By Topic

Science, Measurement and Technology, IEE Proceedings -

Popular Articles (October 2014)

Includes the top 50 most frequently downloaded documents for this publication according to the most recent monthly usage statistics.
  • 1. Circuit properties of coils

    Page(s): 234 - 239
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (512 KB)  

    Measurements conducted on cylindrical single-layer coils reveal some of their high-frequency properties. A set of measured resonance and antiresonance frequencies is used to determine a series of partial inductances and partial capacitances of a coil, based on Foster's first form of two-terminal LC networks. Although the procedure departs from most general properties of LC coils, the system of partial capacitances and inductances at low frequencies reduces to coil inductance and self-capacitance. In cases when a coil is operated with one end free, the standard procedure of self-capacitance determination has to be modified accordingly, to take into account the top capacitance of the coil View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 2. Methodology for accurate free-space characterisation of radar absorbing materials

    Page(s): 538 - 546
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (684 KB)  

    Although it is now some 50 years since the first practical application of radar absorbing materials (RAM), there does not seem to have been a comprehensive discussion in the literature of the optimum methodology for characterising such materials using free-space methods, the sources of error that arise in a typical laboratory measurement facility and, perhaps most important of all, an estimate of the measurement uncertainties. A previous paper started to address these problems by discussing calibration techniques for a vector network analyser system used for making complex reflectivity measurements on RAM. It is the aim of this paper to extend the discussion to include the use of a scalar measurement system (since these are still in common use), the factors affecting the design of a free-space reflectivity arch and the verification of measured reflectivity data View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 3. Design theory of thermoelectric modules for electrical power generation

    Page(s): 351 - 356
    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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 4. Optimal battery energy storage system (BESS) charge scheduling with dynamic programming

    Page(s): 453 - 458
    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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 5. Review of chemical indicators of degradation of cellulosic electrical paper insulation in oil-filled transformers

    Page(s): 324 - 334
    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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 6. Design and optimisation of electromagnetic flowmeter for conductive liquids and its calibration based on neural networks

    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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 7. Partial discharge mechanisms in voids related to dielectric degradation

    Page(s): 62 - 68
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (436 KB)  

    The usefulness of time-resolved measurements is shown for the study of degradation processes of insulating materials associated with partial discharges. Using an optimised test set-up the different stages in the degradation process can be recognised. The possibilities for using the time-resolved method in practice are discussed. A promising combination of classic and time-resolved measurements is presented and clarified by the first results obtained with the discharge analysing system TEAS View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 8. Towards a piezoelectric vibration-powered microgenerator

    Page(s): 68 - 72
    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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 9. Phenomenon of sympathetic interaction between transformers caused by inrush transients

    Page(s): 323 - 329
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (524 KB)  

    In power systems with appreciable resistance, the transformers already connected to the supply system can experience unexpected saturation during the inrush transient of an incoming transformer. This saturation, which is established by the asymmetrical voltage drop across the system resistance caused by the inrush current, demands offset magnetising currents of high magnitude in the already connected transformers. This generates a transient interaction between the transformers, a `sympathetic interaction', that affects the magnitude and duration of the inrush current. As a consequence, problems in the operation of the system, such as false operation of transformer differential relays and prolonged temporary harmonic overvoltages, can occur. The sympathetic interaction between the transformers is analysed in the paper. System configurations with transformers in parallel and in series are investigated. The transformers and system models have been validated using small transformers View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 10. Measurements of void gas pressure during combined thermal and partial discharge ageing of epoxy

    Page(s): 17 - 21
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (328 KB)  

    The combined effect of partial charges and temperature on epoxy has been investigated. The void gas pressure exhibited a characteristic development with a short initial fluctuation followed by a linear decrease. The slope of the linear pressure curve was a function of temperature level and voltage stress. During ageing, the initially occurring uniform distribution of large discharges, type I pattern, was replaced by a type II pattern and eventually a type III PD pattern, displaying a few large discharges followed by many small discharges, appeared. The type III pattern possibly indicates that some discharges have changed or are about to change into swarming pulsive microdischarges. No correlation could be found between the appearance of the type III pattern and the development of void gas pressure. In the linear region, the development of void gas pressure was unaffected by any changes in PD activity. Based on this result it is suggested that even if the PD pattern changes, the total contribution to insulation degradation remains the same and hence also the degradation rate as expressed by the continuous development of void gas pressure View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 11. Numerical modelling of the electric field in HV substations

    Page(s): 267 - 272
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (476 KB)  

    A hybrid technique combining the charge simulation and boundary element method has been employed to solve the problem in question. In this model the influence of tower frameworks and of the apparatus construction is taken into account. The basic boundary integral equations are presented and the computer program is briefly described. Selected numerical results concerning a 400 kV outdoor substation are given. The numerical technique and the computer program can be a useful aid for designers of electric power objects as well as for environmental protection authorities. In the near future the program will be applied in a commercial software package for the electric and magnetic-field computation near HV installations. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 12. Circulating current and hysteresis losses in screens, sheaths and armour of electric power cables-mathematical models and comparison with IEC Standard 287

    Page(s): 101 - 110
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1004 KB)  

    Computation of the current carrying capacity of a cable involves evaluation of electrical and thermal parameters of the circuit. Formulas for the calculation of these parameters are summarised in Standard No. 287 published by the International Electrotechnical Commission (IEC). The first edition of this Standard was issued in 1969 and the latest revision in 1994/5. The formulas for the computation of the electrical parameters of the cable date to the late 1920s and early 1930s. The computation of the loss factor for cables with magnetic armour wires is based on work performed in the 1960s and is applicable to cables spaced at least 10 m apart. IEC Standard 287 provides loss formulas for simple symmetric cable configurations such as those in flat or trefoil arrangements. Many practical applications deal with more complicated configurations such as less symmetry, multiple circuits in close proximity, and multiple cables per phase within a circuit. The paper introduces accurate equations for the computation of the sheath and armour losses, treating these two components separately. The formula for the sheath skin effect is expanded and the inductance of hollow conductors is derived. The expressions for the sheath and armour loss factors derived in the paper are compared with those given in IEC 287 and the simplifications required to develop standard equations are explained. A numerical example shows the effect of these simplifications on the rating of a typical cable circuit View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 13. Partial discharge detection: theoretical and practical aspects

    Page(s): 29 - 36
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (592 KB)  

    The phenomenon of electricification by electrostatic induction is introduced. This fundamental approach allows the concepts of Poissonian and Laplacian induced charge to be clearly developed. These concepts form the necessary basis for partial discharge detection analysis. Thereafter a quantitative theory is developed. This field-theoretical approach furnishes the correct input parameters for the subsequent study of the detection-circuit response, in which the electrodes of the field analysis serve as the input terminals in the circuit analysis. Subsequently the response of a basic partial-discharge detection circuit is examined with reference to the induced-charge signal. It is concluded that the maximum value of this signal will be most accurately determined if a detection circuit with a longtime constant is employed View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 14. Huygens' principle in electromagnetics

    Page(s): 103 - 105
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (296 KB)  

    A simple way of deriving Huygens' principle in electromagnetic and transmission-line theory is given without recourse to Green's functions and Green's formulas. Huygens' principle is derived for the electromagnetic fields simply by truncating Maxwell's equations. The same is done for the voltage and current in a transmission line by truncating the telegrapher's equations. Some simple consequences are also discussed View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 15. Current measurement using compensated coaxial shunts

    Page(s): 471 - 480
    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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 16. Measurements of the electrical conductivity of water

    Page(s): 320 - 322
    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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 17. Degradation of cellulosic insulation in power transformers .4. Effects of ageing on the tensile strength of paper

    Page(s): 285 - 290
    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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 18. Analysis of neural and fuzzy-power electronic control

    Page(s): 25 - 33
    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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 19. Human ECG: nonlinear deterministic versus stochastic aspects

    Page(s): 279 - 284
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (728 KB)  

    The authors discuss aspects of randomness and determinism in electrocardiographic signals. In particular, they take a critical look at attempts to apply methods of nonlinear time series analysis derived from the theory of deterministic dynamical systems. It is argued that deterministic chaos is not a likely explanation for the short-time variability of the inter-beat interval times, except for certain pathologies. Conversely, densely sampled full ECG recordings possess properties typical of deterministic signals. In the last-mentioned case, methods of deterministic nonlinear time-series analysis can yield new insights View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 20. Analytic model for field-plate-edge breakdown of planar devices terminated with field plate and semiresistive layer

    Page(s): 21 - 24
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (266 KB)  

    An analytic model for calculating the surface field of high-voltage devices terminated with a field plate and SIPOS (semiresistive polycrystalline) layer is presented. This allows determination of the breakdown voltage at the field-plate edge in terms of the field-plate length, the effective length of the SIPOS layer, the thickness of oxide buffer layer, and the silicon doping concentration. The results show a fair agreement with the numerical simulations as well as the experimental results reported. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 21. Recognising multiple partial discharge sources in power transformers by wavelet analysis of UHF signals

    Page(s): 119 - 127
    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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 22. Direct voltage and trapped charge effects on the protective characteristic of ZnO surge arresters

    Page(s): 442 - 448
    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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 23. Capacitance and charge distribution of two cylindrical conductors of finite length

    Page(s): 280 - 286
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (516 KB)  

    The authors present a method of finding the effect of fringing on capacitance and charge distribution of conducting structures consisting of coaxial cylinders or of parallel cylinders of identical diameter, each of finite and equal length. The moment method, employing pulse and delta functions as the basis and testing functions, respectively, is used for the analysis. Numerical data on charge distribution and capacitance per unit length, normalised to the same quantity for similar structure of infinite length, are presented View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 24. Calculating attenuation in waveguides below cut-off

    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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 25. Acoustic fields from PVDF interdigital transducers

    Page(s): 250 - 259
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1076 KB)  

    Interdigital transducers (IDTs) made from the piezoelectric polymer PVDF have been built; they transmit ultrasonic Lamb waves into 1-2 mm thick steel and aluminium plates and receive signals reflected from features in the structure. The IDTs are designed to be permanently bonded to the structure under inspection. Such IDTs have considerable potential for use in smart-structure monitoring applications. However, before this potential can be realised, the nature of the acoustic field that they produce must be thoroughly understood. Experimentally measured acoustic fields are presented for two example IDTs, one that produces a collimated beam for line inspection and one that produces a divergent beam for sector inspection. The development of modelling software based on Huygens' principle, which enables the acoustic field from such IDTs to be predicted rapidly, is then described. Example results from this software are presented and compared with experimental measurements. Further predictions made with the model are then used to elucidate certain basic guidelines for IDT design View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 26. Electric field breakdown at micrometre separations in air and nitrogen at atmospheric pressure

    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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 27. Complete surface current distribution in a normal-mode helical antenna using a Galerkin solution with sinusoidal basis functions

    Page(s): 272 - 276
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (411 KB)  

    An investigation of the surface current distribution in a normal-mode helical antenna (NMHA) is reported. This enables precise prediction of the performance of NMHAs, since traditional wire-antenna simulations ignore important details, such as non-uniform and transverse current distributions. A moment-method formulation is developed, using two-dimensional basis functions to represent the total non-uniform surface current distribution over the surface of the wire of the helix. Piecewise-sinusoidal basis functions are employed in two normal directions, with an exact kernel formulation and application of Galerkin's solution method. The numerical solution of the singular integrals associated with self-impedance terms was computed with a very low relative error. The surface current distribution was computed for different helix geometries. It was found that the axially-directed component of the current distribution around the surface of the wire was highly non-uniform and that there was also a significant circumferential current flow due to inter-turn capacitance, both effects that are overlooked by standard filamentary current representations. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 28. Virtual instrumentation for clinical assessment of cardiovascular and autonomic function

    Page(s): 397 - 402
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (988 KB)  

    Information about the activity of the autonomic nervous system can be derived by analysis of key physiological signals, including ECG and blood pressure, on a beat-to-beat basis. Due to the large amount of data and mathematical processing involved, analysis by hand is prohibitive. The solution developed facilitates this procedure by performing the processing on a PC-based instrument incorporating existing medical equipment, a data acquisition board and a computer program to acquire and process the physiological signals. The automated virtual instrument was written using LabVIEW(c) as the main platform. The techniques implemented include impedance cardiography, time- and frequency-domain analysis, invasive and non-invasive baroreflex sensitivity assessment, and forearm blood flow measurements. The system was designed to study patients suffering vasovagal blackouts, where the changes that occur in the heart and circulation during an attack could increase understanding of the physiological processes that underlie their blackouts View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 29. Modelling losses in electrical steel laminations

    Page(s): 218 - 221
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (356 KB)  

    The possibility of obtaining a voltage-driven solution of the diffusion equation by using a history-dependent hysteresis model based on the transplantation principle and a model for excess loss simulation derived from the Landau-Lifshitz-Gilbert equation for magnetic viscosity is presented. The proposed solver appears to be more versatile than existing models and can predict the total losses under arbitrary magnetising conditions as well as reproduce any frequency dependence of the excess losses. The model was tested on nonoriented (NO) and grain-oriented (GO) electrical steels under sinusoidal flux density over a frequency range from 50 to 400 Hz. Initial calculations, performed without viscosity being taken into account, gave underestimated losses with reduced RMS errors which varied from 5% for NO to 10% for GO steels. By introducing viscosity, this error reduced to 1% for both materials. The model parameters are thought to be material dependent so it is reasoned that the model can be used to accurately predict losses in a wide range of materials magnetised under sinusoidal as well as nonsinusoidal flux waveforms. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 30. Comparison of analytic, numerical and approximate models for shielding effectiveness with measurement

    Page(s): 61 - 66
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (496 KB)  

    The authors present a comparison between different estimates of the shielding effectiveness (SE) of cavities containing apertures and predictions made using a rigorous variational solution. Although the rigorous solution is computationally intensive, the method can be used as a standard against which more practical approximations, numerical methods and laboratory measurements can be compared. SE predictions from three methods are compared to the rigorous solution. These are: electromagnetic time domain modelling using the transmission line modelling (TLM) method, experimental measurements in a screened room, and an approximate solution based on the interaction of the lowest order waveguide mode and the aperture field. These comparisons of shielding effectiveness evaluations were made for a rectangular cavity with a range of aperture sizes and for frequencies in the range 200 MHz to 1.0 GHz. The results show that the measurements compare well with the rigorous solution, time domain simulations have a relatively long computation time and may still have noticeable discrepancies while the approximate solutions are computationally very efficient but may be significantly in error in particular for observation points close to the aperture View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 31. Modelling of capacitance tomography sensors

    Page(s): 203 - 208
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (544 KB)  

    Current electrical capacitance tomography (ECT) systems reconstruct cross-sectional images directly using the `raw' capacitance data measured from the multielectrode sensors. These `raw' measurements are affected by the pipe wall and/or external interelectrode capacitances, and hence it is impossible to reconstruct accurate quantitative images. The author analyses four types of pipe-mounted sensor, as categorised by their electrode and radial screen arrangements, and gives methods of calculating the internal interelectrode capacitances which exclude other interfering capacitances, thus enabling quantitative measurements and improved images to be obtained View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 32. Review of radio frequency microelectromechanical systems technology

    Page(s): 93 - 103
    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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 33. Electrostatic separation of metals and plastics from granular industrial wastes

    Page(s): 47 - 54
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1284 KB)  

    Recycling of metals and plastics from wastes is one of the major applications of the electrostatic separation technologies. The paper analyses the multitude of factors that affect the efficiency of this technique, to establish design principles and formulate operation recommendations. The theoretical analysis of corona and induction charging of, respectively, insulating and conducting particles allows a crude evaluation of the role of the various factors involved, including the electric field strength E0 and the current density J in the active zone of the separator. A first set of experiments has been carried out for estimating E0, J and the charging time constant τ, based on the measurement of the current voltage characteristic of a standard electrode arrangement. A second set of experiments consisted of three series of separation tests performed on samples of millimetre-sized granulated electric wire scrap (62.5%, copper, 37.5%, PVC). By using a combined corona-electrostatic field and a three-stage separation scheme, a PVC concentrate containing less than 0.04%, copper (recovery: 92.2%,) and a copper product with less than 0.1%, PVC (recovery: 90.8%,) were obtained. Design and operation recommendations were formulated regarding the optimum electrode arrangement, high-voltage level, roll speed and feed rate for typical industrustal applications View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 34. Three-phase VSCF induction generator synchronised by a single-phase supply through a passive single-element phase converter

    Page(s): 153 - 158
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (484 KB)  

    A passive single-element phase converter connected between phases of a 3-phase cage-induction machine and a single-phase supply connected to the combination sets up a synchronously rotating field in the machine airgap. The rotor is driven supersynchronously by a prime mover and balanced 3-phase power is generated. For small slips the machine is a variable-speed constant-frequency (VSCF) generator. In remote areas capacitor self-excited stand-alone induction generators are often used. Where single-phase supply is available, the system presented eliminates the need for capacitors, and the torque on the turbine is maintained constant by dissipation in the resistive element of the phase converter. Variation of the phase-converter parameters as a function of slip maintains output phase balance. Symmetrical component analysis gives the power balance of the generating system. The range of possible supersynchronous operation is defined by the operational range of the phase converter. It is shown that, for certain operating slips, no dissipation occurs in the phase converter. Verification of operation is presented by MATHCAD simulation and laboratory experimentation with a resistive load. A simple nonvoltage-distorting 3-phase output VSCF generating system with single-phase synchronising source and passive phase conversion at small negative slips is presented View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 35. Diakoptics for electrostatics

    Page(s): 317 - 323
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (496 KB)  

    An electrostatic formulation for the diakoptic theory applied to induction phenomena is presented. The purpose is to propose a useful and simple computational tool, which appears well tailored to multielement structures, when partial and overall capacitances and effective electrostatic heights are the parameters demanded. An experimental test was carried out to investigate the major causes affecting the method approximation. These can be mainly ascribed to the choice of the first-order models representing the conducting elements given by the tearing process. However, some basic properties of the theory permit the final error to be restricted to a few percent when odd-shaped elements are simulated by ellipsoidal models. A number of practical applications involving high-voltage systems and sensitive electronics subjected to ESD (electrostatic discharge) are suggested View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 36. Finite-element computation of capacitance networks in multiple-electrode systems: application to ZnO surge arresters

    Page(s): 129 - 135
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (668 KB)  

    In the low-conduction regime, the capacitive current in ZnO surge arresters is dominant, about 40 times greater than the resistive current. Therefore, the voltage distribution along surge arrester columns is mainly determined by the location and shape of the arrester terminals and the floating electrodes formed by the arrester flanges and the metallised surfaces of the ZnO elements. Terminal current and voltage measurements are not usually sufficient to quantify the effect of location and shape of the various electrodes, A method to determine the capacitance network that exists in systems with multiple-electrode configurations is described. The method is based essentially on the numerical electric field computation using commercially available finite-element software. The modelling of a distribution polymeric zinc oxide surge arrester in the low-conduction regime is used for illustration. The arrester is modelled in terms of capacitances based on its geometric and dielectric properties using the finite-element method. A full equivalent capacitance network, which takes into account the ZnO material properties and the stray capacitances to the floating electrodes, is derived. A simplified method requiring only a single finite-element computation to obtain a reduced capacitance network is also described View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 37. Impact of technology on the defeat of the U-boat September 1939-May 1943

    Page(s): 343 - 355
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1384 KB)  

    From the 3rd September 1939 to 31st May 1943 the Allies lost 11576000 tonnes of shipping. Although the great destructive power of U-boats had been demonstrated during the First World War the essential lesson to be learnt (the need for huge air and sea escort forces) was incapable of being implemented at the outbreak of the Second World War. The expectation that ASDIC (a submarine location system developed by the Admiralty during the interwar years) would prove immediately effective and prevent a repetition of the (1915-1918) U-boat offensive was not realised. There was an urgent need for technology to aid the air and sea forces in their searches for submarines. Notwithstanding the development of airborne and shipborne radars, the breaking of the German naval enigma cyphers, the utilisation of land-based and ship-based HF direction finders, HF radio telephony, Leigh lights, improved ASDICs, operational research and many other innovations the threat to the security of the United Kingdom in March 1943 was, according to the Admiralty, greater than at any other rime of the war. But in May 1943 the U-boats were withdrawn temporarily from the North Atlantic following the introduction of a new radar, ASV Mark III. The paper is based on material held in the Public Record Office and highlights the application of technology in the Battle of the Atlantic View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 38. Prior-online iteration for image reconstruction with electrical capacitance tomography

    Page(s): 195 - 200
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1880 KB)  

    Electrical capacitance tomography (ECT) has been developed for imaging dielectric material distributions. While iterative image reconstruction algorithms may produce high-quality images, they are regarded as being time-consuming and currently can only be used offline. This paper describes a new image reconstruction algorithm for ECT. First, a coefficient matrix is generated through an offline iteration process. The matrix is then used for online image reconstruction in the same way as a sensitivity map is used in the popular linear back-projection (LBP) algorithm. This new algorithm can produce similar quality images to the Landweber iteration algorithm, but at the same speed as the LBP. An optimal step-length has been incorporated into the new algorithm for improved convergence. The algorithm has been evaluated by both simulation and experiment. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 39. Circulating-current loss in transformer windings

    Page(s): 136 - 140
    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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 40. Degradation of cellulosic insulation in power transformers. Part 3: effects of oxygen and water on ageing in oil

    Page(s): 115 - 119
    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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 41. Degradation of cellulosic insulation in power transformers. Part 2: formation of furan products in insulating oil

    Page(s): 110 - 114
    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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 42. Application of ultrasound to the inspection of insulation

    Page(s): 177 - 181
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (492 KB)  

    Ultrasonic methods have been employed for the inspection of electrical insulation, using both the NDT approach (pulse echo techniques) and by acoustic emission. The NDT approach used a commercial ultrasonic flaw detector to produce A-scans of the insulation system under investigation. A PC scanner system has been developed so that the insulation could be mapped according to the signal depth or amplitude. The acoustic emission equipment was also a standard commercial system with a 1 MHz probe. A fibre-optic link was built to isolate the probe and its pre-amp from the rest of the equipment. Fast Fourier transformation of the signals into the frequency domain allowed the use of neural networks for signal recognition. The systems have been utilised to inspect bushings, transformers, switchgear and cables for internal flaws, dimensional integrity, partial discharges and water trees View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 43. Wavelet-based PCA defect classification and quantification for pulsed eddy current NDT

    Page(s): 141 - 148
    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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 44. Inductance and resistance calculations for isolated conductors

    Page(s): 7 - 14
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (673 KB)  

    Various analytical and numerical calculation methods for computing the high-frequency and low-frequency inductance and resistance of isolated conductors are reviewed. The high-frequency estimates are obtained using conformal mapping theory. In both cases, a uniformly distributed return current at an arbitrary radius is assumed. Formulae are presented for the inductance of a strip conductor of zero thickness. The inductance is computed both for DC and for AC infinite conductivity. For regular polygons the conformal mapping is defined by a power series, whereas finite element analysis is used to compute the DC inductance. Conformal mapping theory is used to obtain estimates of the resistance and inductance of a rectangular conductor when the skin depth is small compared to the thickness of the conductor. A method is then presented for calculating the resistance when the skin depth exceeds the thickness of the conductor but remains small in relation to the width of the conductor. Finite element analysis is used to confirm that one of the two resistance estimates always gives a reasonable estimate of the resistance View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 45. Performance improvement of ultrasonic therapy equipment by modifying the classical transducer design

    Page(s): 107 - 112
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (484 KB)  

    In ultrasonic therapy equipment, the construction of the transducer is based on a piezoelectric ceramic glued to a metallic protection layer. The protection layer thickness is commonly chosen to be a multiple of the acoustic half-wavelength. This classical transducer design criterion is focused on maximising the energy transfer through this layer. However, it is demonstrated that the optimum thickness protection layer depends not only on the energy transfer through the layer, but also on the complete ultrasonic therapy system. Other factors such as the finite dimensions of the piezoelectric ceramic, the electrical excitation circuitry, and the propagation medium must be taken into account. By using an electrical model to simulate the piezoelectric material, the protective layer, the propagating medium and the excitation generator, and with the aid of electrical simulation programs, it can be concluded that a different layer thickness would be preferable. The performance improvement in ultrasonic therapy equipment is based on the fact that the variation of the protective layer thickness permits modification of the relative values of the electrical impedance of both the generator and the ultrasonic transducer, i.e., is their electrical matching. Theoretical results, obtained by means of simulations based on the electrical models, are in accordance with the experimental measurements of the transducer made with the proposed design View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 46. Electricity generation in the home: modelling of single-house domestic combined heat and power

    Page(s): 197 - 203
    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»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 47. Simple voltage generator for producing well-defined nanosecond pulses of amplitudes in excess of 1 kV

    Page(s): 229 - 233
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (428 KB)  

    A 50 Ω charged coaxial line generator has been developed to produce extremely well-defined single-shot voltage pulses of amplitudes in excess of 1 kV, which are free from overshoot and ringing. The width of the pulses is adjustable from 0.7 ns to 250 ns with estimated rise-times as low as 105 ps. When driving a matched 50 Ω load, the amplitude of the first reflected pulse replica is of less than 0.5% of the peak voltage of the main pulse View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 48. Maxwell stress dyadic in differential-form formalism

    Page(s): 19 - 26
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (688 KB)  

    The classical Maxwell stress tensor (or stress-energy-momentum tensor) is revisited by introducing the dyadic formalism to that of differential forms. Dyadics, as originally introduced by Gibbs to vector analysis, appear suitable companions to differential forms because of their coordinate-free character. Basic properties of dyadics together with some useful identities are first derived. It is shown that, in terms of the identities, the Maxwell stress tensor can be given a particularly simple dyadic form. This requires that the Lorentz force density be first expressed as a dyadic quantity mapping trivectors to vectors and, in four-dimensional representation, the Lorentz force-power density as a dyadic mapping from quadrivectors to vectors. Finally, it is shown that to be able to define the force density in terms of a stress dyadic, the macroscopic electromagnetic medium (assumed linear, homogeneous and time-independent) must satisfy a certain symmetry condition which turns out to equal the Lorentz reciprocity condition for time-harmonic fields View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 49. Tests on the breakdown of air at elevated temperatures in non-uniform electric fields

    Page(s): 291 - 295
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (500 KB)  

    Sparkover voltage characteristics have been obtained using a 20 cm rod-plane gap at temperatures between 294 and 770 K. Lightning and slow-front impulse and alternating voltages have been applied; pre-breakdown corona has also been investigated under impulse voltages. The nature of the sparkover characteristics depends strongly on the type and polarity of the applied voltage. These are discussed in terms of the changes in relative air density with temperature and the relationship to the recommendations of IEC 60-1 for the adjustment of sparkover measurements to changes in atmospheric conditions View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 50. Design of a foil-coiled inductor for the heating of steel wires

    Page(s): 203 - 206
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (394 KB)  

    The main advantage of induction heating over other electroheating methods resides in its speed and efficiency of heating. In some cases, however, practical constraints can make high efficiencies hard to obtain by using classical solenoid inductors. Therefore, the design of a foil-coiled inductor as a possible alternative for classical coils is presented. This inductor consists of a wide thin copper sheet that is coiled around an insulating central tube. When studying classical induction coils, it is sufficient to consider only one turn. This leads to relatively small finite element models. A similar approach is not possible in the case of the foil-coiled inductor. To avoid very large models, the foil-coiled inductor has been studied by using two small and complementary models. One of these represents the end part of the inductor; the other one represents the middle section. Both non-linear time-harmonic electromagnetic calculations and coupled thermal electromagnetic calculations have been performed on these models. The results of these calculations allowed a prototype coil to be constructed and measurements were carried out on an experimental set-up. The match between calculations and measurements was satisfactory. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.