What is railway track circuit?
What is railway track circuit?
A track circuit itself is an electrical system that detects the absence of a train on a section of track. This information then helps the signalling system know if it’s safe for another train to proceed.
What is audio frequency track circuit?
An Audio Frequency Track Circuit (AFTC), a recent addition to railway signalling, confirms the absence of a train in a section of track. A three-wire model of the track with PSpice as a simulation tool is used for analysis and the reduction in margin due to structure and cross bonds is also established.
How does a track circuit work?
Track circuits work by running a circuit using the rails to connect a power source at one end of the block with a relay at the far end. As long as the circuit is complete, low voltage power flows down one rail, through a relay, and returns to the power source via the other rail.
How does a DC track circuit work?
Track circuit is designed to know whether the portion of rail (track circuited) is clear or occupied by a train. A D.C. track circuit has two ends i.e. feed end and relay end. Both the ends are insulated by a Nylon joint or glued joint. It is short-circuited by any means.
What are the advantages of a jointless track circuit?
Advantages of jointless track circuits: Eliminates insulated block joints, a component liable to mechanical failure (both of insulation and by introducing stress to adjoining rails) and maintenance. In electrified areas, jointless track circuits require fewer impedance bonds than any other double rail traction return track circuits.
Which is jointless circuit uses 1700 Hz and 2300 Hz?
CSEE (now Ansaldo STS) UM71 is another kind of jointless track circuit. It uses 1700 Hz and 2300 Hz on one track and 2000 Hz and 2600 Hz on the other. To reduce the chance of stray currents causing a wrong side failure the modulation frequency is calculated by dividing the base frequency by 128.
What happens when there is no train on the track?
When no train is present, the relay is energised by the current flowing from the power source through the rails. When a train is present, its axles short ( shunt) the rails together; the current to the track relay coil drops, and it is de-energised. Circuits through the relay contacts therefore report whether or not the track is occupied.
How does a track relay work when there is no train?
When no train is present, the relay is energised by the current flowing from the power source through the rails. When a train is present, its axles short ( shunt) the rails together; the current to the track relay coil drops, and it is de-energised.
