Parallel computing aided design of earthing systems for electrical substations in non-homogeneous soil models

An accurate design of grounding systems is essential to assure the safety of the persons, to protect the equipment and to avoid interruptions in the power supply. In order to attain these targets, it is necessary to compute the equivalent electrical resistance of the system and the potential distribution on the earth surface in fault conditions. In this paper, a numerical approach for grounding analysis embedded in stratified soils and its implementation in a high-performance parallel computer are presented. The feasibility of this system is shown with its application to the grounding analysis in layered soils by using the geometry of real grounding grids

Parallel computing aided design of earthing systems for electrical substations in non homogeneous soil models

[Abstract] An accurate design of grounding systems is essential to assure the safety of the persons, to protect the equipment and to avoid interruptions in the power supply. In order to attain these targets, the equivalent electrical resistance of the system and the potential distribution on the earth surface in fault conditions are necessary to compute. In this paper, it is presented a numerical approach for grounding analysis embedded in stratified soils and its implementation in a high-perfomance parallel computer. The feasibility of this system is shown with its application to the analysis of a real grounding system in a layered soil.Ministerio de Educación y Cultura; 1FD97-010

Stability analysis of BEM approximate solutions in grounding analysis

[Abstract] In this paper we present a summary of the Boundary Element Method developed for the analysis of potential problems in the electrical engineering field. The numerical model proposed is shown as a general frame so that other existing computer methods are recognized as particular cases. The stability of these models is analyzed identifying the sources of error.Ministerio de Ciencia y Tecnología; 1FD97-010

Why do computer methods for grounding analysis produce anomalous results?

Aceptado en "IEEE transactions on power delivery"[Abstract] Grounding systems are designed to guarantee personal security, protection of equipments and continuity of power supply. Hence, engineers must compute the equivalent resistance of the system and the potential distribution on the earth surface when a fault condition occurs [1], [2], [3]. While very crude approximations were available until the 70’s, several computer methods have been more recently proposed on the basis of practice, semi-empirical works and intuitive ideas such as superposition of punctual current sources and error averaging [1], [3], [4], [5], [6]. Although these techniques are widely used, several problems have been reported. Namely: large computational requirements, unrealistic results when segmentation of conductors is increased, and uncertainty in the margin of error [2], [5]. A Boundary Element formulation for grounding analysis is presented in this paper. Existing computer methods such as APM are identified as particular cases within this theoretical framework. While linear and quadratic leakage current elements allow to increase accuracy, computing time is reduced by means of new analytical integration techniques. Former intuitive ideas can now be explained as suitable assumptions introduced in the BEM formulation to reduce computational cost. Thus, the anomalous asymptotic behaviour of this kind of methods is mathematically explained, and sources of error are rigorously identified

A boundary element formulation for the substation grounding design

[Abstract] A Boundary Element approach for the numerical computation of substation grounding systems is presented. In this general formulation, several widespread intuitive methods (such as Average Potential Method) can be identified as the result of specific choices for the test and trial functions and suitable assumptions introduced in the BEM formulation to reduce computational cost. While linear and parabolic leakage current elements allow to increase accuracy, computing time is drastically reduced by means of new completely analytical integration techniques and semi-iterative methods for solving linear equations systems. This BEM formulation has been implemented in a specific Computer Aided Design system for grounding analysis developed in the last years. The feasibility of this new approach is demonstrated with its application to a real problem

On the anomalous asymptotic performance of the regular computer methods for grounding analysis

15th International Conference on Boundary Element Technology, Detroit, USA[Abstract] Grounding systems are designed to guarantee personal security, protection of equipments and continuity of power supply. Hence, engineers must compute the equivalent resistance of the system and the potential distribution on the earth surface when a fault condition occurs [1, 2, 3]. While very crude approximations were available until the 70’s, several computer methods have been more recently proposed on the basis of practice, semi-empirical works and intuitive ideas such as superposition of punctual current sources and error averaging [1, 3, 4, 5, 6]. Although these techniques are widely used, several problems have been reported. Namely: large computational requirements, unrealistic results when segmentation of conductors is increased, and uncertainty in the margin of error [2, 5]. A Boundary Element formulation for grounding analysis is presented in this paper. Existing computer methods such as APM are identified as particular cases within this theoretical framework. While linear and quadratic leakage current elements allow to increase accuracy, computing time is reduced by means of new analytical integration techniques. Former intuitive ideas can now be explained as suitable assumptions introduced in the BEM formulation to reduce computational cost. Thus, the anomalous asymptotic behaviour of this kind of methods is mathematically explained, and sources of error are rigorously identified.Ministerio de Educación y Cultura; 1FD97-0108Ministerio de Educación y Cultura; DPI2001-055

Analytical integration techniques for earthing grid computation by boundary element methods

[Abstract] Analysis and design of substation earthing involves computing the equivalent resistance of grounding systems, but also distribution of potentials on the earth surface due to fault currents [1]. While very crude approximations were available in the sixties, several methods have been proposed in the last two decades, must of them on the basis of intuitive ideas such as superposition of punctual current sources and error averaging [2,3]. Although these techniques represented a significant improvement in the area of earthing analysis, a number of problems have been reported. Namely: large computational requirements, unrealistic results when segmentation of conductors is increased, and uncertainty in the margin of error [3]. In this paper, a 1D Boundary Element formulation is presented. Several widespread intuitive methods (such as APM) are identified as particular cases of this general approach. Thus, former intuitive ideas can now be explained as suitable assumptions introduced in the BEM formulation to reduce computational cost. The anomalous asymptotic behaviour of this kind of methods is mathematically explained, and sources of error are pointed out. While linear and parabolic leakage current elements allow to increase accuracy, computing time is drastically reduced by means of new analytical integration techniques. Finally, an application example to a real problem is presented

Circuit - based transient model of grounding electrode with consideration of soil ionization and current rate of rise factors

The behaviour of a grounding electrode can be predicted by using either the electrical circuit model or electromagnetic computation. Despite its advantages over the latter, the grounding circuit model fails to accurately predict the behaviour under transient conditions due to the absence of two key factors, namely the soil ionization, and the current rate–of–rise. A new equivalent circuit model of a grounding electrode with dynamic circuit elements (Rd, Cd, and Ld) was developed to consider both soil ionization and current rate–of–rise factors. A generalized formula was derived to calculate the dynamic inductance, Ld, for all standard current wave shapes such as Conseil International des Grands Réseaux Électriques (CIGRE), double–exponential, and IEC 62305–1 (International Electrotechnical Commission). The computed inductance, Ld, dynamically changes with the change in the lightning current parameters, thus improving its accuracy for all current rate–of–rise conditions. The consideration for the soil ionization effect on grounding electrode resistance, Rd, and soil capacitance, Cd, within the equivalent circuit model was achieved by modelling the soil with a network of two layer capacitors (TLC) in which soil particles and air voids are the TLC components. Differential equations were derived to incorporate the soil ionization phenomenon inside the TLC network. The voltage response of the new equivalent circuit model and the dynamic circuit elements were determined by using the above–suggested methods, is more accurate than that of the conventionally determined grounding circuit models. The overall differences between the equivalent circuit model and several experiments are 3.3% for the electrode resistance and 2.8% for the electrode peak voltage. The new equivalent circuit model helps to optimize the overall grounding electrode design, and to provide a better fast transient protection and insulation coordination

Earthing performance of transmission line towers

This work is primarily concerned with the performance of tower base earthing systems under AC variable frequency and transient conditions. The work has involved the investigation into the performance of practical earthing systems including tests on a full-size 275kV transmission tower base and corresponding calculation and numerical simulations