The AC and DC dielectric properties of hydrofluoroethers (HFE) [C₃F₇OCH₃] and fluorinated ketone (FK) [C₂F₅C(O)CF(CF₃)₂] have been characterised by dielectric spectroscopy and DC conductivity at different temperatures. Results show that DC conductivity and imaginary permittivity of both fluids are positively correlated with increasing temperature. However, the real permittivity decreases with increasing temperature. The breakdown voltages of HFE and FK at 295 K are ∼10 kV mm⁻¹. Reducing temperature is an effective method to increase the breakdown voltage of the FK coolant, but the breakdown voltage of HFE is less temperature dependent. Finally, as expected repeated breakdown had no significant effect on the AC dielectric strength of both liquids.

The microbial inactivation and specific energy of a pulsed electric field treatment system are dependent on the electric field distribution and treatment time since they have opposite behaviour in relation to these parameters, featuring a problem of multi-objective optimisation. This study proposes a computational methodology capable of providing Pareto optimal solutions for these two objectives, using a coupled electrical-thermal model, solved by COMSOL, which has been integrated to a multi-objective algorithm NSGA-II implemented in MatLab. The simulations were run for a computational design of experiment with the following variables: applied voltage, treatment time and the internal electrode radius (three levels for each one). In the post-processing analysis, the Pareto curves were plotted for two typical microorganisms of grape juice: E. coli and S. aureus, providing a set of solutions in terms of the log of the survival rate versus the specific energy. The methodology enables the decision maker to select the best solution from the Pareto curves as a function of a required microbial inactivation and energy features.

An axial magnetic field (AMF) plays an important role in the process of vacuum arc stabilisation during the current breaking process in the vacuum circuit breakers (VCBs) of the AMF type. To minimise the contacts erosion special attention should be paid to reach a possibly high value of the AMF density (between contact plates), especially in the outer electrode region. Various contact geometries are patented all over the world to improve the AMF distribution. Nevertheless, there is an issue which is not raised in the literature as yet. It is the mutual orientation (rotation) of the moving and fixed contacts. This orientation can have an influence on the AMF distribution. The above problem is analysed here numerically using Maxwell (ANSYS) software package based on the finite element method. The own (patented) contact design is considered in the analysis mentioned. However, the beneficial influence of AMF on the arc behaviour is well known for VCB designers, the explanation of this phenomenon is described (in the literature) rather seldom and very cursorily. Therefore, a simplified model accounting for the role of AMF in vacuum arc diffusion is shortly presented at the beginning of this study.

This research work presents the design of the electronics modules of Adam's Hand, a transradial myoelectric prosthesis based on an innovative mechanism which can actuate five three-phalanges fingers (15 degrees of freedom) with just one motor, instead of the five/six motors conventionally used in other prosthetic devices; moreover, the prosthesis uses two servomotors to actuate the wrist movements. Adam's Hand fingertips are provided with temperature and pressure sensors, while the user myoelectric signals are acquired wirelessly by means of the Myo armband, a wearable device provided with eight electromyography electrodes, a nine-axis inertial measurement unit, and a transmission module. These data are received through an HM-11 BLE module, connected to Adam's Hand custom PCB, which features an Arduino Micro board. This board processes all the data and drives the actuators by means of properly chosen drivers. A Raspberry Pi 3 board manages a touchscreen display – which can be used to visualise the gathered data – and sends them to a dedicate cloud platform, so that the orthopaedic technicians who take care of Adam's Hand users can monitor them in real time, thus improving their recovery during the rehabilitation period.

To solve the complexity of the conventional time-domain reflectometry method for locating minor cable ageing degradation, a frequency domain-based method for locating cable ageing degradation based on propagation coefficient spectrum is proposed in this study. First, the change pattern of cable input impedance spectrum in frequency-domain reflectometry is analysed to reveal the relationship between input impedance spectrum and propagation coefficient, and thus finds out the working mechanism of ageing degradation on propagation coefficient spectrum. Then, in the experiment, a vector network analyser is used to measure propagation coefficient spectrum and the inverse discrete Fourier transform is applied to locate cable ageing degradation. Finally, kurtosis analysis is performed on locating curves of different bandwidth and the upper limit of frequency of the testing signal is decided. Within a certain limit, the method proposed in this study can locate degradation with higher accuracy and resolution than several time/frequency-domain based methods currently adopted.

Empirical data is presented on the pulse-echo performance of poly-vinylidenefluoride (PVDF) ultrasound transducers monitored in-situ at temperatures in the range 50–130°C. Measurements were performed over a 5 h period beginning at the sensors’ initial exposure to temperature. A reduction in pulse-echo amplitude was observed at all temperatures in the range and was found to be proportional to temperature increase. Four different thicknesses of PVDF film were used for the trials and small differences in behaviour were observed between sensors constructed using each thickness. On average, the overall loss was found to increase linearly with temperature from a 16% drop in pk–pk pulse-echo voltage observed at 60°C to a 95% drop in performance at 120°C after 5 h. Rates of signal loss were found to follow a logarithmic decay, particularly at temperatures above 70°C where significant reductions were observed in the initial seconds/minutes following exposure to temperature.

Emotion is a most instinctive feeling of a human. Emotion classification finds application in brain–computer interface systems for the assistance of disabled persons. To recognise the emotional state, electroencephalogram (EEG) signal plays a vital role because it provides immediate response to every state of change in the human brain. Here, the utility of tunable-Q wavelet transform (TQWT) is explored for the classification of different emotions EEG signals. TQWT decomposes EEG signal into subbands and time-domain features are extracted from subbands. The extracted features are used as an input to extreme learning machine classifier for the classification of happy, fear, sad, and relax emotions. Experimental results of the proposed method show better four emotions classification performance when compared with the other existing methods.

Electrocardiogram (ECG) signal quality enhancement is a crucial task in the computer-based automated processing system. In this study, a dictionary learning (DL)-based sparse representation framework is presented for ECG signal enhancement through denoising. Unlike, traditional filtering techniques, the proposed method removes both low- and high-frequency noises for complete enhancement of the signal quality. The frequency localised DL-based sparse representation approach is applied to remove both baseline wander and power-line interference. The time-localised and signal characteristics based DL-based sparse representation scheme is employed for extraction of clean ECG components from white Gaussian noise and muscle artefact added noisy ECG record. Both qualitative and quantitative performance analyses are carried out using the Massachusetts Institute of Technology - Beth Israel Hospital (MIT-BIH) database, QT database and synthetic ECG signals. The efficacy of the proposed method is compared with the existing ECG denoising approaches using standard performance metrics: signal-to-noise ratio, root-mean-square error and percentage RMS difference. It is observed through the detailed study and analysis that the proposed approach outperforms the existing ones and can be served to further enhance the overall quality of ECG in a computer-based automated medical system.

This study presents a fault location algorithm (FLA) for series compensated transmission lines (SCLs). It is established based on synchronised voltages sampling and Thevenin impedance estimation from both ends of SCL. The method is based on the use of phasor measurement units technology which is aimed to be independent of current measurements. This method includes two subroutines for the faults located on the right-hand and left-hand sides of series capacitor (SC). Lumped modelling is considered for SCL with SC equipped with metal–oxide varistor (MOV) arrester. The non-linear behaviour of SC-MOV system is investigated in the analysis. The proposed current independent FLA has been thoroughly tested using signals taken from simulations. According to the results, the percentage errors for the fault distances estimation are in proper ranges.

This study demonstrates the accurate signal model to be used for fault generated instantaneous current signals containing decaying DC offset by considering initial loading conditions and response of obvious non-ideal current transformer (CT). The issue of CT core saturation and its impact on signal is evaluated. The comparative performance of existing DC offset estimation methods with modified DC part is discussed. Required modifications in existing least error square based estimation algorithms are proposed. The modified DC signal model is useful for applications such as more accurate phasor estimation, distance relaying and fault locations. Simulation studies are carried out in MATLAB/Simulink to demonstrate accuracy achieved by consideration of the proposed signal model.

The general method for identifying the partial discharge type in a power transformer is based on their fingerprints in the form of phase-resolved discharge patterns. In the case of multiple defects, traditional clustering methods can be applied for separation of active sources. However, such an approach is impractical for online real-time monitoring due to the very large data size. In this paper a new method using stream clustering is introduced. The method separates the active sources by processing the signal once it is captured, then only a synopsis of the discharge data is stored. Two stream clustering algorithms: Density Grids and DenStream are employed. Through measurements obtained from laboratory experimental setups (corona, surface discharge, transformer defect model) performance of the proposed algorithms are evaluated. It is shown that stream clustering method is able to separate the constituent components involved in the stream of a multi-source discharge signal without the need to store a large amount of information. The performance of the Density Grids method depends on a limited number of features that it can accommodate. In comparison, the DenStream method can capture more features which enable better separation of active sources at the expense of longer processing time.

The subject matter of the study applies to determining the possibilities and indicating the scope of application of the analysis of optical spectra emitted by basic forms of electrical discharge in insulation oil, recorded with the use of the optical spectrophotometry method. The main objective of the experimental works was to select a group of descriptors typical of optical signals generated in systems modelling electrical discharge on the basis of which it would be possible to recognise their forms. The study presents the results of measurements and analyses conducted under laboratory conditions for three systems modelling electrical discharge in mineral oil under various technical conditions. The results presented in the study are the initial stage of research aimed at determining the suitability of descriptors describing optical radiation emitted by electrical discharge for identifying the type of defect of insulation systems in high-voltage power devices.

Graphene has attracted much attention due to its advanced properties. In previous work, the relationship between temperature and the conductivity of epoxy-based nanocomposite filled with graphene oxide has been experimentally studied. To understand the charge transport behaviour, the space charge characteristics at different temperatures and field strengths are measured with an improved pulsed electroacoustic measurement system, which is designed for high-temperature space charge measurement. From the measurement results, epoxy resin (ER) filled with multi-layer graphene oxide (MGO/ER) shows suppressed charge migration while ER filled with single-layer graphene oxide (SGO/ER) shows a hetero charge accumulation, which is assumed to be caused by the partial reduction of graphene oxide to graphene. Compared to pure ER, the apparent mobility of the nanocomposites is smaller while the trap depth and number of trapped charges are larger, which is probably caused by the introduction of traps. In the simulation, the relationship between mobility, trap depth, trap density and charge distribution are firstly studied. Then the calculated values of mobility and trap depth are given to the parameters to compare the simulated charge profiles with experiment results. The simulation results agree well qualitatively with the experimental results, giving some support for the proposed explanations.

This article shows results of using surface impedances (Z _SURFACE) in 3D FEM linear model to calculate zero-sequence magnetising impedances (Z _0M) of 3-phase core-type transformers. Initially, results with and without Z _SURFACE are compared to obtain certainty about model validity. Compared results are magnetising reactances and active power losses in tank during Z _0M tests. Subsequently, results of 3D models with Z _SURFACE are compared with Z _0M measurements at different currents, to consider nonlinearity of tank steel. An equivalent permeability for tank steel is estimated for each test point, and accurate results from model are obtained for magnetising reactances. An approximate curve for this equivalent permeability is also found, as in a previous 2D method, and both curves are similar from each other. It is shown that active power losses in tank cannot be properly computed using these 3D linear models. This fact cannot be observed by previous 2D models and it indicates that active power losses in tank are influenced by other phenomena, which are not considered by these FEM models. Main contributions are the application of Z _SURFACE as a powerful tool to compute Z _0M, and an analysis of active power losses in tank which could not be performed by previous 2D models.

A three-dimensional (3D) finite-element analysis model is established based on the structural characteristics of ±1100 kV oblique-dry-type smoothing reactor, to optimisation of the external insulation configuration thereof by the Comsol Multiphysics. The electric field on the grading ring and insulators surface is calculated and analysed. The results show that the electric field is extremely uneven and the electric field strength of the outer layer of the rain cover and the grading ring connected with the lowest layer of the main body is the largest around the whole model. Accordingly, it is proposed to enlarge the diameter of the outer layer of the grading ring, reduce the layer numbers of grading ring on the rain cover, and reduce the smoothing layer numbers of grading ring outside the insulation pillar: this should make the electric field distribution of the reactor surface more uniform. The experimental platform was established in Beijing Changping ultra-high voltage test base and causal-comparative tests of setup were undertaken to compare the external insulation characteristics of the smoothing reactor optimised with the original. The experimental results demonstrate that the switching impulse voltage of the smoothing reactor increases and the external insulation performance of the smoothing reactor are thus improved.

The partial discharge (PD) in a void of epoxy solid insulation is a typical kind of PD behaviour, its occurrences may lead to complete breakdown of the insulation system. The microscopic process of particle movement is simulated here by using particle in cell-Monte–Carlo collision (PIC-MCC) method, which possesses great significance for researching typical discharge. The simulation results of void discharge and point discharge show detailed motion process and the Townsend discharge phenomenon. The PD current pulse waveform possesses similar trends of steep rising edge and gentle falling edge compared with Gaussian function. The behaviour of discharge events is influenced by many factors, such as electric field strength, void thickness, and polarity effect. Thus, the characteristics of PD are discussed and compared by adjusting these simulation parameters to find out internal connection and performance differences.

A novel approach for modelling the corona problem in the wire-duct precipitators using the finite difference technique integrated with multi-grid methods is adopted in this study. The multi-grid method is applied as a fast convergent iterative solution for the finite difference technique to solve Poisson equation especially on finer grids. Two schemes of the multi-grid method, mainly the V-cycle and the full multi-grid method, are adopted in the present study. Compared with Gauss–Seidel method, the above-mentioned schemes are successfully transcendent owing to timing performance. By using finer grids, the proposed algorithm allows to get a more accurate picture about the performance of the precipitators in the design stage without suffering from the excessive computational time. Accurate results for the potential and current density computations, closed to the previous published experimental measurements, are obtained in comparison with earlier numerical techniques for several design parameters of the precipitators. Finally, the effect of changing the effective ion mobility and the surface roughness factor on the voltage–current density is considered.

Electric field analysis around high-voltage insulators is with an extreme importance during the development of new polymeric insulators design. In this study, the authors combine the finite-element method (FEM) with the design of experiment method to investigate and describe the behaviour of textured silicone rubber insulators. First, a 3D FEM model of different silicone textured surfaces is developed. The maximum electric field is calculated taking into account various available patterns of hemispherical protuberance having different diameters. Then the design of experiment methodology is adopted to reduce the number of simulations and to give more significance to the results. Various influencing factors were considered in this stage. Finally, the analysis of variance is used to evaluate the contribution of the studied factors and their interaction on the total variation of the studied responses.