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         T P W S

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Train Protection and Warning System (TPWS) on trains

To prevent train accidents, North Central Railway has installed Train Protection and Warning System (TPWS) on trains. This protection device would automatically apply brakes on a train if it approaches a fitted signal at danger too fast or fails to stop at a signal set at danger. It also automatically applies the brakes if a train is travelling too fast on the approach to certain speed restrictions and buffer stops. The trains on which it has been installed are 12279/12280 Taj Express, 12911/12912 Valsad-Haridwar express, 12189/12190 Mahakausal and 14211/14212 Agra- New Delhi intercity express. Now this system has been providedin 35 engines running over North Central Railway.

A standard TPWS installation consists of an on-track transmitter placed adjacent to a signal and activated when the signal is at `danger’ point. Any train that tries to pass the signal will have its emergency brakes activated. If the train is travelling at speed, this may be too late to stop it before the point of collision, therefore a second transmitter may be placed on the approach to the signal that applies the brakes on trains going too fast to stop at a signal, and this is positioned to safely stop trains approaching at upto 120 km/h.

On-track equipment :  

One pair of electronic loops is placed 50-450 metres on the approach side of the stop signal. The distance separating the loops is used to control the speed of the train.

There is another pair of loops at the signal, also energized when the signal is at “danger”. These are always placed immediately together and will stop a train that runs past the signal, regardless of its speed.

In a standard installation of TPWS, there are two pairs of loops (sometimes referred to as “grids” or “toast racks”). Both pairs consist of an `arming’ and a ‘trigger’ loop. If the signal associated with the TPWS is at “danger”, the loops will be energised. If the signal is at “proceed”, the loops will de-energise.

The first pair, the Overspeed Sensor System, is fitted at a position determined by line speed and gradient. The loops are separated by a distance that should not be traversed within a pre-determined period of time (about 1 second) if the train is running at a safe speed approaching the signal at “danger”. The other pair of loops is back to back at the signal, and is called a Train Stop System ( TSS). 

Equipment on train in cab :

The TPWS panel is located in the train cab along with a TPWS temporary isolation switch. The TPWS panel comprises two indicator lamps and a push switch. One lamp is used to indicate that a TPWS/AWS brake demand has occurred (the AWS and TPWS system are inter-linked). A temporary isolation indicator/fault indicator indicates that the system has been isolated with the temporary isolation switch or a fault has occurred with the TPWS. The push switch marked "train stop override" is used to pass a signal at danger with authority; it temporarily will ignore the TPWS TSS loops at a signal for a period of around 20 seconds or as soon as the loops have been passed.

The temporary isolation switch may be operated when the train is being operated in degraded conditions and multiple stop aspects will be required to be passed at danger with authority, after which the system must immediately be reinstated.

TPWS is a foolproof system that would prevent train accidents and thus ensure safety of passengers. The system would be installed on more trains soon.

Presently the system has been provided in AGC-PWL section of trunk route over North central Railway. Further it is sanctioned in AGC – GWL section. It is also proposed in another trunk route GZB-MGS in which the portion of CNB-MGS is sanctioned.

Source : North Central Railways / Indian Railways Portal CMS Team Last Reviewed : 12-08-2015  

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