Study On Measuring The Grounding Resistance By Adopting Multi Current Auxiliary Electrodes In CDEGS

Grounding is a fundamental gurantee and crucial measure to the reliable operation of power system, the safety of electrical equipment and operating personnel. The value of grounding resistance is a very important parameter indicating the validity and safety of grounding system. Thus, it is very vital to measure the value of the grounding resistance accurately.Nowadays, three-electrode method is mainly used by State Grid of China. However, the current electrode must be located far from the grounding system using the three- electrode method in order to improve the accuracy of measuring the grounding resistance. Sometimes, the distance from the current electrode to the grounding system can't be set long enough because of the topography, which results in that the distribution of the electrical field on the surface of the earth changes a lot and leads to error increase of measuring the grounding resistance. Due to the exsiting problem mentioned above, the predecessor proposes the multi-electrode method to measure the grounding resistance. The multi-electrode method which means that there are several current electrodes around the grounding system, makes the distribution of the electrical field close to true value.The details of the three-electrode method are introduced, and the distribution of the electrical field is theoretically deduced and studied respectively using three-electrode method and multi-electrode method. The general formula of the position of zero-potential points and compensation points are deduced when there are n electrodes around the grounding system.In order to study the differences between the measured values using three-electrode method and multi-electrode method, the comparison and analysis of the measured values and true value is made using three-electrode method, four-electrode method, five-electrode method and six-electrode method, after the simulation and calculation based on the CDEGS which is famous for measuring the grounding resistance in the world. The results indicates that the electrical-field distribution of multi- electrode method is closer to true fact than that of three-electrode method, and measured-value inaccuracy of multi-electrode method is smaller than that of three-pole method, when the distance from the current electrode to the grounding system is the same. Furthermore, the measured-value inaccuracy of three- electrode method is vey big, when the current pole is very close to the grounding system. On the contrary, the measured-value accuracy of multi-electrode method remains high under the same condition.