Carlos Garrido

Nodal frequency analysis of grounding systems considering the soil ionization effect

Soil ionization takes place when the current leaking into the earth is high enough to produce an electric field intensity greater than a critical value. This phenomenon lowers the ground impedance and it is similar to an apparent increase in the electrode dimensions. Soil ionization has a great influence on the performance of small grounding electrodes fed by currents of high magnitude (i.e., lightning waves). In this paper, a new way of including the nonlinear soil ionization in the grounding system analysis is proposed. The study of the grounding system is performed in the frequency domain by means of an equivalent electric circuit.

Low-frequency magnetic fields from electrical appliances and power lines

The relationship between magnetic fields and the health of people is increasingly being investigated. International organizations have proposed bylaws that put limits on the value of the generated magnetic field. In this work, we measure the magnetic field created by electrical appliances and high voltage lines and we analyze the degree of compliance with recent applicable European regulation. The simulation of the magnetic field generated by electrical lines through a simple model accurately predicts the measured values. The model is used to simulate the behavior of the lines under given conditions. In both cases, an FFT analysis of the magnetic field waveform was performed to study the frequency and amplitude of the possible induced currents.

Theoretical model to calculate steady-state and transient ampacity and temperature in buried cables

The temperature distribution and ampacity in a multilayered soil surrounding a system of three cables is calculated in the steady state in emergency situations. We present the mathematical model that solves the heat diffusion equation in cylindrical coordinates inside the cables and in Cartesian coordinates in the surrounding soil. The finite difference method is used to solve the equations. In order to reduce the number of points studied that are of no interest to the results, a variable step discretization is used. We present the development of the model and the effect of some of the parameters that influence the convergence and accuracy of the method. The application of the model in different configurations and situations is given in the second part of this work. The model is applicable to the study of buried cab in both the steady state and transient states for short circuit and overload situations.

Magnetic-Field Evaluation in the Vicinity of High-Voltage Electric Systems

This paper presents a simulation model of the magnetic field generated by electric energy distribution and transport facilities. The aim of this paper is to assess the models compliance with current international regulations and recommendations. One of the principal advantages of this model is its relative simplicity, since it represents the facilitys elements by using a conductor network. This network is energized by injecting a system of currents that model the load state of the facility. The conductor network is subsequently analyzed as a conventional electrical circuit. This paper applies the model to the specific case of an outdoor substation and the results are later validated when compared with the magnetic-field measurements taken at the facility.

A method for predicting time-current characteristics of fuselinks

ABSTRACT In this study a model for the calculation of prearcing time-current in fuselinks is presented. This model is based on the solution of the electric potential, current density and heat diffusion equations using the approximation of the partial derivatives by central finite differences. In this model the variation of the different parameters with temperature is taken into account in the equations. Because of the non linearity of the equations, the solution is obtained by means of a Gauss-Seidel iterative method or relaxation process. The model has been applied to the study of a real fuselink, and a perfect coincidence has been obtained between the theoretical results of the model and the experimental values. The consideration of the variability of the parameters with temperature is fundamental for the above mentioned coincidence. The model has been also used to study the behaviour of different metals as fuse elements. For the studied metals, we can conclude that to obtain different characteristic cu...