SILVA, J. M. C. L.; http://lattes.cnpq.br/3588908659219177; SILVA, João Marcelo Costa Leal da.
Resumo:
A grounding system consists of a purposeful electrical connection of a physical system
to the ground. Its main characteristic is to make the ground a path of low impedance,
preferential to currents coming from short circuit, phase unbalance, switching surge or
lightning surge. Therefore, grounding systems can act for currents at different levels of
intensity and frequency. The behavior of ground systems against low frequency current
is widely known. However, the high current and frequency current behavior is influenced
by ionizing, inductive or capacitive effects, individually or simultaneously. As an
example of a current of high intensity and frequency, one has the impulsive current
coming from an atmospheric discharge (lightning surge). In this way, the present work
has proposed to analyze the behavior of grounding systems against impulsive currents.
For this, field experiments (with impulsive current injection) were carried out in four
different grounding systems, installed in different resistivity soils. From the field trials,
the parameters, or variables were obtained: soil stratification; ground resistance; impulse
current curve; voltage response curve; characteristic curve of the relation between
measured voltage and applied current (curve V x I); transient impedance; impulsive
impedance; impulse coefficient; forward and half-stroke times of the current and voltage
signals. From then on, the transient behavior of the grounding systems was analyzed, and
the transient effects (ionization, inductive or capacitive) present were identified. It was
verified that the inductive effect is influenced by the number of ground rods, independent
of soil resistivity, however, the higher the resistivity, the more the capacitive effect exerts
influence. The opposite occurs with the inductive effect that increases with decreasing
soil resistivity. Finally, a generic equation of undefined coefficients was identified that
represents the contribution of the frequency dependent transient effects to the voltage
response of the analyzed systems.