Electrical insulation of high voltage (HV) power equipment/apparatus plays very important roles in the sound functioning of power systems. Examining the insulation condition through partial discharge (PD) measurements has considerable importance as the presence of PDs in any HV systems stands for a sign of defects and degradations in electrical insulation. Generally, the PD measurements are performed with a supply voltage of normal power frequency (PF-50/60 Hz). As an attractive alternative, the PD measurement with a very low frequency (VLF–1 Hz or lower) applied voltage has emerged as a powerful diagnostic tool. A PD event is a random physical process, it depends mostly on the availability of free electrons that triggers the PD and the presence of space charge usually originated after a discharge. As the discharge characteristics vary with the supply voltage frequency; thus, the existing interpretation knowledge at 50 Hz may or may not be directly applicable to other test frequencies, particularly in the VLF range. Therefore, to provide a general insight, this paper presents various diagnostic aspects of PD measurements, and at the end, various discharge sources (e.g., void, surface, and corona) and their behaviours under varying the test voltage frequencies are discussed in detail.

This study presents a comparative study between two electromagnetic inverse methods based on electromagnetic time reversal (EMTR) technique and genetic algorithms (GAs) for radiating sources characterisation in the near field (NF). Indeed, frequency-inverse methods reveal insufficiencies in transient radiations study. For instance, it leads to a repetitive process for multiple distinct frequencies. To overcome the frequency method limitations, EM inverse method in time domain (TD) successively based on GA and EMTR technique are implemented using analytical equations governing equivalent dipoles radiations. The performance of the two methods is compared in terms of complexity, accuracy, and calculation time. A TD measurement test bench is given using the NF scanning technique. Experimental results confirm that both methods are efficient and provide adequate equivalent models. Nevertheless, GA-based method depends on simplifying assumptions and thus the convergence is not always guaranteed. Therefore, EMTR-based method is more suitable, particularly for high switching frequencies in electronics systems.

The analysis of adjacent grounding systems under lightning currents which is responsible for many safety problems to human beings and damages to devices is very important. In this study, the behaviours of such grounding grids under lightning conditions which are not well documented in the literature are analysed using the multi-conductor transmission line method in a two-layer soil model. To achieve this goal, the expressions related to the study of a single grounding grid extracted from the recent study of the authors are developed to be appropriate to the analysis of adjacent grounding systems under lightning currents. Also, through the representation of the connectivity matrix, the analysis of the adjacent grounding grids with any size and degree of complexity is facilitated. Furthermore, the behaviours of the adjacent grounding grids under different lightning and soil characteristics are examined and some conclusions are derived.

Suppressing the background noise of partial discharge (PD) is one of the key issues for accurately diagnosing the state of electrical equipment insulation. To solve this problem, this study proposes a new denoising method based on frequency spectrum clustering and local mean value decomposition. First, the K-means clustering is employed on the frequency spectrum to pick out narrow-band interference frequencies. Next, the PD signal with white noise is decomposed by local mean decomposition into different product function components, and the components contain more information about time–frequency than the intrinsic mode functions originated from empirical mode decomposition. Besides, the adaptive threshold is utilised to eliminate white noise in the components. Finally, the denoised PD signal is synthesised by these denoised components. The proposed method and three traditional methods are applied to simulated and field-detected noisy PD signals, respectively. The results of the evaluation indicators confirm that the proposed method is better than the existing PD denoising methods.

The first 500 kV AC cross-linked polyethylene (XLPE) cable in the world has been installed in China in 2019. The insulation performance of insulation material under the electro-thermal stress is the basis for its service life. At here, the AC breakdown voltage values and the breakdown time of the 500 kV AC XLPE submarine cable insulation material under the electro-thermal step stress was analyzed. The lifetime prediction accuracy of a new proposed model was compared to the classic FALLOU, SIMONI/RAMU and CRINE lifetime model. Results show that the AC breakdown strength and lifetime of the XLPE samples increase slowly at low temperatures (40–65°C) and decrease rapidly at high temperatures (65–85°C). The lifetime prediction error of the classic FALLOU, SIMONI/RAMU and CRINE models present that their fit goodness cannot meet the accuracy requirement. The new lifetime model using stepwise regression method could optimize the combination of variables, which considers the coupling effect of electrical and thermal stress. The evaluation error of the new proposed model is better than the FALLOU, SIMONI/RAMU and CRINE model, which is suitable for analyzing the lifetime of the AC 500 kV XLPE submarine cable insulation material.

An improved model for the motion dynamics of a metallic particle located in the non-uniform electric field area in the gas insulated system is proposed. To represent the special area, a diverging conducting electrode is used in this study. Based on the fluid mechanics theory, the forces imposed on metallic particle are first developed. The motion process is then divided into two modes, i.e. the particle rolls on the electrode surface and moves in the gap. The collision and reflection processes between the particle and the electrode are crucial to the motion, and they are fully considered in the proposed model. The trajectory of the particle under different voltages is obtained. The evolution of metallic particle is divided into four stages, and it is featured by four quantities, i.e. the critical jumping point, the minimum horizontal position, the falling point, and the motion time. The characteristics for each stage are analysed, and the sensitivity analysis of the quantities are performed. The impacts of the applied voltage, the particle radius, the initial position etc. are discussed. The results provide guidance for particle trap design.

Periodic boundary conditions are a set of boundary conditions that are often used to simulate large periodic structures by analysing an elementary cell. To enforce these boundary conditions over the side surfaces, the classical method requires identical meshes on opposite faces. This condition is not always easy to satisfy for arbitrary meshes. In this study, the authors introduce a new method to impose the periodic boundary conditions on an arbitrary mesh in the finite-element method using the second-order Whitney elements. This method is applied for computing the magnetic induction and it is based on two steps. The first one consists in expressing the magnetic induction flux through a facet (triangle) on a face as a function of the flux of the associated facets on the opposite face. In the second step, the periodic relations are introduced in the finite-element system. To show the effectiveness of the proposed method, the numerical results are presented and compared with those of the classical method.

Ethylene–propylene rubber (EPR) cable is the most commonly used type in high-speed railway. Several flashover accidents take place in cable termination in an extremely cold environment. In this study, EPR cable terminations were tested in a simulated low-temperature system with varied applied voltages. The results showed that the differences in elastic modulus and free space volume between EPR insulation and stress control tube (SCT) in a frigid environment would lead to structural defects between them. Damages on the EPR insulation occurred in the form of flashover point when the ambient temperature declined to −30°C and below, with the growth rate of discharge and resulting extent of damage across the EPR/SCT interface being non-linearly related to ambient temperature. Besides, the partial discharge (PD) initial voltage and PD extinction voltage under low-temperature conditions reduced by >40% compared with those at 20°C. The flashover probability of EPR terminations increased significantly, and the shape characteristics of PD patterns have also changed obviously at low temperatures. It can be verified that under the high-voltage and low-temperature conditions, the EPR/SCT interface is prone to organisational mismatch, which will lead to the PD phenomenon and seriously affect the stable operation of EPR cable terminations.

Grounding grid is an important process in design substation and power plant that makes a safe and reliable power system. It is therefore necessary to optimise the design of the grounding network, and to seek to minimise costs. To this effect, this study deals with a new method based on multi-objective particle swarm optimisation (MOPSO) to find optimum grounding grid design for a new 220 kV power plant with substation based in Adrar (south of Algeria). First, the authors present a contribution of a generalisation of methods using one objective function or cost function of the grounding grid with constraints of the grounding resistance like the step voltage and touch voltage and ground potential rise, accordingly to IEEE Std.80.2013. The main advantage of the proposed method is the simultaneous location of all optimal solutions on only one analysis. The problem is while transformed to multi-objective problem, and the evolutionary algorithms proved to be particularly effective in solving this type of problem. In this study, the authors present also a new objective functions or cost functions that are developed to distinguish between the construction and the electrical cost functions. The four objective functions obtained are minimised by MOPSO to determine the optimal solutions.

Transformer oil is widely used in high-voltage transformers as a cooling and insulation medium. Electrical and thermal stresses expose transformer oil to degradation, which may produce dissolved decay products (DDPs) that are partially adsorbed on the insulation paper and accelerate the degradation of oil and paper. An evanescent field D-shaped plastic optical fibre (POF) sensor was fabricated using the side-polishing technique to detect DDPs in transformer oil. A laser light source and power meter were used in the prototype to measure the output power of the POF sensor. The measurement of DDPs was conducted on seven samples of insulating oil collected from the field. The sensor performance was evaluated based on different sensing areas, and the sensor sensitivity was measured. Results show an excellent correlation between the output power and DDPs. A correlation analysis was conducted amongst sensor output power, transformer oil refractive index and area under the absorbance curve. The performance of the sensor demonstrates improved linearity and sensitivity of 97.49% and 26.6779 µW/RIU, respectively. The POF sensor is easily fabricated, low cost and can be used for real-time monitoring of high-voltage transformers.

High-resolution algorithms to estimate the depth of near-surface interface using ground-penetrating radar (GPR) can provide a measurement of thin to thick top layer using synthetic data for surface-coupled antennas. In practice, the air-coupled antenna configuration in the target depth estimation needs to determine the air-gap distance between the antenna module and the surface. In this study, the authors present an improved approach of estimating the antenna height for measuring thin to thick top coal layer using the high-resolution algorithms. In GPR, backscattered echoes are generally correlated in nature. In order to apply high-resolution algorithms, the authors use two improved spatial smoothing techniques for fighting against the correlation between echoes. Here, in the existence of air–coal–shale–clay and air–coal–shale–coal interface, step frequency continuous wave GPR is used to measure the thickness of the coal layer. Simulation results on the antenna height estimation using synthetic data models, full-wave model and plane wave model are shown to assess the estimation algorithm's effectiveness.

Partial discharge (PD) investigations can identify and localise incipient failures in power transformers early, thus avoiding considerable financial losses. The feature extraction of PD signals is a fundamental step for the development of such location techniques since it directly influences the performance of a location method. This study presents a detailed comparative analysis of four traditional approaches for the obtaining of attributes towards a better set of signal features for the location of PDs. The approaches were critically compared regarding their ability to locate experimentally generated discharges between adjacent layers of a prototype winding. In order to perform such analysis, a localisation structure based on logistic regression models was elaborated, capable of determining both layers and sections of the winding affected by PDs and easily applicable in practice. The results show energy features of wavelet coefficients, obtained through the decomposition of high-frequency current signals acquired at the winding endings, achieve better performance in the PD localisation, accurately indicating discharge occurrence points among layers and sections of the winding.

The proposed liquid level transmitter using a force resistive sensor as a secondary sensor is simple, cost-effective, and applicable for all types of liquid. The force resistive sensor is located at the bottom of a liquid measuring tank. The pressure exerted by the liquid height on the measuring tank changes the force resistive sensor's resistance. In the long term application, due to the creeping behaviour of force resistive sensor, the proposed level transmitter has low repeatability, hysteresis, and non-linearity. In this study, the artificial neural network (ANN) has been used to eliminate the hysteresis and non-linearity present in the proposed liquid level transmitter. The performance of the proposed technique has been experimentally verified. The hysteresis and non-linearity error has been decreased from 7 to 0.89% of full-scale observation (FSO) and 9 to 0.14%, respectively.

Ever-increasing energy demands and limited right of way over land motivates the adoption of six-phase power transmission. However, the wider recognition of six-phase transmission necessitates the development of a reliable protection system. Soaring assimilation of non-linear loads has complicated the protection task due to the intrusion of harmonics. This work aims at imparting necessary protection to six-phase transmission systems with immunity against harmonics. The issue pertaining to harmonics and sensor noise-induced non-linearity in the signal being fed to the protective relays has been addressed by modelling the current–voltage profile using a non-linear autoregression approach. Conventional relays are known to malfunction during non-linear loading and noisy measurement. In this context, an adaptive window-based approach has been employed to capture the non-linear dynamics, followed by mapping the model coefficients with the state of the six-phase system using decision trees. The inclusion of parameters in the non-linear auto regressive model for representing harmonic intrusion and noise imparts necessary robustness to the proposed protection scheme against non-linear loading and noisy sensor measurement. The appropriateness of the non-linear autoregression-based scheme has been tested for varying fault scenarios by considering wide variation in the fault attributes, non-linear loading, and noise level in the sensor measurement.

This study aims to predict the flashover voltage (FOV) of silicone rubber (SiR) insulators. Accordingly, it benefits from two methods, including an artificial neural network (ANN) model and a FOV gradient fitting model. The FOV and leakage current (LC) tests are carried out on one un-aged and three aged specimens under uniform and longitudinal non-uniform pollution circumstances. The proposed ANN model is designed based on equivalent salt deposit density (ESDD), pollution non-uniformity degree, aging time, LC first harmonic magnitude , and total harmonic distortion. Furthermore, a FOV gradient model is proposed based on ESDD, , and creepage distance. To validate the proposed models, the FOV and LC tests are conducted on two different types of SiR insulators. Then, the predicted FOV from the ANN model and calculated FOV from the voltage gradient model are obtained. The results indicate that the relative errors of the ANN model and FOV gradient fitting model are <6.4 and 7.3%, respectively.

Identifying problems in insulators is a task that requires the experience of the operator. Contaminated insulators generally do not represent a system failure, however, due to higher surface conductivity, they may suffer from electrical discharges and may result in irreversible failures. The identification of possible failures in inspections can help to forecast faults to improve reliability in the power grid. Based on this need, this article presents a study on fault prediction in distribution insulators, through a laboratory evaluation in a contaminated insulator, where 13.8 kV (root mean square) was applied considering an ultrasound detector connected to a computer for data set acquisition. In the sequence, a time series prediction, using a hybrid deep learning technique defined as wavelet long short-term memory (LSTM), was performed. The hybrid LSTM was proposed considering feature extraction through the wavelet energy coefficient. Finally, for a complete evaluation, deeper LSTM layers were included, and both the training method and the hardware configuration were evaluated. The wavelet LSTM algorithm showed interesting accuracy results when compared to classic prediction algorithms like the non-linear autoregressive exogenous model.

Envelope analysis is a dominant approach in detecting modulated fault signals in rotating machinery. The Hilbert transform is a popular method used to obtain envelopes. However, envelopes based on the Hilbert transform are only suitable for narrowband signals. Signals are usually filtered before envelope demodulation, which leads to the challenging issue of filter selection. A modulated fault signal detection method using the upper and lower envelopes of the signals is proposed. This method can demodulate the modulated fault signals directly from the raw data, which can include wideband and narrowband signals. The proposed method uses a simple algebraic operation instead of a transform function, so it is convenient in practical applications. It is tested with some simulated signals and some real-measured data. The test results show that the method can effectively demodulate a modulated fault signal directly from the raw data.

The following study investigates the use of a coaxial transmission line for determining the properties of powdery dielectric materials (1–10 GHz). Four powdery materials with dielectric constants ranging from 3.5 to 70 (SiO₂, Al₂O₃, CeO₂, and TiO₂) were experimentally investigated at varying volume loading fractions. Powder particles were mixed with a paraffin matrix and properties of the powder were analysed using ten mixing equations to verify their accuracy. These powder-paraffin composites were also modelled at varying volume loadings for comparison with experimental data to gain a better understanding of the interactions between the different phases. The optimal volume loading fraction was determined to be 10% for all powders tested. A metric for selecting the most well-suited mixing equation was proposed that involved taking the ratio of the particle dielectric to that of the matrix. This study ultimately provides guidance for experimentally measuring the dielectric properties of unknown powdery materials that have applications for new devices that utilised powder-based dielectric materials.

The DC conductivity of insulating oil is key to converter transformers, in which AC and DC electrical fields simultaneously exist. Research on the influence of the electric field on oil conductivity can optimise the insulation design of converter transformers. Although numerous studies have been conducted on the conductance mechanism of non-polar liquids, the explicit mechanism and properties of oil conductivity under a high electrical field remain unclear. This study developed an optimised conductance model considering charge carrier elimination, dissociation, and charge injection process. Thereafter, the authors chose three types of oils for converter transformers and measured the variations in oil conductivity and ion mobility under different electric fields with 0–10 kV/mm range. The result indicates that ion mobility will increase under a high electric field owing to the EHD effects. The conductivity of the insulating oil follows a U-shaped pattern with an increasing electric field, thereby generally matching the optimised theoretical model. Therefore, the decrease in conductivity is mainly the result of the elimination process of free ions, whereas the increase is the result of the injection process that occurs on the electrodes.

Voltage endurance coefficient (VEC) is a parameter used in the design of withstand test and insulation thickness of cross-linked polyethylene (XLPE) cables. Thermal ageing is inevitable in operation of cable, but the thermal ageing effect on the VEC is rarely considered. In this study, the trend of VEC of XLPE films under DC voltage during thermal ageing is investigated by 120 and 135°C thermal ageing experiments. The results show that, after 14 days of 120 and 135°C thermal ageing, the VEC decreases from 20.74 to 7.05 and 3.93, respectively. To understand the effect of thermal ageing on the VEC, the VEC is described as a function of the free energy increment which is proportional to the degree of polymerisation (DP) and the electric field. A simulation calculating the free energy increment of several molecular chains is conducted to confirm the proportional relationship between the free energy increment and the DP, the electric field. Based on the function of the VEC, a predicting method for the VEC under thermal ageing is developed. The experimental results of 120 and 135°C thermal ageing are used to confirm the preciseness of the proposed predicting method.

A new research on characterising the dielectric constant and loss tangent of thin-film material with a convenient technique based on simulation is proposed. The authors utilise a set of full-wave electromagnetic simulation data to retrieve the dielectric properties from the measured data. More specifically, a set of simulation data is collected from a commercial full-wave simulator (Ansys HFSS) by solving the electromagnetic model the same as the measurement set-up which employs a grounded coplanar waveguide with a thin film placed on the top surface. The measured transmission coefficients (S21) are iteratively compared with its simulation data to estimate the dielectric constant and loss tangent using an efficient comparison algorithm. For adaptive data acquisitions and comparisons, they have developed a MATLAB code using hfss-matlab-toolbox that makes the whole process quick and automatic. They have successfully retrieved the dielectric properties of four different sprayed thin films at 8, 10, and 12 GHz, and observed that the dielectric constant and loss tangent strongly depends on their compositions, thickness, and frequency.

Using the vibration signals, the facial tissue characteristics may be utilised for the detection of nasal diseases. In this study, the tissue characteristics were specified by applying constant frequency vibration signals to the facial tissue. The temperature changes caused by an external vibration source applied to the human face were investigated using thermal imaging techniques. Vibrations were applied to the forehead, right cheek, and left cheek regions of the facial tissue. Temperature differences were examined using dynamic and static analyses. Temperature increases of 500, 562, and 606 m°C were acquired in the F region, MR, and ML regions, respectively. While the F region has the lowest soft tissue thickness and temperature difference, the ML region has the highest values. The temperature difference between ML and F regions was acquired as 106 m°C. The temperature distributions of the facial area indicate that the change of the temperature is lower in the regions where the soft tissue thickness is low, and higher in the regions where the soft tissue thickness is high. Therefore, the thickness information about the soft tissue can be provided from the temperature distribution of the facial area after the application of the vibration signal.

In the present day, there is an enormous demand in the supply of energy to all users. Since the voltage stability for the distribution system is not steady under any circumstances, therefore, to solve the problem of voltage instability the entire distribution system must simplified properly. Thus, some active support is provided for balancing the demand for electrical energy supply. Hence, the problem of voltage instability has been solved by considering phasor measuring units (PMUs) using antlion optimisation proposed in this study. The cost of PMU has been analysed along with other factors such as observability for effectively placing the PMUs with the identification of the weakest node. The problem is solved by using a non-linear model and the effectiveness of the proposed approach is tested using IEEE-15, IEEE-33, IEEE-69 Radial Distribution Systems and Croatia distribution grid. The result shows that the suggested algorithm is more effective in getting the optimal PMU placements considering multi-objective. Hence, the maiden state estimation values for distribution topologies are used.

The proposed training system helps the examined people to generate motor images based on the example maps of the activity of neuronal cell fractions presented to them. The study involved 16 students at the Laboratory of Neuroinformatics and Decision Systems of the Technical University of Opole. The group was divided into two equal subgroups, one of which was acquainted with the operation of the system, while the other – considered as a control – was not. Electroencephalographic signals were recorded when users were imagining the upper limb movement for two subgroups before and after the imagery training in order to verify the introduction of the proposed training system. The area used for data acquisition as part of the monitoring session implemented with the use of the Emotiv EPOC Flex device is a sensorimotor cortex. As it results from the carried-out literature analysis, it was the first attempt to use the 32-channel Emotive EPOC Flex device in the scope of the training system construction in the field of motor imagery.

The principle of centrifugal force produced by flowing fluid through the semicircular section of a pipe line is not sufficient to explain the characteristic of the centrifugal force type flow transducer developed from this principle. In this study, a modified form of this flow transducer is developed using a modified force sensing technique. This modified force principle explains the characteristic of the flow transducer to a very good extent. The modified force produced in the modified transducer system is composed of four components namely, centrifugal force, momentum force, damping force and restoring force. These forces produce the identical downward and upward movements of the lever ends of a common balance which is initially made horizontal at zero flow by using similar sensing U-tube and dummy U-tube. These movements are sensed by two identical inductive sensors. The static characteristic equation of the prototype unit of the transducer using the modified force sensing technique is derived mathematically in the study. The equation coefficients are calculated from the design parameters and are found to be matched with the same obtained from the average characteristic of repeated experiments performed under the same laboratory environment. Thus the proposed modified model appears to be established.

The proposed study compares the electrical, thermal and mechanical performances of thermally aged cellulose pressboard material impregnated in mineral oil, synthetic ester fluid and mixed oil. The electrical insulation characteristics of oil-impregnated pressboard (OIP) are studied by means of surface discharge inception voltage (SDIV) using an ultra-high frequency technique and surface potential measurement analysis. It indicates that OIP aged in mineral oil has higher surface potential due to higher charge trap density compared to that of the mixed oil and synthetic ester fluid. Mechanical and thermal characteristics of the aged OIP are studied by means of tensile strength measurement and thermo-gravimetric analysis, respectively. The change in the chemical composition of OIP is studied by means of laser-induced breakdown spectroscopy, which indicates lower plasma temperature with mineral oil-based OIP indicating higher degradation state. To further understand the microscopic structure of the thermally aged OIP in different oils, scanning electron microscopy and X-ray diffraction studies have been performed. The pressboard thermally aged in synthetic ester fluid and the mixed oil has better electrical, thermal and mechanical properties as compared with the pressboard aged in mineral oil.

Respiratory rate is an essential indicator of serious illness. Compared to heart rate or systolic blood pressure, its change is more evident, hence is a better means to discern stable patients from those at risks. In addition, the respiration rate is a crucial indication of sleep quality associated with sleep disorders such as obstructive sleep apnea. Oronasal pressure, as a clinical respiratory signal for sleep analysis, can be used in polysomnography both in labs of hospital and homes. Besides, it is often taken as a reference signal in research as opposed to the estimated respiration rate. This study aims to provide an automated respiratory rate estimation system with signals taken from oronasal pressure transducer that can cope with noises and is adaptive to various respiratory frequencies. A robust approach is presented here that employs Ensemble empirical mode decomposition method to remove signal noise, together with Butterworth band-pass filter to obtain the breathing frequency by means of zero-crossing. Among 97.6% of the test data, the study yields a root mean square error of 1.031. Compared to other methods, the current approach provides a more accurate respiration rate estimation in the application of orinasal pressure to sleep analysis.

This study proposes a new approach to hybrid a circuit and field analysis in order to evaluate the susceptibility of a low-noise amplifier against electromagnetic interference. The proposed method employs an equivalent circuit model for active elements and a full-wave time-domain analysis for the passive parts. To this end, two methods, finite integrated technique and the method of moments, are combined through an innovative algorithm. The output of the suggested hybrid technique is an equivalent circuit model which predicts well the susceptibility of the illuminated low noise amplifier. To validate the model, measurements are performed in an anechoic chamber. The authors will show that the proposed method provides a satisfactory accuracy.

Water droplets on the surface of insulators can distort the electric field and cause the generation of surface partial discharge or flashover. In this study, the inception and the development of surface partial discharges on a 110 kV composite insulator were evaluated by using a solar-blind ultraviolet imager. Several experiments were conducted by using water droplets differing in volume, conductivity, and position on an insulator housing. The results showed that the corona inception voltage decreases with the increasing volume of the water droplets. The relative permittivity of the water droplet decreases with the increase of the conductivity and then reduces the electric field intensity and increases the corona inception voltage. Installing the grading ring can increase the value of the corona inception voltage by 38% at most. To investigate the influence of the water droplets on the corona inception characteristics of the insulator, the sheath and shed models were proposed according to the feature of the electric field distribution. By changing the parameters of the water droplets, the corona inception voltage, discharge position, and electric field were analysed. Furthermore, the flashover voltage of the water droplets is influenced by its conductivity, while the corona inception voltage by its relative permittivity.

The sweep frequency response analysis (SFRA) technique is based on measuring the power transformer electrical transfer functions over a wide frequency range to identify the abnormal areas prior to serious failure. This study presents the proposed diagnostic adjusted R-square technique to identify the transformer faults using the SFRA technique. The SFRA measurements are ranged up to and beyond 1 MHz. The proposed technique is used to calculate the relative factor for adjusted R-square coefficient between the actual data and new measurement data sets. The results of the proposed method are evaluated and compared with existing Chinese Standard factor DL/T 911-2016 and CCF factor of IEEE Std. C57.149™ Standard indicates that the suggested methodology is more reliable to identify and analyse the internal faults of the transformers. This technique is considered to be effective indicator to predict the internal physical condition inside the transformer, which moves the field forward.

Epoxy aluminium nitride (AlN) nanocomposites were prepared to understand the influence of thermal ageing on dielectric and space charge performance of the material. It is observed that the real relative permittivity values of epoxy AlN nanocomposites are higher than epoxy resin when wt% of AlN is >1 wt%. Also, the epoxy AlN nanocomposites depicted an increase in dielectric loss compared to the neat epoxy specimen. The space charge variations in the test specimens are analysed by adopting a pulse electro-acoustic technique. It is observed that the nanocomposites have lesser space charge in the bulk volume of insulating material compared with pure epoxy resin. Also, it is realised that the local electric field is less with nanocomposite material in both virgin and thermally aged specimens. The threshold electric field is observed to be lesser with epoxy resin compared to nanocomposites. Laser-induced breakdown spectroscopy (LIBS) analysis clearly indicates the reduction in plasma temperature with epoxy AlN nanocomposites compared to pure epoxy resin. Principle component analysis (PCA) has classified the nanocomposite materials having different filler concentrations from the pure epoxy resin, qualitatively based on their LIBS spectra. Thermally aged epoxy AlN nanocomposites are successfully classified from unaged nanocomposite specimens, using PCA.

Many catastrophes may occur due to the interference between the metallic pipeline and the high voltage overhead transmission lines (HVOHTLs). These problems exist due to the neighbouring between the HVOHTLs and the other infrastructures. Many types of research cover cathodic protection points, detailed description for the production of the AC voltage, and preliminary mitigation ways. Mainly potassium hydroxide-polarisation cells (KOH-PCs) have been applied to discharge this voltage to the soil. Based on the KOH-PCs electrical model introduced previously, this study investigates a novel mitigation technique, where the discharged AC voltage converts to DC voltage that is proper for the cathodic protection for the metallic pipelines. An integrated system consists of power electronic circuits and distributed intelligent controllers designed to discharge the AC induced voltage and use in the cathodic protection for the pipelines. Different controllers such as the artificial neural network, a fuzzy logic controller, and adaptive neuro-fuzzy inference system controllers have been implemented. Two key performance indicators have been investigated to show the superiority of these controllers, where the total discharged energy per annum from the pipeline to the soil, and the total saved per year .

The accumulation of insulator surface contamination is closely related to the distribution of flow field around the insulator. In order to study the unevenness of the insulator surface contamination, a three-unit lxy-160 insulator is selected. Based on the principle of fluid mechanics, the fluid movement state on the insulator surface is determined by the calculation of Reynolds number and boundary layer, then the flow field distribution around the insulator is obtained. On this basis, the artificial contamination test and numerical simulation are carried out to study the characteristics of contamination uneven distribution on the insulator surface. The results show that when the wind speed is 3–7 m/s and the particle diameter is 1–60 µm, there is obvious boundary layer separation phenomenon, and the flow state before the separation point is laminar, while the flow state behind the separation point is turbulent. From top to bottom, the degree of accumulation on each insulator is different, and the contamination on the windward and leeward sides are unevenly distributed in a fan shape. The increment of wind speed as well as particle diameter will aggravate the unevenness of the contamination.

The methodological background of the virtual element method is presented and applied to model permanent magnets via the Kikuchi formulation, considering both linear and non-linear magnetic permeability of the ferromagnetic regions. The authors examine several study cases: a permanent magnet in free space, a permanent magnet energising a ferromagnetic core, a four-pole permanent-magnet motor. In order to validate the proposed approach, comparisons with both virtual and finite element potential formulations are presented and discussed.