Condition Monitoring of Rotating Electrical Machines

303 Pages·2008·3.341 MB·English

by  Tavner, Peter, Ran, Li, Penman, Jim, Sedding, Howard

Condition Monitoring
of Rotating Electrical
Machines
Peter Tavner, Li Ran, Jim Penman
and Howard Sedding
TheInstitutionofEngineeringandTechnology
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Nomenclature
Symbol Explanation
A effectivecross-sectionalareaofacoil,m2
A availability,A=MTBF/(MTBF+MTTR)
A(t) availabilityfunctionofapopulationofcomponentsasafunction
oftime
a scalingfactoroftimeinamotherwavelettransform
α scaleparameterinapowerlawexpression
α andb straincoefficientsforthestrainenergyofthestatorcore
n n
α cross-sectionalareaofatooth,m2
t
α scaleparameterinaWeibullfunction
α resistancetemperaturecoefficient,degree/ohm
r
α skewangleofastator,degree
s
B(f ,f ) bispectrum
1 2
B radialfluxdensityinanairgap,Tesla
b orb statororrotorsideinstantaneousradialfluxdensity,Tesla
1 2
b time-shiftingparameterinamotherwavelettransform
β shapeparameterinaWeibullfunction
β half-anglesubtendedbyashortedturn,degrees
C volumetricconcentrationofadegradationproductinamachine
C Carterfactortoaccountforairgapslotting
C(y,v) inversewavelettransform
C(t) cepstrumfunction
c dampingconstantofasupportsystem,N/m/s
D dampingfactorforrotorvibrations
d rollingelementdiameter,m
E Young’smodulusofamaterial
E storedenergyinanelectricalsystem,Joules
e
e specificunbalancee=mr/M,m
e(t) instantaneousinducedEMF,V
(cid:3) straininamaterial
θ MTBFofacomponent,θ =1/λhours
θ spacepositioninthestatorfield,degrees
1
θ spacepositionintherotorfield,degrees
2
F parameterfromshockpulsemeasurementofarollingelementbearing
xx ConditionMonitoringofRotatingElectricalMachines
F (θ,t) forcingfunctiononarotororstatorexpressedincircumferential
m
angleθ andtimet,N
F(t) failuremodeprobabilitydensity,aWeibullfunction
ForF−1 forwardorbackwardFouriertransform
f firstcriticalornaturalfrequencyofarotorsystem,Hz
0
f orf (t) statororrotorsideinstantaneousmagnetomotiveforce(MMF),N I
1 2 1 1
orN I ,ampere-turns
2 2
f electricalsupplysidefrequency=1/T,Hz
se
f PWMswitchingfrequency,Hz
sw
f highermthnaturalfrequenciesofthestatorcore,Hz
m
f mechanicalvibrationfrequencyonthestatorside,Hz
sm
f thenthcomponentofanunbalancedforcingfunction
n
f mechanicalrotationalfrequency=N/60,Hz
rm
G straingaugefactor
G degreeofresidualunbalanceasdenotedbythequantityG =eω
G(f ) generalisedpowerspectralfunctionoffrequency,f ,thek thharmonic
k k
G∗(f ) complexconjugateofG(f )
k k
G(m) stiffnessfunctionofanmthnaturalfrequenciesofthestatorcore
G(t ) generalisedperiodicfunctionoftime,t
n n
g accelerationduetogravity,m/s2
g airgaplength,mm
g (z) naturalfrequencyfunctionannthsolutionofthebalanceequation
n
h heattransfercoefficientfromaninsulationsurface,W/m2K
h toothdepth,m
t
I orI statororrotorsidermscurrent,A
1 2
i ori (t) statororrotorsideinstantaneouscurrent,A
1 2
J polarmomentofinertiaofthecorecylinder,joules2
k integerconstant,indicatesthestatorMMFspace
harmonics,1,3,5,7…
k heattransfercoefficientthroughaninsulatingmaterial,W/mK
k stiffnessconstantofasupportsystem,N/m
k reflectioncoefficientintherecurrentsurgeoscillography(RSO)test
r
k integernumberofcommutatorsegmentsinaDCmachine
c
k/nq Halleffectconstantofanelectronicmaterial
k integerconstant,indicateseccentricityordernumber,whichiszero
e
forstaticeccentricityandalowintegervaluefordynamiceccentricity
k integerconstant,indicatesthecircumferentialmodesinavibrating
c
statorcore
k integerconstant,indicatesthelengthwisemodesinavibrating
l
statorcore
k statorwindingfactorforthenthharmonic
wn
L activelengthofacore,m
Nomenclature xxi
L inductanceofacoil,H
(cid:7) integernumberofstatortimeharmonicsorrotorwinding
faultharmonics
(cid:8) magneticpermeance
λ instantaneousfailurerateorhazardfunctionofacomponentormachine,
failures/component/year
λ(t) failurerateofacomponentormachinevaryingwithtime,
failures/component/year
M massofarotatingsystem,kg
M massofasupportsystem,kg
s
m integerconstant
m equivalentunbalancemassonashaft,kg
µ permeabilityinamagneticfield
N orN integernumberofstatororrotorsideturnsofacoil
1 2
N speedofamachinerotor,rev/min
N integernumberofrotorslots
r
N integernumberofstatorslots
s
n numberofchargecarriersperunitvolumeinasemiconductor
n integerconstant,1,2,3,4…
n integernumberofrollingelementsinarollingelementbearing
b
P statorsidepower,watt
1
p (t) instantaneousstatorsidepower,watt
1
p integernumberofpolepairs
Q heatflow,watt/m2
Q maximumpartialdischargerecordedinpartialdischargetests
m
usingacalibratedcoupler,mv
q electroniccharge,coulomb
q integerphasenumber
(cid:9)R changeinresistance
R resistance,ohms
R shockpulsemeterreading
R(t) reliabilityorsurvivorfunctionofapopulationofcomponents
asafunctionoftime,failures/machine/year
R (t) auto-correlationfunctiononatimefunctionf(t)witha
ff
delayof gt
R (t) cross-correlationfunctionbetweentimefunctionsf(t)andh(t)
fh
withadelayof gt
R resistanceofadevicemadeofthemetalat 0 °C,ohm
0
R resistance,ohm
T
r effectiveradiusofanequivalentunbalancedmass,m
r meanradiusofacore,m
mean
r radiusofairgap,m
airgap
S constantrelatedtothestiffnessofawinding,insulationand
toothcomponents
xxii ConditionMonitoringofRotatingElectricalMachines
s slipofaninductionmachine,between0and1
T torque,Nm
T temperatur e , °C
T periodofawave,sec
T(cid:7) volumetricvibrationkineticenergy,joules/m3
T(f ,f ,f ) trispectrum
1 2 3
τ radialthicknessofastatorcoreannulus,m
0
ρ densityofamaterial,kg/m3
σ electricalconductivityofaregion,ohm.m
σ andσ radialandtangentialMaxwellstressintheairgap,N/m2
r q
τ timedurationofanoverheatingincident,s
w
τ residencetimeofanoverheatingproductinamachine,or
r
leakagefactor,s
τ timedelayinacorrelationfunction,s
u lateraldisplacementofamachinerotor,µm
ur anduθ radialandperipheraldisplacementsinastrainedstatorcore,µm
V rmsvoltage,volts
V machinevolume,m3
V(cid:7) volumetricstrainpotentialenergy,joules/m3
v velocityoftherotor,relativetothetravellingfluxwaveproduced
bythestator,m/s
ν˙ volumetricrateofproductionofadetectablesubstance,m3/s
ν˙ backgroundrateofproductionofthesubstance,m3/s
b
ν Poisson’sratioofamaterial
φ flux,Webers
φ contactanglewithracesofarollingelementbearing,degree
φ electricalphaseangleofastatorMMFwaveF ,degree
s
ψ angularfrequencyofanelectricalsupply,rad/s
ψ firstcriticalornaturalangularfrequencyofarotorsystem,rad/s
0
ψ electricalsupplysideangularfrequency,rad/s
se
ψ mechanicalangularvibrationfrequencyonthestatorside,rad/s
sm
ψ mechanicalrotationalangularfrequency =2pN/60,rad/s
rm
ψ angularvelocityofaneccentricity,rad/s
ecc
ψ(t) motherwaveletfunctionoftime
W workfunctionforstrainenergyinstatorcore
W(a,b) wavelettransform
w weightperunitlengthperunitcircumferentialangleofastatorcore
cylinder,N/m
w ,w,w andw weightsofacoreyoke,teeth,insulationandwindings,
y t i w
respectively,kg
X secondharmonicmagnetisingreactance,ohm
m2
X secondharmonicleakagereactance,ohm
12
z longitudinaldistancefromthecentreofamachine,m
Z surgeimpedanceofawinding,ohm
0
Preface
Condition monitoring of engineering plant has increased in importance as more
engineeringprocessesbecomeautomatedandthemanpowerneededtooperateand
supervise plant is reduced. However, electrical machinery has traditionally been
thought of as reliable and requiring little attention, except at infrequent intervals
whentheplantisshutdownforinspection.Indeedthetraditionalapplicationoffast-
acting protective relays to electrical machines has rather reduced the attention that
operatorspaytotheequipment.
Rotatingelectricalmachines,however,areattheheartofmostengineeringpro-
cesses and as they are designed to tighter margins there is a growing need, for
reliability’s sake, to monitor their behaviour and performance on-line. This book
isaguidetothetechniquesavailable. Thesubjectofconditionmonitoringofelec-
tricalmachinesasawholecoversaverywidefieldincludingrotatingmachinesand
transformers. To restrict the field the authors deal with rotating machines only and
withtechniquesthatcanbeappliedwhenthosemachinesareinoperation,neglecting
themanyoff-lineinspectiontechniques.
Thefirsteditionofthisbook,ConditionMonitoringofElectricalMachines,was
writtenbyPeterTavnerandJimPenmanandpublishedin1987byResearchStudies
Press,withtheintentionofbringingtogetheranumberofstrandsofworkactiveatthat
timefrombothindustryandacademia.Inacademiatherewasagrowingconfidencein
themathematicalanalysisofelectricalmachines,incomputermodellingofcomplex
equivalent circuits and in the application of finite-element methods to predict their
magneticfields.Inindustrytherewasgrowinginterestinprovidingbettermonitoring
forlargerelectricalmachinesasrisingmaintenancecostscompetedwiththeheavy
financialimpactoflargemachinefailures.
The original book was primarily aimed at larger machines involved in energy
production,suchasturbinegeneratorsandhydrogenerators,boilerfeedpumps,gas
compressors and reactor gas circulators. This was because at that time those were
theonlyplantitemscostlyenoughtowarrantcondition-monitoringattention.Italso
reflectedthefactthatoneoftheauthorsworkedinthenationalisedgeneratingutility,
colouringhisapproachtothesubject.
The original book showed that, in respect of condition monitoring, electrical
machines are unusual when compared with most other energy conversion rotating
plant.Theall-embracingnatureoftheelectromagneticfieldintheenergyconversion
process,whichistheraisond’êtreoftheelectricalmachine,enablesoperatorstoinfer
farmoreabouttheiroperationfromtheirterminalconditionsthanisusuallythecase
withnon-electricalrotatingmachinery.Inthisearlierworktheauthorswereinspired
xiv Conditionmonitoringofrotatingelectricalmachines
by a much earlier book by Professor Miles Walker, The Diagnosing of Trouble in
ElectricalMachines,firstpublishedin1921.
Ourbookcoveredtheelementalaspectsofelectricalmachineconditionmonitor-
ingbutexposedanumberofimportantfacetsofunderstandingthathavesubsequently
leadtoagreatdealoffurtherwork,namely
• theelectromagneticbehaviourofelectricalmachines,
• the dynamic behaviour of electrical machines, particularly associated with the
controlnowavailablewithmodernpowerelectronics,
• thebehaviourofelectricalmachineinsulationsystems.
Each of these facets have now matured and are a rich source of fundamental
knowledge that has been related to the behaviour of machines in their operating
state, especially under fault conditions. Two examples of this further work are
Professor Peter Vas’, Parameter Estimation, Condition Monitoring and Diagnosis
ofElectricalMachines,publishedin1996;andGregC.Stone’s,ElectricalInsulation
forRotatingMachines, Design, Evaluation, Ageing, TestingandRepair, published
in2004.
Theeconomicsofindustryhasalsochanged,particularlyasresultoftheprivati-
sationandderegulationoftheenergyindustryinmanycountries,placingfargreater
emphasisontheimportanceofreliableoperationofplantandmachinery,throughout
thewholelifecycle,regardlessofitsfirstcapitalcost.
Finallytheavailabilityofadvancedelectronicsandsoftwareinpowerfulinstru-
mentation,computersanddigitalsignalprocessorshassimplifiedandextendedour
abilitytoinstrumentandanalysemachinery,notleastintheimportantareaofvisu-
alisingtheresultsofcomplexcondition-monitoringanalysis. Asaresult, condition
monitoring is now being applied to a wider range of systems, from fault-tolerant
drivesofafewhundredwattsintheaerospaceindustry,tomachineryofseveralhun-
dredmegawattsinmajorcapitalplant.Thevalueofthefundamentalcontributionto
theseadvancesbymanyanalystsoverthelast20yearscannotbeunderestimatedand
theywillplayamajorpartinthefuture.
In this new book, Condition Monitoring of Rotating Electrical Machines, the
originalauthorshavebeenjoinedbytheircolleagueDrLiRan, anexpertinpower
electronics and control, and Dr Howard Sedding, an expert in the monitoring of
electrical insulation systems. Together we have decided to build upon the earlier
book,retainingthesamelimitswesetoutatthestartofthispreface,mergingourown
experience with that of the important machine analysts through the years to bring
the reader a thoroughly up-to-date but practicable set of techniques that reflect the
workofthelast20years.Thebookisaimedatprofessionalengineersintheenergy,
process engineering and manufacturing industries, research workers and students.
Wehaveplacedanadditionallimitonthebookandthatistoconsiderthemachine
itselfratherthanitscontrolsystems.Whilerecognisingtheenormousgrowthofthe
applicationofelectronicvariablespeeddrivesinindustry,wedonotdealwiththeir
specificproblemsexceptinpassing.Weacknowledgethatthisisimportantforfuture
growthbutleavethisareaofinvestigationtoafutureauthor.
Preface xv
The examples of faults have concentrated on conventional machines rather
than the emerging brushless, reluctance, permanent magnet and unusual topology
machines. This is because the industry is still dominated by these conventional
machines. The ‘failure mode’ information for newer designs has not yet emerged
butwillbebasedonearliermachineexperience.Inthiseditionwehaveomittedcase
studiesbecausetherangeofapplicationofcondition-monitoringtechniquesonelec-
tricalmachinesisnowsowideandcomplexthatitisdifficulttoselectappropriate
applicationsfromwhichgeneralconclusionscanbedrawn.
Wehaveintroduceda‘Nomenclature’sectionandextendedthereferencestocover
major recent journal papers and books that have illuminated the subject, including
someoftheolderseminalworks,whichstilldeservescrutiny.Theauthorshavealso
taken the opportunity to correct errors in the previous book, rearrange the material
presentedandaddimportantinformationaboutfailuremechanisms,reliability,instru-
mentation,signalprocessingandthemanagementofrotatingmachineassetsasthese
factorscriticallyaffectthewayinwhichconditionmonitoringneedstobeapplied.
Finally, the diagrams and photographs representing the machines, the monitoring
systemsandthesignalprocessingusedhavebeenupdatedwhereappropriate.
PeterTavner
DurhamUniversity,2006
Contents
Preface xiii
Acknowledgments xvii
Nomenclature xix
1 Introductiontoconditionmonitoring 1
1.1 Introduction 1
1.2 Theneedformonitoring 4
1.3 Whatandwhentomonitor 7
1.4 Scopeofthetext 9
1.5 References 10
2 Construction,operationandfailuremodesofelectricalmachines 13
2.1 Introduction 13
2.2 Materialsandtemperature 14
2.3 Constructionofelectricalmachines 16
2.3.1 General 16
2.3.2 Statorcoreandframe 18
2.3.3 Rotors 18
2.3.4 Windings 18
2.3.5 Enclosures 20
2.3.6 Connections 26
2.3.7 Summary 26
2.4 Structureofelectricalmachinesandtheirtypes 26
2.5 Machinespecificationandfailuremodes 33
2.6 Insulationageingmechanisms 35
2.6.1 General 35
2.6.2 Thermalageing 36
2.6.3 Electricalageing 36
2.6.4 Mechanicalageing 37
2.6.5 Environmentalageing 38
2.6.6 Synergismbetweenageingstresses 39
2.7 Insulationfailuremodes 39
2.7.1 General 39
2.7.2 Statorwindinginsulation 40
2.7.3 Statorwindingfaults 45