The Calculation And Analysis Of Impulse Characteristics And Surface Potential Of Gas Insulated Substation Grounding Grids

The grounding device of substation is composed of grounding grids,down conductor and lighting arrester,which is an important part of power plants and substations.Among them,the grounding grids is a large net grounding device with the function of discharge and pressure equalization,which is usually consists of horizontal grounding body and vertical grounding.When the power system fails,the grounding grids play a role in the rapid discharge of current,which is an important method to safely operate the power system by improving the surface potential of the geometrical conductor and substation field.In recent years,with the rapid development of Chinese power system,the area of GIS substations is also gradually increasing.When the substation fails,the impulse current flowing into the grounding grids is also increasing,resulting in abnormal surface potential or uneven distribution,which poses a threat to the physical safety of the operating person,so that the insulation of secondary equipment in power system is destroyed.Therefore,it is an important task to study the impulse characteristics and the distribution of the surface potential of the GIS substation grounding grids.In this paper,the transient mathematical model of GIS grounding grids is established based on the consideration of the spark effect,inductance effect and the propagation of the wave on the ground conductor.Firstly,analyze the influence of injection location of lightning current to voltage waveform and amplitude of each node of the grounding grids and the current of grounding grids dissipate in the soil.And analyze that the influence of lightning current waveform to the nodes voltage.Then,the validity of the transient model is verified by comparing with the experimental results in the foreign literature.Secondly,taking a800 kVGIS substation grounding grids as an example,according to the layout of the substation and grounding grids,the three dimensional finite element model of the 800 kV GIS grounding grids is established by using the electromagnetic analysis software ANSYS.And the surface potential distribution of the grounding grids under lightning current is calculated.And then different buried depths of grounding grids and soil resistivity on the impact regularity of surface potential distribution are analyzed.Finally,calculate the surface potential under the grounding grids fault,and then the BP neural network is used to identify the fault of grounding grids according to the surface potential distribution.The results show that when the lightning current is injected into the inside of the grounding grids,the peak value of the voltage wave compared to the corner injection significantly decreased.The peak value of the voltage wave on each node of the grounding grids is inversely proportional to the wave head time.In the process of the lightning current flowing along the conductor to the soil,the current in the conductor decreases gradually,and the current flow is related to the position of the injection point.The peak value of the voltage wave of each node is inversely proportional to the wave head time of the injected impulse current wave.The maximum surface potential appeared at the injection point.The change of the buried depth and soil resistivity will affected the surface potential.The surface potential nearing the fault dropped significantly,and the whole surface potential value changed,combining with the BP neural network detection method to identify the fault,it has engineering value.