30-03-2015, 11:41 AM
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.