Chapter: Electric Energy Generation and Utilisation and Conservation - Electric Drives and Traction

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Merits and Advantages of electric traction

The locomotive in which the driving or tractive force is obtained from electric motors is called Electric traction.

Merits of electric traction:


 The locomotive in which the driving or tractive force is obtained from electric motors is called Electric traction.

 

 Electric traction has many advantages as compared to other non-electrical systems of traction including steam traction.

 

Electric traction is used in:

 

i)  Electric trains

 

ii)  Trolley buses

 

iii)     Tram cars

 

iv)     Diesel-electric vehicles etc.

 

Traction systems:

 

All traction systems, broadly speaking, can be classified as follows:

 

1. Non-electric traction systems:

These systems do not use electrical energy at some stage or the other.

 

Examples:  Steam engine drive used in railways at some stage or the other.

These are further sub divided into the following two groups:

 

a) Self contained vehicles or locomotives

 

Examples:

 

i) Battery-electric drive ii) Diesel-electric drive

 

b) Vehicles which receive electric power from a distribution network or suitably placed sub-stations. Examples:

 

i) Railway electric locomotive fed from overhead A.C supply;

 

ii) Tramways and trolley buses supplied with D.C.supply.

 

Here power is applied to the vehicle from an overhead wire suspended above the track. Electric traction systems may be broadly categorized as those operating on:

1.   Alternating current supply         

2.   Direct current supply.                

In general following electric traction systems exist:

 

a)  AC 3 phase 3.7 kV system

b)  AC single phase 15/16 kV -161/25 Hz

c)   AC single phase 20/25 kV - 50/60 Hz

d)  DC 600 V

e)   DC 1200 V

f)    DC 1.5 kV

g)  DC 3 kV.

 

Advantages:

 

Electrical transmission, which is usually applied to high power units, has following advantages:

 

1.  It has smooth starting without shocks.

 

2.  Full driving torque is available from standstill.

 

3.  Engine can be run at its most suitable speed range. This given higher efficiency range.

 

4.  Characteristics of traction motor and generator are so chosen that the speed of the traction unit automatically adjusts according to the load and gradient so as to maintain constant output and not to overload the diesel engine.

 

5.  Electrical transmission docs not only work as torque converter but also works as reversion gear.

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