Research On Impulse Characteristics Of Grounding Resistance Reducing Materials Under Lightning Current

With the rapid development of China’s economy, the contradiction between land supply and demand continues to deepen, and power transmission corridors and substations have been gradually put into more complex geological environment in remote areas, which are with higher soil resistivity generally. In order to obtain more cost-effective grounding devices, grounding modules, resistance reducing agent, ion grounding rods begin to be widely used in grounding grid reconstruction project.Based on the deliberate selection of resistance reducing materials, their testing fields and advanced impulse testing equipments, the impulse grounding impedance measurement method of resistance reducing materials is discussed firstly. We select 4 representative grounding modules with different shapes,4 ion grounding rods with different main body materials and one resistance reducing agent as the test objects, and in order to compare the economy of resistance reducing materials, we make stainless steel grounding bodies with the same shapes of grounding modules and ion grounding rods. These ground materials are embedded in testing field with low soil resistivity, testing field with middle soil resistivity and testing field with high soil resistivity one year ago.At the same time of grounding test, we measure the soil resistivity of the testing fields and calculate the accurate soil layer structure parameters by using the ground calculation software CDEGS. Using the measuring method of impulse grounding resistance which is proposed above and straight line method, the impulse grounding resistance and the power frequency grounding resistance of resistance reducing materials and the metal blocks which are used for contrast test is obtained. In the measurement of impulse grounding resistance, this thesis increases the amplitude of the current flowing through resistance reducing materials to 1kA above, and the maximum current amplitude can reach 15kA, which is much closer to the amplitude of the lightning current flowing through the grounding device.The concept of dispersion coefficient is proposed, and the calculation formula is the reciprocal of the product of the impulse resistance of the module and its superficial area; The concept of dispersion conductance is presented, and the calculation formula is the product of the dispersion coefficient of the modules with the volume of 1 cubic meters and the same length. We analyze the test data with impulse grounding resistance, dispersion coefficient and dispersion conductance, and comprehensively compare the ability of dispersing current of 4 grounding modules, and get the law of the impulse grounding resistance which changes with the amplitude of the impulse current. According to the results of the analysis, the guidance for the selection and laying of the grounding module in the project is acquired, and the new idea that using the curve of dispersion coefficient to get the impact grounding resistance is presented.Based on the test data, the effect of body material, body length, internal filler on impulse and power frequency grounding performance of ion grounding rod is studied, and the impulse and power frequency grounding resistance reducing effect of resistance reducing agent is analyzed.Finally, based on the data from the impulse and power frequency grounding test, the grounding performance and economy of the grounding modules, ion grounding rods, drag reducing agent, copper clad steel and zinc clad steel are compared, the applicability of resistance reducing materials is analyzed.