| The power demand in China is growing due to its fast-growing economy,resulting in an increase in power load density.As a consequence,the insufficiency of power supply capacity for the 10 kV medium-voltage distribution network is becoming more discernible.To guarantee power reliability and minimize power wastage,several areas in China have conducted experimental initiatives and studies regarding the 20 kV distribution network.The Chinese medium-voltage distribution network’s standard is expected to grow to 20 kV moving forward.The selection of voltage for China’s railway power supply system is of great importance due to the fast and extensive development of railways in the country.For a long time,most of China’s railway power lines have adopted 10 kV voltage level.However,as the State Grid promotes the development of a 20 kV distribution network,it becomes possible to connect the railway power supply system with the 20 kV power supply.The increasing focus on the railway power lines is due to the adoption of the 20 kV voltage level.This study delves deeply into the transmission capacity and compensation of reactive power for overhead lines and cable lines utilized in the railway’s 20 kV power transmission line.The specific research contents are as follows:(1)This paper introduces the classification of conductors and cables and the calculation of relevant electrical parameters under two forms of railway power through line: overhead line and power cable.Based on this,the selection and parameter calculation of overhead conductors and cables for 20 kV power through line are analyzed.At the same time,two commonly used mathematical models for transmission lines are introduced,and an equivalent mathematical model for power through line is established.(2)For the 20 kV overhead power through line,based on the concentrated parameter equivalent circuit of the overhead power through line,the calculation formulas for voltage offset,transmission efficiency,and load torque representing transmission capacity are derived.Through example analysis,it is found that the 20 kV voltage level of overhead power through line has stronger transmission capacity than 10 kV.The series capacitor method is utilized to compensate for reactive power in overhead power transmission lines in order to address voltage loss issues.The selection of compensation positions and degrees is summarized,and the load torque before and after compensation for two voltage levels of transmission lines is compared and analyzed through numerical examples.(3)Using the distributed parameter equivalent model,the formulas for the terminal voltage offset and transmission efficiency were determined for the 20 kV power transmission line with full cable.Additionally,examples were used to analyze the transmission capacity of the 20 kV cable line for railway purposes.In response to the issue of capacity rise effect of cable through lines,a compensation method with concentrated and dispersed sections at the head end was adopted to calculate the required compensation capacity for 20 kV cable through lines.The analysis suggests that there is a significant need for compensation capacity in order to power the 20 kV cable through line.A feasibility study of the compensation scheme was conducted by creating a simulation model using Matlab,which involved analyzing and comparing the effects before and after the compensation process.(4)Based on the typical load model of power transmission lines,simulation calculations are conducted on two examples of power transmission lines laid in two different voltage levels,analyzing the voltage deviation at each node and the distribution of voltage along the line under full load,as well as the terminal voltage deviation under different load rates.For two examples of power transmission lines laid in two different forms,analyze the reactive power compensation demand and compensation capacity of the power transmission line at a voltage level of 20 kV,and verify the effect before and after compensation through simulation. |
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