Study On Transient Overvoltage Of UHV AC-DC Hybird System

In recent years,power industry is in a period of rapid development.Power demand led to the construction of power.The scale of grid construction is gradually expanding,while the power capacity of transmission is increasing and the voltage level is also increasing.Chinese power grid is in a period of rapid development toward UHV transmission mode.AC-DC hybrid network gradually formed.The operation difficulty and complexity of large-scale AC/DC hybrid power system are unprecedented.There may be a series of major technical issues such as the content of this topic and problems in AC-DC system interaction,which will not be able to ensure the reliable transmission of electricity and will not be able to ensure that the power grid can operate stably.Over-voltage phenomenon exists widely in the UHV AC and DC systems and seriously affects the insulation and safety of the equipment.Analyzing overvoltage conditions under various types of faults,providing over-voltage form identification criteria,and quickly determining fault types are very important for ensuring the safe operation of the power grid.In this paper,Simulink and other software are used to simulate and analyze the power system.Combined with the actual UHV AC/DC actual engineering data,an electromagnetic transient simulation model for the UHV AC/DC system is established to analyze the overvoltage and identification criteria of the AC/DC system.The conclusion provides reference suggestions for fault diagnosis and overvoltage protection.First,based on the existing 1 000kV UHV AC system engineering,the mathematical model of AC system in UHV system is established,and the main factors that affect the transmission capacity of the AC system are analyzed.On this basis,the Simulink model of UHV AC transmission system is established.This paper,referring to the existing 800kV UHVDC System Engineering,established the mathematical model of UHVDC transmission system,and established the Simulink model with reference to the actual transmission engineering,and took the parameters of the DC system and high voltage AC system in the hybrid system to carry out simulation analysis.Secondly,on the basis of the established Simulink model of UHV AC/DC hybrid transmission system,the Internal Overvoltage of UHV AC system is analyzed theoretically and simulated,and three kinds of main overvoltage types in the system are analyzed.In the model,three kinds of operating conditions are simulated,and the related parameters under normal operating conditions are carried out.Comparative analysis,analysis of its impact on the operation of the grid,and through the analysis of the simulation waveform,the measures to inhibit it are obtained.Then,the overvoltage simulation of UHVDC System is carried out on the AC/DC hybrid system model built before,and the theoretical and practical analysis of the Internal Overvoltage in the DC system caused by the fault is analyzed and the conclusion is drawn.In overvoltage analysis,each DC voltage waveform obtained by simulation is supplemented by the current waveform and the AC voltage waveform at both ends of the DC system to analyze the specific overvoltage.Finally,in view of the possible overvoltage situation of the AC and DC hybrid system,this paper simulates the overvoltage situation of the two typical working conditions,and obtains the corresponding fault identification of the important parameters of the AC system and the DC system.