Improved Method And Application Research On Grounding Impedance Measurement Of Grounding Systems

In recent years, many accidents were happened in the domestic power station for the defect of grounding. And the reason was that the power station grounding impedance is unqualified. When the grounding impedance of the grid is too large to ground fault occurs, the voltage deviation of the neutral point increase, and such an increase between each phase line and neutral point voltage is too high, more than the requirements of the insulation level and cause the equipment damage. When lightning overvoltage or network operating overvoltage acts on the earth, as a result of the current gradient is large, the resulting residual pressure can put the equipment in counter potential threats, and reduce the grounding network’s endurance of protecting electric equipment(overhead transmission lines and power station electrical equipment), and damage to the equipment which can’t meet the design requirements. The system’s grounding impedance is directly related to the safety of the operators and maintenance. Long running of power station gird, due to the effect of corrosion of the soil, will cause the connection between grounding conductor thinner or disconnect, and the performance of the grounding network gradually reduced that is danger for the running equipment. So we must vigorously strengthen the regular monitoring of the grounding impedance for the ground gird.At present, although all testing equipment from the equipment manufacturers identifies the current and frequency of different measuring method, it isn’t elaborated that the advantages and disadvantages of different methods and the operation for the interference factors during the measurement process. In addition, it has not been further research in the domestic detection institutions of specific work that the effect of the environmental factors of the measuring scene and the choice of current and frequency. Today, we face the problem that how to regulate and accurately measure the power station and substation gird and other large earth grounding impedance, how to reduce the interference factors in the process of testing, how to modify the testing results.In this paper, we will test and find a better testing method in the principle of the grounding impedance measurement from the existing measuring methods, and further control the effect of the mutual inductance between lines in the better testing method so that we can get the more real grounding impedance data for guiding our daily testing word. We should meet the technical requirements of customers, and reflect the condition of the power station’s grounding gird to the greatest extent so that the power station can running safely and normally.