ELECTRIC
TRACTION
PRESENTED BY: NIKHIL JAIN
13085086
Introduction
Driving forward of vehicle is called traction and
the system, which employs this type of
mechanism is called Traction system.
Classified
broadly into groups namely:
Non-Electric traction system.
Electric traction system.
What is electric traction?
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, trolleys etc.
For traction purposes mostly 3-Phase Induction motors
and d.c. series motors are used and both have high
starting torque, prevailing requirement for the high
speed acceleration.
Ideal Traction System
High starting pulling effort in order to have rapid
acceleration.
Equipment should be capable of overloads for short
period .
The wear caused on the track should be minimum.
Braking should be possible without excessive wear on
the brush.
Capacity of withstanding voltage fluctuation and
temporary interruption of supply.
Parallel running usually more than one motor (two or
four) should be possible.
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.
Italian Railways were the first in the world to introduce the
electric traction.
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 along the Harbour Line of
CR, on February 3, 1925, a distance of 9.5 miles
Types of Electric
Traction Systems
Electric Traction
Systems
DC Traction
AC Traction
Multi Systems
DC Traction
DC traction units use direct current drawn from either a conductor
rail or an overhead line.
The most popular line voltages for overhead wire supply systems
1500V DC and 3000V DC.
600V DC750V DC volt range used for third rail systems (a
means of providing electric power to a railway train, through a
semi-continuous rigid conductor placed alongside or between the
rails of a railway track and that additional rail is called conductor
rail)
Disadvantage- expensive substations are required at frequent
intervals and the overhead wire or third rail must be relatively
large and heavy.
The low-voltage, series-wound, direct-current motor is well suited
to railroad traction, being simple to construct and easy to control.
AC Traction
AC Traction units draw alternating current from an overhead
line.
Typical Voltages Used are:
15 kV AC, 16Hz (16.7 Hz)
25 kV AC, 50 Hz
25 kV AC, 60 Hz
Fewer substations are required and the lighter overhead
current supply wire can be used
Reduced weight of support structure
Reduced capital cost of electrification
Multi Systems
Because of the variety of railway electrification systems,
which can vary even within a country, trains often have to
pass from one system to another. One way to accomplish
this is by changing locomotives at the switching stations.
These stations have overhead wires that can be switched
from one voltage to another and so the train arrives with
one locomotive and then departs with another.
Often, this is inconvenient and time-consuming Another way
is to use multi-system locomotives that can operate under
several different voltages and current types.
ADVANTAGES & DISADVANTAGES
OF A.C. SYSTEM OVER D.C.
SYSTEM
Advantages:
Light overhead catenary
Saving in sub-station
More flexibility
Lesser equipment used & easy to maintain
Starting efficiency
Disadvantages:
Single-phase A.C. system imposes unbalancing effect
Produces interference with telecommunication lines
System of Track Electrification
Trolley wire or contact wire suspended with minimum of
sag so that contact between the trolley wire and current
collector can be maintained at higher speeds.
This wire is supported by another wire known as catenary.
Two different types of Catenary construction can be used
Single Catenary
Compound Catenary
System of Track Electrification
Single Catenary
Construction
Provided for speeds upto
120kmph
Relatively Cheaper
Less Maintenance
Suitable where traffic
density and operating
speeds are low.
Compound Catenary
Construction
Provided for speeds ranges
190-224kmph
Additional wire called
intermediate wire is used to
increase current carrying
capacity i.e., to have
increased traffic density.
CIRCUIT
CIRCUITDIAGRAM
DIAGRAMOF
OFAA
TRACTION
TRACTION
COMPONENTS OF AN A.C
LOCOMOTIVE
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
This motor has surpassed the d.c series motor in terms of
size, weight cost for the same rating.
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.
Train Lightning/Air Conditioning
Individual coaches are powered by axle-driven generators
which charge storage batteries that power lights, fans and
other electrical fittings.
Older coaches use banks of 24V batteries while 110V in
newer coaches.
For powering air-conditioning equipment, an inverter was
used to convert the DC output of a set of batteries to 415V
AC. For some time now, however, groups of 110V
alternators delivering 18-22kW each have been used to
power air-conditioning equipment (the voltage is stepped
up to 415V)
ADANTAGES OF ELECTIC
TRACTION
High power-to-weight ratio than other forms of traction such
as diesel or steam that generate power requiring on board
prime mover. Higher power-to-weight ratio, resulting in
Fewer locomotives
Faster acceleration
Higher practical limit of power
Higher limit of speed
No exhaust fumes or carbon emissions
Less noise pollution (quieter operation)
The maintenance cost of an electric locomotive is nearly
50% of that for a steam locomotive. Moreover, the
maintenance time is also much less.
An electric locomotive can be started at a moments notice
whereas a steam locomotive requires two hours to heat up.
The motors used in electric traction have a very high
starting torque. Hence, it is possible to achieve higher
acceleration of 1.5 to 2.5 km/h/s as against 0.6 to 0.8
km/h/s in steam traction.
Since height of an electric locomotive is much less than
that of a steam locomotive, its centre of gravity is
comparatively low. This fact enables an electric locomotive
to negotiate curves at higher speeds quite safely.
Electric trains may be powered from a number of different
sources of energy (e.g. hydroelectricity, nuclear, natural
gas, wind generation etc.) as opposed to diesel trains that
are reliant on oil.
In electric traction, regenerative breaking is used which
feeds back 40% of the energy.
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, addition equipments required.
Interference with telecommunication lines.
A Glimpse on Indian Railways
4th largest network in the world, with 16 Zones,
transporting over 10billion passengers and over 1050
milliontonnes of freight annually.
Typical Voltages used for electric Traction are 1.5kV DC and
25kV AC for mainline trains.
The Delhi Metro uses 25kV AC overhead traction with a
catenary system on the ground-level and elevated routes.
Railway authorities purchases the power from the supply
authorities and they give voltage supply of 132/110 KV at
substation.
References
https://library.e.abb.com/public/6061e79d39b529f8c1257a77003
ec0d7/ABB%20Traction%20systems%20for%20locomotives
%20and%20high-speed%20applications_low%20res%20web.pdf
http://www.railway-technical.com/elec-loco-bloc.shtml
http://ieeexplore.ieee.org/xpl/mostRecentIssue.jsp?
reload=true&punumber=5239454
Thank you!
