Avaliação do desempenho de novas concepções de malhas de aterramento.

Abstract

The grounding of an electrical system is essentially an electrical connection to the ground, where the value of grounding resistance represents the effectiveness of this connection: the lower the resistance, the better the grounding. Some applications require low values of grounding resistance, about a few ohms, even if a the area available for electrodes placement is small. If the soil has high resistivity, conventional electrodes cannot achieve the specified resistance value, and even if it does, the cost would be very high. In an attempt to minimize the effects of the high resistivity of the soil, reducing the values of grounding resistance through a simple and practical alternative, will be sought a new grounding system that, with lower earthing resistance, independent of changes in moisture levels soil compared to the conventional grounding system formed by bare copper rods. Two new designs of grounding systems were developed using rods involved in concrete and rods involved in concrete with bentonite as an additive. The new systems of ground rods will have its performance assessed by applying current impulses of various intensities and with periodic measurements of grounding resistance at low frequency. Concreted rods depend on accommodation of surrounding soil to stabilize the values of grounding resistance at low frequencies. The impulse tests showed that the concreted rods, with and without bentonite, behavior is similar to that of the conventional copper rod. The touch voltages were higher than the maximum allowable limits. In the other hand and the step voltage, always showed values below the maximum allowed. There was a substantial reduction in the impulsive impedance values for concreted rods with and without bentonite, by increasing the charging voltage thereby to increasing the voltage established at the terminals of the rods. All the concreted rods supported the efforts produced by the high currents without presenting breaks in the concrete structure.