Study On Fault Identification And Protection Of HVDC Transmission Line

As China's implementation of "west to east electricity transmission" and " south-north mutual supply" project,and the advancement of the global energy internet process,the construction of high voltage direct current(High Voltage Direct Current,HVDC)transmission project become imperative.On the one hand,the transmission lines of HVDC system are far away,and the climate and environment in the area where they go through is very bad;on the other hand,the traditional relay protection of the HVDC transmission lines is defective.Therefore,the fault identification and protection of HVDC transmission lines are studied in detail.In order to get the faults transient characteristics of HVDC transmission lines,this paper think CIGRE(Conseil International Des Grands Reseaux Elecctriques,CIGRE)HVDC standard test system as a starting point,and use PSCAD/EMTDC to establish two ends and bipolar HVDC transmission system model.Based on this HVDC transmission system,the influencing factors of the traveling wave protection in the traditional relay protection of HVDC transmission lines are studied.The response characteristics and fault recovery characteristics of the control system are analyzed when the protective device act correctly.In order to study the fault identification and protection method of HVDC transmission lines more comprehensively and make the protection more practical,it is necessary to establish a lightning strike simulation model for HVDC transmission lines.By changing the lightning current amplitude and the location of lightning strike,the simulation of beat and counterattack is carried out,and the transient electrical characteristics are extracted,which lays the foundation for the study of lines fault identification and protection.In order to overcome the shortcomings of traditional relay protection for HVDC transmission lines,this paper analyzes the characteristics of lines boundary,according to the difference of high frequency energy attenuation of transient electrical quantities when crossing the boundary elements,a method for identifying internal and external faults of HVDC transmission lines based on the difference of high frequency energy ratio is presented;according to the differenct characteristics of transient electrical quantities between lightning interference and transmission lines faults,a method based on correlation analysis and wavelet energy spectrum entropy is proposed for lightning interference,lightning fault and common ground fault identification;according to the fault and no-fault poles pole-wave difference in changing,a method of the fault poles identification based on pole-wave mean ratio is given.Thus,a set of fault identification and protection schemes for HVDC lines based on transient characteristics are formed.