Improvement of ground impedance measurment using single rod method

Abstract

In city centers, measurement of ground impedance is found to be crucial to prevent any hazard to the city citizens and equipment due to lightning and short circuits. Although various methods introduced to measure ground impedance but they mostly require a large site area or adoptable only for low frequencies. Therefore, a new approach is needed to accurately measure the ground impedance value. In this study, an innovative method is developed based on one-rod measurement technique to overcome the limitation of site area measurement as well as to consider the frequency influence on ground electrode. In this method, a 5V-AC is injected by a signal generator with a variable frequency (from 5 Hz to 300 kHz) into the driven rod. The measured current is recorded accordingly. The ground resistance is then determined as the ratio of voltage and current. The corresponding resistivity is obtained based on Dwight formula. For the validation of the method in low frequency range, the obtained ground resistance from one-rod method was compared to that value obtained from fall-of-potential (FOP) method. In addition, for the validation of the method in high frequency range, the obtained ground resistances from one-rod method were compared to those values obtained from Visacro-Alipio theoretical model. The results show that the resistivity value obtained from the developed method and FOP were 113.28 Ω.m and 117.36Ω.m, respectively, which shows 3.5% difference. In addition, the resistivity value obtained from the developed method and Visacro-Alipio for the frequency range of 100 Hz to 300 kHz showed a minimum difference of 1.33% only. The simulation results of Single Rod method using CDEGS and EMTP showed the maximum of 1.09 % and 0.08% difference between simulation and experimental results respectively. These results validated the reliability of using one-rod method as an alternative method for measuring ground resistance especially in the congested area.