The act of propulsion (movement) of a vehicle is known as traction. The system of traction (i.e. for railways, trams, trolleys, etc.) involving the use of electricity is called an Electric Traction System. Electric traction is a wheeled transport system using electrical energy and motors i.e., a driving force is obtained from electric energy and motors.
In railways, electric traction plays a dominant role due to its number of advantages which makes it an environmentally clean technology compared to other traction systems. In this article let us see the advantages and disadvantages of the electric traction system.
Advantages of Electric Traction :
The following are the advantages of electric traction,- Due to the absence of smoke and coal dust, it is clean and healthier from a hygienic point as compared to all other systems of traction. Hence it is pollution-free.
- No water and coal depots are required which in turn helps in saving high-grade coal where its availability is very low in the country.
- Since the required electrical energy can be taken directly from the lines. There is no need for an additional generator in electric traction that supplies power to the lights and fans.
- Generally diesel locomotive takes time to start due to the warming up of the huge internal combustion engine. Thus there is a loss of time in case of diesel locomotives to put into service. But there is no such loss of time for starting in the case of an electric locomotive.
- Maintenance costs and running costs are comparatively low (nearly 30% less than diesel locomotives).
- The time required for maintenance and repair work of an electric locomotive is much lesser compared to other locomotives, and if required, an electric locomotive can be put into service more than 95% of the day.
- Electric traction is most economical in high traffic density areas particularly, if the electrical energy is cheap.
- The vibration in electrically operated vehicles is less as the torque exerted by an electric motor is continuous.
- Because of its large capacity and higher schedule speed, the electric train can handle the traffic of any amount i.e. nearly double the amount of steam locomotive and is more suitable for suburban and urban railways.
- No difficulty is being experienced during the period of sudden and temporary overloading as the system is capable of drawing more energy from the supply network.
- The electric train can be divided and run in sections during the periods of light traffic density, thus enabling a frequent service to be maintained.
- Owing to the better speed control of the electric motor, locomotion on steep gradients at slow speed is possible.
- In the case of electric traction, in addition to mechanical brakes, electric braking is also employed which reduces the wear on brake shoes, wheels, and tracks as heat energy is dissipated in the resistance instead of brake shoes.
- Moreover, in the case of regenerative braking, part of the electrical energy is fed back to the supply system instead of wasting as heat in brake shoes, thereby saving the overall consumption of electric energy.
Disadvantages of Electric Traction :
The following are the disadvantages of electric traction,- High initial expenditure is involved for the power system if electric traction is involved.
- In case of power supply failure, the entire system will come to standstill.
- The electric locomotives are able to run only on electrified tracks since a normal track cannot supply electricity to an electric locomotive.
- Additional equipment required for regeneration adds to the overall cost.
- In cold countries, special equipment at extra cost is required for heating up tram compartments.
- The system is somewhat complicated as the leakage of current from distribution mains and drop of voltage in track have to be kept within prescribed limits.
- If the power supply used is alternating current (ac), there will be considerable interference to the communication lines running along the catenary.
- In cold countries, where there is snowfall, a layer of ice is accumulated on the line. Thus a service locomotive is required to clear the ice off the overhead lines.
- A change in power supply tariff changes the traction costs.
Efficiencies of Different Types of Locomotives :
| Traction System | Efficiency |
|---|---|
| Electric locomotive with hydro-electric power plant | 40-45% |
| Electric locomotive with thermal power plant | 32-38% |
| Diesel Locomotive | 25-30% |
| Gas Turbine Locomotive | 15% |
| Steam Locomotive | 10% |
