ADVANCED MAINTENANCE OF RAIL TRACTION USING MAGNETIC LEAKAGDE FLUX TECHNIQUE

8/20/2019 ADVANCED MAINTENANCE OF RAIL TRACTION USING MAGNETIC LEAKAGDE FLUX TECHNIQUE

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ASEMINAR REPORT

ON

ADVANCED MAINTENANCE OF RAIL TRACTIONUSING MAGNETIC LEAKAGDE FLUX

TECHNIQUE

By

Kiran D. Chavanke

Under the guidance of

Pr!. Shra""ha Vin#h$rkar

Submitted in partial fulfillment for the award of the Degree of

%ACHELOR OF ENGINEERING

IN

ELECTRICAL ENGINEERING

De&ar'(en' ! E)e#'ri#a) En*ineerin*

SANDIP FOUNDATION+S

SANDIP INSTITUTE OF ENGINEERING , MANAGEMENT

Tri(-ak Ra" P/' Mahiravani Na/hik Mahara/h'ra 011123

1420526

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CERTIFICATE

This is to certify that the seminar entitled “ ADVANCED MAINTENANCE OF RAIL

TRACTION USING MAGNETIC LEAKAGE FLUX ” is a bonafide record of

the seminar done by Miss. KIRAN D. CHAVANKE under my supervision and guidance, in

partial fulfillment of the requirements for the award of Degree of Bachelor of Engineering in

Electrical Engineering from Sandip nstitute of Engineering ! "anagement, #ashi$ for the

year %&'()

Pr!. Shra""ha Vin#h$rkar

(Guide) In'erna) E7a(iner

*sst) +rofessor *sst) +rofessor

e!t" of Electrical Engineering Dept) of Electrical

Engineering

PROF. H. R KULKARNI e!art#ent $ea%

+rofessor ! ead Dept) of Electrical Engineering

P)a#e8 Na$hi&

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ANO*+EGEMENT

I ,ou%d %i&e to e-!re$$ #y gratitude and a!!reciation to a%% tho$e ,ho ga.e

#e $u!!ort and he%!ed #e in under$tanding the $u/0ect and fina%%y to

co#!%ete #y $e#inar $ucce$$fu%%y"

A $!ecia% than&$ to #y $e#inar guide Pr!.Shra""ha Vin#h$rkar ,ho

ha.e gi.en hi$2her fu%% effort in guiding #e in under$tanding #y $e#inar a$

,e%% a$ hi$ encourage#ent to #aintain our !rogre$$ and a%$o for he%!ing

$ti#u%ating $ugge$tion$ and encouraging to coordinate #y $e#inar and

$ucce$$fu%%y conc%uding it a$ thi$ re!ort"I ,ou%d a%$o %i&e to ac&no,%edge ,ith #uch a!!reciation the crucia% ro%e of

the head of de!art#ent Pr!. H.R K$)karni ,ho ga.e the !er#i$$ion to

u$e a%% re3uired faci%itie$ a.ai%a/%e in the de!art#ent"

Kiran D. Chavanke

Da'e8

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A%STRACT

Asynchronous induction motors are actually themost used in rail vehicle traction chains. Althoughmore reliable and robust than dc motors, they arevulnerable to insulation failures, particularly in dirtyenvironments.

The dirt accumulated inside motors is one themain causes of insulation failure. Excessiveaccumulation of dirt blocks in ventilation vents and

motor air gap may lead to overheating and, in severecases, abrasion of the insulation. Taking advantage of the peculiarities of environmental rail dirt (dirt with ahigh concentration of ferromagnetic particles), a newpredictive techniue has been developed which isable to detect the presence of excessive motor dirt inoperating conditions.

This new techniue to determine the degree of

contamination in the motor air gap is based on themeasurement of magnetic leakage !ux and itssubseuent analysis in the freuency domain. Theresults of the techniue make it possible to detectdirt accumulations early, before breakdown occursand without the need to stop the machine.

Index Terms"A# motors, insulation, magnetic $eldmeasurement,

predictive control, rail transportation reliability

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CONTENTS

Cha&'er N TITLE Pa*e n

2 INTRODUCTION 9 1"1 A #otor

1"' Magnetic fie%d #ea$ure#ent

1 S'$": ! #n'a(ina'in 22 '"1 Beha.ior in e-terna% fie%d

'"' #ea$uring the P6 inde-

'"4 i$tur/ance$ to the #agnetic fie%d

3 Ma*ne'i# !)$7 !re;$en#: /&e#'r$( 29 4"1 fre3uencie$ generated /y

$tator current 4"' fre3uencie$ generated /y

rotor current

4"4 f%u- $!ectra 4"5 fre3uencie$ to /e $tudied in

e#!irica% #ode%$

0 E7&eri(en'a) /'a'i#a)): #rre)a'in/ 14 5"1 $tudy of a%% the #otor ty!e

u$ing funda#enta% har#onic

5"' $tatica%%y $tudy

5"4 $tudy of fre3uencie$

6 Te/' re/$)' 19

9 Cn#)$/in 1<

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CHAPTER NO. 2

INTRODUCTION

THE RAILWAY traction motor is a fundamental part of the cars

of a railway system, and it is considered to be critical equipment in thelatter. he insulation system in any electric rai%,ay traction #otor$ i$ the onethat i$ #o$t !rone to aging or da#age" 8ariou$ $tudie$ carried out 91: 9': ha.e

de#on$trated that 47; of fai%ure$ occurring are due to !ro/%e#$ ari$ing in the $tator

in$u%ation $y$te# ,hich degenerate into $hort circuit$" It can /e $een therefore that

,inding fai%ure$ !articu%ar%y $tator ,inding$ ha.e a con$idera/%e inf%uence on the %ife of the traction #otor"


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!i". #. Accumulated dirt in the stator

In the special case of under"round railway operations, the

surroundin" en$ironment has certain peculiarities with respect to other

types of railway operations. %ne of the characteristics of metropolitanrail distin"uishin" it from lon"&distance rail is the fact that most of thetra$el is into tunnels. he drawbac' of tunnels is the "radualaccumulation of dirt which e$entually "ets into critical parts of $ehicles. (etectin" dirt in the motors, mainly in the air "ap, is of $italimportance when it comes to optimi)in" maintenance and increasin"the useful life of motors.

%.% A# &'T' Dia*ra(/ 5 %a/i# S'a'r an" R'r O&era'in

An AC M'r con.ert$ e%ectric energy into #echanica% energy" An A Motor

u$e$ a%ternating current = in other ,ord$ the direction of current f%o, change$ !eriodica%%y" In the ca$e of co##on A that i$ u$ed throughout #o$t of the United State$

the current f%o, change$ direction 1'> ti#e$ e.ery $econd" Thi$ current i$ referred to a$

? cyc%e A? or ? @ert A? in honor of Mr" @ert ,ho fir$t concei.ed the A

current conce!t" Another characteri$tic of current f%o, i$ that it can .ary in 3uantity" or e-a#!%e the f%o, can occur in 7 a#! 1> a#! or 1>> a#!" It ,ou%d /e rather difficu%t for

the current to /e f%o,ing at $ay 1>> a#!$ in a !o$iti.e direction one #o#ent and then

f%o, at an e3ua% inten$ity in the negati.e direction" In$tead a$ the current i$ getting readyto change direction$ it ta!er$ off unti% it reache$ ero f%o, and then gradua%%y /ui%d$ u! in

the other direction" The #a-i#u# current f%o, (the !ea&$ of the %ine) in each direction i$

#ore than the $!ecified .a%ue (1>> a#!$ in thi$ ca$e)" Therefore the $!ecified .a%ue i$gi.en a$ an a.erage" *hat i$ i#!ortant to re#e#/er i$ that the $trength of the #agnetic

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fie%d !roduced /y an A e%ectro=#agnetic coi% increa$e$ and decrea$e$ ,ith the increa$e

and decrea$e of thi$ a%ternating current f%o,"

2.2.2 %a/i# AC M'r O&era'in.

An A #otor ha$ t,o /a$ic e%ectrica% !art$D a ?$tator? and a ?rotor? a$ $ho,n in igure "The $tator i$ in the $tationary e%ectrica% co#!onent" It con$i$t$ of a grou! of indi.idua%

e%ectro=#agnet$ arranged in $uch a ,ay that they for# a ho%%o, cy%inder ,ith one !o%e

of each #agnet facing to,ard the center of the grou!" The ter# ?$tator? i$ deri.ed fro#the ,ord $tationary" The $tator then i$ the $tationary !art of the A #otor" The rotor i$ the

rotating e%ectrica% co#!onent" It a%$o con$i$t$ of a grou! of e%ectro=#agnet$ arranged

around a cy%inder ,ith the !o%e$ facing to,ard the $tator !o%e$" The rotor i$ %ocated

in$ide the $tator and i$ #ounted on the A #otorF$ $haft" The ter# ?rotor? i$ deri.ed fro#the ,ord rotating" The rotor then i$ the rotating !art of the A #otor" The o/0ecti.e of

the$e #otor co#!onent$ i$ to #a&e the rotor rotate ,hich in turn ,i%% rotate the #otor

$haft" Thi$ rotation ,i%% occur /ecau$e of the !re.iou$%y di$cu$$ed #agnetic !heno#enon

that un%i&e #agnetic !o%e$ attract each other and %i&e !o%e$ re!e%" If you !rogre$$i.e%ychange the !o%arity of the $tator !o%e$ in $uch a ,ay that their co#/ined #agnetic fie%d

rotate$ then the rotor ,i%% fo%%o, and rotate ,ith the #agnetic fie%d of the $tator"

A$ $ho,n in igure the $tator ha$ $i- #agnetic !o%e$ and the rotor ha$ t,o !o%e$" At

ti#e 1 $tator !o%e$ A=1 and =' are north !o%e$ and the o!!o$ite !o%e$ A=' and =1 are$outh !o%e$" The S=!o%e of the rotor i$ attracted /y the t,o N=!o%e$ of the $tator and the

t,o $outh !o%e$ of the $tator attract the N=!o%e of the rotor" At ti#e ' the !o%arity of the

$tator !o%e$ i$ changed $o that no, =' and B=1 and N=!o%e$ and =1 and B=' are S= !o%e$" The rotor then i$ forced to rotate degree$ to %ine u! ,ith the $tator !o%e$ a$

$ho,n" At ti#e 4 B=1 and A=' are N" At ti#e 5 A=' and =1 are N" A$ each change i$

#ade the o!!o$ite !o%e$ on the $tator attract the !o%e$ of the rotor" Thu$ a$ the #agneticfie%d of the $tator rotate$ the rotor i$ forced to rotate ,ith it"


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%. &A*+ET# -EE/ &EA01&E+T

Magnetic fie%d $trength i$ #ea$ured u$ing a .ariety of differenttechno%ogie$" Each techni3ue ha$ uni3ue !ro!ertie$ that #a&e it #ore $uita/%e for !articu%ar a!!%ication$" The$e a!!%ication$ can range fro# $i#!%y $en$ing the !re$ence or

change in the fie%d to the !reci$e #ea$ure#ent$ of a #agnetic fie%dH$ $ca%ar and .ector

!ro!ertie$" A .ery good and e-hau$ti.e funda#enta% de$cri!tion of /oth #echanica% ande%ectrica% #ean$ for $en$ing #agnetic fie%d$ can /e found in +ion 91:" +e$$ detai%ed /ut

#ore u!=to=date $ur.ey$ of #agnetic $en$or techno%ogie$ can /e found in 9' 4:" It i$ not

!o$$i/%e to ade3uate%y de$cri/e a%% of the$e techno%ogie$ in the $!ace a.ai%a/%e in a

@and/oo&" Thi$ cha!ter concentrate$ on $en$or$ that are co##on%y u$ed in #agneticfie%d #ea$uring in$tru#ent$" A$ $ho,n in igure 1"'"1 #agnetic fie%d $en$or$ can /e

di.ided into .ector co#!onent and $ca%ar #agnitude ty!e$" The .ector ty!e$ can /e

further di.ided into $en$or$ that are u$ed to #ea$ure %o, fie%d$ (1 #T) and high fie%d$(J1 #T)" In$tru#ent$ that #ea$ure %o, fie%d$ are co##on%y ca%%ed magnetometers" @igh=

fie%d in$tru#ent$ are u$ua%%y ca%%ed gauss meters"


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FIGURE 2.1.2 Ma*ne'i# !ie)" /en/r/ are "ivi"e" in' '= #a'e*rie/ -a/e" n 'heir

!ie)" Len*'h/ an" (ea/$re(en' ran*e8 (a*ne'(e'er/ (ea/$re )= !ie)"/ an" *a$//

(e'er/ (ea/$re hi*h !ie)"/.

The induction coi% and f%u-gate #agneto#eter$ are the #o$t ,ide%y u$ed .ector

#ea$uring in$tru#ent$" They are rugged re%ia/%e and re%ati.e%y %e$$ e-!en$i.e than theother %o,=fie%d .ector #ea$uring in$tru#ent$" The fi/er o!tic #agneto#eter i$ the #o$trecent%y de.e%o!ed %o,=fie%d in$tru#ent" A%though it current%y ha$ a/out the $a#e

$en$iti.ity a$ a f%u-gate #agneto#eter it$ !otentia% for /etter !erfor#ance i$ %arge" The

o!tica% fi/er #agneto#eter ha$ not yet %eft the %a/oratory /ut ,or& on #a&ing it #orerugged and fie%d ,orthy i$ under ,ay" The $u!erconducting 3uantu# interference de.ice

(S6UI) #agneto#eter$ are the #o$t $en$iti.e of a%% #agnetic fie%d #ea$uring

in$tru#ent$" The$e $en$or$ o!erate at te#!erature$ near a/$o%ute ero and re3uire $!ecia%ther#a% contro% $y$te#$" Thi$ #a&e$ the S6UI /a$ed #agneto#eter #ore e-!en$i.e

%e$$ rugged and %e$$ re%ia/%e" The @a%% effect de.ice i$ the o%de$t and #o$t co##on high=

fie%d .ector $en$or u$ed in gau$$ #eter$" It i$ e$!ecia%%y u$efu% for #ea$uring e-tre#e%y

high fie%d$ (J1 T)" The #agneto re$i$ti.e $en$or$ co.er the #idd%e ground /et,een the%o,= and high=fie%d $en$or$" Ani$otro!ic #agneto re$i$tor$ (AMR) are current%y /eing

u$ed in #any a!!%ication$ inc%uding #agneto#eter$" The recent di$co.ery of the giant

#agneto re$i$ti.e (GMR) effect ,ith it$ tenfo%d i#!ro.e#ent in $en$iti.ity !ro#i$e$ to /e a good co#!etitor for the traditiona% f%u-gate #agneto#eter in #ediu#=$en$iti.ity

a!!%ication$"

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The !roton (nuc%ear) !rece$$ion #agneto#eter i$ the #o$t !o!u%ar in$tru#ent

for #ea$uring the $ca%ar #agnetic fie%d $trength" It$ #a0or a!!%ication$ are in geo%ogica%

e-!%oration and aeria% #a!!ing of the geo#agnetic fie%d" Since it$ o!erating !rinci!%e i$

/a$ed on funda#enta% ato#ic con$tant$ it i$ a%$o u$ed a$ the !ri#ary $tandard for ca%i/rating #agneto#eter$" The !roton !rece$$ion #agneto#eter ha$ a .ery %o, $a#!%ing

rate on the order of 1 to 4 $a#!%e$ !er $econd $o it cannot #ea$ure fa$t change$ in the#agnetic fie%d" The o!tica%%y !u#!ed #agneto#eter o!erate$ at a higher $a#!%ing rate

and i$ ca!a/%e of higher $en$iti.itie$ than the !roton !rece$$ion #agneto#eter /ut it i$

#ore e-!en$i.e and not a$ rugged and re%ia/%e" Ta/%e 1"'"1 %i$t$ .ariou$ #agnetic fie%d$trength in$tru#ent$ and their characteri$tic$"

#2A3TE +'.

0T1/4 '- T2E #'+TA&+AT'+

he feasibility of detectin" contaminated motors by themeasurement of lea'a"e *u+ is hi"hly dependent on the ma"neticproperties of the materials accumulated in the motor air "ap. If thisaccumulation of contaminants had a diama"netic beha$ior, thepresence or absence of contaminants in the motor air "ap will be of ne"li"ible in*uence and $ery possibly undetectable with a$ailablemeasurin" instruments. hus, before proceedin" to the ine$itable

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e+perimental phase, it is essential to question the technical feasibilityof the method that it is sou"ht to apply.

any contaminated motors of the same type wereobser$ed by some of the authors -a set of more than / motors of 001

2 and #1/ 'W, which wor' in a lar"e metropolitan under"roundtransportation networ'3 studyin" the $isual and physical properties of the contamination present. he dirt usually ta'es the form of acompact layer with a thic'ness of se$eral millimeters, at the bottom of the stator. his solid layer is not easy to remo$e from the windin"s andis formed by dry "rease, part of which comes from the motor4s own ballbearin"s-see !i". #3.

Althou"h there was no e+hausti$e analysis of the chemicalcomposition of the contaminants, such a le$el of detail is not needed.

In fact, all that was intended in this phase of the research wor' was todetermine whether there are physical reasons su""estin" that thepresence of contamination will disturb the ma"netic *u+ su5ciently tobe detected. herefore, in principle, a qualitati$e and macroscopicstudy of the possiblesource of the contamination is su5cient, as well as an estimation of itsma"netic properties.

6tudy of the en$ironmental conditions of a railway runnin"into a tunnel, alon" with its operatin" conditions and the actual physicsof wheel7rail contact, re$ealed some initial plausible hypotheses

concernin" the constituent parts of the contaminanta""re"ate. hese hypotheses are summari)ed in the followin" points.

#3 5entilation. E$en where there are forced $entilation systems torenew the air in the tunnels, the absence of hi"h speed air currentsleads to hea$y concentrations of dust in the tunnel.

83 Associated mechanism. Rail systems require $ehicles with a hi"hstartin" torque, so the electric traction motor is coupled to a "earbo+which compensates the limitations on the startin" torque of asynchronous induction motors. he "earbo+ has its own lubricatin"

oil, and sometimes, because of hermetic failures in the couplin" seals,small amounts of lubricatin" oil can *ow from the "earbo+ to themotor.

93 ail e6ect. he wheel7rail system is formed by two metallicelements in permanent contact, so a minimal lubrication is a conditionneeded for a$oidin" serious problems of o$erheatin", planes, :ssures,sei)ure, etc.

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he lubricant used is "rease of characteristics adequate to

the operatin" conditions. his "rease is supplied throu"h "reaserswhich can be installed on the $ehicle itself, on the trac', or both.E+cess of "rease is accumulated on the trac' and pro;ected from the

wheels onto other elements under the rail $ehicle frame. In the speci:ccase of traction motors, surplus "rease is pro;ected onto the motorhousin" and accumulates close to the motor coolin" air input $ents. he area of the motor housin" is hot so that the "rease $iscosity isreduced, and this reduced $iscosity allows the "rease to *ow into themotor, aided by the suction caused by the motor $entilation.

hus, the accumulated contamination can be described as ahomo"eneous mass of "rease and dust which is dried and solidi:ed bythe temperature to form the compact layers seen when the motors areopened durin" their periodic inspections.

o date, howe$er, no lin' has been established between thecomposition of the contamination and its ma"netic properties. he 'eyto disco$erin" this relation is in the source of the "rease accumulatedinside the motor. As e+plained in the third hypothesis, this "reasecomes from wheel7rail contact when it is thrown onto the motorhousin". In other words, it is used "rease and so shall contain microparticles from wheel7rail wear.


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-ig. .%. &ovement of contaminant particles in the presence of magnetic $elds

the sensiti$ity of the contamination to the ma"netic :elds and $alidatethe hypotheses raised, the two followin" tests were performed.

.% 7ehavior in External -ields

his e+periment is desi"ned to con:rm the presence of ferroma"netic particles in contamination residues found and to obser$eits beha$ior in wea' ma"netic :elds created by a small permanentma"net.

his was done by collectin" $arious samples of contaminationfrom di=erent motors. Where necessary, they were sub;ected to adryin" process so that the residue obtained was dry. his process wasnecessary because some samples were "reasy in appearance. Whendried, the oily base of the "rease is lique:ed and lea$es a residue. If

this is not done, the e=ects of the $iscosity and adherence of the"rease ma'e it impossible to percei$e displacements in wea' ma"netic:elds.

hey were placed on a hori)ontal surface, and a smallpermanent ma"net was passed o$er the samples, crumbled into smalllumps 8 or 9 mm in diameter. he lumps were seen to mo$e, followin"the mo$ements of the ma"net -see !i". 8.#3.

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his simple e+periment con:rmed the presence of ma"neticparticles in the contamination samples> howe$er, was the presence of these particles su5cient to alter the *u+ appreciably? he need for aquantitati$e e+periment was clear.

. &easuring the 38 ndex

@nli'e concentration -usually measured in parts per million orppm3, the article Buanti:er inde+ is a non dimensional $alue whichindicates the amount of ma"netic particles in a sample C9D. In "eneralterms, this $alue is calculated accordin" to the relati$e ma"neticpermeability of the sample. he B inde+ is not sensiti$e to particles of less than 1 μm or more than 1// μm.

Howe$er, its non dimensional nature "i$es it the ad$anta"e

that it pro$ides $alues, which are easily comparable. he B inde+ ispart of a technique which is $ery "enerali)ed in predicti$emaintenance based on lubricant analysis because it is sensiti$e to thesi)e of the particles which occur in the wear processes in machinery,such as internal combustion alternatin" motors, "ear sets, bearin"s,etc. Hi"h B $alues point toe+cessi$e lubricant contamination caused by ferrous particles, themain cause of which is the premature wear of elements in contact inthese machines -normally made of steel3.

i$en that the contamination samples to be analy)ed are

ma"netic as a consequence of the wear particles from wheel7railcontact, it can be e+pected that the sample4s B inde+ will be hi"h. hus, samples were prepared for analysis> equal quantities of contaminants were dissol$ed in 9/ ml of neutral soapy solution. hishas to be done to brea' down the lumps of "rease and try tohomo"eni)e the samples as much aspossible, to a$oid false B meter readin"s. As already pointed out, one of the main bene:ts of the Binde+ is because it is non dimensional and it is easy to compare. ocorrectly e$aluate the de"ree of ma"netic particle contamination, the$alues "i$en in able I were obtained from the contaminant samples

with typical B inde+ $alues for lubricant oils from one&sta"e"earbo+es of a #1/&'W power motor in $arious states> compare those$alues with the B typical $alue found for dirt in the air "ap of anunder"round traction motor.


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his technique in$ol$es situatin" a :eld e+plorer coil on the motorhousin" on a line parallel to the motor rotation a+is. he followin" is adiscussion on how to perform this analysis and detection.

.9 /isturbances to the &agnetic -ield #aused by

#ontamination

-ig. 9. &agnetic leakage !ux spectrum.

he presence of dirt in the motor air "ap pro$ides a mediumwhose ma"netic permeability di=ers si"ni:cantly from that of the$acuum -air3. While full resolution of the a+well equations for $ariable:elds in time usin" numeric methods would sol$e the problem of de:nin" the ma"netic *u+ that would pass throu"h the e+plorer coil,

the problem is e+tremely comple+ for a number of reasons. !irst of all, the problem cannot be simpli:ed by applyin"some form of symmetry because the contamination fundamentally"ets into the area of the coil head -a+ial symmetry is lost3 and isspread alon" a $ariable a)imuth -trans$ersal3 an"le that is un'nownand not homo"eneous. In other words, the thic'ness of the layer of dirtis not constant nor in an a+ial direction or in an a)imuth direction. hiswould ma'e it necessary to simulate a 9&( problem on a computer in

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un'nown outline conditions, which may ma'e interpretation of theresults e+tremely di5cult. Another un'nown factor is the ma"neticpermeability of the contamination. his $alue may $ary "reatly, as itdepends on the ferric particle content of the dirt. he di5culty arisin"from this uncertainty is in the interpretation of results. If, durin" a test,

an intense $ariation of the ma"netic *u+ occurs and it is interpreted ascontamination, it would not be possible to decide whether the $ariationis due to e+cessi$e dirt with a moderate composition of ferric particlesor to a small amount of contamination but with a hi"h concentration of ma"neticparticles.

A possible solution must be e+plored to o=er an appro+imatesolution to the problem of detectin" the contamination in the motor air"ap. his new solution has been obtained throu"h a lar"e number of tests in the frequency domain which ha$e been

run on a lar"e number of motors.

$g. measuring 38 index

#2A3TE +'. 9

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&A*+ET# -1: -E81E+#4 03E#T1&

!lu+ spectra are hi"hly comple+ -see !i". 93, and thefundamental problem is to identify the frequencies most sensiti$e to

the presence of contaminants. o do this, the si"ni:cant di=erences willbe e+amined between the spectra for clean and for dirty motors.

Howe$er, are $ariations in *u+ caused by the presence ofcontaminants su5ciently lar"e to be detected? It is well 'nown that thema"netic induction :eld _B has its ori"in in electric currents. Whenthese currents are sinusoidal, of frequency ω, the ma"netic induction:eld "enerated will also be of the same frequency.

he $alue of the pre$ious inte"ral is a scalar, a numericalquantity, demonstratin" that, if the ma"netic induction :eld is

sinusoidal of a "i$en frequency ω, then the ma"netic *u+ will also besinusoidal for that same frequency. It can therefore be concluded thateach pea' seen in the *u+ spectrum has its ori"in in an electric currentof the same frequency.

Accordin" to the abo$e, the ne+t step is to determine whichcurrents may be present in the induction machine in the conditions inwhich the test was conducted, and the 'nowled"e of the frequencies of these currents will "i$e the 'ey to determinin"the rele$ant frequencies.

he basic operational principle of a three&phase asynchronousinduction -squirrel ca"e3 motor is to create a rotary sinusoidalma"netic :eld usin" windin"s :tted in a "i$en form, into which a rotoris immersed formed by a set of interconnected conductor rods C1D.


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he current in the stator windin"s is fundamentally the currentof the supply mains. he three&phase industrial electrical networ' -inEurope, 0// 271/ H)3 has minimum harmonic content, so a !ourierde$elopment of it would "i$e a sin"le predominant pea' -precisely 1/

H)3.

Howe$er, the tests were not done with this power supply but with anelectronic frequency $ariator at a fundamental frequency of G/ H). hisfrequency was used as supply because the measurements were donesimultaneously with other tests performed durin" the repairin" of thetrains. In the real situation, the frequency $ariator used supplies alar"e quantity of harmonics which could not be discarded, meanin"that theseharmonics circulate in the stator coils and so "enerate ma"netic *u+precisely at those frequencies. In other words, usin" a frequency

$ariator ma'es the study more di5cult because of the introduction of numerous harmonics of the supply frequency in the *u+ spectra. hus,in the test conditions, the stator is a source of ma"netic *u+, at themultiples of the supply frequencyF fL, 8 · fL, 9 · fL, . . .

9. -reuencies *enerated by otor #urrents

wo types of currents "enerated in the rotor conductors can bedistin"uishedF #3 those induced directly by !araday7Len)4s law, alreadydiscussed -these currents must necessarily be of the same frequencyas those of the stator inducin" them3, and 83 the

other currents that are circulatin", associated with the rotation speedsof the mechanical elements connected.

he set of rotor bars and the two short&circuit rin"s can beconsidered to be a succession of closed coils arran"ed successi$ely. Itis 'nown that, when current *ows throu"h one coil within a ma"netic:eld, a ma"netic moment _M is created dependin" on the spiral"eometry and the current *owin" throu"h it only.

he mechanical torque _M/ appearin" on this coil when it issubmer"ed inside a ma"netic :eld is "i$en by the e+pression _

M/ _M × _B . -03

1


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-ig. 9..%. ayout of the traction motor in the rail bogiestudied.

In summary, the mechanical torque arisin" depends on the coil"eometry, the current *owin" throu"h it, and the ma"netic induction:eld in which it is immersed. the test is under way, the motor isrunnin" a complete shaft of wheels throu"h a "earbo+ submitted to apneumatic bra'in" -see !i". 9.8.#3. he system4s mechanicalimbalances "enerate oscillations in the mechanical torque precisely atthe rotation frequencies of the elements which are rotatin". otherwise, the ma"netic moment necessary tocounteract the resisti$e torque would not be "enerated. In fact, ta'in"

modules in the $ectors in -03 would "i$e

M/ M · B · senθ -13

where θ is the an"le formed by $ectors _M and _B . Replacin" Mby -93,:nally, it is obtained

'>


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M/ I · |_S| · B · senθ. -3

If a condition is established that M/ shall pulse at "i$en frequencies,there is no alternati$e other than to induce a current I at that samefrequency because _B only has components of the supply current

harmonics. hen, independently of the currents induced by the statorcurrents, there are other currents induced by the resisti$e torque of themechanical elements coupled to the motor. he frequencies of thesecurrents are 8. and9.G H). he ma"nitude of these currents is relati$ely hi"h because theyshall o$ercome the forces at which the motor is sub;ected durin" thetest that runs at 1/K of the nominal load. hese su5ciently hi"h *u+$alues are associated with these frequencies to be able to detectanomalies between dirty and clean motors.

9.9 -lux 0pectra; Appearance of &odulations

When !ast !ourier ransform is applied to obtain the *u+spectrum in the frequency domain based on the temporary wa$eform,$ery often, the low frequencies do not appear isolated but asmodulations on hi"her frequencies. his is referred to as sidebandappearance.M

!or e+ample, consider a si"nal formed by the superposition of a wa$eof #// H) and another of 8 H). If mo$ed to the frequency domain, it ispossible to see them as two independent pea's and, also, as theappearance of 8&H)&wide sidebands around a main pea' of #// H). In

other words, a main pea' occurs at #// H), and other smaller onesoccur at #/8, #/0, #/, . . . and at G, , 0, . . ..

his happens when electrical hi"h frequencies aresuperimposed on mechanical frequencies, which are usually lowfrequencies.

9.< -reuencies to 7e 0tudied in Empirical &odels

hrou"hout the pre$ious considerations, the frequencies whichare e+pected in the ma"netic *u+ spectrum ha$e been determined

durin" the motor operatin" condition testsin which *u+ was measured. hese frequencies were as followsF

#3 supply frequency and harmonicsF fL, 8 · fL, 9 · fL, . . .>83 frequency associated with motor rotation speedF fms -8 /p3 · fL,where p is the number of motor poles>93 frequency associated with wheel shaft rotation speedF fws -8 /p3 ·fL · - Z # /Z 83, where Z # /Z 8 is the transmission ratio in the "earbo+>

'1


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03 modulations of motor rotation speed on the supply frequencyF fL ± n· fms, where n #, 8, . . .>13 modulations of wheel shaft rotation speed on the supply frequencyFfL ± n · fws, where n #, 8, . . ..If the accumulated contamination a=ects the *u+, these e=ects shall

be felt :rst on all those frequencies, which are the ones whichcontribute to the "reatest de"ree to the total*u+.

It must be ta'en into account that these same frequenciescould also appear e$en if the motor is perfectly clean. hese harmonicsare always e+pected in the ma"netic *u+ spectrum in dirty and cleanmotors since they are due to phenomena such as the motor4s ownstator eccentricity, nonuniform air "ap, rotor eccentricity, rotorunbalance, residual unbalances in the mechanical coupled to themotor, etc. Howe$er, the presence of contamination in the motor

"enerates a chan"e in the amplitude of the ma"netic *u+ spectrum of these frequencies, and the presence of these $ariations in amplitude iscompared to the cleanM state which is to be detected. herefore, the$ariable used for the dia"nosis of the state of contamination in themotor is the di=erence in the amplitude, measured in decibels,between each of the harmonic analy)ed and the supply frequency-fL3.

he methodolo"y used for this detection is based on theapplicationof statistical techniques on measurements performed o$er a

representati$e number of motors, and con:dence inter$als for therelati$e di=erence in the amplitude of the characteristic harmonics ofthe motor between clean and dirty motorsha$e been established.

#2A3TE +'. <

E:3E&E+TA 0TAT0T#A #'EAT'+0


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complete maintenance cycle of // /// 'm, there are cases of cleanand dirty motors. !i". 1 shows e+amples of motors with di=erentcleanness indices.

A study is to be made with all the motors, from type # -the

dirtiest3 to type 1 -the cleanest3, with the aim of obtainin" a statisticalmodel for each of the ma"nitudes of the *u+ harmonics to be studied. he best way of detectin" the beha$ior of each *u+ harmonic in cleanor dirty motors is to analy)e the statistical distribution of eachharmonic. his statistical distribution is obtained from /measurements of motor *u+.

In theoretical terms, "reater accumulation of contamination willmodify more the ma"netic permeability in the motor air "ap and willfacilitate the path of the ma"netic *u+ out of the machine. It is to bee+pected that hi"her contamination le$els will be associated with

hi"her *u+ lea'a"e $alues in the most representati$e harmonics.

83 8 · fL O ffm>93 9 · fL − ffm>03 9 · fL>13 1 · fL − ffm>3 1 · fL. (i=erencess

'4


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!i". 1. 2isual classi:cation of motors accordin" to cleanness inde+F

!rom -top left3 a $ery dirty one -type #3 to -bottom ri"ht3 a clean one-type 13.

(i=erences rather than absolute ma"nitudes were usedbecause this ma'es it possible to measure the e$olution of theharmonics independently of the load and the motor bein" studied.

It can be emphasi)ed that it was obser$ed e+perimentally that,althou"h wor'in" with the same motor, the le$el of the spectrum,de:ned as the hi"h or low le$el of the noise band in terms of ma"nitude, $aries "reatly from one motor to another, irrespecti$e of

the amount of dirt. Palculation of the statistical distributions of theharmonics of interest requires prior transformation of the data, andthese transformations, alon" withthe form of distribution An attempt was made subsequently to see' arelation betweenthese parameters and the clean or dirty state of the motor, based one+perimental and theoretical methods, for which thefollowin" si+ parameters were de:nedF

'5


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#3 α#, the percentile associated with the $alue measured for theharmonic ffm, within its statistical distribution>83 α8, percentile associated with the $alue measured for the harmonic8 · fL O ffm, within its statistical distribution>

93 α9, percentile associated with the $alue measured for the harmonic9 · fL − ffm, within its statistical distribution>03 α0, percentile associated with the $alue measured for the harmonic9 · fL, within its statistical distribution>13 α1, percentile associated with the $alue measured for the harmonic1 · fL − ffm, within its statistical distribution>3 α, percentile associated with the $alue measured for the harmonic1 · fL, within its statistical distribution. he e+perimental correlationobtained amon" these parameters,ma+imi)in" the probability of the correctness of themathematical model, is as followsF

K 8 · α#Oα8O8 · -#−α93Oα0O-#−α13O8 · -#−α3.

A motor is considered as dirty if K >0.0.

'7


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-ig. =. -lowchart of criterion A. he *owchart in !i". shows the process of dia"nosis. he bestrelation obtained was adequate for the GK of dirty motors and for theN8K of clean motors.


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produced by the sidebands around the supply frequency, caused bymodulations of the wheel shaft. hese sidebands ha$e a separationfrom the line frequency equal to the rotation speed of the output shaft.As the motor iscoupled to a "earbo+, the rotation speed -or wheel shaft rotation speed

fws3 is fws 8

p· Z # Z 8

· fL fsb · fL -G3

where p is the number of motor poles, Z # /Z 8 is the transmission ratioin the "earbo+, fL is the line frequency, and fsb is the sidebandfrequency.

he harmonics of use in constructin" the dia"nostic model arethe two bands on the left of the line frequency and the two sidebandsto the ri"ht. able III shows the dia"nosis criteria for dirty motors. henecessary conditions to implement the process of these critical $aluesare e+plained in the *owchart in !i". N.

he criterion was able to be adequate for the GK of clean motors andfor the N/K for dirty motors.

'C


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-ig. ?. -lowchart of criterion 7.


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he ei"ht harmonics selected for this study are as followsF#3 two sidebands related to the rotation speed of the motorfm -# ±-8 /p33 · fL · -# − s3 -83 si+ sidebands related to the wheel shaft rotation speed fw -# ± n ·- Z # /Z 83 · -8 /p33 · fL · -#−s3 where n#, 8, 9.

!or each harmonic, the di=erence between the amplitude of theharmonic and the line frequency fL for each measurement made toclean motors has been calculated. he $alue of xi is de:ned as themedian of the sample of measures xi med -|fi − fL|3 . -##3In this way, the $ector C x #, x 8, . . . , x GD representati$e of a patternof beha$ior for clean motors is obtained. With this model and all the motors, the correlation coe5cient isestablished, thus "i$in" a $alue of so much per one, meanin" that,when there is a si"ni:cant linear relation between motors, the $alue iscloser to one CD, CND.

Let C x #, x 8, . . . , x GD be the $alues of the harmonics of themodel for clean motors and ! C " #, " 8, . . . , " GD be the $alues of the*u+ harmonics of the motor that it wished to analy)e. hen, thecorrelation coe5cient CD, C#/D is calculatedusin" the 'nown e+pression.

#x" $%& - ,! 3'x · '"

where $%& - , ! 3 is the co$ariance between and ! and 'x and '" arethe typical de$iations of and ! . With the characteristic statisticalmeasurements, di=erences are obser$ed between dirty and clean

motors so that, as in the precedin" studies, a criterion is establishedwhich indicates whether the motor is dirty or clean. he criterion is asfollows.

#3 If the correlation coe5cient between the model and themeasurements of the motor under analysis is less than /.98, then themotor is dirty.83 If the correlation coe5cient between the model and themeasurements of the motor under analysis is equal to or more than/.98, then the motor is clean. he steps necessary to implement theprocess are e+plained in the *owchart in !i". G.

With this condition, the de"ree of correctness is somethin" o$er 1#Kfor dirty motors and N9K for those which are clean. While thesepercenta"es are low, the stren"th of the method is in the combinationof the three methods described.

'


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PHAER Q%. 1

E6 RE6@L6

Each of the three aforementioned studies classi:es the motorsas dirty or clean. able I2 shows the summary of the dia"nosis criteria.


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-ig. @. -lowchart of criterion #.

While not bein" perfect, these results open the way for a newmethodolo"y for detectin" dirt in railway traction motors usin"predicti$e techniques in maintenance of these motors. he aim of ;ustinter$enin" in those motors with a ma;or le$el of dirt is achie$ed withthe doubt remainin" that, if the de"ree of dirtiness was not hi"h, itwould ha$e been possible to ha$e continued for more time withoutrequirin" any inter$ention. We ha$e obtained C##D that the applicationof this methodolo"y to the maintenance of these types of motors hasled to :nancial sa$in"s of appro+imately #/K and a reduction in theso&called catastrophic failures by nearly /K.

41


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#2A3TE +' =

#'+#10'+

raction motors of railway $ehicles "radually accumulate dirt andcontamination in the air "ap. i$en the special characteristics of thisdirt, which contains iron particles from the wheel7rail contact, thedeposit of this dirt of hi"h ma"netic permeability modi:es thema"netic *u+ in the motor, and therefore, the lea'a"e *u+ will bea=ected.

4'


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he method has been enabled o$er / motors to $erify the e+istenceof the relationship between the state of the motor -cleanJdirty3 and thema"netic lea'a"e *u+. he study analy)es the components onfrequency of the lea'a"e *u+, pro$ides the harmonics that are themost sensiti$e to the accumulation of contamination, and describes

dia"nosis criteria based on the amplitudes of these harmonics. heseharmonics are related to the supply frequency of the motor, thenumber of poles, and the transmission ratio in the "earbo+, as well asmodulations between them.

Application of the de$eloped dia"nosis method has reached "oodresults in terms of the success rateF N9K for dirty motors and G8K forclean motors. he ad$anta"e of this method with respect to other teststo determine the state of dirtiness lies in the fact that the motor canwor' in normal conditions when data are bein" collected.

his clearly leads to impro$ed motor a$ailability.

Documents

ADVANCED MAINTENANCE OF RAIL TRACTION USING MAGNETIC LEAKAGDE FLUX TECHNIQUE