A new method for measuring rail transit transition resistance using impulse voltage

Author： GOZ Electric Time：2024-07-29 09:33:44 Read：22

    At present, rail transit is being developed all over the world. International metropolises such as Tokyo, Moscow, and New York all have developed rail transit network systems. my country began to build its first rail transit line, Beijing Subway Line 1, in 1953, and it was put into operation in 1971. After that, cities such as Tianjin, Shanghai, Guangzhou, and Nanjing also began to develop gradually. At the same time, the stray current problem caused by the DC traction system of rail transit has also received widespread attention. The DC traction system refers to the traction substation transmitting 1500V or 750V low-voltage DC power to the contact network through the feeder line, and the contact network is transmitted to the locomotive through the pantograph for the locomotive to use, and then returned to the negative pole of the traction substation through the return rail and return line.

    In order to save construction costs and reduce construction difficulties, most countries in the world use running rails as return rails. Most of the current can return to the negative pole of the traction substation through the running rails. However, due to wear and tear after long-term operation and moisture and water leakage in the tunnel, the running rails cannot be completely insulated from the ground, so some current leakage will occur, thereby generating stray current. Stray current flows irregularly underground. Some of it can flow back to the drain cabinet through the drain network and then reach the negative pole of the traction substation, but there is still a small part that cannot flow back to the running rail and eventually flows to the metal pipe. This will not only damage the buried metal nearby, but also interfere with the communication of nearby information equipment and precision instruments, and in serious cases, it will endanger personal safety.

    The transition resistance of the rail to the drain network is the most important factor affecting stray current. At present, many scholars at home and abroad have conducted extensive and in-depth research on subway transition resistance. Lin Yanhua "Based on the theory of stray current distribution path, he built a subway stray current distribution model using CDEGS software, and proposed a calculation method for using the cable outer insulation layer to equal the transition resistance of the rail insulation pad during the modeling process. CDEGS software was used to simulate the rail-ground stray current modeling, and the stray current distribution and rail potential changes under different transition resistance values were discussed. The results show that the transition resistance is linearly related to the resistivity of the rail conductor insulation layer. The main factors affecting the transition resistance of the rail were analyzed, a subway stray current simulation model was established, and the influence of rail fasteners on subway stray current was analyzed in detail.

    Based on the DC traction system of rail transit and the formation mechanism of stray current, a new impact method is proposed to measure the transition resistance of rail to drainage network according to the propagation law of voltage traveling wave in rail and the principle of fast Fourier transform. Finally, it is verified by simulation and experiment, and the following conclusions are obtained:

(1) A T-type rail simulation model is built in ATP-EMTP software, and the selection criteria of the segment length of the rail model are analyzed. In the simulation, it is verified that the attenuation law of the rail potential can be fitted with an exponential function, so as to obtain the propagation distance of the voltage traveling wave on the rail.

(2) From the simulation results, it can be seen that the transition resistance value calculated by the impact method is slightly larger than the value set in the simulation model, mainly due to the influence of the longitudinal resistance of the rail. However, the longitudinal resistance of the rail per unit length is only 0.04Ω/km, so the influence of the longitudinal resistance on the transition resistance measured by the impact method can be ignored.

(3) The traditional DC method and the new impact method are measured on a certain line of Shanghai Metro, and the experimental data of the two are compared. The results show that the error between the two is 3.7%, which verifies the feasibility of the impact method to measure the transition resistance. The impact method is simpler and has stronger anti-interference ability than the DC method.