The need for good energy efficiency, lower emission and low operating costs lead to the replacement of the principal diesel engine with electric railways. Electric railways use electric locomotives which are normally more powerful, noiseless, responsive and more reliable than the diesel engines. In diesel locomotives, petroleum is burnt. On the other hand, electric railway, electricity generated from various sources, including renewable energy is used. Also, they do not have local emissions, which is a significant advantage while comparing with the diesel.
Electric railway needs a power supply which is accessible all times, usually AC or DC. Electricity is transmitted to the traction or to the moving train using a conductor which usually takes the form of either overhead line or the third rail. As the return conductor, both of them use the running rails. Third rail and the overhead lines come under the contact system of railway electrification.
Overhead Lines
Generally known as a catenary, overhead lines are wires hanging over the tracks which supply current to the moving train using devices like pantograph or bow collector. The wires used in overhead lines must be:
• Able to carry current
• Resist the wind
• Withstand hostile weather conditions like extreme heat or extreme cold
• Stay in line with the route
The traction wires consist of two major wires, contact and catenary wire. The contact wire is the contact cable which carries electricity. Being the lowest overhead wire, the contact wire is pressed against the pantograph which is electrically conductive and makes possible the flow of current throughout the train. In order to achieve a better high-speed current, it is important to keep the geometry of the contact wire within defined limits.
Catenary wire or the messenger wire is used to support the contact wire. The curve formed by this catenary wire is used to negotiate the geometry of the contact wire. Then the entire system achieves a mechanical tension. Thus the contact and catenary wire functions mutually in the entire system. The considerable difficulties in the system include:
• Presence of more than one pantograph
• Incorrect tension of the wire
• The wrong speed of the train
Few demerits of Electric Trains
Though electric trains are effective while comparing it with diesel locomotives high lack of costs, lack of flexibility, exposure to power interruptions and causing unfortunate death for humans as well as animals prevents it from acclaiming as the best option.
On the other hand catenary wire are basically cords of uniform density across a specific cross-section that is perfectly flexible but not capable of being stretched and therefore hangs.