Electric Traction System Requirements, Terms, Advantages
Requirements, Advantages & Disadvantages of Electric Traction System
 What are the requirements of an ideal electric traction system?
The requirements of an ideal traction system are
- The locomotive should be self-contained and able to run on any route braking should be such that minimum wear is caused on the brake shoes if possible the braking energy should be regenerated and returned to the supply.
- Speed control should be easy.
- The wear on the track should be the minimum.
- The starting tractive effort should be high so as to have rapid acceleration.
- There should be no interference to the communication lines running along the lines.
- It should be Pollution free.
- Low initial and maintenance costs.
 What are the advantages and disadvantages of electric traction system?
- Coefficient of adhesion is better.
- Cheapest method of traction.
- Less vibration.
- less maintenance cost.
- Rapid acceleration and braking.
- High starting torque.
- It has great passenger carrying capacity at higher speed.
- Free from smoke and few gases, so used for underground and tubular railways.
- Electrically operated vehicles have to move on guided track only.
- Problem of supply failure.
- The leakage of current from the distribution mains and drop of volts in the track are to be kept within the prescribed limits.
- Additional equipments is required for achieving electric braking and control.
- High capital cost.
 What is meant by speed-time curve? Why it is used?
- The moment of the train and their energy consumption can be studied by means of speed-time and speed-distance curves, it shows the speed at different time instances after start of run and speed at different distances from the starting point respectively.
- Among these curves, the speed-time curve is generally is used.
- The curve drawn between speeding km/hr along Y-axis and timing seconds along X-axis is called speed-time curve.
- The speed time curve gives the complete information about the motion of the train. This curve gives the speed at various time instance after the start of run directly. Slope of the curve at any point gives the speed at that instant. The area under the curve gives the total distance travelled by the train.
 What are the different types of speed used in electric traction system?
1. Crest Speed:
The maximum speed attained by the train during run.
2. Average Speed:
The mean of the speeds from start to stop , ie the distance between two stops divided by the actual time of run is known as average speed.
Average speed = [ Distance between stops in km] / [ Actual time of running hours]
3. Schedule speed:
The ratio of distance covered between two stops and total time of run including time of stop is known as schedule speed.
Schedule speed = [ Distance between stops in km] / [ Actual time of running hrs + Stop time in hrs]
The schedule speed is always smaller than the average speed. The difference is large in case of urban and suburban services and it is negligibly small in case of main line services.
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