Practical Setting Principle Of Line Protections For HVDC Transmission Lines

Due to the advantages in high-power,long-distance transmission,and large-area interconnection,HVDC transmission technology has developed rapidly.Because of the length of transmission lines and complex working environment,the risk of failure of HVDC transmission lines is high.In order to ensure the reliability of power supply,reliable action of line protection is required when impedance fault occurs on the HVDC transmission line.And the effective setting principle of line protection should be proposed to achieve high-performance line protection.For this reason,this paper focuses on practical setting principle of protections for HVDC transmission lines.The main research and contributions are summarized as follows:In section Ⅰ,the practical setting principle of traveling wave protection for HVDC transmission lines is proposed.This paper proposes the practical setting principle of traveling wave protection for HVDC transmission lines,which can provide technical support for the actual setting calculation work and improve the efficiency of setting calculation.Considering the different fault types in the HVDC transmission lines,the dynamic response characteristics of d U_d/dt,ΔU_dandΔI_d are analyzed and the function of the protection criterions is revealed.The practical setting principle of traveling wave protection is proposed considering the sensitivity and selectivity and the availability of the criterion are verified by PSCAD/EMTDC simulation platform.In section Ⅱ,the practical setting principle of differential under-voltage protection is proposed.This paper proposes a practical setting principle of differential under-voltage protection for HVDC transmission lines,improving the efficiency of setting calculation.Considering the different fault types in the HVDC transmission lines,the dynamic response characteristics of d U_d/dt,U_dare analyzed and the function of the protection criterions is revealed.The practical setting principle of differential under-voltage protection is proposed considering the sensitivity and selectivity and the availability of the criterion is verified by PSCAD/EMTDC simulation platform.In section Ⅲ,the practical setting principle and an optimized criterion of current differential protection are proposed.Current differential protection,the backup protection for HVDC transmission line,is of great significance to the safe and stable operation of the HVDC systems.However,due to the existence of the 600ms block logic,the operation time of the current differential protection may be increased under the line high-impedance ground fault,resulting in malfunction of the pole control protection.By analyzing the fault action sequence of current differential protection and pole control protection,this paper points out that the key factor that causes the HVDC system being blocked under high-resistance ground fault is the unreasonable blocking logic.Combined with the variation characteristics of differential current for different faults,an optimized blocking criterion combining AC system fault and commutation failure detection is proposed,which can improve the rapidity and reliability of current differential protection effectively.Based on PSCAD/EMTDC software,the actual±800k V HVDC engineering test example is built.The simulation results in different fault scenarios show the effectiveness of the proposed scheme.