Objective validation and ranking of measurements and simulations may be done by methods such as feature selective validation (FSV). FSV is used to compare two EMC-measurement results. Owing to the noisy nature of these type of data, the FSV results are corrupted. The reasons are discussed and solutions are proposed to make FSV feasible in a broader area of applications. The final solution is a combination of denoising the data and changing the weight of the data to be in accordance with our visual interpretation.
The rotational power losses measured in the clockwise and anticlockwise directions differ noticeably. There are many factors that contribute to this difference, but these have not previously been explained in the literature. A discussion on the physical phenomena that contribute to the power loss along with the experimental measurements and analysis are presented.
A full mathematical description of the complex interaction of adjacent point-plane coronae has yet to be given. An essential feat-Lire of the phenomenon is the electric field on the planar line running directly below the points. Experimental data, obtained elsewhere, have been manipulated to reveal the functional dependence of this field on the control or independent variables of voltage and geometry. A model in terms of simple functions has then been derived that fits the measurements within reasonable bounds and which is a valuable tool from the point of view of predictive engineering. As for single points, the behaviour is shown to be separable, with a linear dependence on the voltage and an inverse dependence on the gap separation. The distribution is further shown to be represented by cosine power functions of the angles subtended from each planar position to the electrode points and to locations on the central axis between the points. The modelling uses centre-of-charge concepts, and gives an insight to the mutual interactions of the multipoint discharges that are used commercially and also into the behaviour of neighbouring coronas on high-voltage equipment in the environment. What is known of single-point phenomena leads one to expect that the description derived here is likely to hold for a large range of gap sizes and also for positive DC discharges in the absence of streamers.
The paper deals with the numerical analysis of electromagnetic shielding effects in the context of low-frequency electromagnetic compatibility problems in power installations. The indirect version of the boundary element method (BEM) is applied for the consideration of 3D eddy-current fields. Basic formulas and equations that describe the problem in question are presented. The reported numerical technique is implemented in the author's software package BEMsolver 3D. The correctness of both the applied numerical algorithms and the computer program has been tested using measurement results taken in the laboratory. A simplified model of the transformer chamber of a 110/15 kV indoor substation has been proposed. Selected numerical results for the magnetic field strength inside the substation are exhibited. The effectiveness of the electromagnetic shield, which reduces the magnetic field strength in the control room (abutting the transformer chamber), has been computationally tested.
The coupling between a two-wire transmission line and the electromagnetic field inside a reverberation chamber is analysed. The chamber field is represented by the superposition of plane waves with random incidence. The signal, induced along the line by such a field, is analytically found under general load conditions for the line, including a strong mismatching. Therefore this approach allows the parasitic elements introduced by real terminations and by measuring sensors to be accounted for. The statistics of the current flowing into the line load are analysed in terms of the cumulative distribution function and in terms of the maximum-to-mean ratio, an important parameter in immunity tests. All results are compared with those experimentally obtained in a real reverberation chamber, showing a satisfactory agreement; a discussion about the overall measurement uncertainty is also reported. Finally, some advantages of the use of reverberation chambers for immunity tests are highlighted
The perfect electromagnetic conductor (PEMC) is a generalisation of both perfect electric-conductor (PEC) and perfect magnetic-conductor (PMC) media. Its definition, through differential-form formulation, corresponds to the simplest possible electromagnetic medium definable by a single parameter, the PEMC admittance. Its realisation for time-harmonic fields appears possible by a layer of bi-isotropic material on a PEC plane. As a basic problem, the extension of Kelvin's electrostatic image theory for the PEC sphere to that for the PEMC sphere is considered here. It is shown that, applying a suitable duality transformation, classical results for the PEC sphere can be applied to find the image solution which, for an electric point charge, involves both electric and magnetic point and line sources. The analytic result is checked by some known special cases.
A hierarchical-clustering-scheme-based analysis of the electromagnetic interference (EMI) effects due to an electrostatic discharge (ESD) which can sometimes cause serious damage to electrical systems is presented. A hierarchical clustering scheme is used to classify the EMI-related properties that result from ESD events. The scheme can classify target objects into several groups with a tree-like structure. Furthermore, to evaluate the effect of a high-speed moving discharge one-shot discharges were repeatedly generated and the resulting ESD current measured in the time domain. Based on the measured data for charging voltages of 2, 5, 10 and 15 kV several differential properties of ESD waveforms have been examined including the maximum absolute peak level and the energy level for the three frequency regions, and the data has also been analysed using the hierarchical clustering scheme. The results show that high-speed moving discharges can increase the maximum amplitude and relative energy of ESD events and that clusters of ESD events can be effectively divided according to similarities in EMI-related properties.
Fatigue testing machines dynamically apply forces to the device under test. Standards for the characterisation of fatigue testing machines exist but their instrumentation is not traceable to national electrical standards. Thus, the dynamic characterisation of the electronic instrumentation used in the calibration of fatigue testing machines is considered. In particular, the principles of operation and the evaluation of the National Physical Laboratory's dynamic force standard for the characterisation of the electronic instrumentation used in the calibration of fatigue testing machines under static and dynamic conditions are given.
Power systems contain distorted voltage and current waveforms. Currently, there is not a preferred set of voltage and current waveforms for the calibration of power and energy meters under non-sinusoidal conditions. The paper concentrates on the calibration of power and energy meters under sinusoidal and non-sinusoidal conditions. In particular, criteria for selecting voltage and current waveforms, a calibration procedure and a set of voltage and current waveforms for the calibration of power and energy meters under non-sinusoidal conditions are proposed
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.
Currently, the UK's national standards for impedance measurements are only available for frequencies up to 50 GHz in a coaxial line and 110 GHz in a metallic rectangular waveguide. No standards exist above these frequencies. A need to provide measurement standards and measurement assurance above these frequencies has led to research into a new form of impedance standard for precision metrology applications across the entire millimetre-wave band and perhaps beyond (i.e. extending to at least 300 GHz). We report the development of the new standards and other devices that utilise a dielectric waveguide as the transmission medium, and we show how these standards can be used to calibrate measuring instruments, such as vector network analysers (VNAs), and to provide traceability to national standards
An active shield is designed to reduce the stray magnetic field of an induction heater, which heats a workpiece using a strong magnetic excitation field. The shield consists of a number of coils at well-chosen positions and generates a magnetic field that is opposite to the induction heater stray field in a defined target area. The presented software controller maximises the field reduction by using amplitude and phase information of the relevant frequency components in the spectrum of the excitation current and of the Euclidian space components of the magnetic field at a point. The average field reduction in the target area is equal to 25 dB.
The paper describes a multiphysical finite-element approach to simulation of the three-dimensional modelling of metallic structures that are transiently subjected to heavy electromagnetic loading, as in the metal forming industry. Electromagnetic, thermal and structural effects are all taken into account, and very good agreement is obtained in detailed comparisons with measurements from non-destructive experiments. Acceptable agreement also exists in the peak field prediction of destructive experiments, in which single-turn coils are used to generate ultrahigh magnetic fields, typically for use in solid-state experimental physics.
A method is described for measuring the cross-polar transmission coefficient of a flat-panel sample in free space using a quasi-optical bench between 8 and 13 GHz. Impedance matching to both co- and cross-polar components simultaneously, so as to prevent reflection of one of them from the rectangular waveguide feed, is provided by resistive vanes within the flares of the horn antennas. The bench is calibrated by means of a modified through-reflect-line (TRL) or through-short-delay (TSD) technique and uses a wire grid as a calculable reference standard. The calibration algorithm is based on Speciale's 'super-TSD' algorithm, which has been modified so that its stability is enhanced. The method is validated by comparison of measurements on wire grids with theoretical predictions, which showed excellent agreement, provided the test grid was accurately positioned with respect to the reference plane. The method was also compared with approximate experimental methods, which showed moderate agreement
It is widely thought that ageing a metal halide (MH) lamp will result in changes in the acoustic resonance eigenfrequencies but to date no experimental data on this topic has been reported in the literature. A study on the influence of the operating time on the stability of low-wattage MH lamps is now presented. It is shown that the age of a lamp does not affect the fundamental acoustic eigenfrequency values. The upper limit of the frequency of the highest acoustic resonance band at which the arc will become unstable is not affected by the age of the lamp. However, the lamp age does influence the extent of instability inside the lamp with the lamp voltage significantly increasing.
The performance of two fog-type porcelain insulators is investigated in the case of condensation wetting and uniform as well as non-uniform contaminant distribution. Both insulators have been employed simultaneously on the same transmission line poles and exceed the minimum required creepage distance. However, their field performance was remarkably different. The analysis performed indicates that, in the case of condensation, the total creepage distance is exposed to wetting, including the parts that are considered 'protected' along the fog-type profile. In addition, these parts tend to accumulate more pollution, resulting in an inferior insulator performance. Consequently, for the specific environmental conditions, in addition to the creepage distance, the insulator profile is a parameter that greatly influences the service performance and therefore must also be considered in the selection of an insulator.
Investigations of the lightning impulse breakdown characteristics of a SF6/N-2 gas mixture, N-2 gas and CO2 gas have been carried out. In the case of the SF6/N-2 gas mixture the 50% breakdown (electric) field strength for the positive impulse voltage was slightly lower than that for the negative impulse voltage, and the pressure of the SF6/N-2 gas mixture must be increased to approximately twice the pressure of SF6 gas to obtain the same dielectric strength as that of SF6 gas. For CO2 gas, the 50% breakdown field strength for the negative impulse voltage was lower than that for the positive impulse voltage in the case of SF6 gas. However, the dielectric strength of CO2 gas, even at twice the pressure of SF6 gas, was approximately 60% of the strength of SF6 gas, so that the CO2 gas-insulated busbar may be approximately 1.6 times as large as the SF6 gas-insulated busbar. In the case of N-2 gas, the 50% breakdown field strength for the positive impulse voltage was lower than that for the negative impulse voltage, and the dielectric strength of N-2 gas, even at twice the pressure of SF6 gas, was less than 50% of the strength of SF6 gas, so that the N-2 gas-insulated busbar may be approximately 2.1 times as large as the SF6 gas-insulated busbar. A remarkable difference between CO2 and N-2 gas was found from the observation of discharge forms and partial discharge properties.
To ensure the safe and reliable operation of a gas-insulated substation (GIS), it is crucial to quickly identify partial discharge (PD) sources to prevent the occurrance of breakdowns. A method based on wavelet packet transform techniques is developed to meet this requirement. The proposed method extracts is able to extract features from ultra-high frequency resonance signals measured from a test GIS section. These features are subsequently used to train a neural network that is then able to quickly and reliably diagnose PD events. A quality-assurance scheme is developed that ensures the robustness of the PD classification to changes in the background noise level and the location of the PD event within the test GIS section.
The direction of the magnetic forces on currents, at right-angles to the conductor, leads to an apparent failure of the action-reaction force balance when applied to the component parts of a current-carrying circuit. The electromagnetic railgun provides an example showing the need for a force in the direction of current flow. These and other applications continue a long-standing debate, originating in Ampere's analysis of the nature of the forces on current elements. The paper examines the consequences of Maxwell's 'dynamical' approach to currents in terms of 'electrical fluids'. The conductor surfaces transfer the transverse force on the conduction electrons to the crystal lattice but, since there are no similar constraints in the axial direction, a current element cannot be treated as a single entity. The implications of the separation into two groups of charge are examined. It is shown that the hydraulic fluid, or 'hosepipe', analogue provides a useful insight in terms of momentum and pressure. The corresponding electromagnetic properties provide a 'dynamical' alternative to the magnetostatic Maxwell stresses in the field. This also accounts for the reaction in a self-consistent way, but requires such high levels of energy and stress in empty space as to be widely regarded as 'unreal'.
Vector measurements of modulated RF signals are demonstrated using a sampling oscilloscope with in-phase and quadrature referencing. Certain sampling oscilloscope designs exhibit sub-picosecond time-correlation between channels. This correlation allows independent referencing of the carrier frequency and the modulation signals. This measurement technique, which can be implemented using simple RF components, provides an alternative to real-time digitising oscilloscopes or real-time spectrum analysers and can be used at higher RF frequencies than is currently possible with these other methods for repetitive RF waveforms. Experimental results are presented for a pulsed RF power application and for 4QAM, 16QAM and DQPSK wireless communication coding schemes
