Leila Mokhnache - Academia.edu (original) (raw)
Papers by Leila Mokhnache
2000 Annual Report Conference on Electrical Insulation and Dielectric Phenomena (Cat. No.00CH37132)
In this paper, we have computed fields of the positive ions and electrons created at the head of ... more In this paper, we have computed fields of the positive ions and electrons created at the head of avalanche in a positive point-barrier-plane air gap. The polarisation field effect of the dielectric is taken into account. The general problem will be formulated with finite elements and it is focussed on the polarisation field formulation. It was found that the effect
Proceedings of the 2004 IEEE International Conference on Solid Dielectrics, 2004. ICSD 2004.
The ageing process of insulation can be monitored by several properties measurements, which need ... more The ageing process of insulation can be monitored by several properties measurements, which need long test period to have a complete database to predict the dielectric behaviour of the HV insulation. The main purpose of insulation monitoring is to limit stoppage of electric service by giving the information on dielectric deterioration leading to a failure of HV equipment. Prediction of
Annual Report Conference on Electrical Insulation and Dielectric Phenomena
Back propagation Algorithm is applied in transformer oil diagnosis. The Algorithm is trained by L... more Back propagation Algorithm is applied in transformer oil diagnosis. The Algorithm is trained by Levenberg-Marquardt technique, Momentum technique and Momentum & adaptive learning rate technique. A comparison between the three techniques is done.
IEE Proceedings - Science, Measurement and Technology, 2004
ABSTRACT A model is developed for the computation of the electric field and potential in the pres... more ABSTRACT A model is developed for the computation of the electric field and potential in the presence of a space charge, which is determined after the knowledge of the efficient ionisation factor. The computation is performed in a point-barrier-plane air gap under a positive voltage using finite elements. As a typical electrostatic application, the electric field distribution is computed in the presence of a space charge and a dielectric barrier in the air gap. The proposed model deals with the phase of electronic avalanches.
Journal de Physique IV (Proceedings), 2005
... properties for longer periods. 4.1 Oil breakdown voltage BDV test is carried out in a BDV tes... more ... properties for longer periods. 4.1 Oil breakdown voltage BDV test is carried out in a BDV tester model OIT-100M (SIVANANDA-India). The test is carried out by keeping the distance between the electrodes 2.5mm. In figure 3 ...
Annales de Chimie Science des Matériaux, 2006
ABSTRACT The effect of thermal aging on the mechanical properties of the cross-linked polyethylen... more ABSTRACT The effect of thermal aging on the mechanical properties of the cross-linked polyethylene (XLPE), used in insulation of high voltage cables, was studied. We showed that elongation at rupture and tensile strength of the polymer decrease as functions of aging time. This decrease is faster when the temperature is higher. The values of the activation energy and the temperature index were determined. The degradation of the material, attributed to an antioxidant loss, takes place according to three stages with various speeds. The consequences of the degradation were highlighted: mass loss, colour change, shrinking and decrease in degree of cross-linking. The thermal behaviour of the insulator is in agreement with the Arrhenius law
COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, 2010
Purpose – The purpose of this paper is to propose a numerical method in time domain in order to s... more Purpose – The purpose of this paper is to propose a numerical method in time domain in order to solve the electric and magnetic fields radiated from lightning in the presence of the tall tower. This paper is very important in calculating lightning electromagnetic field – obtaining directly the solution in time domain with a reduced computation time and reduced
IET Generation, Transmission & Distribution, 2009
In this paper improved fuzzy stator resistance estimation for a Direct Torque Controlled (DTC) in... more In this paper improved fuzzy stator resistance estimation for a Direct Torque Controlled (DTC) induction motor is investigated. This estimation method is based on an on-line stator resistance correction regarding the variations of the stator current estimation error and its variation. The Fuzzy Logic Controller (FLC) gives the future stator resistance increment at the output. The stator resistance estimation will avoid the drive instability that may occur in certain situations and ensure the tracking of the actual value of the stator resistance. But in such drives, there is an error between the filtered stator current modulus and its estimated value in the steady state which is due to the pseudo random commutations of the PWM inverter switches. This may worsen the performance of the fuzzy stator resistance estimator. An offset has been introduced in order to overcome this problem for different speed command values and load torques. Simulation results show that the proposed estimator...
Lecture Notes in Electrical Engineering, 2015
The aim of this paper is to apply the Monte Carlo Method to describe the behavior of electrons in... more The aim of this paper is to apply the Monte Carlo Method to describe the behavior of electrons in the oxygen gas, under the effect of uniform electric fields, in the presence of (elastic, excitation, ionization and attachment) collisions with gas molecules. We try to reproduce an electrical discharge; by following the random histories of free produced electrons and using the sampling laws, we can determine some electrical discharge parameters. In addition, we use the MCM simulation results to verify the electrical breakdown criteria for small distances under an homogenous field. The obtained results are compared with those collected from literature.
Journal of Electrical Engineering and Technology
The objective of this paper is to study the discharge phenomenon for a point-plane air interval u... more The objective of this paper is to study the discharge phenomenon for a point-plane air interval using an original fuzzy logic system. Firstly, a physical model based on streamer theory with consideration of the space charge fields due to electrons and positive ions is proposed. To test this model we have calculated the breakdown threshold voltage for a point-plane air interval. The same model is used to determine the discharge steps for different configurations as an inference data base. Secondly, using results obtained by the numerical simulation of the previous model, we have introduced the fuzzy logic technique to predict the breakdown threshold voltage of the same configurations used in the numerical model and make estimation on the insulating state of the air interval. From the comparison of obtained results, we can conclude that they are in accordance with the experimental ones obtained for breakdown discharges in different point-plane air gaps collected from the literature. T...
The Dissolved Gas Analysis (DGA) is probably the most important oil test for oil-filled power tra... more The Dissolved Gas Analysis (DGA) is probably the most important oil test for oil-filled power transformers. About twenty DGA interpretation techniques have been developed empirically so far. All of these techniques, based on heuristic in nature and not on scientific formulation, still show a certain percentage of wrong diagnoses. Among the pitfalls, it was recently recognized that some of the contaminants in the oil contribute to gassing. In this contribution, aged oil samples were submitted to thermal and electrical stresses (considering various scenarios) and the dissolved gasses analyzed by chromatography. This contribution intends to show that the gassing of oil is a more complex phenomenon. Experimental evidence that the chemical composition of the hydrocarbon blend and the oil born decay products are also contributing factors to oil gassing is reported.
Conference Record of the 2008 IEEE International Symposium on Electrical Insulation, 2008
The major aim of our investigations is the computation of the voltages induced by an external tra... more The major aim of our investigations is the computation of the voltages induced by an external transient electromagnetic excitation, especially due to the lightning discharge coupling to overhead transmission line networks. In this paper we propose a hybrid method for evaluating the electromagnetic field radiated by lightning The Agrawal et al. model coupling model will be used in order to
Conference Record of the 2008 IEEE International Symposium on Electrical Insulation, 2008
In this paper we propose a hybrid method for evaluating the electromagnetic field radiated by lig... more In this paper we propose a hybrid method for evaluating the electromagnetic field radiated by lightning. The proposed method is a combination between the images method and the finite difference time-domain (FDTD) method. We first calculate the magnetic field with the images method and then; the electric field based partially on the FDTD method. The suitability of this method (hybrid
Advanced Materials Research, 2011
The generation of plasmas and the initiation of electrical breakdown are realized by the phenomen... more The generation of plasmas and the initiation of electrical breakdown are realized by the phenomenon of electrical discharge which is provoked when we apply a sufficient electric field in a gas. Consequently the free charges are accelerated, new charged particles are created and others are destructed. This can be ranged in four phenomena: elastic collision (recombination), attachment, excitation and ionization. The aim of this paper is to study the basic phenomena in an electrical discharge in the case of Oxygen O2. Monte Carlo Simulation is used to follow the random trajectory of free charges determining in each path many parameters of the discharge. To determinate electrical and physical parameters, we have used the sampling laws. The spatial distributions of space charges (electrons, positive and negative ions) are also obtained. The determination of electrical field depends on distributions of charged particles obtained by solving the Maxwell equations.
2014 IEEE 11th International Multi-Conference on Systems, Signals & Devices (SSD14), 2014
There is a general agreement that in service conditions the quality of insulating fluids graduall... more There is a general agreement that in service conditions the quality of insulating fluids gradually deteriorates under the impact of electrical, thermal and chemical stresses. The object of this contribution is to compare the variation of transformer oil parameters in different aging tests: thermal aging, electrical aging and the combination of both. The effects of the three different types of aging on the physicochemical and electrical properties of transformer oil have been examined, with the aim of investigating the stress which strongly affects the gassing tendency and physicochemical properties of oil under the service conditions. In this regard, various scenarios were considered. The study was carried on mineral oil under: electrical stress, thermal aging and a combination of both stresses. The ASTM methods are used to monitor the deterioration of liquid insulation step by step. The results obtained using laboratorygrade equipments indicate that the rate of increase or decrease in parameters is different from aging type for other and the electrical field accelerate strongly the degradation of new and aged oil. The study is made on a naphthenic commercial-based mineral oil.
Electric Power Systems Research, 2011
The objective of this paper is to study the discharge phenomenon for a point-plane air interval u... more The objective of this paper is to study the discharge phenomenon for a point-plane air interval using an original fuzzy logic system. Firstly, a physical model based on streamer theory with consideration of the space charge fields due to electrons and positive ions is proposed. To test this model we have calculated the breakdown threshold voltage for a point-plane air interval. The same model is used to determine the discharge steps for different configurations as an inference data base. Secondly, using results obtained by the numerical simulation of the previous model, we have introduced the fuzzy logic technique to predict the breakdown threshold voltage of the same configurations used in the numerical model and make estimation on the insulating state of the air interval. From the comparison of obtained results, we can conclude that they are in accordance with the experimental ones obtained for breakdown discharges in different point-plane air gaps collected from the literature. The proposed study using fuzzy logic technique shows a good performance in the analysis of different discharge steps of the air interval.
![Research paper thumbnail of Erratum to “Determination of ionization conditions characterizing the breakdown threshold of a point-plane air interval using fuzzy logic” [Electr. Power Syst. Res. 81 (2011) 2038–2047]](https://attachments.academia-assets.com/79173140/thumbnails/1.jpg)
](Electric Power Systems Research, 2012
Erratum Erratum to "Determination of ionization conditions characterizing the breakdown threshold... more Erratum Erratum to "Determination of ionization conditions characterizing the breakdown threshold of a point-plane air interval using fuzzy logic" [Electr.
Compel-the International Journal for Computation and Mathematics in Electrical and Electronic Engineering, 2010
Purpose – The purpose of this paper is to propose a numerical method in time domain in order to s... more Purpose – The purpose of this paper is to propose a numerical method in time domain in order to solve the electric and magnetic fields radiated from lightning in the presence of the tall tower. This paper is very important in calculating lightning electromagnetic field – obtaining directly the solution in time domain with a reduced computation time and reduced
Journal De Physique Iv, 2005
... properties for longer periods. 4.1 Oil breakdown voltage BDV test is carried out in a BDV tes... more ... properties for longer periods. 4.1 Oil breakdown voltage BDV test is carried out in a BDV tester model OIT-100M (SIVANANDA-India). The test is carried out by keeping the distance between the electrodes 2.5mm. In figure 3 ...
2000 Annual Report Conference on Electrical Insulation and Dielectric Phenomena (Cat. No.00CH37132)
In this paper, we have computed fields of the positive ions and electrons created at the head of ... more In this paper, we have computed fields of the positive ions and electrons created at the head of avalanche in a positive point-barrier-plane air gap. The polarisation field effect of the dielectric is taken into account. The general problem will be formulated with finite elements and it is focussed on the polarisation field formulation. It was found that the effect
Proceedings of the 2004 IEEE International Conference on Solid Dielectrics, 2004. ICSD 2004.
The ageing process of insulation can be monitored by several properties measurements, which need ... more The ageing process of insulation can be monitored by several properties measurements, which need long test period to have a complete database to predict the dielectric behaviour of the HV insulation. The main purpose of insulation monitoring is to limit stoppage of electric service by giving the information on dielectric deterioration leading to a failure of HV equipment. Prediction of
Annual Report Conference on Electrical Insulation and Dielectric Phenomena
Back propagation Algorithm is applied in transformer oil diagnosis. The Algorithm is trained by L... more Back propagation Algorithm is applied in transformer oil diagnosis. The Algorithm is trained by Levenberg-Marquardt technique, Momentum technique and Momentum & adaptive learning rate technique. A comparison between the three techniques is done.
IEE Proceedings - Science, Measurement and Technology, 2004
ABSTRACT A model is developed for the computation of the electric field and potential in the pres... more ABSTRACT A model is developed for the computation of the electric field and potential in the presence of a space charge, which is determined after the knowledge of the efficient ionisation factor. The computation is performed in a point-barrier-plane air gap under a positive voltage using finite elements. As a typical electrostatic application, the electric field distribution is computed in the presence of a space charge and a dielectric barrier in the air gap. The proposed model deals with the phase of electronic avalanches.
Journal de Physique IV (Proceedings), 2005
... properties for longer periods. 4.1 Oil breakdown voltage BDV test is carried out in a BDV tes... more ... properties for longer periods. 4.1 Oil breakdown voltage BDV test is carried out in a BDV tester model OIT-100M (SIVANANDA-India). The test is carried out by keeping the distance between the electrodes 2.5mm. In figure 3 ...
Annales de Chimie Science des Matériaux, 2006
ABSTRACT The effect of thermal aging on the mechanical properties of the cross-linked polyethylen... more ABSTRACT The effect of thermal aging on the mechanical properties of the cross-linked polyethylene (XLPE), used in insulation of high voltage cables, was studied. We showed that elongation at rupture and tensile strength of the polymer decrease as functions of aging time. This decrease is faster when the temperature is higher. The values of the activation energy and the temperature index were determined. The degradation of the material, attributed to an antioxidant loss, takes place according to three stages with various speeds. The consequences of the degradation were highlighted: mass loss, colour change, shrinking and decrease in degree of cross-linking. The thermal behaviour of the insulator is in agreement with the Arrhenius law
COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, 2010
Purpose – The purpose of this paper is to propose a numerical method in time domain in order to s... more Purpose – The purpose of this paper is to propose a numerical method in time domain in order to solve the electric and magnetic fields radiated from lightning in the presence of the tall tower. This paper is very important in calculating lightning electromagnetic field – obtaining directly the solution in time domain with a reduced computation time and reduced
IET Generation, Transmission & Distribution, 2009
In this paper improved fuzzy stator resistance estimation for a Direct Torque Controlled (DTC) in... more In this paper improved fuzzy stator resistance estimation for a Direct Torque Controlled (DTC) induction motor is investigated. This estimation method is based on an on-line stator resistance correction regarding the variations of the stator current estimation error and its variation. The Fuzzy Logic Controller (FLC) gives the future stator resistance increment at the output. The stator resistance estimation will avoid the drive instability that may occur in certain situations and ensure the tracking of the actual value of the stator resistance. But in such drives, there is an error between the filtered stator current modulus and its estimated value in the steady state which is due to the pseudo random commutations of the PWM inverter switches. This may worsen the performance of the fuzzy stator resistance estimator. An offset has been introduced in order to overcome this problem for different speed command values and load torques. Simulation results show that the proposed estimator...
Lecture Notes in Electrical Engineering, 2015
The aim of this paper is to apply the Monte Carlo Method to describe the behavior of electrons in... more The aim of this paper is to apply the Monte Carlo Method to describe the behavior of electrons in the oxygen gas, under the effect of uniform electric fields, in the presence of (elastic, excitation, ionization and attachment) collisions with gas molecules. We try to reproduce an electrical discharge; by following the random histories of free produced electrons and using the sampling laws, we can determine some electrical discharge parameters. In addition, we use the MCM simulation results to verify the electrical breakdown criteria for small distances under an homogenous field. The obtained results are compared with those collected from literature.
Journal of Electrical Engineering and Technology
The objective of this paper is to study the discharge phenomenon for a point-plane air interval u... more The objective of this paper is to study the discharge phenomenon for a point-plane air interval using an original fuzzy logic system. Firstly, a physical model based on streamer theory with consideration of the space charge fields due to electrons and positive ions is proposed. To test this model we have calculated the breakdown threshold voltage for a point-plane air interval. The same model is used to determine the discharge steps for different configurations as an inference data base. Secondly, using results obtained by the numerical simulation of the previous model, we have introduced the fuzzy logic technique to predict the breakdown threshold voltage of the same configurations used in the numerical model and make estimation on the insulating state of the air interval. From the comparison of obtained results, we can conclude that they are in accordance with the experimental ones obtained for breakdown discharges in different point-plane air gaps collected from the literature. T...
The Dissolved Gas Analysis (DGA) is probably the most important oil test for oil-filled power tra... more The Dissolved Gas Analysis (DGA) is probably the most important oil test for oil-filled power transformers. About twenty DGA interpretation techniques have been developed empirically so far. All of these techniques, based on heuristic in nature and not on scientific formulation, still show a certain percentage of wrong diagnoses. Among the pitfalls, it was recently recognized that some of the contaminants in the oil contribute to gassing. In this contribution, aged oil samples were submitted to thermal and electrical stresses (considering various scenarios) and the dissolved gasses analyzed by chromatography. This contribution intends to show that the gassing of oil is a more complex phenomenon. Experimental evidence that the chemical composition of the hydrocarbon blend and the oil born decay products are also contributing factors to oil gassing is reported.
Conference Record of the 2008 IEEE International Symposium on Electrical Insulation, 2008
The major aim of our investigations is the computation of the voltages induced by an external tra... more The major aim of our investigations is the computation of the voltages induced by an external transient electromagnetic excitation, especially due to the lightning discharge coupling to overhead transmission line networks. In this paper we propose a hybrid method for evaluating the electromagnetic field radiated by lightning The Agrawal et al. model coupling model will be used in order to
Conference Record of the 2008 IEEE International Symposium on Electrical Insulation, 2008
In this paper we propose a hybrid method for evaluating the electromagnetic field radiated by lig... more In this paper we propose a hybrid method for evaluating the electromagnetic field radiated by lightning. The proposed method is a combination between the images method and the finite difference time-domain (FDTD) method. We first calculate the magnetic field with the images method and then; the electric field based partially on the FDTD method. The suitability of this method (hybrid
Advanced Materials Research, 2011
The generation of plasmas and the initiation of electrical breakdown are realized by the phenomen... more The generation of plasmas and the initiation of electrical breakdown are realized by the phenomenon of electrical discharge which is provoked when we apply a sufficient electric field in a gas. Consequently the free charges are accelerated, new charged particles are created and others are destructed. This can be ranged in four phenomena: elastic collision (recombination), attachment, excitation and ionization. The aim of this paper is to study the basic phenomena in an electrical discharge in the case of Oxygen O2. Monte Carlo Simulation is used to follow the random trajectory of free charges determining in each path many parameters of the discharge. To determinate electrical and physical parameters, we have used the sampling laws. The spatial distributions of space charges (electrons, positive and negative ions) are also obtained. The determination of electrical field depends on distributions of charged particles obtained by solving the Maxwell equations.
2014 IEEE 11th International Multi-Conference on Systems, Signals & Devices (SSD14), 2014
There is a general agreement that in service conditions the quality of insulating fluids graduall... more There is a general agreement that in service conditions the quality of insulating fluids gradually deteriorates under the impact of electrical, thermal and chemical stresses. The object of this contribution is to compare the variation of transformer oil parameters in different aging tests: thermal aging, electrical aging and the combination of both. The effects of the three different types of aging on the physicochemical and electrical properties of transformer oil have been examined, with the aim of investigating the stress which strongly affects the gassing tendency and physicochemical properties of oil under the service conditions. In this regard, various scenarios were considered. The study was carried on mineral oil under: electrical stress, thermal aging and a combination of both stresses. The ASTM methods are used to monitor the deterioration of liquid insulation step by step. The results obtained using laboratorygrade equipments indicate that the rate of increase or decrease in parameters is different from aging type for other and the electrical field accelerate strongly the degradation of new and aged oil. The study is made on a naphthenic commercial-based mineral oil.
Electric Power Systems Research, 2011
The objective of this paper is to study the discharge phenomenon for a point-plane air interval u... more The objective of this paper is to study the discharge phenomenon for a point-plane air interval using an original fuzzy logic system. Firstly, a physical model based on streamer theory with consideration of the space charge fields due to electrons and positive ions is proposed. To test this model we have calculated the breakdown threshold voltage for a point-plane air interval. The same model is used to determine the discharge steps for different configurations as an inference data base. Secondly, using results obtained by the numerical simulation of the previous model, we have introduced the fuzzy logic technique to predict the breakdown threshold voltage of the same configurations used in the numerical model and make estimation on the insulating state of the air interval. From the comparison of obtained results, we can conclude that they are in accordance with the experimental ones obtained for breakdown discharges in different point-plane air gaps collected from the literature. The proposed study using fuzzy logic technique shows a good performance in the analysis of different discharge steps of the air interval.
Electric Power Systems Research, 2012
Erratum Erratum to "Determination of ionization conditions characterizing the breakdown threshold... more Erratum Erratum to "Determination of ionization conditions characterizing the breakdown threshold of a point-plane air interval using fuzzy logic" [Electr.
Compel-the International Journal for Computation and Mathematics in Electrical and Electronic Engineering, 2010
Purpose – The purpose of this paper is to propose a numerical method in time domain in order to s... more Purpose – The purpose of this paper is to propose a numerical method in time domain in order to solve the electric and magnetic fields radiated from lightning in the presence of the tall tower. This paper is very important in calculating lightning electromagnetic field – obtaining directly the solution in time domain with a reduced computation time and reduced
Journal De Physique Iv, 2005
... properties for longer periods. 4.1 Oil breakdown voltage BDV test is carried out in a BDV tes... more ... properties for longer periods. 4.1 Oil breakdown voltage BDV test is carried out in a BDV tester model OIT-100M (SIVANANDA-India). The test is carried out by keeping the distance between the electrodes 2.5mm. In figure 3 ...