Study On The Influence Of Sichuan-Tibet Railway On Power Quality And Safety Stability Of Weak Power Grid In Tibet

As the second railway into Tibet in China,the Sichuan-Tibet Railway connects Sichuan Province and Tibet Autonomous Region.However,the Sichuan-Tibet Railway lacks high-voltage power grid,and the Sichuan-Tibet 500 k V power networking project is far away from the line,so the external power supply conditions of most sections are weak and lack of strong power grid support.At the same time,as a special power load in the power system,traction load has a strong impact on the power grid and a large random fluctuation.Moreover,traction load is single-phase and nonlinear load,which will cause negative sequence and harmonics.Therefore,the above problems need to be taken into comprehensive consideration.Firstly,this dissertation builds a simulation model of electric locomotive traction power supply system in the MATLAB /Simulink simulation environment,conducts simulation research on each component of traction power supply system with AT full parallel power supply mode and the structure and control strategy of CRH2 AC-DC-AC locomotive,summarizes the current and voltage characteristics under different working conditions and conducts harmonic analysis.Then,combining with the measured real-time fluctuating traction load,this dissertation uses MATLAB programming language to build the traction load probability model from the perspective of single vehicle power and traffic density,and describes the real-time power changes of a series of locomotives from the perspective of traction substation when they pass through adjacent traction substation successively based on normal distribution.Secondly,from the perspective of the carrying capacity of the power grid,the weak links of Xizang weak power grid are identified and deeply studied in combination with the characteristics of the weak power grid.The accuracy of the weighted edge toughness as the objective function is determined by comparing the two proposed methods which take edge toughness and weighted edge toughness as the fitness.From the perspectives of topological structure and power supply capacity,the BPSO particle swarm optimization algorithm is used to screen the weak links of the power network,and the IEEE 39-node system is used to verify them.Different from the ranking of vulnerability degree of traditional methods,the proposed method focuses more on the overall impact of weak links.The results of particle swarm iteration confirm the effectiveness of the proposed method and provide a new way to evaluate the security and stability of power systems.This dissertation obtains actual data through Baidu Map API to model Xizang power grid.Lalin Railway,a typical example of Sichuan-Tibet Railway,is taken as a case.The probability model of traction load for 11 traction substations of Lalin Railway Station is established.The weak links in Xizang power grid are identified by three-time nodes before,1h and 9h of the operation of Lalin railway,and the dynamic changes of the weak links are analyzed with the operation of Lalin railway.The simulation results show that this method can effectively track the traction load change and reflect the distribution of weak links in the power network.The proposed method considering the vulnerable line identification under moving impact load is of great significance to the safe operation of the power grid along the railway.Finally,combined with the research results of this dissertation,the influence of electrified railway on power quality of power grid is analyzed,and the treatment scheme is proposed according to the actual situation of Sichuan-Tibet railway.The influence of harmonic negative sequence on relay protection is analyzed and summarized,the misoperation cases caused by harmonic negative sequence are studied in detail,and the specific prevention and control measures are given from the aspects of monitoring,governance and configuration.