The locomotive is a powerhouse mounted on a frame that produces the motive power needed for traction on railways. There are three distinct locomotives used on the railways, each drawing its power from a different energy source. In a steam locomotive, the motive power is the steam generated in a pressure vessel called the boiler. Thus the thermal energy of fuel is converted into the mechanical energy of motion. In a diesel locomotive, the motive power is an internal combustion engine, which uses high-speed diesel oil as its source of energy. An electric locomotive derives its power from an electric conductor running along the track.
Types of Traction
There are three types of traction on Indian Railways.
(a) Steam traction by steam locomotives
(b) Diesel traction by diesel locomotives
(c) Electric traction by electric locomotives
Diesel and electric locomotives are comparatively more efficient than steam locomotives. They have greater hauling capacity, permit better acceleration and deceleration, and are capable of carrying heavy loads at higher speeds. In view of these factors, diesel and electric locomotives are fast replacing steam locomotives, as can be seen from Table 24.1.
Table 24.1 Different types of locomotives on Indian Railways
It may be noted here that though the total holdings of locomotives on Indian Railways have been decreasing since the last 25 years, the average tractive effort has increased progressively due to the provision of more efficient diesel as well as electric traction in place of steam traction.