Speed - time Curve of Train

In this theory, the speed time curve of the train is discussed. The curve between speed in km per hour ( Y – axis ) and time in second on X – axis is known as speed – time curve of the train.

Importance of speed time curve

• It gives completes information regarding motion of the train.
• It gives information about speed of train at particular time.

The simplified speed – time curve for urban and sub-urban service for electrical traction is shown in the Figure.

Quadrilateral Speed – Time Curve

The study of Quadrilateral speed time curve is given below.

Let

α = Acceleration in km per hour per second

Factor affecting schedule speed

 

Acceleration and retardation

• If the acceleration increases for a given run and with fixed crest speed, the actual time of run decreases and this will increase in schedule speed.

Schedule speed = Distance between stops / ( Actual time of run + stop time )

• Similarly braking retardation will also affect the schedule speed. 

Trapezoidal Speed - time Curve

 

• The speed – time curve of the main line service is replaced by trapezoidal curve. 
• The running and coasting period in the trapezoidal curve is simply replaced by constant speed as shown in the figure. 
• The area of the speed – time curve represents total distance travelled by the train.

Crest Speed, Average Speed & Schedule Speed

 

Crest Speed

• The maximum speed attained by the vehicle during its running is called as crest speed.

Average Speed

• The mean or average speed of the vehicle during from start to stop is called as average speed.