Current in the rails
Supplying energy to railway trains- Distribution of electricity

Whatever the type of traction current distribution, catenary or lateral conductor, the current returns via the running rails. The empirical formula R_v = 0.9/p gives the linear resistance R _v as a function of rail weight per metre. For a standard track with a 60 kg/m rail, R _v ≍ 0.015 Ω/km. There are two cases to consider, depending on the nature of the current to be conveyed.

In direct current, the high currents absorbed by prime movers generate significant voltage drops.

This voltage drop is reduced, by approximately half, by connecting the two rails in parallel by means of cross-connections. Nevertheless, a residual voltage remains, causing stray currents to circulate between rail and ground, as it...