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Papers by Liliana Arevalo

Journal of Atmospheric and Solar-terrestrial Physics, 2009

A numerical study of a negative corona discharge in air at atmospheric pressure in a non -uniform... more A numerical study of a negative corona discharge in air at atmospheric pressure in a non -uniform electric field: A cylindrical arrangement with earthed inner electrodes is presented. Results were obtained by solving numerically Poisson's equation coupled with the continuity equations for electrons, positive, and negative ions, and considering the space -time evolution, as well as the electric field distribution and the current behaviour. The effects of ionization, attachment, recombination, electron diffusion are included. Calculations were made using a cylindrical discharge channel and a truncated cone. The calculated values were compared with the experimental results.

The results of numerical simulation of the positive corona development in atmospheric air in a ne... more The results of numerical simulation of the positive corona development in atmospheric air in a needle placed in the inner cylinder of a cylindrical coaxial arrangement are presented. The Poisson's equation was simultaneously solved with the continuity equations for electrons, positive ions and negative ions, including the effects of ionization, attachment, recombination and photo ionization. The values of electric field and corona current are shown and compared with the experimental ones. Comparisons of two different discharge channels are shown. A truncated cones and a cylindrical discharge channel were investigated.

The rural distribution transformer failure ratio due to lightning activity is a critical matter i... more The rural distribution transformer failure ratio due to lightning activity is a critical matter in several regions of Colombia. Different research projects have been funded by Colombian electrical companies in order to solve this problem. In some colombian regions, such as Rionegro, Cundinamarca, the tramsformer failure ratio has been as high as 50%. In different places around the world with a lightning activity similar to our country, the failure ratio has been kept close to 1%. The problem could be solved by developing an integral solution that includes: reduction of grounding resistance and inductive loops, specific transformer design and extensive use of surge arresters on the low and medium voltage transformer windings.

Journal of Electrostatics, 2011

The design of the lightning protection system LPS of transmission lines is based on the well know... more The design of the lightning protection system LPS of transmission lines is based on the well known electro-geometrical model. The electro-geometrical model assumes that the first point on a power transmission line that will come within striking distance of the tip of a down-coming stepped leader channel is the strike point of the lightning flash. The model neglects almost all of the physics associated with the lightning attachment.

A floating electrode is an insulated metallic body that is immersed in a background electrostatic... more A floating electrode is an insulated metallic body that is immersed in a background electrostatic field. This floating electrode can be electrically charged by corona discharges. The gathered charge on a floating electrode surface can be used to generate a fast current impulse. The Fast Impulse Current Generator, described in previous works and based on the floating electrode principle, produces almost constant current impulses probably due to: a) the low inductance of its discharge path, or b) the corona space charge recombination process that could occur in the corona charging mechanism. In the present work we study the dependence of output current amplitude and discharge repetition frequency with the modification of the corona charging mechanism. For a certain load value the number of corona sources will be increased from a single source to a number of them. The corona charging current will be analysed by the measurement of the output current. Air at atmospheric conditions will be used as discharge controlled switch in the generator.

A simplified model of leader development based on physical and engineering approximations for lab... more A simplified model of leader development based on physical and engineering approximations for laboratory long gap discharges under switching impulses was proposed and tested. The model was derived from the physical analysis proposed by Bondiou-Gallimberti and the engineering approximation for the potential drop on the tip of the leader proposed by Rizk. The calculated leader development characteristics with this model were compared with experimental results and numerical models. The proposed model is in close agreement with the existing published data. The calculation method was applicable to long gaps with rise times higher than 100 ¿s.

Journal of Electrostatics, 2009

a b s t r a c t A numerical methodology using two different leader channel criteria has been impl... more a b s t r a c t A numerical methodology using two different leader channel criteria has been implemented. The methodology is based on Bondiou and Gallimberti's proposition [A. Bondiou, I. Gallimberti, Theoretical modelling of the development of the positive spark in long spark, J. Phys. D: Appl. Phys. 27 (1994) 1252-1266]. The leader channel criteria used are Rizk engineering criterion [Rizk, A model for switching impulse leader inception and breakdown of long air gaps, IEEE Trans. Power Deliv., 4(1) (1989)] and Local thermodynamic -L.T.E. -physical concept [I. Gallimberti, The mechanism of the long spark formation, Colloque C7, J. Phys. (supplement au nro 7, Tome 40) (July 1979) C7-193]. The methodology was tested in three different cases; a deterministic case, a statistical variation and a typical constant level test. Deterministic calculation considered corona inception using stabilization corona electric field criterion of Gallimberti [I. Gallimberti, The mechanism of the long spark formation, Colloque C7, J. Phys. (supplement au nro 7, Tome 40) (July 1979) C7-193] and the leader moving as segments. The statistical simulation has two different statistical delays, one at inception and the other due to the tortuous characteristics of the leader channel. The constant level test consists of 200 positive switching impulses with the same characteristics such as maximum applied voltage, time to crest and time to fall. Time to breakdown and breakdown voltage were found based on the results obtained from the constant level test characteristics. All the numerical results presented are based on experimental conditions reported in [Les Renardiè res Group, Research on long gap discharges at Les Renardiè res, Electra N 35 (1973)] from the world class research group namely Les Renardieres Group.

Journal of Electrostatics, 2010

At present the design of the Lightning protection systems (LPS) for structures as stipulated in s... more At present the design of the Lightning protection systems (LPS) for structures as stipulated in standards is based on the electro e geometrical method, which was initially used to protect power lines from lightning. A derivative of the electro-geometrical method is the rolling sphere method. This method together, with the protection angle method and mesh method are used almost in all lightning standards as the measure in installing the lightning protection systems of grounded structures. In the mesh method, the dimension of the cell size in different levels of protection is determined using the rolling sphere method. Since the rolling sphere method does not take into account the physics of the lightning attachment process there is a need to evaluate the validity of the stipulated value in standards of the minimum lightning current that can penetrate through the mesh in different levels of protection. In this paper, meshes of different sizes as stipulated in the lightning protection standards were tested for their ability to intercept lightning flashes using a lightning attachment model that takes into account the physics of connecting leaders on. The results are in reasonable agreement with the specifications given in the lightning protection standards.

Journal of Atmospheric and Solar-terrestrial Physics, 2009

A numerical study of a negative corona discharge in air at atmospheric pressure in a non -uniform... more A numerical study of a negative corona discharge in air at atmospheric pressure in a non -uniform electric field: A cylindrical arrangement with earthed inner electrodes is presented. Results were obtained by solving numerically Poisson's equation coupled with the continuity equations for electrons, positive, and negative ions, and considering the space -time evolution, as well as the electric field distribution and the current behaviour. The effects of ionization, attachment, recombination, electron diffusion are included. Calculations were made using a cylindrical discharge channel and a truncated cone. The calculated values were compared with the experimental results.

The results of numerical simulation of the positive corona development in atmospheric air in a ne... more The results of numerical simulation of the positive corona development in atmospheric air in a needle placed in the inner cylinder of a cylindrical coaxial arrangement are presented. The Poisson's equation was simultaneously solved with the continuity equations for electrons, positive ions and negative ions, including the effects of ionization, attachment, recombination and photo ionization. The values of electric field and corona current are shown and compared with the experimental ones. Comparisons of two different discharge channels are shown. A truncated cones and a cylindrical discharge channel were investigated.

The rural distribution transformer failure ratio due to lightning activity is a critical matter i... more The rural distribution transformer failure ratio due to lightning activity is a critical matter in several regions of Colombia. Different research projects have been funded by Colombian electrical companies in order to solve this problem. In some colombian regions, such as Rionegro, Cundinamarca, the tramsformer failure ratio has been as high as 50%. In different places around the world with a lightning activity similar to our country, the failure ratio has been kept close to 1%. The problem could be solved by developing an integral solution that includes: reduction of grounding resistance and inductive loops, specific transformer design and extensive use of surge arresters on the low and medium voltage transformer windings.

Journal of Electrostatics, 2011

The design of the lightning protection system LPS of transmission lines is based on the well know... more The design of the lightning protection system LPS of transmission lines is based on the well known electro-geometrical model. The electro-geometrical model assumes that the first point on a power transmission line that will come within striking distance of the tip of a down-coming stepped leader channel is the strike point of the lightning flash. The model neglects almost all of the physics associated with the lightning attachment.

A floating electrode is an insulated metallic body that is immersed in a background electrostatic... more A floating electrode is an insulated metallic body that is immersed in a background electrostatic field. This floating electrode can be electrically charged by corona discharges. The gathered charge on a floating electrode surface can be used to generate a fast current impulse. The Fast Impulse Current Generator, described in previous works and based on the floating electrode principle, produces almost constant current impulses probably due to: a) the low inductance of its discharge path, or b) the corona space charge recombination process that could occur in the corona charging mechanism. In the present work we study the dependence of output current amplitude and discharge repetition frequency with the modification of the corona charging mechanism. For a certain load value the number of corona sources will be increased from a single source to a number of them. The corona charging current will be analysed by the measurement of the output current. Air at atmospheric conditions will be used as discharge controlled switch in the generator.

A simplified model of leader development based on physical and engineering approximations for lab... more A simplified model of leader development based on physical and engineering approximations for laboratory long gap discharges under switching impulses was proposed and tested. The model was derived from the physical analysis proposed by Bondiou-Gallimberti and the engineering approximation for the potential drop on the tip of the leader proposed by Rizk. The calculated leader development characteristics with this model were compared with experimental results and numerical models. The proposed model is in close agreement with the existing published data. The calculation method was applicable to long gaps with rise times higher than 100 ¿s.

Journal of Electrostatics, 2009

a b s t r a c t A numerical methodology using two different leader channel criteria has been impl... more a b s t r a c t A numerical methodology using two different leader channel criteria has been implemented. The methodology is based on Bondiou and Gallimberti's proposition [A. Bondiou, I. Gallimberti, Theoretical modelling of the development of the positive spark in long spark, J. Phys. D: Appl. Phys. 27 (1994) 1252-1266]. The leader channel criteria used are Rizk engineering criterion [Rizk, A model for switching impulse leader inception and breakdown of long air gaps, IEEE Trans. Power Deliv., 4(1) (1989)] and Local thermodynamic -L.T.E. -physical concept [I. Gallimberti, The mechanism of the long spark formation, Colloque C7, J. Phys. (supplement au nro 7, Tome 40) (July 1979) C7-193]. The methodology was tested in three different cases; a deterministic case, a statistical variation and a typical constant level test. Deterministic calculation considered corona inception using stabilization corona electric field criterion of Gallimberti [I. Gallimberti, The mechanism of the long spark formation, Colloque C7, J. Phys. (supplement au nro 7, Tome 40) (July 1979) C7-193] and the leader moving as segments. The statistical simulation has two different statistical delays, one at inception and the other due to the tortuous characteristics of the leader channel. The constant level test consists of 200 positive switching impulses with the same characteristics such as maximum applied voltage, time to crest and time to fall. Time to breakdown and breakdown voltage were found based on the results obtained from the constant level test characteristics. All the numerical results presented are based on experimental conditions reported in [Les Renardiè res Group, Research on long gap discharges at Les Renardiè res, Electra N 35 (1973)] from the world class research group namely Les Renardieres Group.

Journal of Electrostatics, 2010

At present the design of the Lightning protection systems (LPS) for structures as stipulated in s... more At present the design of the Lightning protection systems (LPS) for structures as stipulated in standards is based on the electro e geometrical method, which was initially used to protect power lines from lightning. A derivative of the electro-geometrical method is the rolling sphere method. This method together, with the protection angle method and mesh method are used almost in all lightning standards as the measure in installing the lightning protection systems of grounded structures. In the mesh method, the dimension of the cell size in different levels of protection is determined using the rolling sphere method. Since the rolling sphere method does not take into account the physics of the lightning attachment process there is a need to evaluate the validity of the stipulated value in standards of the minimum lightning current that can penetrate through the mesh in different levels of protection. In this paper, meshes of different sizes as stipulated in the lightning protection standards were tested for their ability to intercept lightning flashes using a lightning attachment model that takes into account the physics of connecting leaders on. The results are in reasonable agreement with the specifications given in the lightning protection standards.