Problems Of Earthing And Return Current For High-Speed Railway

Since the policy of reforms and opening was putted in practice, the carrying trade using railway in China has been in face of huge opportunity and challenge. Country's quick development can't leave the continual improvement of the traffic condition. For keeping away from the passive and unenlightened situation, the works improving actively the velocity of current railroads and studying to develop high-speed railway have become a key point and urgent affairs for railway development in China. Electrical high-speed railway requires more reliable operational condition. For the safety of people and devices nearby the railway system, it is important and necessary to adopt measures to reduce touch voltage in substation and rail potential along railway of railway system, as well as the transmission of dangerous voltage to the three part installations.Firstly, the advantages and disadvantages on direct current power supply network (DC) and alternate current power supply network (AC) are analysed at the beginning of the thesis, and two methods belonging to AC power supply system called autotransformer power supply (AT) and track-return with return conductor power supply (TRRC) are considered to be more conformable for high-speed electrified railway. Secondly, according to actual measurements of soil resistivity and earth resistance for Beijing-Tianjin Dedicated Passenger Line (JJ-line), the soil condition of JJ-line is analysed, and principle and method for measure are introduced. Thirdly, the safety problem of persons and equipments in and around railway system is analysed. Models describing that one person may suffer from dangerous voltage in substation and along railway are set up and analysed. And the difference and relation of safety assessment standard for grounding systems defined by different criterions are analysed. According to EN 50122-1 and HD 637 S1, values of maximum permissible voltages which people can endure are recommended by table and curves graphic. Finally, according to lots of simulations, facters influencing value of rail potential and distribution of return currents are analysed under operation or fault conditions. The conclusions are that integrated earth system and spacing of equipotential bonding have significant function for reduction of accessible touch voltage in substation and rail potential along railway under normal and fault condition for railway system. And aerial return conductor and buried earth wire have obvious function for decreasing the rates of return currents flowing through running rails and earth, and therefore decreasing rail potential.