High frequency response of grounding electrodes: effect of soil
dielectric constant
Abstract
“This paper is a postprint of a paper submitted to and accepted
for publication in IET Generation, Transmission & Distibution (GTD) and
is subject to Institution of Engineering and Technology Copyright. The
copy of record is available at the IET Digital Library.”
Abstract:
Grounding electrodes have an important role in electric power
transmission and distribution systems. They are used to prevent
excessive hazardous voltages between metallic structures and ground in
the case of system faults or lightning surges. It is important that they
provide a low impedance path for the current in to the ground. The
electrical properties of soil, which vary substantially with
geographical location and time of year, affect the process considerably
along with the properties of the grounding electrode itself, such as its
dimensions.
In order to have an accurate estimation of the developed overvoltages
and the backflashover rate of the transmission lines due to a lightning
strike, one has to take into account the effect of the value of the soil
electrical parameters, such as the electrical conductivity and
dielectric constant.
This paper investigates the high frequency behavior of the grounding
electrodes by solving a full-wave electromagnetic problem using the
Finite Element Method (FEM). The focus is on taking into account the
effect of the variation of soil relative permittivity which has been
neglected in the previous studies of the grounding systems. This allows
an evaluation of the response of grounding systems due to seasonal
changes and specifically change of the water content of the soil, which
would cause its electrical properties to vary significantly. This
study
demonstrates the importance of considering the variation of relative
permittivity of the soil especially in the modeling of electrodes buried
in highly resistive soil.