The Experts below are selected from a list of 13869 Experts worldwide ranked by ideXlab platform
Farhad Rachidi - One of the best experts on this subject based on the ideXlab platform.
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a semi analytical method to evaluate lightning induced overvoltages on Overhead Lines using the matrix pencil method
2018Co-Authors: Jun Guo, Yanzhao Xie, Farhad RachidiAbstract:Lightning electromagnetic fields can couple to Overhead power transmission and distribution Lines, causing serious effects to the power system. Lightning electromagnetic fields that couple to Overhead Lines have a nonuniform distribution along the line conductors. Therefore, to ensure the accuracy of the numerical calculation results, a large number of discretization points are needed along the line, which might dramatically increase the computation time since the evaluation of lightning electromagnetic fields in the presence of a lossy soil involves, in general, Sommerfeld integrals, or, even in the case of a perfectly conducting ground, numerical integration along the channel. This paper proposes a new approach to address this problem. The proposed approach is based on the Agrawal et al . coupling model, in which the horizontal lightning electric field along the line is represented by the complex exponential functions in the frequency domain using the matrix pencil method. The method is highly efficient in terms of computation time since the lightning-induced response of the line can be solved semi-analytically. The proposed approach is validated by two different validation examples.
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evaluation of lightning electromagnetic fields and their induced voltages on Overhead Lines considering the frequency dependence of soil electrical parameters
2013Co-Authors: Majed Akbari, Alberto Borghetti, Farhad Rachidi, Keyhan Sheshyekani, Abolfazl Pirayesh, Mario Paolone, C A NucciAbstract:This paper presents a comprehensive study on the effect of the frequency dependence of soil electrical parameters on the lightning radiated electromagnetic fields as well as their associated induced voltages on Overhead Lines. To this aim, a full-wave approach based upon the finite-element method (FEM) is utilized. In the analyses, frequency dependence of soil conductivity and relative permittivity is introduced, using available analytical formulae that is obtained from experimental data. It is shown that the radial electric field is the only component which is significantly affected by the frequency dependence of soil electrical parameters at observation points as close as some tens of meters from the lightning channel. The vertical component of the electric field and the azimuthal component of the magnetic field are not much influenced by this property of soil at moderate distances (up to several hundred meters) from the lightning channel. For distant observation points and for poorly conducting grounds, however, these components are also affected. It is also shown that for soils characterized by relatively moderate and low resistivity values (less than 1000 Ω.m), lightning-induced voltages are not significantly affected by the frequency dependence of soil electrical parameters. For poorly conducting soils, instead, the frequency dependence of soil electrical parameters results in a decrease of lightning-induced voltages.
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Influence of a lossy ground on lightning-induced voltages on Overhead Lines
1996Co-Authors: Farhad Rachidi, Carlo Alberto Nucci, M Ianoz, Carlo MazzettiAbstract:A comprehensive study on the effect of a lossy ground on the induced voltages on Overhead power Lines by a nearby lightning strike is presented. The ground conductivity plays a role in both the evaluation of the lightning radiated fields and of the line parameters. To be calculated by means of a rigorous theory, both fields and line constants need important computation time, which, for the problem of interest, is still prohibitive. The aim of this paper is to discuss and analyze the various simplified approaches and techniques that have been proposed for the calculation of the fields and the line constants when the ground cannot be assumed as a perfectly conducting plane. Regarding the radiated electromagnetic field, it is shown that the horizontal electric field, the component which is most affected by the ground finite conductivity, can be calculated in an accurate way using the Cooray-Rubinstein simplified formula. The presence of an imperfectly conducting ground is included in the coupling equations by means of two additional terms: the longitudinal ground impedance and the transverse ground admittance, which are both frequency-dependent. The latter can generally be neglected for typical Overhead Lines, due to its small contribution to the overall transverse admittance of the line. Regarding the ground impedance, a comparison between several simplified expressions used in the literature is presented and the validity limits of these expressions are established. It is also shown that for typical Overhead Lines the wire impedance can be neglected as regard to the ground impedance.
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lightning induced voltages on Overhead Lines
1993Co-Authors: Carlo Alberto Nucci, Farhad Rachidi, M Ianoz, Carlo MazzettiAbstract:A modeling procedure that permits calculation of lightning-induced voltages on Overhead Lines starting from the channel-base current is discussed. The procedure makes use of a coupling model already presented in the literature, based on transmission line theory, for field-to-Overhead line coupling calculations. Both models are discussed and compared with experimental results. The hypothesis of perfect conducting ground, used to analyze the voltages induced on an Overhead line by a nearby lightning return stroke with a striking point equidistant from the line terminations, and the limits of its validity are determined. A comparison shows that peak value and maximum front steepness of the induced voltages calculated using other lightning return-stroke models differ. It is also shown that another coupling model used in the power-lightning literature by several other authors may result in a less accurate estimation of the induced voltages. >
Liu Zhenguo - One of the best experts on this subject based on the ideXlab platform.
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development of parallel gap lightning protection device for 110 kv and 220 kv Overhead Lines
2006Co-Authors: Liu ZhenguoAbstract:To reduce the damage of insulators and fittings caused by power frequency follow current after lightning flashover,a parallel gap lightning protection device for 110 kV and 220kV Overhead transmission Lines was developed. With this device the lightning impulse flashover and power frequency arc characteristics were investigated and the voltage distribution along insulator strings and trip out rate of transmission Lines with the device are calculated. As a function of gap distance, the fifty percent lightning-stroke flashover voltage was analyzed. Based on above studies the design of the device was improved, serial tables of electrode’s design dimension were given, and the specimens were provided, so that engineers and technicians could select the dimension of the parallel gap according to insulator pieces of the strings and lightning-stroke trip-out rate of transmission Lines.
Alberto Borghetti - One of the best experts on this subject based on the ideXlab platform.
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inverse laplace transform of sunde s formula for the ground impedance of buried cables
2019Co-Authors: Fabio Tossani, Fabio Napolitano, Alberto BorghettiAbstract:The time-domain calculation of electromagnetic transients in multi-conductor lossy Overhead Lines and buried cables requires the evaluation of the transient ground resistance matrix. For the case of Overhead Lines, analytical expressions for the transient ground resistance obtained by solving the inverse Laplace transform of Sunde’s formula have been recently presented. This paper presents the expressions obtained by the analytical inverse Laplace transform of Sunde’s formula for the case of buried cables. The results provided by the proposed analytical expressions agree with those given by the numerical inverse transform of Sunde’s formula. The new expressions are adopted for the calculation of the per-unit-length voltage drop in a multiconductor underground line. The voltage drop waveforms are compared with those given by recently proposed time-domain analytical expressions that neglect displacement currents.
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Inverse Laplace Transform of the Ground Impedance Matrix of Overhead Lines
2018Co-Authors: Fabio Tossani, Fabio Napolitano, Alberto BorghettiAbstract:This letter deals with the calculation in time domain of the transient ground resistance matrix of an Overhead transmission line (TL). Each element of the matrix is evaluated by solving analytically the inverse Laplace transform of the general integral expressions of the ground impedance in frequency domain proposed by Sunde. The presented expressions are suitable for the direct implementation in an electromagnetic transient program (e.g., EMTP-like ones) based on a time domain solution of the TL's equations.
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evaluation of lightning electromagnetic fields and their induced voltages on Overhead Lines considering the frequency dependence of soil electrical parameters
2013Co-Authors: Majed Akbari, Alberto Borghetti, Farhad Rachidi, Keyhan Sheshyekani, Abolfazl Pirayesh, Mario Paolone, C A NucciAbstract:This paper presents a comprehensive study on the effect of the frequency dependence of soil electrical parameters on the lightning radiated electromagnetic fields as well as their associated induced voltages on Overhead Lines. To this aim, a full-wave approach based upon the finite-element method (FEM) is utilized. In the analyses, frequency dependence of soil conductivity and relative permittivity is introduced, using available analytical formulae that is obtained from experimental data. It is shown that the radial electric field is the only component which is significantly affected by the frequency dependence of soil electrical parameters at observation points as close as some tens of meters from the lightning channel. The vertical component of the electric field and the azimuthal component of the magnetic field are not much influenced by this property of soil at moderate distances (up to several hundred meters) from the lightning channel. For distant observation points and for poorly conducting grounds, however, these components are also affected. It is also shown that for soils characterized by relatively moderate and low resistivity values (less than 1000 Ω.m), lightning-induced voltages are not significantly affected by the frequency dependence of soil electrical parameters. For poorly conducting soils, instead, the frequency dependence of soil electrical parameters results in a decrease of lightning-induced voltages.
Andrea Michiorri - One of the best experts on this subject based on the ideXlab platform.
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Overhead Lines dynamic line rating based on probabilistic day ahead forecasting and risk assessment
2019Co-Authors: Romain Dupin, George Kariniotakis, Andrea MichiorriAbstract:Abstract Dynamic Line Rating is a technology devised to modify an Overhead line’s current-carrying capacity based on weather observation. The benefits of this modification may include reduced congestion costs, an increased renewable energy penetration rate, and improved network reliability. DLR is already well developed, but few papers in the literature investigate DLR day-ahead forecasting. The latter is central to DLR development since many of the decisions related to grid management are taken at least on a day-ahead basis. In this paper, two problems related to DLR forecasts are dealt with: how to achieve precise, reliable calculations of day-ahead forecasts of Overhead line ampacity and how to define a methodology to calculate safe rating values using these forecasts. On the first point, four machine-learning algorithms were evaluated, identifying the best approach for this problem and quantifying the potential performance. On the second point, the developed methodology was tested and compared to the current static line rating approach.
Carlo Mazzetti - One of the best experts on this subject based on the ideXlab platform.
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Influence of a lossy ground on lightning-induced voltages on Overhead Lines
1996Co-Authors: Farhad Rachidi, Carlo Alberto Nucci, M Ianoz, Carlo MazzettiAbstract:A comprehensive study on the effect of a lossy ground on the induced voltages on Overhead power Lines by a nearby lightning strike is presented. The ground conductivity plays a role in both the evaluation of the lightning radiated fields and of the line parameters. To be calculated by means of a rigorous theory, both fields and line constants need important computation time, which, for the problem of interest, is still prohibitive. The aim of this paper is to discuss and analyze the various simplified approaches and techniques that have been proposed for the calculation of the fields and the line constants when the ground cannot be assumed as a perfectly conducting plane. Regarding the radiated electromagnetic field, it is shown that the horizontal electric field, the component which is most affected by the ground finite conductivity, can be calculated in an accurate way using the Cooray-Rubinstein simplified formula. The presence of an imperfectly conducting ground is included in the coupling equations by means of two additional terms: the longitudinal ground impedance and the transverse ground admittance, which are both frequency-dependent. The latter can generally be neglected for typical Overhead Lines, due to its small contribution to the overall transverse admittance of the line. Regarding the ground impedance, a comparison between several simplified expressions used in the literature is presented and the validity limits of these expressions are established. It is also shown that for typical Overhead Lines the wire impedance can be neglected as regard to the ground impedance.
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lightning induced voltages on Overhead Lines
1993Co-Authors: Carlo Alberto Nucci, Farhad Rachidi, M Ianoz, Carlo MazzettiAbstract:A modeling procedure that permits calculation of lightning-induced voltages on Overhead Lines starting from the channel-base current is discussed. The procedure makes use of a coupling model already presented in the literature, based on transmission line theory, for field-to-Overhead line coupling calculations. Both models are discussed and compared with experimental results. The hypothesis of perfect conducting ground, used to analyze the voltages induced on an Overhead line by a nearby lightning return stroke with a striking point equidistant from the line terminations, and the limits of its validity are determined. A comparison shows that peak value and maximum front steepness of the induced voltages calculated using other lightning return-stroke models differ. It is also shown that another coupling model used in the power-lightning literature by several other authors may result in a less accurate estimation of the induced voltages. >
