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Railway Signalling |
As the use of electrical systems increased The Track Circuit was developed. Here advantage is taken of the fact that wood, normally used for the track sleepers, is a poor conductor of electricity, In its simplest form a track circuit simply uses the wheels of a train as a switch. Making an electrical circuit when the train is in the section.
By changing the system so the train shorts out the circuit the system can be made fail safe. This means that a section will be shown to be occupied by a train if a fault such as a broken wire or a flat battery occurs.
Track circuit animation
The Track Circuit is an isolated section of track insulated from its neighbors by insulated fishplates. Normally Current from the battery (limited by the series resistor) is connected to the two isolated running rails. The relay connected across the rails is energized and the lamp circuit is broken.
When the rails are short-circuited by a wheelset the current is diverted through the wheelset and the relay de-energizes making the lamp circuit. Any fault in the track circuit wiring will also cause the relay to de-energize, giving an indication of train.
Track Circuit at Grosmont Crossing
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