Third Rail System in Metro's, Working of Third Rail System
In This article We will learn about third rail system in metro, how it works, voltage in third rail system.
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| Third Rail System |
A third Rail is a system of supplying power to a railway train, through a rigid conductor placed alongside or between the rails of a track.
It is used mostly in a mass transit or rapid transit system, which has alignments in its own corridors, almost fully segregated from the outside environment.
This system is usually employed in d.c railways operating at low voltage up to 600 Volts.
Third rail systems are a means of providing power to railway trains, and they uses an additional rail called as a conductor rail, for the purpose on most of all systems, the conductor rail is placed on the sleeper ends outside the rails, but in some system a central conductor rail is used.
The conductor rail is supported on ceramic insulators or insulated brackets at intervals of 10 feet (3 metres ) or So.
The above image shows the method of mounting a flat bottom contact rail. On the sleeper carrying the track rail a pedestal type porcelain insulator is fixed with two bolts or iron clamps.
The above figure shows the method of mounting a side contact conductor rail.
The insulator as in the earlier case is mounted on the same wooden sleeper which carries the track rails.
A hollow wooden block is fitted around the insulator on which rests the conductor rails.
The function of the guards, distance pieces keys and spring clips is to secure the rail in correct position.
The above figure shows the conductor rail is placed outside the rail track.
The usual distance between the rail conductor and nearest track rail is kept approximately in the neighborhood of 40.6 cm.
The height of the rail conductor is kept about 7.62 cm above the height of the track rails.
Traditionally, electric traction is used in suburban systems as a prerequisite for
requirement of high acceleration and pollution-free services in urban areas.
There
are three standard and proven systems of electric traction for use in suburban and
metro lines, viz., 750V dc third rail, 1500V dc overhead catenary and 25kV ac
overhead catenary system.
Presently, all these three systems are in use in India (750
V dc third rail in Kolkata Metro, 1500V dc catenary in Mumbai suburban of Central & Western Railways and 25kV ac catenary in Delhi Metro & Indian Railways). 1500 V dc system presently operational in few suburban sections of Central Railways will be converted to 25kV ac soon to meet increased traffic demand. Western Railways have already switched to 25 KV AC traction systems.
SELECTION OF TECHNOLOGY
01. Low life cycle cost
The low life cycle cost is achieved by the way of reduced scheduled and unscheduled maintenance and high reliability of the sub-systems.
It also be possible to achieve these objectivesby adopting suitable technologies. The selection of third rail system Technologies has been adopted to ensure low life cycle cost.
02. Bogies
Bolster less lightweight bogies with rubber springs are now universally adopted in metro cars.
These bogies require less maintenance and overhaul interval is also of the order of 4,20,000 km.
The use of air spring at secondary stage is considered with a view to keeps the floor level of the cars constant irrespective of passenger loading unlike those with coil spring.
The perturbations from the track are also dampened inside the car body on account of the secondary air spring along with suitable Vertical Hydraulic Damper.
These bogies require less maintenance and overhaul interval is also of the order of 4,20,000 km.
The use of air spring at secondary stage is considered with a view to keeps the floor level of the cars constant irrespective of passenger loading unlike those with coil spring.
The perturbations from the track are also dampened inside the car body on account of the secondary air spring along with suitable Vertical Hydraulic Damper.
