M. Teguar

Influence of discontinuous pollution width on the surface conduction. Frequency characteristics of the leakage current

In this report, we have examined the influence of the discontinuous pollution layer width on the behavior of a laboratory plan model on which we reproduce the surface state of the 1512L insulator greatly used in Algerian desert areas. The investigations were carried out by analyzing the leakage current magnitude, the phase angle current-voltage, the flashover process and leakage current characteristics. Because the recorded current waveforms include too many distortions, we have elaborated a numerical tool treating the leakage current signal allowing one to determine its frequency spectra using the discrete Fourier transform. The phase angle is determined from voltage and current phase spectra or also from the angles of their fundamentals.

Elaboration of novel image processing algorithm for arcing discharges recognition on HV polluted insulator model

Insulator flashover under pollution is one of the most important problems for power transmission. Occurrence of flashover is preceded by discharges propagation. This paper is dedicated to monitor discharges activity through arcing discharges pattern recognition using a combination of efficient image processing and classification algorithms. Images are extracted from recorded videos of flashover process over a plane model insulator under various contamination levels. Then, an algorithm is proposed and tested over a large image database. This algorithm processes in four stages. First, Otsu image segmentation algorithm is initially applied on images. Next, morphological filtering by combining erosion and dilation operations is computed to eliminate unwanted noises such as light reflections on the insulator model. Afterwards, connected components on filtered image are labelled enabling the calculations of four important morphological indicators consisting in the number of the connected labeled components (Nl) and the number of pixels, the length and the width of the largest connected component region (Np, L and W respectively). These indicators characterize different properties of discharges activity and are used as an input of three well know classification algorithms (Knn, Naïve Bayes, Support Vector Machines) to distinguish between the presence or not of arcing discharges on the insulator surface. This paper introduces image processing as an efficient and fast tool for discharges activity analysis and insulator flashover monitoring. The proposed methodology dispenses the heavy instrumentations and tedious processing of conventional laboratory tests.

Minimization of Grounding System Cost Using PSO, GAO, and HPSGAO Techniques

In this paper, three metaheuristic techniques have been developed to propose a safe and economic grounding system for the future power plant of Labreg situated in Khenchela City (400 km east of Algiers). The corresponding algorithms have been elaborated using particle swarm optimization (PSO), genetic algorithm optimization (GAO) and hybrid particle swarm genetic algorithm optimization (HPSGAO). The aim is to minimize the cost of the considered grounding system basing on the optimal decision of its construction and geometrical parameters in accordance with the security restrictions required by the ANSI/IEEE Standard 80-2000. A new mathematical model has been proposed for the cost function. This later includes the number of conductors, conductor dimension, grid depth, number of rods, length of rods, total area of excavation, and revetment. The results show that the HPSGAO technique presents lower values of the cost than those obtained using GAO and PSO methods. The good accordance between HPSGAO technique safety parameters and those of the CYMGrd code confirms the efficiency of the proposed algorithms.

Recurrence quantification analysis as a novel LC feature extraction technique for the classification of pollution severity on HV insulator model

Recently, Recurrent Plot (RP) was introduced to study Leakage Current (LC) for polluted insulator performance monitoring. Based on complex graphical representations, RP only provides a qualitative overview of the insulator state. To overcome this issue, we present in this paper a novel technique, named Recurrence Quantification Analysis (RQA) able not only to indicate RP structures, but also to quantify LC dynamics during the contamination process. RQA is introduced to investigate RP structures, quantify LC dynamics and extract features from LC waveforms for polluted insulator monitoring and performance diagnostic. For this purpose, LC acquisition is firstly carried out on a plan insulator model uniformly polluted with saline solution. Eight RQA indicators are presented to investigate LC waveforms under various pollution conductivities. Finally, mean values of RQA indicators are proposed as input for three well-known classification methods (K-Nearest Neighbors, Naïve Bayes and Support Vector Machines) in order to classify the contamination severity into five classes. Results show excellent correlation between RQA indicators and the pollution severity level.

Optimal design of corona ring on HV composite insulator using PSO approach with dynamic population size

This paper deals with the use of corona ring at the HV end fitting for improving the electric field and potential distributions and then for minimizing the corona discharges on 230 kV AC transmission line composite insulator. A single corona ring is installed at the energized end side. Three-dimensional finite element method (FEM) software is employed to compute the electric field. As the performance of high voltage insulator strings closely depends on designs and locations of corona ring, the effects of the corona ring radius, the ring tube radius and the ring vertical position are examined. The minimization of the electric field necessitates the optimization of corona ring. For this purpose, new nonlinear mathematical objective function linking the electric field strength to the corona ring structure parameters is established. The optimization problem is achieved by minimizing the objective function using a modified particles swarm optimization (PSO) algorithm with a dynamic population size. The algorithm adjusts the size of population for each iteration. Based on the average value and the best solution of the objective function, we propose a new mathematical model to update the population size. This algorithm enables the population size reduction leading to computing time decrease. According to the results, FEM-PSO hybridization technique could be very helpful in optimization of corona ring design.

Prediction of polluted insulators characteristics using artificial neural networks

In this paper, we propose three prediction algorithms using the artificial neural networks to generalise some characteristics describing the electrical arc propagation on polluted insulators. For that purpose, three Radial Basis Function Gaussian (RBFG) networks with one output have been elaborated. The difference between these configurations consists in the nature of the input and output units. The chosen networks are trained by Random Optimisation Method (ROM). A discussion to determine the best configuration is presented.

Investigation into the dissipated energy under accelerated thermal aging in PVC/B used in low-voltage cables insulation

Due to their excellent insulating characteristics, polymer materials are widely used in electric power transmission and power cables. However, the thermal stress is one of the most severe service constraints that can lead to the reduction of insulating polymers lifetime. In light of this, an experimental study on polymer samples was carried out to investigate the impact of the accelerated thermal aging on the dissipated energy through the insulating material. In this study, polyvinyl chloride (PVC, class B or PVC/B), used as electrical insulation in low-voltage cables, was chosen as the studied material. Accelerated thermal aging on circular shaped samples of PVC/B was performed at two temperatures, 80°C and 120°C, during 3024 hours (126 days). The measurements of the cumulative charge were carried out in order to follow the evaluation of energy at different aging stages and for five AC applied voltage levels ranging from 3 kV to 12 kV. The variation of mechanical characteristics as well as the evolution of dissipated energy were examined and analyzed. The investigation results show a significant increase of the dissipated energy with thermal aging due to material degradation. This increase was clearly observed at 120°C. Furthermore, a good correlation between the mechanical properties and the dissipated energy of the material has been found. Through this paper, the dissipated energy and mechanical properties have commonly proved to be effective to evaluate the aging level of insulating materials, which can be used to assess the conditions of low-voltage cables operating.

Effect of space charge layers on the electric field enhancement at the physical interfaces in power cable insulation

This paper intends to investigate the effect of two vented water trees w1 and w2 growing simultaneously from both conductor and insulation screens of medium voltage cable in the presence or not of space charge, on the electric field distribution. +12 kV DC voltage has been applied. Such simulation has been implemented under Comsol Multiphysics® environment using the finite element method. Particular interest is assigned to the effect of the polarity, density and layers thickness of the space charge as well as to the behavior of this charge initially accumulated at water trees tips. Note that for the polarity influence, the four polarities configurations related to the space charge accumulated at w1 and w2 have been considered. As results, the electric field enhancement at the semiconductor layers especially close to the water tree defect is strongly dependent not only upon the relative permittivity distribution inside water trees, but also on the amount, density and layers thickness of the space charge. In the absence of space charge, we show that, with regard to the inhomogeneous (linear and parabolic) distribution of the permittivity, the homogeneous one causes much more local enhancement of electric field at the trees tips. Moreover, the electric field distribution depends on the geometrical parameters (length and width) and shape of trees; the spherical form engenders a higher electric field than elliptical one. In addition, the association of the space charge could lead to the initiation of the electric trees even at lower voltages. Furthermore, the initiation of electrical trees from the physical interfaces is more probable in the case of opposite polarities especially for negative-positive configuration. Such electrical trees start not only from the tip but also from the water tree root (interface of treed region, un-treed one and semiconductor) which is particularly more vulnerable than inside.

Analysis of the total alternating current through insulating polymers under accelerated thermal aging

This work is devoted to analyze the alternating dielectric current flows through polymeric materials used in electrical cables insulation. The insulating compound based on poly (vinyl chloride) (PVC/B), used as electrical insulation in medium and low voltage cables manufactured by the electric cables factory CABEL of Algiers (Algeria), was chosen as the studied material. Accelerated thermal aging on circular shaped samples of PVC/B was performed at two temperatures, 80°C and 120°C, during 2016 hours (84 days). Spectral analysis of the obtained current waveform parameters, such as magnitude and harmonic content as indicated by the total harmonic distortion (THD), were analyzed using fast Fourier transform (FFT) method at different stages during aging time and for five levels of AC applied voltage, ranging from 3 kV to 15 kV. Through this work, the study of the current waveforms offers significant information about the degradation level of the material, which can be used for the diagnostic of electrical cables.

Hybridization of modified particle swarm optimization with gravitational search algorithm for solving optimal power flow including wind generation in isolated Adrar region

This paper proposes a new hybrid particle swarm optimization with gravitational search algorithm to solve the economic/environment optimal power flow dispatching incorporating wind power generations into the isolated Adrar Algerian power system. Taking into account the intermittent of the wind speed, the maximum probable active wind power generation is estimated by computing the wind speed carried maximum energy. The simulation results obtained from the proposed algorithm shows that this algorithm is capable to give higher quality solutions to solve a real optimal power flow dispatching problem with a fast convergence.