What is Specific Energy Consumption in Electric Traction?

Specific Energy Consumption

The amount of energy input to the traction motors is known as energy consumption of the train. It is the energy consumed for the propelling the train. The total energy drawn from the distribution system is greater than this energy and is equal to the energy consumed by the various parts of the train and the quantity of the energy required for lighting, heating, control and braking, etc.

This amount of energy consumed by the various parts of the train per ton per kilometer is termed as specific energy consumption and is expressed in watt-hours per ton per km. Therefore,

$$\mathrm{Specific\: energy\: consumption\mathrm{\: =\: }\frac{Total\: energy \: consumption\: in\: Wh}{Weight\: of\: train\: in\: ton\times distance\: convered\: by\: train\: in\: km}}$$

Factors Affecting Specific Energy Consumption of Electric Train

The specific energy consumption of an electric train operating at a given schedule speed is affected by the following factors −

• Distance between stops
• Acceleration
• Retardation
• Maximum speed
• Specific resistance of train
• Gradient or slope
• Distance travelled by the train while power is on
• Nature of route
• Type of train equipment

The specific energy consumption is equal to the specific energy output divided by the overall efficiency of the locomotive, hence the specific energy consumption depends upon the overall efficiency of the electric train. Greater the overall efficiency lesser will be the specific energy consumption for a given specific energy output at axles.

Here, the specific energy consumption by the train depends upon the above mentioned factors as −

• The greater the distance between the stops lesser will be the specific energy consumption.

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

• Steep gradient or slope will cause specific energy consumption.

• If the specific resistance of the train is more, the greater will be the specific energy consumption.

For suburban railway services, the typical values of the specific energy consumption are 50 to 75 watt-hours per ton-km. While for main line services, it is 20 to 30 watt-hours per ton-km.

The variation of the specific energy consumption with the increase in value of acceleration or retardation and the distance of run is illustrated in the following figures.