This investigation is devoted to study, in time domain, the transient behaviour of vertical and horizontal grounding conductors submitted to impulse current using state space representation-based transmission line method. This study has been carried out with and without incorporating soil ionisation and mutual coupling between conductor elements for soils of low and high resistivities. The results are focused on the time-domain solution of the electrode's transient potential rise and its impulse performance parameters. The results show the importance of including the mutual coupling between segments of the same electrode and soil ionisation. The results are compared with both published theoretical approaches and experimental measurements, and show acceptable agreement. This method has been applied to compute the transient potential of horizontal electrodes buried in vertically stratified soil, a situation which can occur where long horizontal counterpoise is buried in a highly contrasting soil along its length.

Surface charge accumulation on spacer is an important factor to cause surface flashover. An experimental set-up is established to measure surface potential over a truncated cone-type spacer under DC voltage in SF₆ gas at atmospheric pressure using a Kelvin vibrating electrostatic probe. The surface charge density is calibrated based on multipoint measurement technique, which takes the influence of electrostatic probe into account. The experimental results show that surface charge distribution patterns can be divided into three classes including centrosymmetric distribution, spot-like distribution, and cloud-like distribution. The symmetrically distributed charges are injected by electrode, which migrate along spacer surface through the surface conductivity. While the charges showing spot-like and cloud-like distribution are generated by the ionisation of SF₆ due to local electrical field concentrated. Besides, the hetero-charges are more easily to be saturated with different charging durations and the polarity of the net charge is the same as that of applied voltage.

This study proposes a method to measure the leakage error of vector network analyser (VNA) in the National Institute of Metrology of Thailand (NIMT). To achieve this, a leakage model of the VNA is presented and analysed. Here, a programmable attenuator is represented as device under test (DUT) with an attenuation of A _DUT and a fixed attenuator with an attenuation of A _L is used to represent the radio frequency (RF) attenuation in air between the two ports of the VNA. The DUT is first analysed in terms of phase and attenuation as a function of frequency to represent any RF device with a constant insertion loss. Second, the phase shifter is adjusted to vary the phase of DUT. Also, the amplitude and phase of the leakage signal are measured as a function of (A _L−A _DUT) and they are compared with the mathematical model of leakage error. Finally, the maximum amplitude deviation of the leakage signal can be used as an uncertainty budget of leakage error of the VNA.

Bioimpedance spectroscopy (BIS) measurement is widely used in various biological medical applications. Broadband excitation signals with sparse spectra can be beneficial to increasing the signal-to-noise ratio (SNR) and decreasing the time of BIS measurements. This study introduces a rapid synthesis method to generate near-binary multisines (NBMs) with arbitrary sparse spectra that have the advantage of lower crest factor and less aliasing compared with the traditional multisines or binary signals. One of the NBM examples, abbreviated as Quasi-Log-Flat-19, which contains 19 quasi-logarithmical and flat desired components from 1 kHz to 1 MHz is used as the voltage source or the current source for BIS measurements (only 1 ms required). The results show that the impedance SNR by using Quasi-Log-Flat-19 (68.9 dB in average from the voltage source and 63.5 dB in average from the current source) is always higher in comparison of the corresponding optimised multisine with the same desired spectrum (65.1 dB in average from the voltage source and 58.5 dB in average from the current source). It can be concluded that NBMs can be used as good alternatives to traditional optimised multisines with sparse spectrum distribution in fast BIS measurement.

Studies are conducted to estimate the evaporation duct refractivity structure inversely using signal strength sampled in the point-to-point propagation measurements. The repulsive particle swarm optimisation (RPSO) is adopted as an efficient optimisation algorithm to improve the efficiency of the inverse process. To verify the performance of the RPSO algorithm, numerical simulations are done to compare it with genetic algorithm and particle swarm optimisation for a typical inverse problem in estimating evaporation duct height and transmitting distance simultaneously. Moreover, to get better inversion accuracy, a layered evaporation duct model is also adopted and further numerical study based on measured refractivity profiles clearly demonstrate the better performance of layered model over other models to exhibit a closer match to the sonde data.

The ion mobility and ion density are key physical parameters in research of ion flow field of high-voltage DC (HVDC) transmission lines. The Gerdien tube is one of the practical tools that can be utilised in situ measurement of ion mobility and ion density of coronated lines. The mobility spectrum, connecting the ion mobility and ion density, is an effective approach in analysis of the characteristics of corona ions and the effects of environmental factors on them. In previous studies, single measurement-electrode Gerdien tube is frequently used to get the mobility of one single ion via graphical method or the total ion density when the tube is operating as a counter. To enable it to obtain the ion mobility spectrum, a method is devised by the analysis of graphical method and the transition phenomenon in current–voltage characteristics of the tube. Furthermore, the method is applied to the raw data of current–voltage characteristics published in the literatures. The ion mobility spectra are obtained and compared with those having been reported. By doing this, the method is validated. This new approach makes applications of Gerdien tubes more advantages in experimental researches of ion flow field of HVDC transmission lines.

The front-face temperature rise of Al alloy subjected to the high-energy long continuing current (LCC) component in lightning is important but difficult to measure. Therefore, a numerical inversion model based on the control volume finite element method is proposed to analyse the front-face temperature rise of Al alloy deduced from the rear-face temperature rise measured in simulated LCC experiment. In this model, Al sample is divided into discrete control-volume units with continuous medium by grids, forming internal nodes, surface nodes, edge nodes, and corner nodes. Temperature governing equations for different nodes are derived from Fourier's heat conduction law and solved with finite difference method in time and spatial domain. The secant method is used to make the optimal approximation to experimental data. The results show that subjected to LCC with amplitude 404 A and duration 520 ms, the highest front-face temperature rise of Al alloy is 10,800 K. The damaged area calculated by the proposed model is 298.7 mm². The relative error is 4.8% compared with the experimental result 314.0 mm². The energy consumed in all processes is 6710.1 J calculated by this model, in contrast to the total energy 7140.9 J generated from the arc and Joule heat.

Normal belt conveyors transfer materials by utilising the friction force between driving rollers and the conveyor, resulting in sag resistance and friction. In order to overcome this shortcoming, this study presents a new permanent magnet low resistance belt conveyor, which is used to replace the original mechanical contact with the permanent magnetic support system. The simplified mechanical three-dimensional model of its permanent magnet support system was established. The mathematical expressions of suspension force, reluctance force and lateral force were deduced with Maxwell equations based on reasonable assumptions. The approximate relationship among air gap length, magnetic flux density and magnetic force was derived from the analysis of air gap characteristics of the permanent magnet support system and the finite-element simulation of the permanent magnet support system under different air gap conditions. A self-designed test device of the permanent magnet low-resistance belt conveyor was used to apply different sets of loads and carry out the experimental research on the permanent magnet support system under different air gap lengths, so as to obtain the pressure distribution of the magnetic conveyor belt. The findings provide theoretical references for further research on the permanent magnet low-resistance belt conveyor.

Electromagnetic and heat issues are more complex in the end region of a generator than in the line segment area. In this study, the electromagnetic field and related challenges are discussed. Stepped cores are considered in the performed calculations. Eddy-current losses variation mechanisms for structures in the end region and iron losses of end stepped cores are investigated under rated load condition, using space vectors. The effects of the end windings stretching out the end cores from the rotor and stator on the electromagnetic losses of the end structures studied in detail. The obtained results can be employed for developing large turbo-generators, and reveal a novel approach for reducing eddy currents and iron losses.

This study presents a novel design of high-efficiency two-stage electrostatic precipitator (ESP). For its design, different electrode configurations were tested and the corresponding onset and breakdown voltages were measured and compared. Based on findings, an optimal arrangement was then defined and a novel design of a two-stage ESP prototype, using needle electrodes instead of long wires utilised in conventional ESPs, is realised. For comparison, a single-stage ESP was also built. The influence of various parameters on the performances of both two-stage and single-stage ESPs was evaluated numerically using 2D modelling and compared with the experimental ones for the same dimensions of laboratory-scale ESP. The numerical simulation was implemented using COMSOL Multiphysics package that uses finite element method (FEM) solver. The main investigated parameters are the electric potential, electric field distribution and collection efficiency under the loading conditions as a function of air flow velocity, magnitude and polarity of voltage, ESP geometry design (size, shape and number of discharge electrodes). It is shown that the collection efficiency of this novel ESP increases when decreasing air flow velocity; and its effectiveness is higher when using negative ionisation polarity. Also, the collection efficiency of this ESP could greatly improve the existing ESPs under the same applied physical conditions.

One of the main drawbacks of the frequency response analysis (FRA) technique that is widely accepted as the most reliable tool to detect transformer internal mechanical deformations is the inconsistent interpretation of the measured signature because of its reliance on personal expertise more than standard codes. Moreover, conventional FRA signature has a very low accuracy in detecting incipient and low mechanical fault levels. In order to avoid inconsistent interpretation for the transformer FRA signatures and improve its accuracy to detect minor fault levels, a reliable automated technique has become essential. This study investigates the feasibility of utilising FRA polar plot to detect minor radial deformation levels within two, three-phase power transformers of different ratings and winding configurations simulated using three-dimensional finite-element analysis software. Simulation results are validated through experimental measurements. Results of this study are also compared with the results obtained for other types of transformer winding deformations that are published in the literature in order to identify unique impact for each fault type on the proposed method. Findings reveal the superiority of the proposed approach over existing conventional technique in terms of accurate identification and quantification for minor transformer winding deformations.

In order to optimise the mechanical error and to avoid electrical interface from a rotating plate of the capacitive rotary encoder, a state-of-the-art designing approach is presented in this article. In contrast to the multi-electrode capacitive sensing pattern, the proposed structure is very simple. It has three pairs of stator electrodes and a rotor plate (RP). In each stator plate, three isolated conductive arc sectors are fabricated using standard PCB technology. Likewise, an arc sector, an aluminium oxide-based metallic plate is placed between the stator pairs and the plate is firmly attached with a shaft. This plate is named as RP. Since the RP acts as a dielectric medium hence; it is free from any electrical interface. Henceforth, the angular position of an object has been determined by analysing the variation of three parallel capacitances, which develops due to the rotation of dielectric medium inside the stator pairs. In this preliminary investigation, a prototype has been designed, developed and tested in laboratory condition to proof of this concept. A satisfactory result has been found with an accuracy of ±0.6°, resolution of 0.0003° and repeatability of ±1° in the measured range of 0–360°.

Wire wound H-coils used for rotational measurements are not completely immune to off-axis components of magnetic field strength H. As a result, such components are capable of introducing the significant difference between the rotational power loss measured in the clockwise (CW) or anticlockwise (ACW) direction of rotation. These measurement errors do not influence the average value, and they are distinctly different from the errors caused by the angular misalignment of the sensors in the field metric method. As demonstrated in this study even ideal angular positioning of the H-coils could still produce CW–ACW differences at the level of ±15% at lower flux density and ±30% close to saturation.

In this study, a new method is proposed to monitor axial displacement (AD) of transformer high-voltage (HV) winding using electromagnetic waves. The proposed method employed two receiving antennas and one transmitting antenna to exchange ultra-wideband (UWB) signals with the winding. The magnitude Euclidean distance (MED) index is used to compare the received signals when winding is sound or defective. Two receiving antennas receive signals at two different positions upon ADs in winding which causes different values in the amplitude of the received signals as well as the MED index of two receiving antennas. Hence, taking advantage of this feature, the occurrence, direction, and extent of AD can be identified. The proposed method is assessed using a simulation model. Then, experiments are conducted on an actual transformer winding using an experimental setup.

This study deals with the application of kurtosis and skewness based approximate and detailed coefficients in walking speed measurement. Gait data (force information of foot and positional information of ankle) are gathered through sensors during level walking on motorised treadmill of normal individuals at various speeds and features are extracted from the data using discrete wavelet tools, namely kurtosis of approximate coefficients, kurtosis of detailed coefficients, skewness of approximate coefficients, and skewness of detailed coefficients. The features corresponding to the different discrete wavelet transformation levels are analysed and results are demonstrated. Specific relations have been found between walking speeds and those parameters, where from optimisation has been done with respect to a parameter, type of sensors, and number of sensors. Finally, an algorithm is proposed accordingly for walking speed measurement using the gait data and subsequently validated through experiments.

The axial section line of the ring forging is the key parameter to measure whether the ring forging process meets the technical requirements. To ensure the quality of the ring forgings, an online measuring method of the axial section line in ring forging process is proposed in this study. First, the axial section line data of the ring forging is obtained online by laser scanning device. Then, the axial section line data is locally sorted and is screened to eliminate the edge noise. Second, the axial section line data is converted to line grey image data by merger and derivation theory. Finally, the line grey image data is smoothed by bilateral filtering based on information entropy selection factor. Then, the shape of the axial section line is constructed to complete the measurement of the axial section line. The experimental results show that the measurement speed of axial section line meets the requirements and the measurement accuracy of the axial section line meets the requirements.

Accurate estimation of paper-moisture in transformer insulation is necessary for ensuring their satisfactory operation. Paper-moisture in transformer insulation can be estimated from their corresponding transfer function zero obtained from insulation model that is parameterised using polarisation depolarisation current data. However, paper-moisture estimated using transfer function zero is less reliable for a new unit. Considering the fact, a method is proposed in this work that can estimate the paper-moisture with greater accuracy. Instead of using only transfer function zero, tanδ has also been employed for estimating the paper-moisture. In order to investigate the effectiveness, the proposed technique has first been applied on several test samples in the laboratory. The proposed technique is then applied on few power transformers to estimate their paper-moisture. Results obtained from the experiment show that this technique can estimate the paper-moisture content within test samples and power transformer insulation with better accuracy.

An improved electro-geometric model (EGM) based on upward corona leader system consideration is introduced. The proposed method is a modified version of EGM and its high accurate results are independent of the height, voltage level, and circuit type of structure. The equations of the proposed method are modified by means of genetic algorithm based on the leader progression models (LPM) results which are consistent with the experimental results. To evaluate the performance of the proposed method, the shielding failure rates (SFR) of a single-circuit transmission line with different protection angles are calculated and compared to those of LPM and a revised EGM. The comparisons show that the results of the improved method roughly agree with the results of LPM. To ensure about the performance of the proposed method, it is applied on ten different practical structures with different characteristics. The results of IEGM are compared to the field data and the results of the revised EGM. The comparisons demonstrate that the proposed IEGM is an appropriate method for SFR calculation irregardless of the height, voltage level, and circuit type. In other words, the proposed IEGM is as simple as conventional EGM and as accurate as LPM.

The aim of this study is to determine if navigation movements, used in surgical training, follow a particular power law which describes the relationship between the hand trajectory's curvature, torsion, and speed. Based on this approach, this study proposes the affine velocity as an appropriate classification feature to solve the surgical movement recognition problem. Eight subjects with different surgical experience were involved in the experiments. They were asked to do two kinds of movements that involve depth perception skills with their right arm. Using six video cameras and an instrumented laparoscope, the 3D trajectory of the end effector was recorded for each participant. A power law was used to fit the data sets and the exponents that relate the torsion, curvature, and speed were calculated. The exponents involved and the affine velocity for each trajectory were then computed, using a multi-variable linear regression, and compared between participants. It is shown that fitting residual follows a normal distribution indicating no regression biases. Finally, it is presented that an affine velocity analysis could be able to classify between both trajectories showing a correlation with the surgical skills and a clear difference for people with some surgical training.

This study presents induction machine fault detection possibilities using smartphone recorded audible noise. Acoustic and audible noise analysis for fault detection is a well-established technique; however, specialised equipment for diagnostic purposes is often very expensive and difficult to operate. To overcome this obstacle, a simple pre-diagnostic procedure, using hand-held smartphones is proposed. Different faults of the three-phase squirrel cage induction machine such as various numbers of broken rotor bars and dynamic rotor eccentricity are inflicted to the machine and the resulting audible signals are recorded in laboratory circumstances using two widely available commercial smartphones. The analysis is performed on audible noise and compared with the results of mechanical vibrations measurements, recorded by vibration sensors. Rotational speed frequency and twice-line frequency are used as diagnostic indicators of faults. A simple neural network is composed and probabilities of fault detection using such diagnostic measures are presented. The necessity for further study as well as further implementation and method refinement necessity is pointed out.

Optical linear encoder error is of a great concern for its wide applications. Temperature plays an important role in the realistic environment error factors, and influences the encoder's accuracy. In this study, an incremental optical linear encoder error model is built and estimated by a prior analysis, error processing of least-square fitting, empirical mode decomposition and cross-correlation methods. The errors of the different temperatures can be used for error separation during the cross-correlation calculation. The experimental measurement with different temperatures is carried out, and analysed by the authors’ model. Finally, an ‘ad hoc’ compensation formula is obtained and demonstrated.

In the state of oil-film instability coupled with rub–impact, the vibration signal of rotor-bearing system generally presents the weak non-linear frequency modulation (FM) features. In order to get a deep insight into the complicated FM phenomenon, the mechanism analysis is carried out on the motion model of non-linear Jeffcott rotor in oil-film instability coupled with rub–impact fault. The method of directional cyclic demodulation is proposed to extract the weak FM information embodied in the strong oil-film instability vibration. In this method, the directional cyclic autocorrelation density (DCRD) is adopted to infuse the information of two-directional vibration signals, and then is sliced along the cyclic frequency axis. The FM features and rotor motion direction are extracted from the slice of DCRD. Then the experimental research on the rotor-bearing system demonstrates the validity of the proposed method.