Electric Traction

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An electric traction system is the type of traction system that uses electrical energy for the movement of vehicle at any stage.
 The electric traction system is classified into two groups as − Self-contained vehicles or locomotives 

An electric traction system is the type of traction system that uses electrical energy for the movement of vehicle at any stage.

The electric traction system is classified into two groups as −

  • Self-contained vehicles or locomotives (Ex. – battery-electric drive and diesel-electric drive)

  • Vehicles or locomotives which receive electric power from a distribution network or suitably placed substations (Ex. - railway electric locomotives, tramways and trolleybuses, etc.)

Here, we described different types of electric traction systems along with their advantages and disadvantages 

Straight Electric Traction System

In the straight electric traction system, either DC series motor or single phase AC series motor or three-phase induction motor is used for providing the required propelling torque. In this system, the electrical power is directly fed to the motor and the torque is generated.

Advantages of Straight Electric Traction System

The straight electric traction system possesses the following advantages −

  • Due to the absence of smoke, ash, etc. this system is clean and hence is suitable for underground railways.

  • This system provides high starting torque, high acceleration and retardation.

  • Straight electric traction system has high traffic holding capacity and flexibility in operation which is suitable for urban areas.

  • The starting time of straight electric traction system is quite less.

  • This system has high power to weight ratio.

Disadvantages of Straight Electric Traction System

The disadvantages of straight electric traction system include the following −

  • Due to the presence of overhead equipment, the capital cost is high.

  • Traction is tied to electric routes.

  • In this system, provision of negative booster is necessary.

  • It causes disturbance in neighboring communication lines.

  • Power failure of few minutes causes distortion in traffic.

I.C. Engine Electric Drive or Diesel-Electric Drive

In diesel-electric drive, a diesel engine (internal combustion engine) is used which is coupled to a DC generator. The speed of the diesel engine is maintained constant and this DC generator supplies power to the traction motors which are connected to the driving axels.

Advantages of Diesel Electric Drive

The advantages of the diesel electric drive are as follows −

  • Low capital cost due to the absence of overhead equipment.

  • It has high acceleration and retardation.

  • No requirement of modification in the existing tracks while converting from non-electric to diesel-electric traction.

  • This locomotive and train is a self-contained unit, therefore, it is not tied to any route.

  • The diesel electric drive can be put into service at any moment.

  • Overall efficiency of this system is high.

Disadvantages of Diesel-Electric Drive

The disadvantages of the diesel electric drive are given as follows −

  • The diesel engine cannot be overloaded.

  • This system has high running and maintenance costs.

  • The life of a diesel engine is comparatively shorter.

  • It is required to provide a separate cooling system for the diesel engine.

  • The dead weight of this type of locomotive is more which requires more axels.

  • In this type of traction system, the regenerative braking is not possible.

Battery-Electric Drive

In battery-electric drive system, the locomotive carries the secondary batteries which supply power to DC series motors employed for driving the vehicle.

This type of traction system is suitable for frequently operated services like daily run of 40 to 60 km for local delivery of goods, shunting and traction in industrial works and mines. The motors and batteries used in this system are flame proof.

Advantages of Battery-Electric Drive

The main advantages of the battery-electric drives are as −

  • Cleanliness, i.e., absence of fumes and ash, etc.

  • Easy maintenance and the maintenance cost is low.

  • The speed control is very easy and effective.

Disadvantages of Battery-Electric Drive

The following are the disadvantages of the battery electric drives −

  • The batteries require charging at regular interval due to small capacity.

  • In battery driven vehicles, the speed range is also limited.

Hybrid Drive

  • In the hybrid drives, the power is taken partly from the overhead lines and partly from batteries.

  • In this system, the locomotive receives power from overhead lines for most of the journey and at the end, the batteries are switched ON, so now locomotive is powered by the batteries.

  • The batteries are charged by taking the power from overhead lines.

  • The hybrid vehicles are generally used in mines where long tunnels are to be excavated.

Electric Drive

In this type of electric traction system, the locomotive is driven by the electric motors which are fed from the overhead distribution system.

Advantages of Electric Drive

Now-a-days, the electric drives are widely used in traction work due to the following advantages −

  • Cleanliness − it has no smoke, hence it is most suited for underground railways.

  • The motors used in electric traction have a very high starting torque.

  • These drives have high scheduled speed.

  • This type of traction system provides increased traffic handling capacity.

  • The electric locomotive requires easy maintenance and less maintenance cost.

  • Regenerative braking is possible in case of this electric traction system.

Disadvantages of Electric Drive

The disadvantages of the electric drive traction system are listed below −

  • High capital cost due to overhead equipment.

  • Power failure for few minutes can cause traffic distortion.

  • Interference with the communication lines.

  • This electric traction system is completely tied with electrified routes.

Blog Posted By

Sri J.JAGAN RUPCHAND.M.E.,
Lecturer / EEE


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