Marcio Matias Afonso

An Adaptive Deep-Cut Ellipsoidal Algorithm Applied to the Optimization of Transmission Lines

This paper presents a computational tool intended to calculate and minimize the electric fields at ground level of high surge impedance loading transmission lines (TLs). This type of TL achieves higher power transmission rates utilizing optimized configuration for the phase conductors. This method is advantageous over other actions taken by the utility company, such as increasing the maximum operation temperature of the line, increasing the size of the conductors, or the utilization of multiple conductors per phase. In this paper, an enhanced deep-cut ellipsoidal method is applied to find a new optimized configuration for the phase conductors. The new proposed configuration results in reduced profiles of electric fields. Two different TLs are analyzed and optimized.

Transient response of grounding electrodes for the frequency-dependence of soil parameters

This study evaluates the response of a horizontal grounding electrode against impulsive currents whose waveforms and time front is typical of lightning. The electrode is found buried in soil with different resistivity values and whose conductivity and permittivity vary with spectrum frequency of lightning according four formulations exists in literature. It was possible to observe the intense propagation effects responsible for the grounding impedance values significantly different from the resistance at low frequency and also difference according to each formulation, which has decreased the potential, the impedance impulsive and impulsive coefficient compared to traditional data from the technical literature specialist.

Evaluation of Singular Integral Equation in MoM Analysis of Arbitrary Thin Wire Structures

In this paper, a new simple and efficient numerical procedure is presented for evaluating electric field singular integral equations found in the method of moments (MoM) analysis of electromagnetic scattering by arbitrary thin wire structures. The analysis is conducted using triangular basis and weight functions. The singular kernel is modeled as a first-kind elliptical integral and evaluated using the arithmetic geometric mean. Numerical integration is used only when there are no singular kernels. Tests in dipoles, a loop, and a spiral are provided to illustrate the proposed techniques accuracy and computational efficiency.

Periodic Boundary Conditions in the Natural Element Method

The purpose of this paper is to introduce periodic and antiperiodic boundary conditions in the natural element method (NEM). It is shown that as the NEM shape functions verify the Kronecker delta property, the imposition of such boundary conditions can be done in an easy way as in the finite-element method (FEM). These boundary conditions are important because they allow exploitation of the inherent symmetry of the electromagnetic devices. Therefore, with these techniques the NEM can now easily take advantage of the symmetry of electrical machines. The proposed approach is evaluated, and its results are compared with those obtained by the traditional FEM.

Electromagnetic Scattering Analysis of Arbitrary Structures by the Natural Element Method Coupled With Absorbing Boundary Condition

The problem of determining the electromagnetic scattering of arbitrary structures consisting of both dielectric and conducting materials are analyzed in this paper by the natural-element method coupled with the absorbing boundary condition (NEM-ABC). By this method, the target is first enclosed by a fictitious boundary. Maxwells equations are then solved by NEM inside and ABC is applied on the fictitious boundary. The results are compared with analytical and finite-element method-ABC ones which show the robustness, applicability and relevance of the method.

A Meshless Approach Using EFG Interpolating Moving Least-Squares Method in 2-D Electromagnetic Scattering Analysis

In this paper, the element-free Galerkin method with special interpolating shape functions is used to solve an electromagnetic scattering problem. These shape functions make use of the interpolating moving least-squares method that guarantees the Kronecker delta property. This allows enforcing the absorbing boundary condition directly in the discrete system, consisting of a more practical way when compared with other methods, such as the Lagrange multipliers. The technique is applied to the analysis of electromagnetic scattering generated by an infinite dielectric cylinder illuminated by a TMZ plane wave and a sensibility analysis is done in which the numerical results are compared against the analytical solutions.

Voltage Distribution Along Earth Grounding Grids Subjected to Lightning Currents

This paper applies a rigorous electromagnetic model to determine the transient distribution of potentials along a substation earth grounding grid subjected to lightning currents. The obtained results show that, in the initial period of the transient, equipment pieces that are earth grounded at distinct points of the grid and are electrically linked (for example, by aerial communication cables) experience impulsive loop currents. Such loop currents can cause equipment malfunctions, failures, and damage. A remarkable conclusion of this paper is that such loop currents can reach substantial values even in the case of soils of low resistivity. Some practical aspects are highlighted in order to reduce the risks due to the nonuniform distribution of potentials along earth grounding.

Approximated raising of the curvature of a double-ridged waveguide horn antenna in a computational model

In this paper the curvature and the shape of the double ridged horn antennas is studied in its computational modeling, whose application is very significant for EMC/EMI tests. The ridges, curved structures inside the double ridged horn antennas, are an important structural parameter. Its curvature is described by a function, and this function needs a mathematical treatment when building its 3D geometry in a computational model. When the function of the ridges is not known, an approximated function is an available approach to build its 3D structure. To accurately characterize the double ridged horn, an approximated function of the ridges is raised and implemented in a computer simulation. The approach was verified and results show significantly consistency with manufacturers data.

Assessment of a frequency dependent soil model impact on lightning overvoltages

A key aspect in the evaluation of the lightning performance of an overhead line is the tower grounding modeling approach. It affects the insulator string overvoltages and the ground potential rise (GPR). This work aims to assess the impact of the soil model i.e. using frequency independent and frequency dependent parameters. The developed grounding system model was implemented in the EMTP-ATP program. A RLC synthetized network is used instead of a constant lumped resistance. The RLC elements are derived from the rational approximation of the grounding system response obtained using a rigorous model based on the direct solution of Maxwells equations in the frequency domain. An application example is presented, showing that the computed overvoltage is sensitive to the frequency dependence of the soil parameters. This effect is more pronounced for high resistivity soil.

An efficient two-level preconditioner based on lifting for FEM-BEM equations

The system resulting from the coupled Finite Element Method and Boundary Element Method formulations inherits all characteristics of both finite element and boundary element equation system, i. e., the system is partially sparse and symmetric and partially full and nonsymmetric. Consequently, to solve the resulting coupled equation system is not a trivial task. This paper proposes a new efficient lifting-based two level preconditioner for the coupled global system. The proposed approach is applied to solve the coupled systems resulting from the electromagnetic scattering problem and its performance is evaluated based on the number of iterations and the computational time. Traditional methods based on incomplete and complete LU decompositions are used for comparison.