ELECTRIC TRACTION – PART - 04 – SPECIFIC ENERGY OUTPUT FROM DRIVING AXLES AND SPECIFIC ENERGY CONSUMPTION

DIFFERENCE BETWEEN ENERGY CONSUMPTION AND SPECIFIC ENERGY CONSUMPTION OF A TRAIN

ENERGY CONSUMPTION

The energy input to the motor is called the energy consumption of the train as it is this energy which is utilized for movement of the train.

SPECIFIC ENERGY CONSUMPTION

It is defined as the energy consumed per Ton-metre. 

ENERGY OUTPUT

Total energy consumption Et= Ea + Eg + Er

Ea = Energy required for acceleration

Eg = Energy required to overcome gradient

Er = Energy required to overcome train resistance

Ea = 0.01072WeVm² watt-hour

Eg = 27.25WGD’ watt-hour

Er = 0.2778WrD’ watt-hour

Where 

We  is the accelerating weight

Vm is the maximum speed in km per hour

G is the Gradient

W is the dead weight of the train

D’ is the distance for which force due to resistance exists and

r is the train resistance.

SPECIFIC ENERGY OUTPUT

Espec- Outpu = Et / WD in watt-hour/ton-km

Espec-output = = [(0.01072WeVm²)/WD] + [(27.25GD’)/D] + [(0.2778rD’)/WD] watt-hour per ton-km
Where D is the total run length

FACTORS AFFECTING SPECIFIC ENERGY CONSUMPTION

1. DISTANCE COVERED

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

Suburban service it is higher compared to the main line service.

Typical values for the two services are 60 and 25 per ton-km.

2. ACCELERATION AND RETARDATION

For a given run and a give schedule speed, the specific energy consumption is lower and for higher the acceleration and retardation since with a longer coasting period can be obtained and for a smaller period the supply is switched on.

3. TRAIN RESISTANCE

The specific energy consumption depends upon the train resistance which depends upon the nature of track, speed of the train and shape of the rolling stock.

The train resistance also depends upon the front and rear portion of the train.

4. GRADIENT

While going up steep gradients, more energy is needed through the specific energy consumption may be modified by regenerative braking.

5. MAXIMUM SPEED

The specific energy consumption increases with increase in maximum speed.

6. TRAIN EQUIPMENT

By using more efficient train equipment the specific energy consumption may be reduced.

SKIN FRICTION

The resistance of the air comes into play on front end of the locomotive known as head resistance and on the sides of the top and under sides of the coaches.

Head resistance may be streamlined the shape of the engine.