Research On Relay Protection Method Of Hybrid Bipolar HVDC Transmission Lines

In order to give full play to the advantages of the LCC-HVDC and VSC-HVDC,Hybrid-HVDC has gradually become a research hotspot.Research on relay protection methods for Hybrid Bipolar HVDC transmission lines is particularly important.The topology,system parameters,mathematical model and control method of Hybrid Bipolar HVDC system are studied.The model of Hybrid Bipolar HVDC system was built by PSCAD simulation software.Then,based on the above model,the Hybrid Bipolar HVDC line protection method is studied.The fault characteristics of the DC line are analyzed,Three DC line protection methods are studied and the overall configuration scheme of DC line protection is given.A longitudinal protection method of Hybrid Bipolar HVDC transmission lines based on Transient power polarity is studied.The quadratic B-spline wavelet transform is used to extract the transient power polarity.According to the difference of the transient power polarity between the two sides in the internal fault zone or external fault zone,the criterion for distinguishing between internal and external faults is formed.The positive and negative rectification side transient power components are constructed as energy functions for fault pole selection.A longitudinal protection method of Hybrid Bipolar HVDC transmission lines based on longitudinal impedance is studied.The concept of longitudinal impedance was introduced.The longitudinal impedance of the DC line is analyzed,and the value of the value is used to distinguish between the internal and external faults,and the fault pole selection can be realized by itself.A single-ended protection method of Hybrid Bipolar HVDC transmission lines based on instantaneous energy of voltage fault component is studied.The inductor is connected in series at both ends of the DC transmission line,and the rate of change and amplitude of the voltage fault component are analyzed.The Teager energy operator is used to obtain the instantaneous energy of the voltage fault component in the internal fault zone or external fault zone,and the criterion for distinguishing between internal and external faults is formed.The positive and negative rectification side voltage and current fault components are constructed as energy functions for fault pole selection.The above three kinds of protection are compared with the traditional traveling wave protection of the line.Longitudinal protection method based on transient power polarity requires less communication channel,but requires additional fault pole discrimination algorithm.Longitudinal protection method based on longitudinal impedance can identify the fault pole by itself,but requires a higher communication channel.Single-ended protection method based on voltage fault components does not require communication at both ends and can quickly identify faults.The overall configuration scheme of the Hybrid Bipolar HVDC transmission lines protection is given,with single-ended protection as primary protection and the double-ended protection as backup protection.