Railway track admittance, earth-leakage effects and track circuit operation

A railway track acts as a pair of leaky ground-return conductors for propulsion current in the immediate vicinity of trains and as an imperfectly insulated conductor pair for double-rail track circuits. The authors consider the effect of ground admittance and leakage conditions from both the traction and signaling viewpoints. Problems concerning rail voltage safety level, earth leakage currents, and rail current distribution are examined. Capacitive compensation is evaluated as a means of improving the shunting sensitivity of track circuits with high ballast conductivity