A Refined Transmission Line Model For Wave Process Of Half Wavelength AC Transmission Lines

The half wavelength transmission line is long and sensitive,and there may be over voltage and over current along the line,so it is necessary to establish a refined transmission line model.Based on the multiconductor transmission line theory,a piecewise modeling method is proposed in this paper.Considering the complicated environment,the distribution parameters of the line are solved,and each section of the circuit is connected in series through the chain parameter matrix.Combined with some UHV line parameters and segments,the influence of soil resistivity,adjacent lines,load impedance and hybrid transmission line on distribution of voltage,current and power along the half wavelength transmission line is analyzed.The method of sag in half wavelength transmission lines is also analyzed.Through detailed analysis,the sag coefficient 1/3 is still suitable for half wavelength transmission lines.The calculation results show that the soil resistivity has influence on the half wavelength transmission line when the three-phase line is asymmetric.The influence of adjacent lines on the half wavelength transmission lines is related to their length,distance and location.The load impedance is smaller;the maximum voltage along the half wavelength transmission line is greater.The influence of hybrid transmission lines on the half wavelength transmission line is related to the proportion and location of the mixed lines.And the voltage and current fluctuations along the line is greater if the proportion is higher.So it is necessary to consider complex environment and establish a refined transmission line model for half wavelength line.Based on the theory of transmission line and the principle of electromagnetic field,this paper presents a new method for scaling the longitudinal and transverse scale of transmission lines in different proportions.Skin effect was considered in the method.The mathematical relationships between the longitudirnal scale ratio,the transverse scale ratio and the conductor conductivity were derived.Based on this relationships,the appropriate longitudinal and transverse scale can be selected as required.In the two examples of coaxial cable and half wavelength transmission line,the effectiveness of the proposed scaling method was examined.According to the scale method,a 1.5km scale experimental line built in Changping Nan Shao UHV experimental base.The refined transmission line model is verified by comparing the experimental results with the calculated results of the refined transmission line model.