Research On Faulted Phase Selection For Half-Wavelength Transmission Line Protection

In the context of the continuous development of the global energy interconnection,to solve the reverse distribution of global energy distribution and power demand distributed,long-distance and large capacity transmission will become the mainstream mode of transmission.Transnational and intercontinental transmission will also become a trend of development.The half wavelength AC transmission line is a transmission line which is half wavelength long under the power frequency state,that is 3000km.The transmission line has the characteristics of no need to install reactive power compensation equipment,strong transmission capability and good economic benefits,so it becomes an attractive long-distance and high-power AC transmission mode.However,because the length of the half wavelength AC transmission line is about 10 times of the conventional transmission line,its electrical parameters show the distribution characteristics,so the traditional protection methods and phase selection methods will no longer be applicable.Aiming at this problem,the research object of this paper is half wavelength transmission line.This paper proposes a fault analysis method for the half wavelength transmission line,analyzes the fault characteristics at protection installation place of the half wavelength transmission line,and sets up the phase selection element suitable for the half wavelength transmission line.The main contents of this paper are as follows:First of all,a method of analyzing the fault characteristics of the half wavelength transmission line is proposed from the perspect of the power source are the same of these two kind of transmission system by using the relationship between the faulted superimposed component and the system impedance based on lumped parameter by comparing the similarities and differences between the half wavelength transmission line and the traditional transmission line.The fault characteristics of half wavelength transmission lines are analyzed,fault characteristics were simulated,which lays the foundation for the selection of phase selector for half wavelength transmission lines.Secondly,this paper analyzes the applicability of the three commonly used phase selection methods,namely,the faulted superimposed current selection method,the current sequence component phase selection method and the impedance phase selection method,and points out the reasons why each phase selection method is not suitable for the half wavelength transmission line.Finally,a half wavelength transmission line phase selection scheme is proposed in this paper.The scheme uses the fault feature extracted in the last chapter at the protection point,and optimizes the data processing method of the phase selection scheme.It is proved that the method can performe correctly in the whole half wavelength transmission line by the simulation of PSCAD/EMTDC.Finally,the different influence factors of phase selection scheme are analyzed.The analysis results show that the phase selection scheme proposed in this paper is less affected by transition resistance,system impedance and the load.The fault phase can be identified accurately for all the faults along the line.