UDAYA KUMAR - Academia.edu (original) (raw)

Papers by UDAYA KUMAR

Research paper thumbnail of Capacitive-Resistive Transients in terms of field quantities

Journal of the Indian Institute of Science

Capacitive-resistive transients in extended media are discussed in tenns of electric field quanti... more Capacitive-resistive transients in extended media are discussed in tenns of electric field quantities. Obviously, in rhese problems, the contribution of the magnetlc field to the electric field is deemcd negligible. For a simple lliuslratlve example, the field solution is compared with the circub-theorelied resuit for the voltage and current. An algorithm for solving such transients in space and time doman with the help of a Laplace solver is presented. Any other Laplace solver can also be used far this purpose. Its applicability is demonstrated with Ceeexamples, one of which i s chosen to have a circuit-theoretical solution. K v o r d s : Capacitive-resistive transients, boundary condition, eicctromagnetic transients.

Research paper thumbnail of Investigation on the Potential Rise and Currents in Insulated Mast Scheme with Single Tower During Stroke Interception

Journal of Lightning Research, 2010

The insulated mast scheme for the lightning protection system can be found in a few practical des... more The insulated mast scheme for the lightning protection system can be found in a few practical designs. Many advantages over conventional protection system are some times envisaged. However, the technical literature on the analysis of such schemes and further quantification of their protection efficacy is rather scarce. As a first step to address this problem, the present work is taken up and the potential rise at the top and ground end currents in insulating mast scheme with single tower is investigated for several tower heights and pertinent values of other parameters. The quantities that are investigated are the potential difference across the insulation and ground end currents for both tower and the ground wires. Quantifications are carried out for the relevant range of stroke current front times. The influence of number of ground wires, their earthing location and to a limited extent, the length of the insulating support have been ascertained. Some relevant discussion on insulation strength is made. These findings are quite novel and aid in quantification of the practical efficacy of the insulated mast scheme. The level of induction to the support tower and possible flashover to the same are not in favour of this scheme.

Research paper thumbnail of Images in linearly conducting dielectrics

IEE Proceedings - Science, Measurement and Technology, 1997

Methods of images for electrostatic fields and steady conduction fields are fairly well known. Wh... more Methods of images for electrostatic fields and steady conduction fields are fairly well known. Whenever applicable, they have made the solution of field problems much simpler. However, when dealing with lossy dielectrics both permittivity and nonzero conductivity are to be considered. A generalised method of images is developed which can deal with such linearly lossy (conducting) dielectrics. For linearly conducting dielectrics, a point charge is equivalent to a point current source and vice versa. At t = 0+, only the dielectric image will be seen. Subsequently, because of the finite nonzero conductivities of the associated media, a current will flow and surface charges will accumulate at the interface due to the mismatch in the material properties. The equattion governing this surface-charge accumulatioin is derived. Linearity of the media permits fields in either medium to be obtained by superposing the fields due to the dielectric images and that due to the interfacial charges. The field can be obtained in either medium by replacing these surface charges by an equivalent point charge kept ait the appropriate image point. This equivalent point charge satisfies a similar differential equation in time to that of the surface charge. The cases of time-varying chargeicurrent sources and the source-current requirement for keeping any point very close to the source at a specified potential are also discussed.

Research paper thumbnail of A Macroscopic Model for First Return Stroke of Lightning

IEEE Transactions on Electromagnetic Compatibility, 2011

Research paper thumbnail of Analysis for the Reflected Waves Transmitted on to the Channel by Tall Grounded Objects Using a Special Case

IEEE Transactions on Electromagnetic Compatibility, 2012

received the B.Sc. degree (first class Hons.) in physics and the Ph.D. degree in electricity with... more received the B.Sc. degree (first class Hons.) in physics and the Ph.D. degree in electricity with special attention to transients and discharges, from the

Research paper thumbnail of On the possible variation of the lightning striking distance as assumed in the IEC lightning protection standard as a function of structure height

Electric Power Systems Research, 2014

ABSTRACT The effect of structure height on the lightning striking distance is estimated using a l... more ABSTRACT The effect of structure height on the lightning striking distance is estimated using a lightning strike model that takes into account the effect of connecting leaders. According to the results, the lightning striking distance may differ significantly from the values assumed in the IEC standard for structure heights beyond 30 m. However, for structure heights smaller than about 30 m, the results show that the values assumed by IEC do not differ significantly from the predictions based on a lightning attachment model taking into account the effect of connecting leaders. However, since IEC assumes a smaller striking distance than the ones predicted by the adopted model one can conclude that the safety is not compromised in adhering to the IEC standard. Results obtained from the model are also compared with Collection Volume Method (CVM) and other commonly used lightning attachment models available in the literature. The results show that in the case of CVM the calculated attractive distances are much larger than the ones obtained using the physically based lightning attachment models. This indicates the possibility of compromising the lightning protection procedures when using CVM.

Research paper thumbnail of Genesis of return stroke current evolution at the wavefront

Atmospheric Research, 2013

ABSTRACT The channel dynamics at the wavefront is quite complex and is basically responsible for ... more ABSTRACT The channel dynamics at the wavefront is quite complex and is basically responsible for the evolution of return stroke current. The physical processes that actually contribute to the current evolution are not very clearly known. The enhancement of channel conductance at the wavefront is necessary for the current evolution and hence, return stroke. With regard to this, several questions arise like: (i) what causes the enhancement of this conductance, (ii) as the channel core temperature and electrical conductance are closely related, does one support the other and (iii) is the increase in core temperature on the nascent section of the channel is the result of free burning arc of the wavefront just below. These questions are investigated in detail in this work with appropriate transient thermal analysis and a macroscopic physical model for the lightning return stroke. Results clearly indicate that the contribution from the thermal field of the wavefront region to the adjacent nascent channel section is negligible as compared to the field enhancement brought in by the same. In other words, the whole process of return stroke evolution is dependent on the local heat generation at the nascent section caused by the enhancement of the electric field due to the arrival of the wavefront.

Research paper thumbnail of Capacitive-Resistive Transients in terms of field quantities

Journal of the Indian Institute of Science

Capacitive-resistive transients in extended media are discussed in tenns of electric field quanti... more Capacitive-resistive transients in extended media are discussed in tenns of electric field quantities. Obviously, in rhese problems, the contribution of the magnetlc field to the electric field is deemcd negligible. For a simple lliuslratlve example, the field solution is compared with the circub-theorelied resuit for the voltage and current. An algorithm for solving such transients in space and time doman with the help of a Laplace solver is presented. Any other Laplace solver can also be used far this purpose. Its applicability is demonstrated with Ceeexamples, one of which i s chosen to have a circuit-theoretical solution. K v o r d s : Capacitive-resistive transients, boundary condition, eicctromagnetic transients.

Research paper thumbnail of Investigation on the Potential Rise and Currents in Insulated Mast Scheme with Single Tower During Stroke Interception

Journal of Lightning Research, 2010

The insulated mast scheme for the lightning protection system can be found in a few practical des... more The insulated mast scheme for the lightning protection system can be found in a few practical designs. Many advantages over conventional protection system are some times envisaged. However, the technical literature on the analysis of such schemes and further quantification of their protection efficacy is rather scarce. As a first step to address this problem, the present work is taken up and the potential rise at the top and ground end currents in insulating mast scheme with single tower is investigated for several tower heights and pertinent values of other parameters. The quantities that are investigated are the potential difference across the insulation and ground end currents for both tower and the ground wires. Quantifications are carried out for the relevant range of stroke current front times. The influence of number of ground wires, their earthing location and to a limited extent, the length of the insulating support have been ascertained. Some relevant discussion on insulation strength is made. These findings are quite novel and aid in quantification of the practical efficacy of the insulated mast scheme. The level of induction to the support tower and possible flashover to the same are not in favour of this scheme.

Research paper thumbnail of Images in linearly conducting dielectrics

IEE Proceedings - Science, Measurement and Technology, 1997

Methods of images for electrostatic fields and steady conduction fields are fairly well known. Wh... more Methods of images for electrostatic fields and steady conduction fields are fairly well known. Whenever applicable, they have made the solution of field problems much simpler. However, when dealing with lossy dielectrics both permittivity and nonzero conductivity are to be considered. A generalised method of images is developed which can deal with such linearly lossy (conducting) dielectrics. For linearly conducting dielectrics, a point charge is equivalent to a point current source and vice versa. At t = 0+, only the dielectric image will be seen. Subsequently, because of the finite nonzero conductivities of the associated media, a current will flow and surface charges will accumulate at the interface due to the mismatch in the material properties. The equattion governing this surface-charge accumulatioin is derived. Linearity of the media permits fields in either medium to be obtained by superposing the fields due to the dielectric images and that due to the interfacial charges. The field can be obtained in either medium by replacing these surface charges by an equivalent point charge kept ait the appropriate image point. This equivalent point charge satisfies a similar differential equation in time to that of the surface charge. The cases of time-varying chargeicurrent sources and the source-current requirement for keeping any point very close to the source at a specified potential are also discussed.

Research paper thumbnail of A Macroscopic Model for First Return Stroke of Lightning

IEEE Transactions on Electromagnetic Compatibility, 2011

Research paper thumbnail of Analysis for the Reflected Waves Transmitted on to the Channel by Tall Grounded Objects Using a Special Case

IEEE Transactions on Electromagnetic Compatibility, 2012

received the B.Sc. degree (first class Hons.) in physics and the Ph.D. degree in electricity with... more received the B.Sc. degree (first class Hons.) in physics and the Ph.D. degree in electricity with special attention to transients and discharges, from the

Research paper thumbnail of On the possible variation of the lightning striking distance as assumed in the IEC lightning protection standard as a function of structure height

Electric Power Systems Research, 2014

ABSTRACT The effect of structure height on the lightning striking distance is estimated using a l... more ABSTRACT The effect of structure height on the lightning striking distance is estimated using a lightning strike model that takes into account the effect of connecting leaders. According to the results, the lightning striking distance may differ significantly from the values assumed in the IEC standard for structure heights beyond 30 m. However, for structure heights smaller than about 30 m, the results show that the values assumed by IEC do not differ significantly from the predictions based on a lightning attachment model taking into account the effect of connecting leaders. However, since IEC assumes a smaller striking distance than the ones predicted by the adopted model one can conclude that the safety is not compromised in adhering to the IEC standard. Results obtained from the model are also compared with Collection Volume Method (CVM) and other commonly used lightning attachment models available in the literature. The results show that in the case of CVM the calculated attractive distances are much larger than the ones obtained using the physically based lightning attachment models. This indicates the possibility of compromising the lightning protection procedures when using CVM.

Research paper thumbnail of Genesis of return stroke current evolution at the wavefront

Atmospheric Research, 2013

ABSTRACT The channel dynamics at the wavefront is quite complex and is basically responsible for ... more ABSTRACT The channel dynamics at the wavefront is quite complex and is basically responsible for the evolution of return stroke current. The physical processes that actually contribute to the current evolution are not very clearly known. The enhancement of channel conductance at the wavefront is necessary for the current evolution and hence, return stroke. With regard to this, several questions arise like: (i) what causes the enhancement of this conductance, (ii) as the channel core temperature and electrical conductance are closely related, does one support the other and (iii) is the increase in core temperature on the nascent section of the channel is the result of free burning arc of the wavefront just below. These questions are investigated in detail in this work with appropriate transient thermal analysis and a macroscopic physical model for the lightning return stroke. Results clearly indicate that the contribution from the thermal field of the wavefront region to the adjacent nascent channel section is negligible as compared to the field enhancement brought in by the same. In other words, the whole process of return stroke evolution is dependent on the local heat generation at the nascent section caused by the enhancement of the electric field due to the arrival of the wavefront.