Concrete Encased Grounding: Lightning Response Analysis Considering the Frequency Dependence of Soil

Grounding system design ensures safety compliance for transmission lines under lightning conditions. In this article, the transient response of short concrete encased grounding electrodes is investigated, that is, a 2.5 m vertical rod and a 10 m horizontal electrode (HE) (counterpoise). Situations of first and subsequent lightning strokes applied to horizontal and vertical concrete encapsulated electrodes are analyzed. The effect of the frequency dependence of soil parameters is considered. Also, soils with low, medium, and high resistivities (300 to 4000 Ω.m) are evaluated. Different lengths of concrete encasement are considered in order to verify situations with either partial or total encapsulation. For all these cases, the harmonic impedance (from 60 Hz to 4 MHz) is calculated, and the respective ground potential rise is derived for median lightning currents. The results obtained indicate that concrete encased electrodes produced reductions in the impulse impedance up to 30% for the HE and 44% for the vertical electrode. Moreover, for the evaluated situations, the percentage reduction on impulse impedance was only slightly affected by the increase in soil resistivity, which is also observed for soils modeled with constant parameters.