N. Mohamad Nor

Determination of Threshold Electric Field of Practical Earthing Systems by FEM and Experimental Work

In this paper, the results of an experimental study and finite-element method (FEM) of the impulse characteristics of simply built practical earthing systems consisting of 2, 3, and 4 rods are reported. These electrodes are installed at three outdoor test sites having nonuniform soil and different soil profiles to provide variation in the result analysis. The tests on these electrodes were intended to determine the nonlinear characteristics of earthing systems which can be seen from their voltage and current traces and reduction of their impulse resistance values. Two-rod electrodes in the highest soil resistivity profile showed the largest reductions in impulse resistance due to soil ionization compared with other earth electrodes. Computer simulations of all the nine earthing systems using the FEM are also conducted, which showed good agreement with the measured results. It was also found from FEM that threshold electric field Ec is dependent on the earthing systems configurations, soil profile, and impulse resistances.

Methodologies of impulse tests on earthing systems by field measurements with different remote earth

Nowadays, with a good design and available facilities of high impulse generators that can be taken to field sites for measurements, much research work can be found on the field measurement on the study of the grounding under fast transients. Moreover, field tests on earthing systems have become interesting since it can provide the closest scenario of the characteristics of grounding system when fast transient current discharged to the earthing systems. However, the field measurements have some limitations on the standard methodologies that should be adopted during the field measurements. There is also very little being mentioned on the arrangements/values of the remote earth. As generally known, the remote/auxillary earth is important not only for the purpose of discharging any high fault current during the tests on the electrode under tests, but also to ensure that the remote earth is not being included in the measurements, hence affect the accuracy of the measurements. Due to these factors, this paper is to aimed to study how different configurations and resistance values of remote earth on the characteristics of main earthing systems. It was found that different results were obtained when higher earth resistance values of remote earth were used for impulse tests on main earthing systems.

Characterizations of a single rod electrode under high impulse currents with different polarities

Under high impulse currents, an earthing system exhibits different impulse characteristics depending on the shape and/or design configuration of the earthing system. These characteristics have been seen to be different with respect to its steady-state as highlighted in many studies. Furthermore, in order to ascertain that a correct design of an electrical system is achieved, it is important to evaluate the impulse characteristics of the earthing system under high impulse conditions. So far little emphasis has been given in previous publications to investigate the characteristics of earthing systems under high impulse conditions by field measurements. For this reason, a rather efficient and reliable technique to solve this problem is by conducting a practical analysis (field experiment). This paper investigates the characteristics of a single rod electrode under high impulse conditions by field measurements under different polarities. The single rod is selected in this paper for its simple configuration and installation. It was observed in this study that the resistance of the single rod earthing system was seen to reduce with increasing current magnitudes for both polarities and negative polarity has higher impulse resistance than that of positive polarity.

Analysis of 4 Mesh Grid Grounding Systems by FEM Simulations and Field Tests

In this paper, the analysis results of the imitative grounding systems consisting of 4 mesh grid with rods are presented by using the Finite Element Method (FEM) and field test. This combined grid with multiple rods configuration was installed by previous researchers [4] and the resistance value is obtained under steady state. The FEM simulations were conducted and the resistance value and electric field profile are obtained. Comparison study in terms of its resistance value is performed between FEM and at steady state, and further analysis of the grounding systems using FEM is presented and discussed in this paper.