Research On Protection Of Stray Current Corrosion

Currently, DC traction are always used in the subway system, traction substation provides power supply for the electric locomotive through paved overhead catenaries along the road or contact rail, and takes locomotive to the rail as a return conductor. In the running of electric locomotives, as the ground track can not be completely insulated, some current leaks to the earth at the poor insulation point between the rail and the earth and flows to low potential land department. Therefore, a kind of stray current without any stray current law is formed. This stray current corrodes underground metal structure, and would seriously affect the normal operation of the subway. Thus, it is very necessary to fully consider the stray current corrosion issue, to explore more effective protective measures for stray current corrosion in order to ensure the safe running of the subway.This thesis is consisted of the following four aspects:1,By taking the way of single and bilateral power supply, from running tracks to the earth resistance structure and the line of rail, then to underground metal, finally to resistivity structure of the earth, the mathematical model of subway stray current is derived, and then two mathematical models is used to complete the subway stray current simulation.. Analysis is made about distribution and influencing factors of stray current in the single and bilateral power modes. The simulation results show that the two ways of power supply and simulation's results under the two mathematical models are basically the same, so we could directly select the unilateral power supply line, from down tracks to the earth's resistance structure, to research on the distribution of subway's stray current when we make in-depth analysis.In addition, main factors of effecting underground stray current are found out, that is, the traction load current, the spacing between electric locomotives and change point, the insulation resistance and the internal resistance tracking the rail line.2,Using the basic principles of metal electrochemical corrosion, reasoning of stray current's corrosion mechanism and influence factors is made, and hazards of the subway stray current if found out. Stray current corrosion is mainly due to that traveling rail and underground metal structure form the two corrosive cascaded (short circuit) original batteries. Through analysis about the current domestic operation situation of subway system, some new harm caused by stray current are summed up, such as device malfunction of rails limiter.3,By analyzing the monitoring result in regards of stray current corrosion's parameters, it makes analysis about several stray current monitoring system commonly used in China. It first proposed some basic parameters needed to monitor in the process of underground stray current corrosion protection, including running track relative to the earth (reference electrode) potential difference and the reference electrode body potential, rail insulation resistance, internal resistance of running track and their monitoring methods and principles. And then, analysis is made about several common domestic monitoring system of stray current, monitoring of metro stray current protection is recommended real-time online monitoring system of the stray current without manual operation.4,It first analyzes the basic techniques of metal corrosion protection, and then analyzes several conventional protection methods of stray current corrosion. Later, it analyzes the advantages and disadvantages of conventional drainage protection methods, compares stray current distribution with additional drainage devices and that without additional drainage devices by simulation, and then a new intelligence drainage system is obtained. Finally, it discusses the new protection methods of stray current in its design and construction. It first makes analysis of metal corrosion protection's basic principles. Then according to Chengdu Metro Line 1 project, it puts forward effective measures for stray current protection, including the conventional protection methods of stray current such as primary and secondary collection network and other new smart devices, rail conditions limitation and methods that need no outside guidelines. It finally comes to the basic requirements of relevant professional in design, construction and operation of stray current corrosion protection of the subway.