Specific Energy Consumption

Tractive effort:

It is the effective force acting on the wheel of locomotive, necessary to propel the train is known as ‘tractive effort’, Ft. The tractive effort is a vector quantity always acting tangential to the wheel of a locomotive. It is measured in newton. The net effective force or the total tractive effort (Ft) on the wheel of a locomotive or a train to run on the track is equals to the sum of tractive effort:

• Required for linear and angular acceleration (Fa).
• To overcome the effect of gravity (Fg).
• To overcome the frictional resistance to the motion of the train (Fr).

Ft = (Fa)+ (Fg)+ (Fr)

Specific Energy Consumption

This quantity of energy consumed by the various parts of train per ton per kilometer is known as specific energy consumption. It is expressed in watt hours per ton per km.

Factors affecting the Specific Energy Consumption

• Distance between stations :  From equation specific energy consumption is inversely proportional to the distance between stations. Greater the distance between stops is, the lesser will be the specific energy consumption.
• Acceleration and retardation : For a given schedule speed, the specific energy consumption will accordingly be less for more acceleration and retardation.
• Maximum speed : For a given distance between the stops, the specific energy consumption increases with the increase in the speed of train.
•  Gradient and train resistance:  From the specific energy consumption, it is clear that both gradient and train resistance are proportional to the specific energy consumption
• Weight of the train
• Crest velocity
• Efficiency of the complete system
• Moment of inertia of the rotating parts

Requirement of Traction Motors

• High starting torque
• Easy speed control
• Regenerate braking facility
• Speed should fall with increased load
• Capacity to withstand voltage variations
• Capacity to parallel operation
• Over load capacity
• Temporary interruption of supply
• High efficiency