Train Movement and Energy Consumption Interview Questions and Answers:

1. What is meant by speed-time curve ?

Ans. The curve drawn between speed and time taking speed on the Y-axis and time on the X-axis is known as speed-time curve.

2. Define terms ‘coasting’ and ‘braking’.

Ans. Coasting. At the end of free running period (i.e., at t₃) power supply is cut off and the train is allowed to run under its own momentum. The speed of train starts decreasing on account of resistance to the motion of train. The rate of decrease of speed during coasting period is known as coasting retardation.

Braking. At the end of coasting period (i.e., at t₄) the brakes are applied to bring the train to rest. During this period speed decreases rapidly and finally reduces to zero.

3. What is meant by crest speed ?

Ans. The maximum speed attained by the vehicle during the run is known as crest speed.

4. What is meant by schedule speed of a train ?

Ans. The ratio of distance covered between two stops and total time of run including time of stop is known as schedule speed.

5. What are those factors which affect the average speed of a train ?

Ans. The average speed of a given train when running on a given service (i.e., distance between two stops) is affected by the (i) acceleration and retardation and (ii) crest speed.

6. What are the factors which affect the schedule speed of a train ?

Ans. The schedule speed of a given train when running on a given service is affected by (i) acceleration and retardation (ii) maximum or crest speed and (iii) time duration of stop.

7. How does increase in acceleration and braking retardation affect the schedule speed of a train for a given run with fixed crest speed ?

Ans. For a given run and with fixed crest speed the increase in acceleration will result in decrease in actual time of run, and therefore, increase in schedule speed. Similarly increase in braking retardation will affect the schedule speed.

8. How does increase in crest speed affect the schedule speed for a given run with fixed acceleration and retardation ?

Ans. For a given run with fixed acceleration and retardation the actual time of run will decrease, and therefore, schedule speed will increase with the increase in crest speed.

9. How does increase in duration of stop affect the schedule speed ?

Ans. For a given average speed, the schedule speed will increase with the decrease in duration of stop.

10. What is meant by coefficient of adhesion ?

Ans. The coefficient of adhesion is defined as the ratio of the tractive effort just necessary to slip the wheels on the track and adhesive weight.

11. How does coefficient of adhesion vary with the increase in speed ?

Ans. The coefficient of adhesion decreases with the increase in speed.

12. What is coefficient of adhesion ? Why a train driven by separately excited motors has better adhesion than a train driven by series dc motors ?

Ans. Coefficient of adhesion (μ) provides a quantitative measure of the tendency of wheels to slip and is defined as the ratio of the tractive effort just necessary to slip the wheels on the track to the adhesive weight (weight on the driving axles).

The coefficient of adhesion depends on the nature of speed-torque characteristics of driving motor and has a higher value for motor with low regulation of speed i.e., when for a given increase of speed drop in torque is large. When a wheel slips, the speed of the driving motor increases. The torque drops by a large amount in motors with low regulation of speed and the wheels regain their grip on rails immediately avoiding slip.

Since separately excited dc motors have low speed regulation than dc series motors, a train driven by separately excited dc motors has better adhesion than a train driven by dc series motors.

13. What do you understand by train resistance and on what factors does this depend ?

Ans. Tractive effort For Overcoming Train Resistance. Train resistance consists of all the forces resisting the motion of a train when it is running at uniform speed on a straight and level track. Under these circumstances the whole of the energy output from the driving axles is expended against train resistance. Train resistance is due to (i) the friction at the various parts of the rolling stock (ii) friction at the track and (iii) air resistance. The first two components constitute the mechanical resistance component of train resistance. The train resistance depends upon various factors, such as shape, size and condition of track etc., and is expressed in newtons per tonne of the dead weight. For a normal train the value of specific resistance has been 40 to 70 newtons/tonne. The general equation for train resistance is given as

R = k₁ + k₂ V + k₃ V²

where k₁, k, and k₃ are constants depending upon the train and the track, R is the resistance in newtons and V is the speed in kmph. The first two terms represent the mechanical resistance and the last term represents air resistance.

14. What is meant by dead weight ?

Ans. The total weight of locomotive and train to be pulled by the locomotive is known as dead weight.

15. Why the accelerating weight of an electric train is greater than its dead weight ?

Ans. With the linear acceleration of the train, the rotating parts of the train such as wheels and motors also accelerate in an angular direction, and therefore, the tractive effort required is equal to the arithmetic sum of tractive effort required to have the angular acceleration of rotating parts and tractive effort required to have the linear acceleration. Hence the equivalent or accelerating weight of the train is taken higher than the dead weight.

16. What is meant by the term ‘specific energy consumption’ ?

Ans. Specific energy consumption is the total energy consumption of the train divided by the product of the weight of the train and distance of run.

17. What are those factors which affect the specific energy consumption of a train ?

Ans. The specific energy consumption of a train operating at a given schedule speed depends upon (i) distance between stops (ii) acceleration (iii) retardation (iv) crest speed (v) nature of route and (vi) the type of train equipment.

18. How is specific energy consumption affected by variation in distance between stops ?

Ans. Greater the distance between stops lesser will be the specific energy consumption.

19. How does the value of acceleration and retardation affect the specific energy consumption for a given run at a given schedule speed ?

Ans. For a given run at a given schedule speed, greater the value of acceleration and retardation more will be the period of coasting and, therefore, lesser the period during which power is on and, therefore specific energy consumption will accordingly be less.

20. What is meant by the term ‘adhesive weight’ ?

Ans. The total weight to be carried on the driving wheels is known as adhesive weight.