Study on Transient Impact Characteristics of Grounding Grid in UHV Converter Station and Its Influencing Factors

When the converter station is suffered by lightning strike, short circuit fault or switch operation, the grounding grid of the converter station may be impacted by high frequency and large current, which makes the grounding grid of the converter station presents a complex impact characteristic, namely, a phenomenon of uneven distribution of transient grounding potential, which may cause the interference of the cable of secondary circuit. With the increase of power system voltage level and transmission capacity, the area of the converter station is also increased accordingly, especially the UHV AC substation and UHV DC converter station share one site, which makes the area of the substation or converter station increases greatly, so that the phenomenon of uneven distribution of transient grounding potential is becoming more and more serious, which makes the probability of interference in the secondary circuit cable greatly increased. In recent years, the fault caused by the disturbance of the secondary circuit due to transient grounding potential rise has occurred from time to time, this poses a serious threat to the power grid and affects the safe and reliable operation of the electric power system. The research of different simulation calculation methods are carried out aimed at transient impact characteristics of grounding grid in UHV converter station, such as circuit analysis method, transmission line model method and electromagnetic field analysis method, and a large number of simulation calculation studies have been also carried out. However, grounding grid is built by using moment method and Fourier transform method based on the typical grounding grid structure of UHV converter station, and the distribution of transient grounding potential in UHV converter station is calculated based on the simulation calculation, meanwhile, the feasibility of the simulation calculation model is verified by comparison between simulation test results and simulation calculation results. Thirdly, the effects of different impulse current waveform, different current injection location, different soil resistivity, different grounding grid material, and different grounding grid structure on the transient impact characteristics of grounding grid are studied based on the simulation calculation model. Finally, by means of the simulation calculation model of transient impact characteristics of grounding grid, the transient characteristics of the grounding grid are optimized by optimizing the structure of grounding grid and optimizing the vertical grounding electrode arrangement for reducing the transient grounding potential rise of grounding grid. It will provide experimental data support for simulation calculation of transient impact characteristics of the grounding grid in UHV converter station, which will provide engineering guidance for the design of grounding grid.