traction introduction

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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, trams, trolleys etc.

  or traction purposes mostly !"#hase Induction motors and d.c series motors are used and both have high starting

tor$ue, prevailing re$uirement for the high speed

What’s it all about?

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   %he year &''& saw the birth of the rst electric ailway

run by a *erman Engineer Werner +an iemens using boththe rails to carry the current. inding this a little too dangerous, iemens soon adopted the overhead electric wires.

  Electric traction was introduced on Indian ailways in

year &-/ on &./ 0+ 12 and the rst electric trainran between 3ombay4s +ictoria %erminus and 0urla along the 5arbour 6ine of 2, on ebruary !, &-/, a distance of -./ miles, 7agged o8 the then *overnor of 3ombay ir 6eslie 9rme Wilson.

   %he rst actual train run (apart from trial runs) using /:+ ;2 was on 1ecember &/, &-/-, on the 0endposi" a 5z ;2 traction based on rench ailway (2)

technology.    %he @umbai region is the last bastion of &/>>+ 12

; 3rief 5istory %o Electric  %raction

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  Italian ailways were the rst in the world to introduce

the electric traction.    %he world4s rst ;2 locomotive in +altelina, northern Italy

(&'-'A&->). #ower supplyB !"phase &/ 5z ;2, !>>> + (;2 motor

=> :mDh).

   It was designed by a 5ungary company.

   %he &> :m +altellina   line was opened on

F eptember &->.

irst ;2 6ocomotive

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   %ypical +oltages used for electric %raction are &./:+ 12

and /:+ ;2 for mainline trains.   2alcutta had an overhead !:+ 12 system until the 4>s.

   %he 2alcutta @etro uses =/>+ 12 traction with a third" rail mechanism for delivering the electricity to the E@Gs (Electric @ultiple Gnits).

   %he 2alcutta trams use //>+ 12 with an overhead line (catenary) system with underground return conductors.

 %he catenary is at a negative potential.

   %he 1elhi @etro uses /:+ ;2 overhead traction with a

catenary system on the ground"level and elevated routes, and uses a rather unusual 4rigid catenary4 or overhead power rail in the underground tunnel sections.

  ailway authorities purchases the power from the supply authorities

and they give voltage supply of &!D&&> 0+ at substation.

+oltages Gsed or Electric %raction In India

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  12 traction units use direct current drawn from either a

conductor rail or an overhead line.    %he most popular line voltages for overhead wire supply

systems A &/>>+ 12 and !>>>+ 12.   >>+ 12A=/>+ 12 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 trac: and that additional rail is

  called conductor rail)   1isadvantages" eHpensive substations are re$uired

at fre$uent intervals and the overhead wire or  third rail must be relatively large and heavy.    %he low"voltage, series"wound, direct"current

motor is well suited to railroad traction, being simple to construct and easy to control.

12 %raction

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  ;2 %raction units draw alternating current from an overhead

line.    %ypical +oltages Gsed areB"

  &/ :+ ;2, & 5z (&.= 5z)

  / :+ ;2, /> 5z

  / :+ ;2, > 5z

  ewer substations are re$uired   and the lighter overhead current   supply wire can be used   educed weight of support

structure  

educed capital cost of electrication

;2 %raction

W;*"- ated #ower"/>>> 5#

 %raction ystem" /0+ ;2 peed" &F> 0mDhr

 %raction @otor" 12 @otor

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  3ecause of the variety of railway electrication

systems, which can vary even within a country, trains often have to pass from one system to another. 9ne way to accomplish this is by changing locomotives at the switching stations.

   %hese 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.

  9ften, this is inconvenient and time"consuming ;nother way is to use multi-system locomotives that can

operate under several di8erent voltages and current types.

In Europe, it is common to use four"system locomotives (&./ :+ 12, ! :+ 12, &/ :+ & 5z ;2, / :+, /> 5z ;2)

@ulti ystems

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  5igh power"to"weight ratio than forms of traction such as diesel

or steam that generate power re$uiring on board prime mover.   higher power"to"weight ratio, resulting in

 ewer locomotives  aster acceleration   5igher practical limit of power   5igher limit of speed

  5igher hauling capability   o eHhaust fumes or carbon emissions    6ess noise pollution ($uieter operation)    %he maintenance cost of an electric locomotive is nearly />J

of that for a steam locomotive. @oreover, the maintenance

time is also much less.   ;n electric locomotive can be started at a momentKs notice

whereas a steam locomotive re$uires two hours to heat up.    %he motors used in electric traction have a very high starting

tor$ue. 5ence, it is possible to achieve higher acceleration of &./ to ./ :mDhDs as against >. to >.' :mDhDs in steam traction.

;dvantages of ;2 %raction ystems

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  It is possible to use regenerative bra:ing in electric traction

system. It leads to the following advantages.  ;bout '>J of the energy ta:en from the supply during

ascent is returned to it during descent. ;nd presently this returned energy is not sent bac: to public networ: but made available for other vehicles within the networ:

 *oods traLc on gradient become safer and speedier.  ince height of an electric locomotive is much less than

that of a steam locomotive, its centre of gravity is comparatively low. %his fact enables an electric locomotive to negotiate curves at higher speeds $uite safely.

  electric trains may be powered from a number of di8erent sources of energy (e.g. hydroelectricity, nuclear, natural gas, wind generation etc.) as opposed to diesel trains that are reliant on oil.

  electric trains do not have to carry around the weight of their fuel unli:e diesel traction.

  ; fully electried railway has no need to switch between

;dvantages of ;2 %raction ystems

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  ignicant capital cost of electrication

  Increased maintenance cost of the lines

  9verhead wires further limit the clearance in tunnels

  Gpgrading brings signicant cost,

especially where tunnels and bridges and other

obstructions have to be altered for clearance

  ailway %raction needs immune power, with no cuts, warranting duplication of %ransmission and 1istribution systems, which obviously comes at a #remium #rice.

1isadvantages of ;2 %raction ystems

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  #rovided for speeds upto &>:mph

  pan of catenary wire F/"-> m

  and sag of &"m.   elatively 2heaper   6ess @aintenance   uitable where traLc density

and operating speeds are

low.

ingle 2atenary

2onstruction

2ompound 2atenary

2onstruction

  #rovided for speeds ranges &->"F:mph

  ;dditional wire called intermediate wire is used to increase current carrying capacity i.e., to have increased traLc density.

ystem of %rac: Electrication

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Single Catenary Construction

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  3ow 2ollector" It uses a light metal strip or bow about &

m long for current collection.   ot suitable for railway wor:

re$uiring speed of &>:mph and higher.   e$uires reversing arrangement of the