A. Beroual

Ecole Centrale de Lyon, Rhône-Alpes, France

Are you A. Beroual?

Claim your profile

Publications (185)152.78 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Gas insulated substations (GISs) are widely used in electrical power transmission and distribution systems. The presence of free and fixed metallic particles can initiate partial discharges (PDs) in GIS which can become a serious defect and reduce the reliability of GIS. The particle initiated PD characteristics depend on the particle size and position. Therefore, the PD characteristics can be used for the estimation of particle size and position on the spacer surface. Knowledge about the particle size and position are the important steps for the reliability improvement of the GIS equipments. This paper investigates the PD characteristics for fixed particle adhering to cylindrical shaped spacer in a simulated GIS. Length of cylindrical particles, their position on the spacer surface and gas pressure is varied to study the PD characteristics that are represented by PD fingerprints. Then these data are used for particle size and position identification. For this purpose, the use of linear support vector machine has been proposed in this paper to classify particle position and size based on the PD fingerprints data acquired at different SF6 gas pressures. It is shown that the proposed method was able to successfully estimate particles size and position at different gas pressures with an accuracy of 94%. Thus in order to improve the reliability of GIS, this approach could be considered as a potential method for particle position and size estimation in GIS.
    Electric Power Systems Research 11/2014; 116:391–398. · 1.69 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The presence of metallic particles has been recognized as a dangerous threat in gas-insulated substation (GIS). Such particles are initially free and move toward higher electric field regions such as triple junction i.e., spacer-electrode-gas interface. However, once these particles reach the spacer surface, they adhere to the spacer easily due to electrostatic image forces. From insulation point of view, the triple junction is the weakest point in GIS. The presence of such metallic particles on the spacer surface deteriorates the insulation strength. Thus, in order to improve the reliability of GIS, it is important to identify the size and the position of the particle adhering to the insulating spacer surface. One of the most promising methods to carry out such identification is by recognizing the partial discharges (PDs) provoked by such particles. This paper is aimed to discuss the particle size and position estimation by using the PD patterns and statistical analysis. The PD patterns were acquired using IEC 60270 method. Measurements were made to determine various PD signals caused by particle of different sizes at different locations on the spacer surface. The acquired PD patterns were characterized by a number of statistical parameters. The results show that the implemented technique could be used to distinguish between various particle sizes and positions at different SF6 pressures with a fairly high accuracy.
    The European Physical Journal Applied Physics 05/2013; 62(2):20801-. · 0.71 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The purpose of this paper is to study the critical breakdown voltage or U50 - corresponding to the 50% probability of breakdown for a single impulse application -of long air-gaps under positive and negative switching impulse voltages, using predictive dynamic models. The knowledge of this important parameter is of practical interest to the design engineer. The models previously developed by the authors are based on equivalent electrical network, gas discharge theories and physical laws. Various gap geometry and atmospheric conditions were considered. The U50, determined using the up and down method along with other important parameters, were compared to experimental data. Good agreements were found between simu lated and experimental results. The results obtained indicate that U50 prediction is possible, using the proposed models. Knowledge of the gap factor and weather conditions might help applying corrections to determine the breakdown strength under various conditions. These dynamic models might therefore be useful to estimate the required clearances of air gaps in the preliminary design phase over a wide range of geometry and some atmospheric factors; therefore reducing the required full-scale testing.
    IEEE Transactions on Dielectrics and Electrical Insulation 02/2013; 20(1):89-97. · 1.36 Impact Factor
  • M.E.-A. Slama, A. Beroual, H. Hadi
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper is aimed at the study of the influence of the chemical constitution of pollution on dc flashover discharge of high voltage contaminated insulators. It's shown that the type of salt and salt mixture has an influence on the critical currents for both polarities but doesn't affect significantly the critical voltages whereas the concentration of insoluble matters (Non Soluble Density Deposit, NSDD) has an influence on both critical current and critical voltage. The discharge parameters characteristics N and n depend on the chemical constitution of pollution, the concentration of NSDD and the polarity of voltage. It's also shown that the most important constituent of the discharge column are water vapour and air; and the transfer of metallic ion has no significant influence on flashover voltage.
    IEEE Transactions on Dielectrics and Electrical Insulation 01/2013; 20(2):401-408. · 1.36 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents an interactive computer package enabling to choose insulators used in polluted conditions. This is accomplished by integrating a self consistent dynamic model we developed in previous works and that includes the successive development of the arc on insulator surface based on an equivalent electrical network model and an analytic arc propagation criterion. This package enables to compute the different characteristic parameters of the temporal evolution of discharge (arc) propagating over polluted insulators (current and electrical charge, discharge length, potential, discharge propagation velocity, resistance of discharge channel and time to flashover). Numerous shapes of insulators are incorporated into the package. The package is capable of handling AC, DC and impulse voltages, in addition to different pollution severities. It constitutes a useful tool to choose insulation device for a given voltage system, and as a maintenance tool to determine the critical contamination level (in terms of pollution conductivity) that will cause flashover of insulator at the operating voltage.
    IEEE Transactions on Dielectrics and Electrical Insulation 01/2013; 20(4):1428-1435. · 1.36 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper is aimed at the study of aging behavior of cellulosic materials in different dielectric liquids under air and nitrogen atmospheres. Paper for copper conductor and high density transformer board were aged at 130°C up to 1128 h in sealed vessels in presence of mineral oil (MO), natural ester (VO) and synthetic ester (SE). The influence of thermal aging on cellulose and oil characteristics are investigated and compared. It's observed that the paper degradation is associated with the generation of CO2 and CO gases. Whatever the type of oil, this generation is more important with vessel under air atmosphere than that under nitrogen gap indicating a protective effect of nitrogen. In mineral oil, the degree of polymerization (DPv) reaches the end of life criteria at around 200 whereas it remains around 400 with ester oils. This is mainly due to the higher water solubility of esters compared to mineral oil. The measured degree of polymerization in MO is comparable to that calculated through 2-FAL (Furanic compounds) content using Vuarchex equation whereas for esters oil, there is no agreement between the measured and calculated DPv through 2-FAL content. This can constitute a limitation in the use of 2-FAL for the diagnosis of ester-filled transformers. Overall, the insulation cellulose/oil behavior seems better under nitrogen atmosphere.
    IEEE Transactions on Dielectrics and Electrical Insulation 01/2013; 20(6):1971-1976. · 1.36 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper deals with the experimental characterization of discharges (namely the shape and stopping length) propagating over pressboard of different thicknesses immersed in mineral and vegetable oils, under AC, DC and lightning impulse voltages (1.2/50 μs) using a pointplane electrode arrangement; the point being perpendicular to pressboard. It's shown that the thickness of pressboard and the type of oil as well as the magnitude and polarity of voltage significantly influence the characteristics of discharges. For a given thickness, the stopping length of discharges Lf increases quasi-linearly with the voltage (U); and it is longer with a positive point than with a negative point whatever the type of voltage. Lf decreases when the thickness increases. The thinner the pressboard, the more branched are the discharge structures. The density of discharge branches increases when the pressboard thickness is reduced. On the other hand, for a given voltage and thickness of pressboard, Lf is longer under AC than under DC whatever the type of oil. Also, the characteristics Lf(U) in presence of processed vegetable oil and mineral oil are very close except for thin pressboard. The influence of electric field and capacitive effects on the propagation mechanism is also evidenced.
    IEEE Transactions on Dielectrics and Electrical Insulation 01/2013; 20(5):1635-1640. · 1.36 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The defects caused by the presence of metallic particles are the most frequent threats in Gas-Insulated Substation (GIS). These particles can move freely in the GIS enclosure and thereby when they come in the vicinity of spacers they can adhere to the solid spacer surface due to electrostatic forces resulting in the initiation of partial discharges (PDs) affecting the GIS reliability. The magnitude and frequency of these PDs depend among others on the size and position of particles. Thus the knowledge of the size and position of contaminating particles and its PD characteristics is essential for the improvement of the reliability of such equipment. This paper is aimed at the use of the Back-Propagation Artificial Neural Network (BP-ANN) technique for recognizing the PD patterns to estimate the particle size (length) and position on the spacer surface in a simulated GIS. The PD patterns were characterized by a number of statistical operators describing the shapes of distributions of the PD signals acquired from the measurements carried out using IEC 60270 method. In developing the BP-ANN, some parameters were varied to find the most optimal network. The results show that the best-developed ANN in this study is able to recognize various PD patterns in the employed GIS model and is able to estimate particle length and position on the spacer surface at different SF6 pressures. The achieved accuracy in detecting the size and location of particle was about 92%. Thus, the proposed method constitutes a helpful tool in improving the reliability of GIS as well as for diagnosis.
    IEEE Transactions on Dielectrics and Electrical Insulation 01/2013; 20(6):2143-2151. · 1.36 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The presence of conducting particles is a well-recognized threat to Gas-Insulated System (GIS) equipments. This study computes the electric field strength in simulated GIS model in the presence of conducting particle adhering to the spacer surface. The simulation results will be helpful to address the difficulties in acquiring accurate measurement and analysis of electric field non-uniformity in GIS due to the presence of conducting particles. The degree of electric field non-uniformity was identified by evaluating the electric field on large number of points within the area between the two electrodes. The information gathered from the simulation was used in estimating partial discharge inception voltage (PDIV) for the parallel-plane electrode configuration. The estimated PDIV values were confirmed by the experimental investigation using the IEC 60270 method.
    Power Engineering, Energy and Electrical Drives (POWERENG), 2013 Fourth International Conference on; 01/2013
  • A. Beroual, Viet-Hung Dang
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper is aimed at the experimental study of discharges propagating over pressboard immersed in mineral and vegetable oils and the analysis and comparison of the fractal dimension of these discharges. The shape, stopping length (i.e., the maximum extension of creeping discharge) Lf, current and electrical charge of discharges are investigated versus the thickness (e) of pressboard and the type of oil in a point-plane electrode geometry stressed by a standard lightning impulse voltage. It is shown that Lf decreases when e increases and it is longer when the point is positive than with a negative point. The smaller e, the more branched the discharge structures are, indicating the important role of the electric field and capacitive effect in the propagation mechanism. Lf is generally greater of 60% in vegetable oils than in mineral oil when the point is positive and it is of 40% greater when the point is negative. By using the box counting method, we show that the observed discharge patterns present a fractal dimension D which depends on e and the kind of oil. D decreases when e increases. The value of the density of branches increases when the e decreases. D is generally higher in mineral oil than in vegetable oil. This dependency on the thickness of pressboard and the nature of oil reveals the existence of a relation between the fractal dimension and the physicochemical parameters of interface.
    IEEE Transactions on Dielectrics and Electrical Insulation 01/2013; 20(4):1402-1408. · 1.36 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Dielectric interfaces can have a significant effect on the insulating performances of HV apparatus. The oil/solid interface represents a relatively weak component of an insulation system in power transformer. Therefore, when we are considering the effect of oil breakdown in oil filled transformer, we should consider the interactions which electrical discharges may have with solid surfaces. This work is devoted to the influence of insulating barrier on the behaviour of transformer oil under ac voltage in point-plane electrode configuration. The influence of the characteristics of barrier such as its position between electrodes, and its diameter on the pre-breakdown and breakdown phenomena is investigated. It is shown that the insertion of barrier near the point electrode increases the breakdown voltage and leads to decrease the pre-breakdown charge. The increase of breakdown voltage is due to the channel elongation of the disruptive charge. By determination of the pre-breakdown charge and breakdown voltage, we can estimate the optimal position of the barrier. The barrier diameter influences the breakdown voltage, the pre-breakdown charge and the trajectory of discharge.
    International Conference on High Voltage Engineering and Application ICHVE, Shanghai, China,; 09/2012
  • [Show abstract] [Hide abstract]
    ABSTRACT: Oil reclamation with Fuller’s earth is known to have an improved effect on conditioning aged oil. In this paper it is shown that aged oil reclamation effectiveness can be monitored with turbidity and spectrophotometry measurements. These low cost testing techniques offer a useful tool to quantify the effect of Fuller’s earth. Experimental investigations performed in laboratory conditions have shown that the quality of properly reclaimed aged oil can compete with that of new oils. Thus, in addition to extending the life cycle of this non-renewable resource, on-line reclamation of liquid might also prevent the premature ageing of paper insulation. Studying the stability of reclaimed service aged oil samples emphasized the important role played by Fuller’s earth absorption capability
    Journal of Energy and Power Engineering. 05/2012; 6(5):703-712.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Oil reclamation with Fuller’s Earth is known to have an improved effect on conditioning aged oil. In this paper it is shown that aged oil reclamation effectiveness can be monitored with Turbidity and Spectrophotometry measurements. These low cost testing techniques offer a useful tool to quantify the effect of Fuller’s Earth. Experimental investigations performed in laboratory conditions have shown that the quality of properly reclaimed aged oil can compete with that of new oils. Thus, in addition to extending the life cycle of this non-renewable resource, on-line reclamation of liquid might also prevent the premature ageing of paper insulation. Studying the stability of reclaimed service aged oil samples emphasized the important role played by Fuller’s Earth absorption capability.
    Journal of Energy and Power Engineering. 05/2012; 6(5):703-712.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Lifetime extension of power transformers is a subject of high importance for electric power systems utilities. The decision of replacing, refurbishing or repairing a service aged power transformer requires considering several factors, especially the cost and time to execute the work. The lifetime of the power transformer being related to the condition of the insulation system; one way of improving the situation is to reclaim insulating oil by Fuller's Earth treatment. This procedure is economically attractive because of increasing prices for both mineral and synthetic transformer coolants, effective cost and environmentally sounds. Reclamation rejuvenates the transformer oil by eliminating contaminants. In this paper, a series of experiments has been performed with service aged oils reclaimed in laboratory conditions. Fast, inexpensive and reliable laboratory testing procedures developed by ASTM (D 6802 and D6181) were also used to monitor decay products as traces impurities. The results obtained in laboratory conditions, indicate that a large number of reclamation passes (around 15 passes) are required to regenerate inservice aged oil to a grade close to new oil. It is also shown that not only the reclamation improves the gassing tendency of oil, but also the type of Fuller's Earth is very important for reclamation process. By upgrading the analytical chemistry of oil, the predictive maintenance of this non-renewable resource is modernized, its cost diminished and the service reliability of transformers enhanced. Currently, Fuller's Earth is only used once. After depletion it must be disposed of in a land fill. By using two organic solvents that are recoverable by atmospheric distillation, it is shown, in laboratory conditions, that this mineral absorbent can be reactivated and successfully reused many times.
    IEEE Transactions on Dielectrics and Electrical Insulation 01/2012; 19(5):1583-1592. · 1.36 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper is devoted to the streamers propagation in natural esters (vegetable oils) in a point - plane electrode arrangement stressed by standard lightning impulse voltage (1.2/50 μs). We mainly investigate the shape and stopping length of streamers as well as the associated current. Six commercial oils (untreated natural ester) extracted from grape seeds (GS), sunflower (SF) and rape seed (RS), corn (CO), rice (RI) and sesame (SS) that could constitute potential liquids for high voltage applications are tested. A mineral oil (MO) is also tested for comparison. It's shown that the streamers are filamentary in the different oils for both polarities. For a given voltage, the stopping lengths (Lf) of streamers are longer when the point is positive than when it is negative; also, except mineral oil when the point is negative, the values of Lf are very close enough in all tested oils.
    High Voltage Engineering and Application (ICHVE), 2012 International Conference on; 01/2012
  • M.E. Slama, A. Beroual, H. Hadi
    [Show abstract] [Hide abstract]
    ABSTRACT: The goal of this paper is to investigate and model the effect of non uniform discontinuous pollution on flashover of laboratory plate insulator. The experimental results show that the discharges appear almost simultaneously at the point and the dry bands whatever the polarity of the applied voltage. The lengths of discharges as well as the critical flashover voltage depend on the configuration of pollution layer and the polarity of voltage. Thus the variation of the local equivalent impedance before each discharge determines the propagation conditions of discharges. The flashover voltages computed using the proposed model are found in a good agreement with the experimental ones. On the other hand, the deduced temperature of discharges depends on the configuration of pollution and the polarity of voltage.
    High Voltage Engineering and Application (ICHVE), 2012 International Conference on; 01/2012
  • M.E. Slama, A. Beroual, H. Hadi
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper is aimed at the experimental study of the influence of non-soluble and low soluble salts and mixtures of salts on dc critical flashover voltage. The influence of the type of pollution on discharge parameters n and N, and their implication on the values of dc critical flashover voltage for both polarities is also analysed and discussed. A mathematical model enabling to compute the critical flashover voltage (Ucri) is proposed. It is shown that the calculated Ucri are in accordance with the experimental ones. It also appears from this study that: (i) the most important components of the discharge column are water vapour and air; and (ii) the transfer of metallic ions has not a significant influence on Ucri.
    Electrical Insulation and Dielectric Phenomena (CEIDP), 2012 Annual Report Conference on; 01/2012
  • [Show abstract] [Hide abstract]
    ABSTRACT: This study is devoted to the optical and electrical characterisation of discharges propagating over insulators made of polytetrafluoroethylene (PTFE) filled with different kinds of micro-mineral fillers immersed in gas or gaseous mixture, under lightning impulse voltage (1.2/50 s), using a point-plane electrode arrangement. The fillers the authors investigated are MoS2, Al2CoO4, SiO2 and CaF2. The gases and mixture the authors considered are SF6, CO2 and SF6-CO2. It is shown that the stopping length of discharges Lf increases quasi-linearly with the voltage; Lf is shorter in SF6 than in CO2 and it is higher when the point electrode is positive than when it is negative while the initiation voltage of discharges is higher with a negative point than with a positive one. The discharges do not always present a radial structure as reported in the literature. Also, the type of filler greatly influences the characteristics of creeping discharges. In a given gas or mixture, the shortest Lf is obtained with PTFE filled with MoS2 or Al2CoO4. Thus, insulators with these fillers appear as the best insulators.
    IET Generation Transmission & Distribution 01/2012; 6(10):951-957. · 1.41 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper deals with the experimental characterization of discharges propagating over pressboard of different thicknesses immersed in mineral and vegetable oils, under AC and DC voltages using a point-plane electrode arrangement. It's shown that the thickness of pressboard and the type of oil significantly influence the characteristics of creeping discharge and especially the stopping length Lf and the density of branches □. For a given thickness, Lf increases with the voltage; it decreases when the thickness increases. For a given voltage and thickness of pressboard, Lf is longer under AC than under DC whatever the oil type. And under DC, Lf is longer with positive point than with a negative point. However, the characteristics Lf(U) in presence of vegetable oil and mineral oil are very close except for thin pressboard.
    High Voltage Engineering and Application (ICHVE), 2012 International Conference on; 01/2012
  • [Show abstract] [Hide abstract]
    ABSTRACT: The purpose of this paper is to simulate an accelerated ageing of paper and high density pressboard type B.3.1 in three different liquids (mineral oil MO, natural ester VO and synthetic ester SE) for different periods of ageing at 130°C. The materials were aged in sealed vessels under two different atmospheres: air and nitrogen gaps. The effects of aging on physicochemical properties of oil and cellulose are analyzed and compared. It is shown that ageing rate of pressboard and paper are comparable in each type of oil. Nevertheless, it can be underlined that cellulosic materials are less affected after aging in ester oils evidencing a higher degree of polymerization (DPv). The use of 2-FAL in ester oils remains questionable. The reduction of oxygen content in mineral oil minimizes ageing of oil more than solid insulating materials.
    Condition Monitoring and Diagnosis (CMD), 2012 International Conference on; 01/2012

Publication Stats

835 Citations
152.78 Total Impact Points

Institutions

  • 1991–2014
    • Ecole Centrale de Lyon
      Rhône-Alpes, France
  • 2007
    • Université Mouloud Mammeri de Tizi Ouzou
      • Laboratory of Electrical Engineering (LGE)
      Tizi Uzu, Tizi Ouzou, Algeria
  • 2001–2007
    • University of Québec in Chicoutimi
      Saguenay, Quebec, Canada
  • 2005
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France
  • 1999
    • Alstom
      Levallois, Île-de-France, France
  • 1995–1999
    • Université de Bretagne Occidentale
      • Département de Physique
      Brest, Brittany, France
  • 1998
    • Wroclaw University of Technology
      • Institute of Electrical Power Engineering
      Wrocław, Lower Silesian Voivodeship, Poland
  • 1993
    • University Joseph Fourier - Grenoble 1
      Grenoble, Rhône-Alpes, France