Gas ultrasonic flowmeters are widely used in natural gas measurement. In order to achieve high accuracy, it is meaningful to study interaction mechanism between flow field and acoustic field. In this study, effects of non-ideal flow on ultrasonic propagation are discussed. Firstly, a flow-acoustic coupling model is established based on COMSOL and its feasibility is verified by experiments. In order to be more in line with actual working condition, flow field is obtained by CFD simulation instead of theoretical formula calculation. Secondly, with this method, two typical non-ideal flows which often exist in real application are mainly analysed, including vortices near transducers and bend flows. The acoustic trajectory offsets, transit time, sound pressure and measurement errors are compared with results of ideal flow field. It is shown that errors will increase 10% caused by vortices near transducers, and increase 13% caused by bend flows. Besides, when passing through vortices near transducers with negative flow, trajectory offsets are opposite to flow direction. Finally, some suggestions for flowmeter design are proposed to improve measurement performance of gas ultrasonic flowmeter.

The service life of a transformer depends on the ageing degree of the internal oil–paper insulation. In order to reliably predict the remaining service life of oil–paper insulation for a single transformer, this study proposes a method based on monitoring the performance degradation data of oil–paper insulation. In this study, the remaining life prediction model of oil–paper insulation is established according to the Wiener stochastic process. The parameters of the model are iteratively updated by using the Bayesian rule and maximum expectation algorithm. The objective of remaining service life prediction of transformer oil–paper insulation is achieved. In the laboratory, multiple groups of oil–paper insulation samples undergo an ageing test at 130°C. Certain amount of performance degradation data is obtained by continuously monitoring the oil–paper insulation. Along with the prediction method of remaining life, the accuracy of the remaining life prediction of transformer oil–impregnated paper is verified when the model parameters are updated. This is a significant guiding factor for predicting the remaining life through the performance degradation data of the continuously operating transformer.

Environmental friendly insulating oils are sought after as an alternative to polychlorinated biphenyls and mineral oil. The ester-based insulating oils are the industry preferred choice as they are fire resistant and non-toxic in nature. They also have moisture tolerance capability and oxidation stability are quite higher in synthetic ester due to its stable chemical structure than seed-based natural ester oil. In this work, attempts were made to develop un-inhibited synthetic-ester-based high dielectric permittivity CaCu₃Ti₄O₁₂ (CCTO) nanofluids. These nanofluids were investigated for the critical parameters such as AC breakdown voltage, dielectric permittivity, loss tangent, DC resistivity, interfacial tension, viscosity, flash point and acidity properties as per the procedure outlined in IEC and ASTM standards. It has been observed that the addition of nanopowder in un-inhibited oil results decrement in overall critical properties. These results suggest that these un-inhibited ester oils are well suitable for high-voltage transformer application in the present form and the combination of oxidation inhibitor and nanoceramic in the ester oils would give rise to enhanced critical parameters.

Because of their several advantages like simplicity, flexibility and adaptability, nature-inspired (NI) optimisation algorithms have attracted significant attention for solving complex optimisation problems. Source of inspiration for NI are multiple. This study aims to propose a new NI optimisation algorithm inspired by the electrostatic discharge (ESD) event. Tested on a large set of benchmarks and compared with several well-known optimisation algorithms the ESD algorithm (ESDA) is found to be a very competitive algorithm. Moreover, the ESDA has been applied for the determination of wort-case scenarios for electromagnetic compatibility (EMC) filter.

This study presents a diagnostic quality assured electrocardiogram (ECG) signal compression algorithm which uses discrete wavelet transform with the selection of appropriate mother wavelet. Since distortion of reconstructed ECG signal depends on the type of mother wavelet used for decomposition. Therefore, appropriate mother wavelet is selected first which produces minimal distortion. Small valued wavelet transform coefficients are discarded using dead-zone quantisation. Further integer conversion of coefficients is performed to improve compression at the cost of very less error. The processed transform coefficients obtained at this stage contain approximate coefficients and detail coefficients, where approximate coefficients consist very less repetition of data instances while detail coefficients are much repetitive. The repetition of detail coefficients is exploited by run–length encoding which represents the data as run and length. Compression performance of the proposed algorithm is evaluated using single-channel ECG records taken from the Massachusetts Institute of Technology-Beth Israel Hospital (MIT-BIH) arrhythmia database, MIT-BIH ECG compression test database and Physikalisch-Technische Bundesanstalt (PTB) diagnostic ECG database. Compression results exhibit better performance than other existing techniques. Subjective evaluation of reconstructed ECG signals is also performed which ensures effective working of the proposed algorithm on the different morphology of ECG signals.

Linear switched reluctance motors (LSRMs) are attractive machines for industrial applications. Their structure is simple, robust, and low cost. Despite these advantages, LSRMs suffer from inherent high force ripples which induce noise and vibration problems. The force performance of these motors is largely influenced by their geometry. Therefore, the dimensions must be optimised to improve the force performance. The aim of the present work was to determine the optimum dimensions of a double-sided LSRM using non-dominated sorting genetic algorithm-II and multi-objective seeker optimisation algorithm along with a three-dimensional (3D) finite element analysis. The analysis and modelling results are presented, and a laboratory prototype is built. The results revealed that the optimised motor has a higher average force, lower force ripple, and lower total mass

The authors use a TMS320 digital signal processor (TMS320-DSP) to determine fault instants and estimate their location in real time in a laboratory environment. The fault instant is determined via examining the instantaneous differential changes in the line currents. After the fault is detected, the fault location is determined by processing the time-domain transient current waves. First, the travelling-wave frequency is determined by application of the fast Fourier transform to the positive-sequence-component line current after the fault, and subsequently, the fault location is estimated by utilising this frequency. The alternative transients programme (ATP)–electromagnetic transient programme is used to simulate the line currents and create short-circuit fault conditions. Furthermore, LabVIEW software and a National Instruments data acquisition board are used to transform the line currents obtained through the ATP programme into analogue signals. The TMS320-DSP determines the fault in real time and estimates the fault location using the completed software and analogue input signals. Their results indicate that the prototype device designed with the use of the TMS320-DSP is suitable for real-time fault detection.

Material characterisation plays a crucial role in many applications such as security, military, communication, bioengineering, medical treatment, food industry and material processing. Since it is useful to identify other properties of materials often tied to other useful parameters, such as stress–strain relation, bio content, moisture content, materials density and so on, the dielectric properties of materials should be achieved with high accuracy using appropriate measurement techniques and extraction techniques. There are many measurement methods to determine the dielectric properties of materials, which depend on parameters such as frequency range, material phase and temperature. In this study, the measurement methods and extraction techniques have been discussed, and alternative ways have been presented with experimental and simulation results. Furthermore, a new numerical extraction technique has been performed to achieve the dielectric properties of materials.

Partial discharge (PD) represents one of the most significant evaluation indicators relevant to transformer insulation degradation. Thus, detection and location of PD are essential. During the last year, a PD localisation method occurred which uses phased arrays. With respect to this method, the choice of localisation algorithm is a particularly important issue, since choosing a suitable localisation algorithm can efficiently improve positioning accuracy and significantly reduce computational complexity. This study introduces and analyses the characteristics of six direction of arrival estimation algorithms, which can be applied as localisation algorithms. Besides, the effect of the element spacing, number of snapshots, and signal-to-noise ratio on the above-mentioned algorithms were also analysed by simulation. The results provide useful guidance for electric engineers engaged in PD location.

Structural health monitoring (SHM) based on the electromechanical impedance (EMI) has been pointed out as a promising method for detecting structural damage. However, practical problems such as the effects of temperature variation on the electrical impedance signatures of piezoelectric transducers have made it difficult to effectively apply this method of detecting damage in real structures. Therefore, in order to contribute to the effective application of the EMI method in real structures, this study presents a new feature extraction approach insensitive to temperature variations. The proposed method is based on the Akaike statistical criterion algorithm, which extracts the number of significant resonance peaks from the electrical impedance signatures. Tests were performed on an aluminium bar with different damage sizes and under different temperatures. The experimental results indicate that the proposed method is capable of detecting and quantifying structural damage in environments under temperature variation.

Dynamic contact resistance measurement (DRM) is an effective technique to evaluate the contact condition in substations without dismantling circuit breakers. However, performing DRM tests with unsuitable test parameters will cause low repeatability of the test results, and even lead to the misdiagnosis of contact condition. Performing the DRM tests at high DC injected current can improve the repeatability. This paper studies the mechanism of the DC injected current on the repeatability of the DRM test results, and it also promotes a new determination method of the DC injected current amplitude. The impact of the DC injected current on DRM test results is reviewed. The mechanism of the DC injected current on DRM test results is investigated by analysing the chemical composition of the contact surface, the force exerted on the contacts, and the temperatures of a-spots on the contacts’ surface. Results indicate that not the Lorentz force, but the temperature of a-spots is the primary influencing factor. The amplitude of the DC injected current can be determined by calculating the temperatures of the a-spot on the contacts’ surface. And this method can also be used for other SF₆ circuit breakers.

In this study, the mode-generation mechanism due to non-uniformity and asymmetry in a differential line (DL) circuit illuminated by a plane wave was analysed using a modal perturbation technique. Through modal decomposition, the field-to-line coupling equation was reformulated in terms of a differential mode (DM) and common mode, and the perturbation technique was applied, interpreting the geometrical unbalance as the mathematical equivalent modal distributed sources. Three types of typical DL structures above a loss ground with different conductivities in the frequency and time domains are discussed. The results show that the non-uniformity of a DL will cause mode perturbation, while asymmetry can lead to mode conversion. The time-domain results show that under plane-wave illumination, the DM response of an asymmetric non-uniform DL (NDL) increases significantly compared with that of a symmetric NDL and uniform DL. With the decrease in ground conductivity, the distortion of the modal response waveform is aggravated and extended with time.

While optical motion analysis systems can provide high-fidelity gait parameters, they are usually impractical for local clinics and home use, due to high cost, requirement for large space, and lack of portability. In this study, the authors focus on a cost-effective and portable, single-camera gait analysis solution, based on video acquisition with calibration, autonomous detection of frames-of-interest, Kalman-filter + structural-similarity-based marker tracking, and autonomous knee angle calculation. The proposed system is tested using 15 participants, including 10 stroke patients and 5 healthy volunteers. The evaluation of autonomous frames-of-interest detection shows only 0.2% difference between the frame number of the detected frame compared to the frame number of the manually labelled ground truth frame, and thus can replace manual labelling. The system is validated against a gold standard optical motion analysis system, using knee angle accuracy as metric of assessment. The accuracy investigation between the RGB- and the greyscale-video marker tracking schemes shows that the greyscale system suffers from negligible accuracy loss with a significant processing speed advantage. Experimental results demonstrate that the proposed system can automatically estimate the knee angle, with R-squared value larger than 0.95 and Bland-Altman plot results smaller than 3.0127° mean error.

In this study, the apparent soil resistivity evaluation is estimated for three-layer soils by four strategies and the obtained values are compared with experimental measurements done by using the four-electrode method. Different methods are suggested with the aid of IEEE 80 to estimate the apparent soil resistivity of three-layer soils, in which a grounding system consisting of a grid with rods is constructed. The effect of the reflection factor on the mesh and the step voltages, the grounding system resistance and the mesh voltage is investigated. It is concluded that the first three methods are close together, and also with the experimental findings done by the authors and others the fourth method gives some tolerance with the first three, but it is in agreement with the experimental measurements. It is concluded also that the reflection factors of non-uniform soil have significant effects on the apparent soil resistivity, the step and the mesh voltages and the ground resistance. For the verification of the calculated results, experimental model is used. It is noted that the measured values are slightly high compared with the calculated values; the reason may be due to the boundary effects of the used model.

A micro-electro-mechanical system (MEMS) trenched piezoelectric energy harvester based on a cantilever structure has been proposed. The trenched piezoelectric layer has increased the output voltage and the generated power. It also provides three additional design parameters such as the trench position, depth and length. A particle swarm approach has been used for optimisation of the piezoelectric energy harvester geometry with the aim of finding the optimum design which transfers the maximum harvested power to a definite load. The optimisations and comparisons have been made for unimorph, bimorph, trenched and non-trenched cantilever beams. The results are quite revealing that the generated power for a trenched bimorph energy harvester is much larger than other structures. The optimum design found by particle swarm optimisation algorithm has asymmetric trenches in the top and bottom piezoelectric layers and can generate much more power than the unoptimised structure.

For the stochastic transient analysis of transmission line with parameter uncertainties under plane wave illumination, a random admittance equivalent circuit model was presented. Based on the polynomial chaos theory and stochastic Galerkin method, the random transmission line equation was cast into the augmented deterministic transmission line equation. By virtue of eigenfunction decomposition and appropriate acceleration of convergence, a SPICE-compatible Foster form of admittance equivalent circuit model was obtained. The random boundary condition for non-linear loads was solved by applying the Gauss quadrature rule. Application examples validate the accuracy and efficiency of the presented methodology.

When the image position measuring method is applied to mover position measurement of a linear motor, the selection of the target source image is crucial to measurement accuracy and anti-interference capacity. In this study, the fence image is used as the original shooting surface, and different kinds of fence images are constructed according to their width standard deviation and grey gradient sum. First, the relationship between the fence image spectrum energy and the correlation of image pixels is analysed. Then the image spectrum energy is used to characterise the feature of fence images during screening to select an aperiodic fence image with a strong anti-interference. Second, the phase singularity method is used to match the two images before and after displacement to obtain a sub-pixel displacement value of two images. Finally, according to the system calibration coefficient, the actual displacement value of the linear motor mover is obtained. Experimental results show that the fence image screening from image spectrum energy exhibits more anti-interference for the position measurement of the linear motor, and the measurement algorithm based on the phase singularity algorithm is more stable. The absolute error of displacement is <0.023 mm, and the relative error change within 0.054–0.862%.

Induction period evaluated from time domain dielectric response of oil-paper insulation (OPI) contains information related to heat dissipating property of oil. In the present paper, effect of aging sensitive oil properties on the value of induction period is investigated. Three types of dielectric liquids (pure mineral oil, synthetic ester, mixture of synthetic ester, and mineral oil) are considered for the present work. A neural network (NN) is used for modelling the non-linear relationship between induction period and various oil properties. The trained network is subsequently used to study the influence of various oil properties on induction period.