Influence of the soil electromagnetic characteristics in the transient responses in electric transmission lines

Abstract

The longitudinal impedance and transversal admittance of a Transmission Line (TL) are dependent on the soil properties which the electrical conductors are suspended. Several models in the literature consider the soil as an ideal conductor. However, real soils are characterized by frequency-dependent electrical parameters (resistivity and permittivity) and show significant variations in high resistivities. Due to these conditions, different formulations to represent the soil with and without the frequency dependence were developed. These formulations are inserted into the soil impedance and admittance o in order to obtain precise transient responses. The transient voltages calculated for two types of phenomena that occur in the electrical system are presented: an energization of the LT (slow transient phenomenon) and an incidence of a lightning strike (fast transient phenomenon) considering real and ideal soils. Results show a significant difference between the transient responses obtained for the two types of soils (ideal and real), being more pronounced in fast transient phenomena characterized by a large frequency spectrum. Thus, TL models considering real soils will be useful in prediction and assessing the overvoltages resulting from the lightning strikes in the LT. Therefore, this project proposes an improvement in the main LT models, such as the Universal Line Model (ULM) with real soils included. The precise assessment of the transient responses will allow the correct specification in the insulator chains and a proper operation of the protection systems, reducing the possibilities of erroneous functioning , increasing the reliability of the power system and in the quality of the electricity supplied. (AU)