01.05.07
Tube Lines invents track circuit device to tackle signal failures
Innovation will help reduce delays on the London Underground
Tube Lines has created a handheld current analyser device to reduce signal failures on the Underground. The invention measures various forms of current flowing through tracks. It will help identify faults which can cause signal failures.
The signalling systems currently in use on the Jubilee, Northern and Piccadilly lines rely on a circuit in the track which closes when a train is on it, turning the relevant signal behind to red. Each section of track is separated by plastic insulators called block joints; however problems can occur when they fail or when metal filings caused by wear and tear of the rail and wheels bridge the plastic. If this happens, a current passes between the two track sections causing a signal failure, in which case signals fail safe and show red, whether a train is near or not.
The new analyser also acts as a preventative measure to identify a signal delay before it occurs which will significantly benefit passenger journeys. Prior to this invention, the process of identifying the causes of similar signal failures was slow and unreliable, involving close inspections and light taps with a hammer to dislodge metal filings which can bridge block joints.
As well as helping to identify faulty block joints, the device can also be used on lengths of track to see if pieces of metal touching them have caused the circuit to earth.
Because the analyser shows how much current is flowing, it can help reveal if insulating block joints are beginning to break down so routine checks using the new device can help Tube Lines prevent problems by identifying potential issues before they fail. This improves maintenance and helps avoid disruption to passengers’ journeys.
This groundbreaking yet simple device can be used in any rail system that uses low current block joints and London Underground have recognised it as an appropriate method of testing. It is small, light and convenient for signals engineers to carry with them and enhances the safety of workers because it does not need to be connected to any circuit protecting them from the risk of minor electrical shocks.
Nick Healey, the technical officer at Tube Lines who designed the device says:
“I came up with the idea to create this analyser because it was almost impossible to identify and prove block joint failures. Using one of the prototypes we managed to quickly find a signal failure at Camden Town that would have been almost impossible to find otherwise. I have had some really good feedback from the signalling engineers who have used the current analyser. Identifying signal faults before they occur will considerably benefit passenger journeys on the underground.”
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