What is Pantograph Collector in Electric Traction?

What is Pantograph Collector?

The current in the overhead system is collected with the help of a sliding contact collector mounted on the roof of the vehicle. The pantograph current collector is used in the railways for collection of current from the overhead system where the operating speed of the train is as high as 100 kmph to 130 kmph and the current to be collected are as large as 2 kA to 3 kA.

The pantograph is mounted on the roof of the vehicle and carry a sliding shoe for contact with the overhead trolley wire. It consists of a jointed frame usually of steel tubing. The contact shoe is usually about 1.2 meters long. The schematic of a pantograph is shown in the figure.

There may be a single shoe or two shoes on each pantograph. The shoes may be straight throughout their lengths or cambered slightly or may be in the form of an auxiliary bow.

The material used for making pantograph is often steel. Sometimes, the wearing plates of copper or bronze are also inserted. The pressure on the trolley wire imposed by the pantograph varies from 5 kg to 15 kg.

The following methods are used for raising or lowering the pantograph from the driver cab −

• Air raised, gravity lowered

• Air raised, spring lowered

• Spring raised, air lowered

A pantograph collector should be designed in such a way that it can exhibits following desirable characteristics −

• The pantograph must be able to maintain continuous contact with the overhead trolley wire at reasonably constant pressure at any height.

• They must be light in weight in order to follow the overhead wire as it changes height above the rails to pass under overhead crossing, etc.

• They must be sufficiently strong and rigid to resist air pressure due to speed of train and wind.

• The pantograph must resist stresses due to the sway of the locomotive at high speeds and due to blows from the overhead system at deflectors or turnouts, etc. and from striking birds.

• The pantograph must be sufficiently pliable so that it will be damaged rather than pulling down the overhead structure.

Advantages of Pantograph Collector

The main advantages of using a pantograph collector include the following −

• A pantograph collector can operate in either direction of motion.

• The height of the pantograph collector can be easily changed from the driver’s cabin by employing simple operations.

• In a pantograph collector, there is no risk of leaving wire junction, etc.

• When a pantograph collector is used, the erection of the overhead network is very simple.