Abstract:

The metro system poses not only a threat of stray currents to the power system but also a magnetic coupling between the traction power supply system and the power system, resulting in induced currents in the system circuit, invading transformers, and ultimately causing direct current(DC) biasing issues. Compared to stray currents, the induced currents generated by magnetic coupling have lower frequencies, making them more difficult to control and protect against. Furthermore, the magnitude of the induced currents due to magnetic coupling is dependent on the relative positions of the subway lines and transformers. In order to investigate the magnetic coupling mechanism between the metro system and the power grid circuit and understand the characteristics of the induced currents on the power grid circuit, a subway-power grid coupling simulation model and a numerical analysis model for the power grid are established, and the distribution characteristics of magnetic flux and induced currents in the circuit are calculated and analyzed. The research results indicate that the extent of magnetic influence from the subway on various transformers in the power grid’s multiple circuits varies depending on factors such as parallel distance and relative positions. Transformers located further away from the subway lines are more severely affected by magnetic coupling. There is a possibility of magnetic coupling currents propagating through the power grid circuit to more distant transformers.

Key words: Magnetic coupling current, transformer, stray current, power grid circuit, subway lines