Research On Line Protection Characteristics Of VSC-HVDC System

The transmission line of HVDC transmission technology has low cost and low line loss,and has strong economic advantages.With the continuous development of semiconductor devices,VSC-HVDC technology has been fully developed and applied,compared with traditional DC transmission.It has been widely applied and developed in urban power grids,new energy grid-connected,and island power supply.However,for the protection setting of flexible DC transmission lines,there is no systematic solution.According to the principle,nature of protection,and the relation-ship between equipment characteristics and fault characteristics,the corresponding fault criterion setting method is proposed.The main protection is researched and analyzed.In the protection strategy based on the polar wave rate change method,the PSCAD/EMTDC simulation platform is used to build the relevant model.The simulation analyzes the changes of the setting values under various factors and the degree of influence on the protection criteria.The results show that the fault distance is more Large,the lower the sampling rate,the smaller the gap between the faults in the area and the fault data outside the area,and the difference in discrimination.Aiming at the problem that the polar wave change rate method still has a low discrimination degree between the faults in the area and outside,a protection strategy based on the wavelet transform method is proposed,which can greatly distinguish the fault degree between the faults in the area and the faults outside the area.By using the excellent time-frequency localization characteristics of the wavelet transform method,the fault wave head can be accurately located,the fault information is comprehen-sively extracted,and the modulus maximum value of the wavelet transform is used as an index.The simulation shows that the degree of differentiation between the region and the outside can be greatly improved in the method of the polar wave change rate,and the reliability and stability of the line protection are increased.