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Currently, in multitrain DC subway system, abnormal increase of rail potential (RP) and stray current (SC) has seriously threatened the safe operation of the system. Over voltage protection device (OVPD) is generally chosen to control the RP, but its action process may increase the amplitude of SC seriously. Here, the grounding resistance of OVPD is optimized by a proposed multi‐objective decomposition algorithm based on differential evolution (MOEA/D‐DE) to suppress the rise of RP and SC synergistically. Firstly, the simulation model of the DC subway system with multitrain is built, the power flow calculation is conducted, and the dynamic RP and leakage current (LC) at the location of traction substation are obtained. Secondly, the double objective optimization model of maximum RP and LC is established and solved by MOEA/D‐DE. Finally, the effectiveness of the proposed method is verified based on the data of Guangzhou Metro Line 2. Results show that the SC of the system can be controlled effectively with OVPD grounding mode after optimization, and integrated control of RP and SC can be accomplished.

In order to calculate the dynamic distribution of rail potential and stray current accurately, a multi‐state unified calculation model of rail potential and stray current is proposed, and the characteristics of different protection devices and reflux system in multi‐state DC railway systems are analysed. In the proposed model, the multi‐state characteristics of the traction substation, train, protection devices and reflux system are uniformly simulated by unified node models. The mixed simulation parameters of the catenary and reflux system are unified to lumped parameter networks, and the multi‐node voltage equations are established based on the simulation model. Then, the power flow of DC railway systems is calculated using an iterative solution, and the dynamic distribution of rail potential and stray current are solved by differential equations. The multi‐state unified calculation model is built and the distribution of rail potential and stray current in different conditions are simulated based on the parameters of Wuxi Subway Line 2. In order to verify the multi‐state unified calculation model proposed, field tests and simulations are carried out. Results show that the multi‐state unified calculation model can unify the complex states of DC railway systems and calculate the distribution of rail potential and stray current accurately.

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