Determination Of Safety Distances From Ground Electrodes Subjected To Impulse Conditions

Abstract

When a high magnitude of current is dis- charged to the ground, a large potential gradient will result in a ground potential rise (GPR, or induced volt- age. This GPR usually decreases with distances, de- pending on the soil resistivity, ground electrode sizes, configurations and steady state resistanceRDC values. The GPR value not only provides an information on the safe distance of the nearby equipment to the grounded electrical systems subjected to impulse con- ditions, but can also identify the right rating of the equipment, particularly sensitive electronic equipment, that are in a vicinity of the ground installations. Fur- ther, during the high voltage testing on the ground elec- trodes at field sites, the results may also be influenced by the electrodes under tests, which can cause inac- curacy in the measurements. This paper is therefore aimed to measure the GPR, where the measured re- sults are still found to be limited in literature, for var- ious soil resistivity and ground electrodes. The mea- sured GPR values are obtained by injecting high mag- nitudes of impulse current of both impulse polarities on the ground electrode, and the voltage magnitudes at distances away from the edge of the electrode under im- pulse are measured. The measurements of GPR allows the investigations on the effect of impulse polarity on these GPR values, which cannot be obtained by compu- tational method.