Advantages of Electric Traction
As compared to steam traction, electric traction has the following advantages :
1. Cleanliness.
- Since it does not produce any smoke or corrosive fumes, electric traction is most suited for underground and tube railways. Also, it causes no damage to the buildings and other apparatus due to the absence of smoke and flue gases.
2. Maintenance Cost.
- The maintenance cost of an electric locomotive is nearly 50% of that for a steam locomotive. Moreover, the maintenance time is also much less.
3. Starting Time.
- An electric locomotive can be started at a moment's notice whereas a steam locomotive requires about two hours to heat up.
4. High Starting Torque.
- The motors used in electric traction have a very high starting torque. Hence, it is possible to achieve higher accelerations of 1.5 to 2.5 km/h/s as against 0.6 to 0.8 km/h/s in steam traction. As a result, we are able to get the following additional advantages:
(i) high schedule speed
(ii) increased traffic handling capacity
(iii)because of (i) and (ii) above, less terminal space is required-a factor of great importance in urban areas.
5. Braking.
- It is possible to use regenerative braking in electric traction system. It leads to the following advantages :
(i) about 80% of the energy taken from the supply during ascent is returned to it during descent.
(ii) goods traffic on gradients becomes safer and speedier.
(iii)since mechanical brakes are used to a very small extent, maintenance of brake shoes, wheels, tyres and track rails is considerably reduced because of less wear and tear.
6. Saving in High Grade Coal.
- Steam locomotives use costly high-grade coal which is not so abundant. But electric locomotives can be fed either from hydroelectric stations or pit-head thermal power stations which use cheap low-grade coal. In this way, high-grade coal can be saved for metallurgical purposes.
7. Lower Centre of Gravity.
- Since height of an electric locomotive is much less than that of a steam locomotive, its centre of gravity is comparatively low. This fact enables an electric locomotive to negotiate curves at higher speeds quite safely.
8. Absence of Unbalanced Forces.
- Electric traction has higher coefficient of adhesion since there are no unbalanced forces produced by reciprocating masses as is the case in steam traction. It not only reduces the weight/kW ratio of an electric locomotive but also improves its riding quality in addition to reducing the wear and tear of the track rails.
Disadvantages of Electric Traction
1. The most vital factor against electric traction is the initial high cost of laying out overhead electric supply system. Unless the traffic to be handled is heavy, electric traction becomes uneconomical.
2. Power failure for few minutes can cause traffic dislocation for hours.
3. Communication lines which usually run parallel to the power supply lines suffer from electrical interference. Hence, these communication lines have either to be removed away from the rail track or else underground cables have to be used for the purpose which makes the entire system still more expensive.
4. Electric traction can be used only on those routes which have been electrified. Obviously, this restriction does not apply to steam traction.