| In DC traction power supply system, more and more attentions have been paid to the problem of metal structure corrosion from stray current. Stray current protection method can be developed by carrying out theoretical analysis and digital simulation of it. And suitable criteria for stray current protection designing, construction and operation that can insure long-term safety and reliability can also be found.In this paper a further discussion of the cause and hazard of stray current in DC traction power supply system and the mechanism of corrosion of it to steel structure and metal pipeline are presented first; and then, three models of the distribution of stray current of DC traction power supply system are built, followed by a theoretical analysis carried out on these three models. Methods of reducing stray current are proposed by analyzing the impact of rail and environment parameters on rail voltage, rail current and stray current. And also the regularities of distribution of rail voltage, rail current and stray current are found. And then the data of stray current of Dalian rapid railway line 3. and Guangzhou subway line 1. are analyzed, and the theoretical analysis and digital simulation in this paper are proved to be true. At last, merits and demerits of several protection methods of stray current corrosion to metal are pointed out by matching them with each other.The main conclusions of this paper are presented as follows:To reduce stray current, first and foremost, the resistance per unit length of running rails/earth needs to be increased. Then, the resistance per unit length of running rails, the length of feeding section and the traction load should be reduced. As for the resistance per unit length of the metallic-conductive interconnected structure, the metal pipeline along rails and the earth, it plays only a minor role in controlling stray current.Selective drainage method is economic and reliable, but its drainage current has to be controlled accurately.
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