Germán Moreno

Using genetic algorithm and the simplex method to obtain equivalent circuits of the grounding systems

There are many methodologies that, using the frequency response of a grounding system impedance, permit to get the coefficients of a transfer function or the electrical parameters of a specific circuit, that behave as equivalents of that system. In this paper in the first part, the coefficients of the transfer function and the parameters of the circuit were obtained using the simplex method to optimize the values and minimize the square error between the objective function and the frequency response of the software Gtierras. The results of the methodologies depend on the selection of the initial values (which change for every case evaluated) to start the process. This happens because the simplex method can get local values. In the second part it is proposed a genetic algorithm (global values) to get the initial values of the simplex method and solve the problem. The result of mixing both methods is compared with the vector fitting method, showing that it is possible to obtain a circuit or a transfer function that reproduce successfully the impedance of the grounding systems in the frequency domain.

Using a grounding system equivalent circuit to evaluate transferred lightning surges trough distribution transformers

Grounding in a distribution system is important to reduce the lightning voltage surges that are transferred from medium voltage to the low voltage network through distribution transformers. These overvoltages produce several damages in equipments connected to distribution system and can cause outages of the electrical power supply bringing economic costs to both electric utility and customer. In this paper, is evaluated the impedance of different grounding geometries in the frequency domain; then, this impedance is used to develop an equivalent circuit of the buried grounding configuration and finally, this equivalent circuit and other models for the distribution system components like transformers, surge arresters, etc, are linked in a circuit model to evaluate the transferred voltages through distribution transformers in the alternative transients program (ATP).