Large Grounding

With the wide application of grounding technique, its importance is gradually showed up. But how to measure grounding resistance of large grounding grid simply and exactly is a difficult problem to electric power staff all the time. This paper has classified measuring methods of grounding resistance at home and abroad, and has analyzed interference factors during measurement, and has summarized principle and characteristic and measuring current and so on of various measuring methods.Recurring to rnathematic figure and examples and aiming at such questions as unbalanced current and induced voltage and high frequency interference, this paper has not only researched anti-jamming ability and measuring process of both three-electrode method and four-electrode method which are combined with reverse phase method, but also summarized actual measuring experiences. Furthermore, problems easy to make mistake are demonstrated, for instance, grounding resistance of large grounding grid is impedance.Based on theory and experiences, this paper has discussed how to choose assistant electrode distance, large-current power, measuring points, measuring lines, etc. in detail. On the other side, measuring errors of grounding resistance and solution of current voltage electrodes reversing has been compared with horizontal two layers and vertical delaminating (three layers soil). Besides, it has been proved that four-electrode method is suitable for measurement of grounding resistance, which disposes current electrode and voltage electrode according to triangle. Finally this paper has corrected one wrong parlance that inherent error exists in four-electrode method.