatus was built to accurately measure the breakdown voltage for electrode spacings as low as 0.5 μm. Breakdown voltage measurements in air and nitrogen are presented and discussed for the gap range 0.5 to 15 μm. Energy dispersive analysis of X-rays (EDAX) confirms the transfer of material from cathode to anode and vice versa during the breakdown mechanism. The Paschen law has been confirmed not to be applicable at gap settings of less than 4 μm. The shape of the curve and the breakdown voltage values are found to be the same for different gases and different high pressures up to 4 μm separation. Below this value, an analytical explanation of the breakdown voltage based on quantum tunnelling of electrons is obtained in terms of electrical field enhancement at microprotrusions and the work function of the electrode material View full abstract»

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  • 15. Quality control of laser welds of tailored blanks using guided waves and EMATs

    Publication Year: 2001 , Page(s): 143 - 148
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1568 KB)  

    In modern design of automobile bodies reduction in weight and maximisation of the structural stiffness and passive safety are the main challenge. The `tailored blank' has contributed to achieving a significant weight reduction in recent years. Single flat sheets are joined by laser welding into the desired configuration without filler wire. Usually the quality of the welds is assured by precise preparation of the plate edges and measurement of two of the process parameters. However, due to process deviations, defects occur, which makes NDT necessary. These defects include incomplete welding, lack of fusion, misalignment of the weld, holes and porosity. The paper presents a versatile ultrasonic inspection technique designed for in-line inspection of laser welds of tailored blanks. Conventional ultrasonic testing is ruled out because of the necessary liquid coupling medium. Therefore, the proposed inspection approach is based on the application of guided ultrasonic (plate) waves with shear horizontal polarisation excited and detected by couplant-free electromagnetic acoustic transducers View full abstract»

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  • 16. Laser generated ultrasound: efficiency and damage thresholds in carbon fibre reinforced composites

    Publication Year: 2001 , Page(s): 139 - 142
    Cited by:  Patents (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (424 KB)  

    Laser techniques are beginning to be used for noncontact ultrasonic inspection of carbon fibre reinforced composites in industry. The ultrasound is normally generated with a high-power pulsed laser and is detected with a laser interferometer. Other non-contact detection methods can also be used, such as simpler laser beam deflection techniques and air coupled transducers. The authors compare the generation efficiency and damage thresholds of a fundamental Nd:YAG laser (1.06 μm), and a TEA CO2 laser (10.6 μm) which is normally preferred for carbon-fibre reinforced composites). A Nd:YAG laser with an optical parametric oscillator (OPO) tunable up to 4 μm is also examined. The laser energy is absorbed within the optical absorption depth; the temperature rise is affected by the wavelength and laser pulse duration. It is essential to remain in the thermoelastic regime in order not to damage the material. A modified Michelson interferometer is used to detect the absolute displacement of the ultrasound. Optical beam deflection techniques and air-coupled transducers are also evaluated as detectors View full abstract»

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  • 17. Chaos in ferroresonant wound voltage transformers: effect of core losses and universal circuit behaviour

    Publication Year: 1998 , Page(s): 39 - 43
    Cited by:  Papers (13)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (400 KB)  

    The damping effects of transformer core losses upon the ferroresonant behaviour of wound instrument transformers, fed from a sinusoidal supply through circuit breaker grading capacitance, are studied using nonlinear dynamical methods. System is shown to exhibit three types ferroresonance; fundamental frequency ferroresonance, subharmonic ferroresonance and chaotic ferroresonance. It is also shown that this ferroresonant circuit can be driven into chaotic behaviour through a sequence of period-doubling bifurcations. Values of Feigenbaum universal number δ are calculated and are shown to be in good agreement with those reported from various other disciplines View full abstract»

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  • 18. Current measurement using compensated coaxial shunts

    Publication Year: 1994 , Page(s): 471 - 480
    Cited by:  Papers (7)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (664 KB)  

    A novel approach to the construction and compensation of a coaxial resistive shunt is shown to produce significant improvements in performance when compared with equivalent shunts employing a conventional method of construction. A full theoretical treatment shows how the adopted measurement and compensation scheme provides a simple and realisable method for the elimination of skin effect errors in thin-walled shunts. These findings are employed in the design and construction of a current measurement system, rated at 5000 A with a 20 ns risetime, for use in a power semiconductor test rig. Experimental results concentrate on a comparison of the new shunt with an equivalent, conventional coaxial shunt and clearly demonstrate the improvements possible. The usable risetime and bandwidth are shown to be improved by an order of magnitude with excellent phase characteristics and a significant reduction in susceptibility to conducted and radiated interference View full abstract»

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  • 19. UHF and current pulse measurements of partial discharge activity in mineral oil

    Publication Year: 2006 , Page(s): 47 - 54
    Cited by:  Papers (20)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (553 KB)  

    Investigations are reported into a range of defects causing partial discharge (PD) activity in high-voltage oil-insulated equipment. The aim is to explore the relationship between radiated ultra-high frequency (UHF) signals and electric charge in a PD current pulse for PD sources in oil insulation. Experiments are performed under high-voltage AC conditions using electrode configurations that included a sharp protrusion, a bad contact, and a free metallic particle. A broadband current transformer is used to measure the PD current pulses with the UHF signals being detected using a pair of sensors mounted inside a metal tank surrounding the PD sources. Current pulses and UHF signals were recorded simultaneously using an oscilloscope with a bandwidth of 3 GHz. The level of correlation between the energy of the radiated UHF signals and the charge content of PD pulses is shown to vary depending on the defect type. Polarity-dependent UHF spectral content and ratio of UHF signal energies measured at the two sensors are shown to exhibit characteristics dependent on the discharge behaviour. These results and the analysis procedures introduced will contribute to the development of effective UHF monitoring systems for oil-insulated high-voltage plant. View full abstract»

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  • 20. Ultrasonic transducers for high temperature applications

    Publication Year: 1998 , Page(s): 229 - 236
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1348 KB)  

    There is an increasing demand ultrasonic transducers to work at high temperatures. Transducers operating in the range from 400 to 1000°C are being applied in the power, process, automotive and aeroengine industries, as well as in materials research. To date, the majority of high temperature transducer designs have been based on adaptations of conventional single and dual-element probes for nondestructive testing (NDT). Such designs are outlined. It is noted, however, that the attempt to construct high temperature versions of conventional transducers has led to overcomplicated, expensive structures. In particular, they are modelled on probes used for scanning at ambient temperatures, although scanning is unlikely to be possible at high temperatures. An alternative approach is therefore described, based on the monolithic ultrasonic array structure. This offers not only lower transducer costs, but also full electronic control of the ultrasonic beam angle and emission point, thus facilitating inspection of a region within a test component using only one or two devices in fixed positions. Typical results demonstrating the beam-steering performance of the array, as well as those from B-scan time-of-flight testing, are presented. It is concluded that the problems of transducer development for ultrasonic, high-temperature NDT are not yet completely solved, and that further effort is required in the key areas of materials science and transducer structure. Moreover, a simple design with the minimum of bond lines is most likely to succeed on the grounds of cost and reliability View full abstract»

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  • 21. Degradation of cellulosic insulation in power transformers. I. Factors affecting the measurement of the average viscometric degree of polymerisation of new and aged electrical papers

    Publication Year: 2000 , Page(s): 86 - 90
    Cited by:  Papers (12)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (432 KB)  

    The degree of polymerisation (DP) of electrical insulation paper is an invaluable tool for assessing its condition and is extensively used in laboratory tests to assess the life expectancy of transformer insulation. Accurate and reproducible determinations are essential if the results are to be used to calculate a meaningful life. Publication IEC 450 was prepared in 1974 as a standard for the measurement of the DP of new and aged electrical papers (the equivalent US standard is ASTM D4243). However, experience across a number of laboratories has indicated the need for further clarification in the experimental method, whichever standard is adopted. Errors arise during preparation of solutions, measurement of viscosity and calculation of DP, due to oxidative degradation of the solution, inconsistencies in the measurement temperature and the conversion of intrinsic viscosity to DP using the Mark Houwink Sakurada relationship. This paper quantifies errors associated with DP measurement which are not described in existing standards View full abstract»

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  • 22. Circulating-current loss in transformer windings

    Publication Year: 1998 , Page(s): 136 - 140
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (448 KB)  

    Circulating-current loss in stranded windings of transformers has always attracted the attention of transformer designers. Analytical formulae based on the axial leakage field have long been used by designers for the calculation of circulating-current loss. The authors discuss these analytical formulae and compares them with 2-D finite element method (FEM) analysis, highlighting the errors involved in calculations for different types of windings. The analytical formulae contain little information on multiple transposition schemes. The paper clearly demonstrates that as the number of parallel conductors in the radial direction increases, analytical formulations should not be used, and in such cases, 2-D FEM is a better option for calculating circulating-current loss in different transposition schemes. The paper also analyses the circulating-current loss in the case of bunched conductors which are increasingly being used in power transformers. The work has helped to evolve comprehensive guidelines for transformer designers to estimate and control circulating current loss in windings View full abstract»

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  • 23. Current-voltage characteristics of corona in rod-plane gaps as influenced by temperature

    Publication Year: 2003 , Page(s): 135 - 139
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (428 KB)  

    A method is described for calculating the onset of positive corona in rod-plane gaps in air as influenced by temperature. The method is based on the criterion of self-sustained luminous filamentary streamers in the gap. The onset voltage is a prerequisite for calculating the current-voltage characteristics using an iterative method that correlates the corona space charge density to the avalanche growth inside the ionisation-zone around the rod. The onset and spark breakdown voltage decrease with the increase of temperature, in conformity with previous experimental findings. Not only the calculated onset voltage but also the current-voltage characteristics agree reasonably with those measured experimentally at room and high temperatures. View full abstract»

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  • 24. Calculating attenuation in waveguides below cut-off

    Publication Year: 2004 , Page(s): 356 - 361
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (328 KB)  

    The author derives the attenuation in a circular waveguide below cut-off with a finite metal conductivity for an arbitrary mode number. There are several potentially confusing points in this calculation particularly relating to the choice of signs, the fine details of the Bessel function behaviour and the definition of attenuation itself. A full derivation from first principles is presented during which any potential sources of confusion in the calculations are highlighted and clarified. Various closed-form approximations for the attenuation are discussed and are compared with full numerical calculations. The author concludes that errors introduced by these approximations can be quite significant (depending on the mode number) and recommends solving the transcendental equation directly for the attenuation rate. View full abstract»

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  • 25. Influence of morphology on electrical treeing in polyethylene blends

    Publication Year: 2003 , Page(s): 58 - 64
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (919 KB)  

    The effect of morphology on the development of electrical trees in semicrystalline polymers has been investigated using a blend of high and low-density polyethylene and for comparison, a low-density polyethylene. In the blend system, which contained 20% high-density polyethylene and 80% of the low-density polyethylene, thermal processing was used to generate a variety of morphologies. Quenching directly from the melt gave a fine-scale banded spherulitic morphology, isothermal crystallisation at 115°C gave a continuous, coarse-banded spherulitic morphology, whereas crystallisation at 124°C and above produced discrete and relatively compact lamellar aggregates of high-density polyethylene within a low-density matrix. The morphology of the low-density polyethylene was characterised by fine-scale banded spherulites. The growth of electrical trees was studied in these materials as a function of the applied AC electrical stress. In the low-density material and the blend materials, the rate of development of these structures was found to follow the well-known sigmoidal time dependence, where the increasing fractal dimension (branch density) of the growing tree structure is coupled with a decrease in the tree growth rate with increasing applied voltage. This leads to a local maximum and minimum in the average growth rates as a function of applied voltage. At all applied voltages, the tree growth rates were found to depend not only on the degree of crystallinity but also on the uniformity of the crystalline phase. Tree growth rates were greatest for LDPE and the quenched blend material and a minimum for the blend material crystallised at 115°C. The high-density inclusions formed at crystallisation temperatures of 124 and 125°C, acted as barriers to the tree growth and resulted in average tree growth rates between the quenched and the 115°C blend materials. View full abstract»

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  • 26. Modelling dynamic behaviour of dot-matrix printer heads

    Publication Year: 2004 , Page(s): 305 - 311
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (453 KB)  

    The dynamic behaviour of nonballistic impact printer heads by means of numerical simulations is predicted. The model is based on a dynamic electromagneto-mechanical finite-element approach, able to include eddy-current effects in bulk and laminated ferromagnetic cores. Experimental analysis validates the simulation results. The numerical investigation focuses on the analysis of the main phenomena that influence the dynamic performance of the device, that is the characteristics of the materials, the drive circuit, and geometry of the device. The analysis has shown the important role of eddy currents and drive circuit characteristics on the dynamic performance of the device, and the usefulness of the proposed approach to define an optimised geometry of the device. View full abstract»

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  • 27. SAR and radiation performance of balanced and unbalanced mobile antennas using a hybrid computational electromagnetics formulation

    Publication Year: 2004 , Page(s): 440 - 444
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (726 KB)  

    A procedure to reduce the effect of the mobile antenna on the handset by using balanced antennas has been investigated. Use of this type of antenna may degrade the antenna performance, such as bandwidth and gain, although it can cause less effect on the body to which they are adjacent. If the antennas are well designed, the maximum specific absorption rate (SAR) values are likely to be reduced when placed next to the head, since the coupling of such antennas to the body of the handset is very weak. A study on balanced and unbalanced antennas for mobile handsets next to the human head is presented, using a hybrid electromagnetics method for the analysis. The method uses the hybridisation technique between the frequency-domain method of moments (MoM) and the finite-difference time-domain method (FDTD). The antenna was modelled using MoM whereas the head tissues were modelled using FDTD. Two antennas were designed and investigated with respect to the SAR and radiation performance for two different antenna positions on the top edge of a mobile handset. Radiation patterns are presented and compared, with and without the head, and the maximum SAR values and field distributions inside the head are discussed. The balanced antenna shows good improvements with respect to the unbalanced antenna in terms of the SAR values and variations of the input impedances. View full abstract»

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  • 28. Direct voltage and trapped charge effects on the protective characteristic of ZnO surge arresters

    Publication Year: 1995 , Page(s): 442 - 448
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (604 KB)  

    In AC power systems, under normal service conditions, surge arresters on isolated lines and cables can experience a direct voltage stress arising from trapped charges. If this is followed on reconnection by switching surges of reverse polarity, it can impose severe response requirements on the arresters. High-amplitude voltage reversal can also arise from restriking transients in circuit breakers. Direct voltage working stress with superimposed surges is also clearly present in HVDC systems. Despite this expected combination of direct voltage with superimposed surges, no analogous tests are specified in the relevant standards. New laboratory tests have been performed on ZnO surge arrester elements and arresters, where impulse voltages have been applied with and without the presence of pre-existing direct voltage or simulated trapped charge. These tests have been analysed to ascertain the effect of prestressing on the current growth and protective characteristic of the arrester. In the laboratory source, the line/cable system has been represented by an equivalent capacitance which has been previously charged from a direct voltage. A single-stage capacitor bank is triggered to provide a lightning impulse test current. For a given level of peak discharge current, a higher level of residual voltage is found to appear across an arrester when the polarity of the applied impulse opposes that of the trapped charge voltage. This effect is especially marked in the peak residual voltage under this combination. Initial results suggest that the effect increases with decreasing protection voltage level View full abstract»

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  • 29. Investigation of propagation of partial discharges in power transformers and techniques for locating the discharge

    Publication Year: 2005 , Page(s): 25 - 30
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (687 KB)  

    The location of partial discharges in a power transformer can be determined based on the characteristics of the transfer function from the discharge source to the measuring terminal. Previous studies partially validated the technique using computer simulation and practical experiments based on a PD calibrator to represent a discharge signal. `Real' discharges produced by insulation defect models were used to study how discharges propagate in an 11 kV plain-disc-type transformer winding. A corona model and a `floating objects in oil' model produced discharge signals with different durations at various locations along the winding. Measurements were taken at the tap of the bushing capacitance through a conventional discharge detector. The signals were filtered, amplified and fed into a digital storage oscilloscope. The frequency spectra of the measured signals showed significant similarities irrespective of the type of discharge source. The characteristic of the transfer functions, i.e. the crests and troughs in the spectra, could be used for locating the source of the discharge. Energising the transformer increased the level of electric noise, which did affect the low frequency end of the spectra, but did not have any impact on the characteristics used for location View full abstract»

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  • 30. Recognising multiple partial discharge sources in power transformers by wavelet analysis of UHF signals

    Publication Year: 2003 , Page(s): 119 - 127
    Cited by:  Papers (9)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (550 KB)  

    Partial discharges (PD) in a transformer generate transient UHF signals that resonate within the tank. Where more than one source of PD or interference is present, the ability to separate incoming signals depending on their point of origin would enhance the diagnostic process. A wavelet-based method for recognising UHF signals from PD sources at different positions in the transformer tank, even when the signal is received at only one UHF sensor, is described. Time-frequency characteristics of the UHF PD signals are established using the wavelet transform, providing a means of mapping the energy distribution of the signal. A similarity function is then defined to provide a measure of the similarity between the various wavelet coefficient distributions. The procedure is demonstrated by means of laboratory experiments and application of the technique to data obtained from a transformer in the field. View full abstract»

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  • 31. Evaluation of eddy losses due to high current leads in transformers

    Publication Year: 1997 , Page(s): 34 - 38
    Cited by:  Papers (8)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (968 KB)  

    An analytical method to calculate eddy loss in a two-dimensional problem is presented. The problem geometry consists of a current carrying conductor of infinite length parallel to a conducting plate of infinite length and width but of finite thickness. The solution method first transforms the original current distribution into sinusoidal current sheets. It is therefore quite general and can be used for different current distributions such as single-phase and three-phase current, different shapes of conductors such as line current, rectangular conductor, etc., and different problem geometries such as conducting plate shielded by electromagnetic screen. As an example, eddy loss is evaluated for the case when a line current passes parallel to a conducting plate. A laboratory experiment conducted to verify the theoretical results is also presented. Experimental results are also compared with the loss calculated by two-dimensional (finite-element) analysis. As a particular case of the application of FEM analysis to a practical problem, a 3-D FEM analysis of 40 MVA furnace transformer LV-lead termination is presented. The analysis confirmed the hot-spot locations observed during the testing of the furnace transformer View full abstract»

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  • 32. PD detection and localisation by acoustic measurements in an oil-filled transformer

    Publication Year: 2000 , Page(s): 81 - 85
    Cited by:  Papers (16)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (340 KB)  

    A pattern recognition method for localisation of the partial discharge (PD) site in an oil-filled transformer by acoustic measurements is presented. By dividing the transformer into a number of 20×20×20 mm3 sub-modules, the PD site is localised by comparing the spatial distance of each sub-module to the acoustic sensors. The numerical cases indicate that the proposed method is general and practical, while avoiding some drawbacks in current algorithms. Moreover, the method improves the accuracy of localisation substantially when compared with the conventional localisation method View full abstract»

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  • 33. Sparkover in the rod-plane gap under combined direct and impulse voltages

    Publication Year: 1998 , Page(s): 207 - 214
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1124 KB)  

    Experiments are described in which composite voltages, produced by superimposing positive and negative switching impulse voltages on pre-stressing positive or negative direct voltages, are applied to a rod-plane gap of lengths up to 1 m. Changes in 50% sparkover voltages are described over a range of positive and negative pre-stressing voltages; it is shown that negative pre-stressing always reduces the composite sparkover voltage, but that positive pre-stress increases the positive composite sparkover voltage and reduces the negative one. Recordings of photomultiplier observations and `still' photography of pre-breakdown corona have been made at the 50% sparkover level and the results related to the sparkover characteristics. It is shown that the latter depend on the way in which leader initiation is affected by the preceding DC corona View full abstract»

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  • 34. Calculating the current distribution in power transformer windings using finite element analysis with circuit constraints

    Publication Year: 1995 , Page(s): 231 - 236
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (376 KB)  

    The paper is concerned with the formulation of an A-V finite element method to simulate the electromagnetic field and current distribution in the windings of power transformers with nonnegligible circulating current. The algorithm combines field analysis and network analysis of the electric circuit in a way that is most efficient for the practical design of transformers. Vector potential A is the variable concerned with the magnetic field and its effect. The eddy current in each conductor is treated by the generally used method, whereas the choice of the terms for the electric circuit is modified so that the transpositions of transformer windings, variant electric circuit connections in or out of windings and sinusoidal excitation, can be formulated easily and systematically under the multiprojection finite element method that is employed to approximate the three-dimensional field. Furthermore, the resulting bandwidth of the coefficient matrix can be reduced when the equation is solved by the elimination method. Validation was verified by experiment View full abstract»

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  • 35. Design and optimisation of electromagnetic flowmeter for conductive liquids and its calibration based on neural networks

    Publication Year: 2006 , Page(s): 139 - 146
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (724 KB)  

    Using Faraday's Law of electromagnetic induction, electromagnetic flowmeters are used to measure the industrial process flow rate of fluids. In these devices, the windings around the pipe are designed to produce the required magnetic field, and electrodes that are mounted on two sides of the pipe wall are used to measure the induced voltage in proportion to the liquid flow rate. The design and optimisation of an electromagnetic flowmeter for conductive liquids are presented. In this respect, a two-dimensional mathematical model with a finite difference (FD) numerical solution approach is used for calculation of the electric potential difference between the electrodes. The basic concepts of the electromagnetic flowmeter design and simulation are presented using m-file programming in Matlab software. Then, with respect to the fact that fluid flow depends on two variables, liquid level and the conductivity coefficient of the liquid and pipe bed, a three-layer neural network is used for accurate calibration of the electromagnetic flowmeter. In this new approach, for a circular cross-section pipe, the correction factor used for the calibration is accurately estimated. Finally, simulation results are provided to show the accuracy of the applied technique. View full abstract»

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  • 36. Soil ionisation under lightning impulse voltages

    Publication Year: 2004 , Page(s): 343 - 346
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (275 KB)  

    Experiments have been carried out to study soil ionisation and the variation of the critical ionisation gradient against the soil resistivity. Compared with relevant experimental results of other researchers a satisfactory convergence has been proved. An accurate estimation of the critical ionisation gradient has been achieved, of the order of 200 kV/m, following the finding that the critical voltage gradient for wet soil decreases to approximately 35% of the corresponding value for dry soil. View full abstract»

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  • 37. Modelling partial discharge inception and extinction voltages of sheet samples of solid insulating materials using an artificial neural network

    Publication Year: 2002 , Page(s): 73 - 78
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (657 KB)  

    This work attempts an estimation of partial discharge inception and extinction voltages (PDIV and PDEV) of sheet samples of solid dielectrics due to void inclusions of different sizes using an ANN. The effect of void dimensions and also the dielectric thickness of three common insulating materials, namely, Leatherite paper, polyethylene film and Perspex sheets on PDIVs and PDEVs are examined. Further, the effect of the permittivity of the insulating materials is also examined View full abstract»

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  • 38. Electricity generation in the home: modelling of single-house domestic combined heat and power

    Publication Year: 2001 , Page(s): 197 - 203
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (608 KB)  

    Two models for predicting potential savings from a domestic combined heat and power unit are developed and compared. The first, a simple spreadsheet calculation based on heating times and energy bills, gives a basic indication of the benefits of domestic combined heat and power. The second predicts the electricity and heat demand profiles of homes based on building structure, weather information and house energy bills, and simulates the operation of the unit to enable the savings for different ratings and efficiencies to be predicted View full abstract»

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  • 39. Method for extracting time-varying rhythms of electroencephalography via wavelet packet analysis

    Publication Year: 2001 , Page(s): 23 - 27
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (568 KB)  

    A method is proposed for detecting time-varying rhythms of nonstationary electroencephalograms (EEG). Multi-resolution decomposition is used to investigate the transition of clinical EEG signals. Wavelet packet transformation is applied to design the filters with different frequency characteristics in order to extract different kinds of dynamic EEG rhythms. Several actual EEG signals with different brain function states are tested and analysed. The parameters of the wavelet packet transform corresponding to the rhythms are developed to reconstruct the time-varying electrical brain activity mapping. From the experimental results, the dynamic characteristics of clinical brain electrical activities can be demonstrated by using wavelet packet decomposition. The presented method can be used for the analysis of other biomedical signals View full abstract»

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  • 40. Evaluation of eddy current losses in the cover plates of distribution transformers

    Publication Year: 2004 , Page(s): 313 - 318
    Cited by:  Papers (8)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1406 KB)  

    The elimination of hot spots and the reduction of eddy current losses in bushing mounting plates is an important consideration in transformer design. The currently used bushing mounting plates are either mild steel plates, or mild steel plates with non-magnetic stainless steel inserts or stainless steel plates. The authors calculate the eddy current losses in bushing mounting plates using four different methods; (i) an analytical formulation; (ii) a three-dimensional finite element method (FEM); (iii) from measured values of the initial temperature rise; and (iv) from measured values of the steady-state temperature rise. There is a close agreement between the loss values obtained using these four methods. The analysis has resulted in a detailed understanding of the loss pattern and temperature rise phenomenon in bushing mounting plates. The authors also analyse tank plates of small pad-mounted distribution transformers. It is shown that judicious use of non-magnetic stainless steel can result in considerable energy savings for pad-mounted transformers. FEM simulations are performed to find out cost-effective materials for the tank plates of the pad-mounted transformers. A T-shaped stainless steel plate is found to significantly reduce the load loss. The results of the simulations have been verified on a 225 kVA pad-mounted transformer. View full abstract»

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  • 41. Wavelet-based PCA defect classification and quantification for pulsed eddy current NDT

    Publication Year: 2005 , Page(s): 141 - 148
    Cited by:  Papers (15)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (195 KB)  

    A new approach for defect classification and quantification by using pulsed eddy current sensors and integration of principal component analysis and wavelet transform for feature based signal interpretation is presented. After reviewing the limitation of current parameters of peak value and its arrival time from pulsed eddy current signals, a two-step framework for defect classification and quantification is proposed by using adopted features from principal component analysis and wavelet analysis. For defect classification and quantification, different features have been extracted from the pulsed eddy current signals. Experimental tests have been undertaken for ferrous and non-ferrous metal samples with manufactured defects. The results have illustrated the new approach has better performance than the current approaches for surface and sub-surface defect classification. The defect quantification performance, which is difficult by using current approaches, is impressive. View full abstract»

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  • 42. Experimental validation of time-domain electromagnetic models for field coupling into the interior of a vehicle from a nearby broadband antenna

    Publication Year: 2004 , Page(s): 430 - 433
    Cited by:  Papers (8)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (596 KB)  

    Numerical electromagnetic models based on a typical automotive immunity measurement scenario have been built from a vehicle manufacturer's CAD data and compared with corresponding measurements on a complete vehicle. The simulations were carried out in the time-domain using the TLM and FDTD techniques. Despite the many limitations of both the numerical models and the measurements, the models are found to provide a satisfactory representation of the measured field coupled into the passenger compartment from a nearby broadband antenna. View full abstract»

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  • 43. Measurements of the electrical conductivity of water

    Publication Year: 2002 , Page(s): 320 - 322
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (357 KB)  

    The electrical conductivity of water is used in many industries as an indication of the purity of the water. A system for the traceable measurement of the conductivity of water in the range 0.01 S/m to 1 S/m is described. The method is based on the measurement of the resistance of a column of water of accurately known dimensions. There is an electrode polarisation effect and the convention is to extrapolate the conductivity as a function of inverse frequency to find the value at zero inverse frequency. The temperature coefficient of the conductivity is 2% per Kelvin at 25°C and this limits the uncertainty of the measurement to about ±0.14% of value in the present system. View full abstract»

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  • 44. Characterising beadless air lines as reference artefacts for S-parameter measurements at RF and microwave frequencies

    Publication Year: 2006 , Page(s): 229 - 234
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (195 KB)  

    Beadless coaxial air dielectric transmission lines can be used as fundamental reference devices for S-parameter measurements at RF and microwave frequencies. However, for these lines to be used for such applications, they must first be characterised accurately in terms of their impedance and propagation characteristics. This includes assessment of the small amount of loss in the line and the associated impact of this loss on other characteristics. A simple method is presented whereby the loss is determined experimentally using a vector network analyser (VNA). The determined loss can then be used to characterise the line so that it can be used for a range of high-precision metrology applications. Two such applications are given: determination of the actual frequency-dependent characteristic impedance of a line; and use of the line's phase constant to verify VNA phase measurements View full abstract»

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  • 45. Partial discharge location in power transformers

    Publication Year: 2000 , Page(s): 249 - 255
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (452 KB)  

    In a power transformer, high levels of partial discharge activity may lead to an insulation failure. If a partial discharge (PD) could be detected and located before the insulation fails, the transformer could be repaired or replaced before any consumers connected to the transformer lose supply. A technique is described in the paper that can be used to locate a PD in a power transformer with a continuous disc type winding. The technique requires knowledge about the physical geometry and design parameters of the transformer and also information about the characteristics of how the pulse or pulses caused by the PD propagate through the winding. The latter is difficult to obtain and consequently numerous simulation studies with slightly different assumptions were necessary before the technique could be considered validated. This involved analysing the data available at the terminals when a PD occurred in the winding and trying to extract the features related to the PD location. An algorithm using feature template matching has been used to locate the PD source in a 110 kV continuous disc type winding. Experimental tests carried out on this type of winding were extremely important in verifying the validity of the PD location algorithm. Results indicate that a location accuracy of better than 5% of the winding length is normally achieved View full abstract»

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  • 46. Prediction of passive intermodulation arising from corrosion

    Publication Year: 2003 , Page(s): 30 - 34
    Cited by:  Papers (6)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (470 KB)  

    Large-signal analysis of a corroded interface subjected to multisinusoidal signals is presented. The special cases of sinusoids with sufficiently small amplitudes and three equal-amplitude sinusoids are considered in detail, and the results are compared, whenever possible, with previously published results. View full abstract»

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  • 47. Engineering aspects and applications of the new Raman instrumentation

    Publication Year: 2005 , Page(s): 241 - 318
    Cited by:  Patents (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (4199 KB)  

    Raman instrumentation design has improved radically in efficiency and ease of use over the past 15 years. New technologies made this possible with introduction of the first commercial high-efficiency (high speed) Raman systems incorporating low power lasers. Systems were introduced for the first time on production and process lines. Higher efficiency systems have continued to evolve, as a result of novel engineering solutions. Raman-near field optical systems and Raman-SEM (scanning electron microscopy) combinations have created a new area of nanoscale spectroscopic measurements. New application areas are: (a) semiconductor processing; (b) pharmaceutical drug processing; (c) gemology; (d) narcotic and explosives forensic detection; (e) coatings on computer hard disks and read heads; (f) endoscopic and Raman detection of oesophageal and other types of cancer. Comparisons are made with competing optical and alternative instrumentation techniques for general Raman work and the applications. View full abstract»

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  • 48. Analysis of neural and fuzzy-power electronic control

    Publication Year: 1997 , Page(s): 25 - 33
    Cited by:  Papers (11)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (864 KB)  

    Current-controlled voltage-source inverters offer substantial advantages in improving motor-system dynamics for high-performance AC-drive systems. The controller switches follow a set of reference current waveforms. Fixed-band hysteresis and sinusoidal-band hysteresis controllers have been studied. Neural network and fuzzy-logic-based current-controlled voltage-source inverters are developed. The models and learning techniques have been investigated by simulation. The implementation of neural networks is described, and simulation results are presented. The new UPS (uninterruptible power supply) with a fuzzy-logic compensator is then proposed. The proposed fuzzy-logic compensator is used to prevent voltage drop from nonlinear loads. The total harmonic distortion (THD) of the proposed scheme is better than that of the conventional deadbeat control method for linear and nonlinear loads. Finally, the application of fuzzy control to DC-DC converters, operating at finite switching frequency, is studied. Several control methods currently used for buck, boost and buck/boost converters are compared to the fuzzy-converter control. The fuzzy-logic and neural-network controller for a unity power-factor rectifier are also discussed. The simulations presented show that the fuzzy-control method has better dynamic performance and less steady-state error View full abstract»

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  • 49. Partial discharge plant-monitoring technology: present and future developments

    Publication Year: 1995 , Page(s): 4 - 10
    Cited by:  Papers (33)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (680 KB)  

    The paper discusses the role of partial discharge measurement in the conditioning monitoring of power plant. Following a discussion of recent developments in partial discharge detection and measurement technologies, the problems and challenges for the future in the different technologies are analysed and discussed. For those unfamiliar with partial discharge detection as a condition monitoring tool, a brief discussion on its relationship to insulation degradation is presented as an Appendix View full abstract»

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  • 50. Evaluation of capacitance matrix of a finite-length multiconductor transmission line

    Publication Year: 2004 , Page(s): 347 - 353
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (309 KB)  

    A method for the evaluation of the capacitance matrix of a system of finite-length conductors is given. It is shown that the problem can be reduced to the solution of a convolution-type integrodifferential equation system and an effective and accurate procedure to cope with this is described. The procedure first applies the convolution theorem to the initial integrodifferential equation system to obtain an algebraic one in terms of the Fourier coefficient of the original unknown function. Next, this new system is diagonalised and reduced to a set of decoupled equations. These are then solved by means of an ad hoc developed algorithm, essentially based on a representation of the Fourier coefficient in terms of the Neumann series. The proposed approach is applied to a two-conductor test line and the obtained numerical results for different conductors radius values are compared with those provided by the classical infinite-length-conductor approximation. View full abstract»

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