24-10-2016, 12:52 PM
Abstract
Railway electric traction describes the various types of locomotive and multiple units that are used on electrification systems around the world.
Various systems for Traction:
1. Steam Locomotive :
This consists of a steam boiler which produces superheated steam at a pressure of 10 to 15 kg/cm2. This steam drives two double acting, non-condensing steam engines which provide the motive power for the train. The speed is controlled by regulating the flow of steam to the engine.
These engines have now become obsolete and are being gradually withdrawn from services.
2. Diesel Engines :
In these engines a multi cylinder diesel engine is. coupled to a dc generator which supplies power to the dc traction motors. These engines are available in 450 HP (shunter) to 2500 HP range. These are manufactured at Diesel Locomotive Workshops.
These engines can be easily started from cold conditions. Their availability is higher as compared to a steam engine. Also these engines have better a overall efficiency (around 25%) as compared to about 5 to 10 percent for steam locomotives.
3. Electric traction :
Here power is applied to the vehicle from an overhead wire suspended above the track.
Electric traction systems may be broadly categorized as those operating on :
1. Alternating current supply
2. Direct current supply.
In general following electric traction systems exist :
(A) AC 3 phase 3.7 kV system
(B) AC single phase 15/16 kV -161/25 Hz
© AC single phase 20/25 kV - 50/60 Hz
(D) DC 600 V
(E) DC 1200 V
(F) DC 1.5 kV
(G) DC 3 kV.
Electric Traction > Advantages :
Electrical transmission, which is usually applied to high power units, has following advantages:
1. It has smooth starting without shocks.
2. Full driving torque is available from standstill.
3. Engine can be run at its most suitable speed range. This given higher efficiency range.
4. Characteristics of traction motor and generator are so chosen that the speed of the traction unit automatically adjusts according to the load and gradient so as to maintain constant output and not to overload the diesel engine.
5. Electrical transmission docs not only work as torque converter but also works as reversion gear.