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ELECTRIC TRACTION IN RAILWAYS
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ABSTRACT
Electric traction is meant for locomotion in which the driving (tractive) force is obtained from
electric motors (called as traction motors). It involves utilization of electric power for traction
systems i.e., for railways, trams, trolleys etc. There is a wide variety of electric traction systems
around the world and these have been built according to the type of railway, its location and the
technology available at the time of the installation. Here we are discussing about needs electric
railways, whole process, working, advantage and disadvantage and conclusion of electric
traction.

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ELECTRIC TRACTION IN RAILWAYS
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CONTENTS
TOPIC PAGE
1. INTRODUCTION……………………………………………………………..01
2. WORKING OF ELECTRIC LOCOMOTIVE………………………………...02
3. NEEDS OF ELECTRIC RAILWAYS………………………………………...03
4. TRACK ELECTRIFICATION SYSTEMS……………………………………04
5. POWER TRANSMISSION SYSTEM………………………………………...05
6. TRACTION MOTORS………………………………………………………..06
7. TRACK CIRCUIT…………………………………………………………….07
8. BRAKING SYSTEM…………………………………………………………08
9. ADVANTAGES OF ELECTRIC TRACTION………………………………09
10. DISADVANTAGES OF ELECTRIC TRACTION………………………….10
11. CONCLUSION……………………………………………………………….11
12. REFRENCES…………………………………………………………………12

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ELECTRIC TRACTION IN RAILWAYS
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INTRODUCTION:
TRACTION - Driving forward of vehicle is called traction and the system, which employs this
type of mechanism is called traction system.
Classified broadly into two groups namely:
1. Non-electric traction systems
2. Electric traction systems
Electric Traction
The system which use electrical power for traction system i.e. for railways, trams, trolleys, etc. is
called electrical traction. OR Electric traction means a locomotion in which the driving force is
obtained from electric motors. Electric traction will continue to play a dominant role in the
Railway since it is an environmentally clean technology compared to diesel traction and also its
running cost is low. There are many advantages of electric traction over other forms of
locomotion.
A Brief History To Electric Traction
 The year 1881 saw the birth of the first electric Railway run by a German Engineer Werner
Van Siemens using both the rails to carry the Current.
 Finding this a little too dangerous, Siemens soon adopted the overhead Electric wires.
 Electric traction was introduced on Indian Railways in year 1925 on 1.5 KV DC and the first
electric train ran between Bombay's Victoria Terminus and Kurla, a distance of 9.5 miles.
 The first train run using 25kV AC was on December 15, 1959.
Voltages Used For Electric Traction In India
Typical Voltages used for electric Traction are 1.5kV DC and 25kV AC for mainline trains.
Calcutta had an overhead 3kV DC system until the '60s. The Calcutta Metro uses 750V DC
traction with a third-rail mechanism for delivering the electricity to the EMU. The Calcutta trams
use 550V DC with an overhead line (catenary) system with underground return conductors. The
Delhi Metro uses 25kV AC overhead traction with a catenary system.

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ELECTRIC TRACTION IN RAILWAYS
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WORKING OF ELECTRIC LOCOMOTIVE
Electric locomotive have been providing howling power since 1837. Unlike stream and diesel
locomotive, electric locomotive do not carry fuel or energy source. The energy that drives them
may be located from 100Km away itself. Electricity produced at distance power station is
conveyed to the locomotive through catenaries. An electric locomotive essentially a box of
transformers and semiconductors. A pantograph collects electricity from overhead wires and
transfers it for transformer, which sets electricity power for desired voltage. The connection with
axel brushes completes the circuit. From the transformer alternating current (AC) drawn from
overhead wires is transferred to main rectifier, which converters it to direct current (DC). The
main and axillary inverters convert DC into three phase AC. The three phase AC powers the
traction motors which than drive wheels. For the traction motor efficiently drive wheels many
small but important components are also needed. Axillary inverter and rectifiers power the
smaller components. Transformer and rectifiers produce lot of heat and have to be kept cool.
This important job is done by cooling fans, which are powered by axillary inverter. The
compressor is also powered by axillary inverter, supplies the air at required presser to operate
pantograph. A battery provides power for start of supplies also supplies essential circuits. The
battery is usually connected between DC controlled supply circuits. Finally traction motors also
produce lot of heat and requires cooling. The traction motors are cooled by separate cooling fans,
which draws power from axillary inverter and rectifiers. So that’s how electric locomotive
works.

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ELECTRIC TRACTION IN RAILWAYS
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TRACK ELECTRIFICATION SYSTEMS
1. DC system: in this case, the distribution system is fed from sub-station which are spaced 3 to 5
km apart for sub-urban railways and 15 to 40 km for main land service. The sub stations receive
ac power at a high voltage of the order of 33 kV to 110kV from overhead transmission lines and
convert it into dc supply using rectifiers. The operating dc voltage is of the order of 1500 to 3000
volts. The motors used are dc series motors to drive the trains.
2. Single phase ac system: In this system, ac series motors are used for deriving the motive
power. The electric power required is obtained from a distribution network of voltage 15 kV to
30 kV at 16
2
3
Hz or 25 Hz. This voltage is stepped down to 300 or 400 volts by a transformer
carried n the locomotive. As the voltage required is low, sub-stations are spaced 50 to 80 km
apart. The supply frequency is changed from 50 Hz to at 16
2
3
Hz or 25 Hz, because low
frequency supply increases commutation, efficiency and power factor of the ac series motor.
3. Three phase ac system: In this system, the motive power required is obtained by the use of
three phase induction motors operating at 3.3 to 3.6 kV at 16
2
3
Hz. The sub-stations receive
power at a high voltage of 220 kV from overhead transmission lines which is stepped down to
3.3 kV by transformers and frequency converters located at the sub-stations.
4. Composite systems : there are two composite systems
a. kando system : in this system, 16 kV, 50 Hz single phase overhead supply is converted
into 3- ⱷ supply by means of phase converter equipment carried on stations
b. s-ⱷ ac to dc system : in this system, the s-ⱷ, 25 kV overhead supply is stepped down by
a transformer in the locomotive and then converted into dc which is fed to the traction
motors.

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COMPARISON BETWEEN AC AND DC SYSTEMS
S.NO ASPECTS DC SYSTEM AC SYSTEM
1 Staring and running torque More Less
2 Speed variation Limited More variation possible
3 Cost, weight Less More
4 Efficiency More Less
5 Maintenance Less More
6 Sub-stations required More Less
7 Overhead distribution system Heavier and costly Lighter and less costly
8 Radio interference Less More
9 Rail conductor system Possible Not possible
SYSTEM OF TRACK ELECTRIFICATION
OVERHEAD CONTACT WIRE: The design of overhead contact wire as used for
tramways, trolley buses and for railways of 1500 V and above is highly difficult because it is not
sure that the collector and contact wire remain in contact at a fairly even pressure. The materials
employed for overhead wire are hard drawn copper, Cadmium-Copper or silicon bronze. Due to
higher electrical resistance and tensile strength, silicon-bronze is mostly used
Bow collector- The current may be collected by a bow collector
instead of a trolley wire. The bow collector is a light metal strip or
bow 60-80 cm in width attached to a framework mounted on the
roof of the car as shown in figure
Pantograph Collector- Main function is to maintain the link
between overhead contact wire and power circuit of the locomotive
at varying speeds in different climate and wind conditions This can be
lowered or raised from cabin by air cylinders.

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GROUND LEVEL
Third rail- A third rail is a method of providing electric power to
a railway locomotive or train, through a semi-continuous rigid
conductor placed alongside or between the rails of a railway track.
It is used typically in a mass transit or rapid transit system, which
has alignments in its own corridors, fully or almost fully
segregated from the outside environment. Third rail systems are
always supplied from direct current electricity.
TRACTION MOTORS
D.C series motors- Develops high torque at low speeds and low torque at high speed, exact
requirement of the traction units. Torque is independent of the line voltage and thus unaffected
by the variations in the line voltage.
Single phase a.c series motors- Starting torque is lower than dc series motor due to poor
power factor at starting Maximum operating voltage is limited to 400 Volts.
Three phase induction motors- Provides constant speed operation, developing low
starting torque drawing high starting current and complicated control networks makes it
unsuitable for electric traction work. Automatic regeneration is the main advantage in electric
traction with this motor.
TRACK CIRCUIT
The basic principle behind the track circuit lies in the connection of
the two rails by the wheels and axle of locomotives and rolling
stock to short out an electrical circuit. This circuit is monitored by
electrical equipment to detect the absence of the trains. Since this is

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ELECTRIC TRACTION IN RAILWAYS
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a safety appliance, fail-safe operation is crucial; therefore the circuit is designed to indicate the
presence of a train when failures occur. On the other hand, false occupancy readings are
disruptive to railway operations and are to be minimized.
Track circuits allow railway signalling systems to operate semi-automatically, by displaying
signals for trains to slow down or stop in the presence of occupied track ahead of them. They
help prevent dispatchers and operators from causing accidents, both by informing them of track
occupancy and by preventing signals from displaying unsafe indication.
RECENT ADVANCEMENT IN INDIAN RAILWAYS
Indian Railways creates history! Indian Railways production unit, Diesel Locomotive Works
(DLW), has for the first time converted a locomotive from diesel to electric traction. A WAGC3-
class diesel locomotive has been converted to electric and the new indigenous ‘Make in India’
engine delivers 5,000 HP, which is a 92% increase from the on rail track 2,600 HP of the older
version of the locomotive. This 5,000 HP unit is one half of a 10,000 HP locomotive, says Indian
Railways. According to the national transporter, two diesel locomotives have been converted to
one “permanently coupled 12-axle, electric locomotive” of 10,000 HP. The older diesel
locomotive had 3,200 HP, but on track it was 2,600 HP. In case of electric there is no loss of HP
and two engines are required, so two 5,000 HP locos have been coupled to yield an 10,000 HP.
Led by the first woman GM of DLW, Rashmi Goyel, the project is a definite step forward
towards reducing carbon emissions and introducing new age technology in Indian Railways.

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According to Indian Railways, two diesel locomotives have been converted to one “permanently
coupled 12-axle, electric locomotive” of 10,000 HP.
ADVANTAGES OF ELECTRIC TRACTION
• Cleanliness. It is free from smoke and flue gasses
• Maintenance cost. Maintenance and repair cost is about 50% of steam traction system.
Starting time. It can be started without loss of time.
• High starting torque. This system uses of DC & AC series motors, which has a very
high starting torque.
• Braking. In electric traction, regenerative breaking is used which feeds back 40%of the
energy.
• Saving in high grade coal. No coal is required for electric traction.
DISADVANTAGES OF ELECTRIC TRACTION
• High initial expenditure
• Failure of supply is a problem
• Electrically operated vehicles have to move only on electrified track
• For braking & control, additional equipment’s required
• Interference with telegraphs and telephone lines.

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CONCLUSION
Now a days for signaling purposes, trains are monitored automatically by means of TRACK
CIRCUIT. Track circuit play important role in stop accidents, traffic. Also subsequent amount of
saving is obtained in consumption of coal which is depleting at a rapid rate, leading to energy
conservation and energy and cost saving.
REFRENCES
1. P M Chandrashekharayya
2. https://www.slideshare.net/lavinkatiyar/track-circuit?qid=388b2e50-f097-47cd-b4b8-
1a4a6d3b9d07&v=&b=&from_search=1
3. https://en.wikipedia.org/wiki/Third_rail