±800kV UHVDC Overvoltage Simulation Research And Experimental Study

Under the background of promoting the construction of global energy Internet,increasing demand of domestic electricity and accelerating “five-AC eight-DC”UHV engineering by State Grid Corporation of China,UHV as the backbone grid,has developed rapidly in our country.The obvious characteristics of UHV transmission technology are large capacity,long distance and low loss.At present,our country is still in the early period of UHV power grid construction.After interconnection,there will be a larger synchronous power grid with more complex structure and difficult control management,which will face more complex problems of security and stability.However,for ±800kV UHVDC transmission project,the level of internal voltage will affect converter station,the whole transmission project and even the safe and stable operation of power grid.This paper takes a 800 kV UHVDC transmission project as an example,achieving the simulation calculation of its internal overvoltage.In PSCAD/EMTDC,establishing the model of converter transformer,filter,converter valve,transmission line and other main elements in converter station.Based on a lot of simulations,under the condition of trip of the last AC circuit breaker in inverter side,grounding fault of DC circuit,single-phase grounding fault of AC system and losing trigger pulse in inverter side pole 1,considering the maximum possible internal overvoltage that inductance and capacitance of AC filter and other measuring points in AC bus of UHVDC transmission system and converter station can withstand.Judging the overvoltage data by simulation calculation.The results are not beyond the rules.Besides,by doing simulation analysis on the phenomenon of lightning arrester explosion flashover in a ±800kV UHVDC transmission project,getting the result that if the operation of metallic return transfer breaker is normal,there will be about 10 kV overvoltage on neutral bus pole 2,the maximum current in lightning arrester will be 2.5kA and the overall energy consumption of lightning arrester will be about 6.3MJ.According to PSCAD simulation data,taking the system test of ±800kV UHVDC transmission project respectively in the transient process of AC filter,the last breaker trip(load rejection of inverter station)of three-phase AC bus monitored by CVT,DC grounding fault,AC grounding fault,DC system outage operation.Through monitoring transient overvoltage,collecting a lot of transient overvoltage data and doing data processing and analysis.