Track Circuit Loss of Shunt
LOSS OF SHUNT
Railway safety systems are in many cases based on track circuits. When a track circuit is occupied by a train, the electrically conductive axles of the train short circuit the running rails. The corresponding way-side signal then switches from green to red.
Under certain circumstances, the rails may be contaminated. Leaves, rust or sand can be the cause of this. The short circuit of the track circuit by the axles does not occur. This is Loss Of Shunt (LOS). LOS is a dangerous situation that must be avoided.
The ACTEL AXLE®active control system is a new solution that helps to solve the LOS problem.
Railway safety systems are in many cases based on track circuits. When a track circuit is occupied by a train, the electrically conductive axles of the train short circuit the running rails. The corresponding way-side signal then switches from green to red.
Under certain circumstances, the rails may be contaminated. Leaves, rust or sand can be the cause of this. The short circuit of the track circuit by the axles does not occur. This is Loss Of Shunt (LOS). LOS is a dangerous situation that must be avoided.
The ACTEL AXLE®active control system is a new solution that helps to solve the LOS problem.
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ELECTRICAL CHARACTERISTICS OF CONTAMINATING LAYERS
The contamination between the railhead and the wheel may have different electrical characteristics: current [I] vs voltage [V] diagrams. A diode characteristic [A] is often observed. Also the nonlinear breakdown characteristic [B] is quite common. Sometimes a linear characteristic occurs. As the train moves, the wheel rotates. The elliptical contact between the wheel and the rail moves along the rail and along the surface of the wheel. In every contact ellipse a new electrical contact must be established and the electrical characteristics may vary rapidly from contact area to contact area. All three kinds characteristics may occur and sometimes even simultaneously. This makes the wheel rail contact an erratic and highly dynamical process.
The contamination between the railhead and the wheel may have different electrical characteristics: current [I] vs voltage [V] diagrams. A diode characteristic [A] is often observed. Also the nonlinear breakdown characteristic [B] is quite common. Sometimes a linear characteristic occurs. As the train moves, the wheel rotates. The elliptical contact between the wheel and the rail moves along the rail and along the surface of the wheel. In every contact ellipse a new electrical contact must be established and the electrical characteristics may vary rapidly from contact area to contact area. All three kinds characteristics may occur and sometimes even simultaneously. This makes the wheel rail contact an erratic and highly dynamical process.
