Investigation of AC Electrical Machine Stators with Fractional Conductor Windings

113 Pages·2010·19.04 MB·English

Investigation of AC Electrical Machine Stators with
Fractional Conductor Windings
HENRIK GROP
Licentiate Thesis
Stockholm, Sweden 2010
Electrical Machines and PowerElectronics
TRITA-EE 2010:013 School of Electrical Engineering, KTH
ISSN 1653-5146 Teknikringen 33
SE-100 44 Stockholm
ISBN 978-91-7415-602-7 SWEDEN
Akademisk avhandlingsommedtillst(cid:229)nd avKungl Tekniskah(cid:246)gskolanframl(cid:228)gges
tillo(cid:27)entliggranskningf(cid:246)ravl(cid:228)ggandeavteknologielicentiatexamentorsdagenden
29 April 2010 klockan 15.00 i H1, Kungl Tekniska h(cid:246)gskolan, Teknikringen 33,
Stockholm.
' Henrik Grop, Mars 2010
Tryck: Universitetsservice US AB
iii
Abstract
Industryalwayssearchestheleastexpensivesolutionforamachinedesign.
Therefore,thereisaneedforintegratingdi(cid:27)erentcustomerorderedmachines
within the same frame, while keeping the foundation of the mechanical de-
sign constant. Since the winding design inelectrical machines is essential for
the performance and relatively inexpensive to adapt, it can be used to meet
di(cid:27)erentcustomer demands.
This thesis investigates the foundations of a special winding named frac-
tionalconductorwinding. Anexpressionforwindingfactors forcertainkinds
of these windings is developed. Calculations showed thatthe selection of the
winding distribution has e(cid:27)ect on the air gap space harmonics produced by
the winding. In some cases, the (cid:28)fth and seventh space harmonics can be
eliminated by the use of fractional conductor windings in combination with
short pitching.
The construction of a prototype fractional conductor wound induction
motor was documented andis presented inthis thesis.
The air gap (cid:29)uxdensityin a dualslotted fractional conductor woundin-
ductionmotorrunningatnoloadisstudied. Analyticalmodelsarecompared
to results obtained by (cid:28)nite elements and measurements. It was found that
analytical results overestimated the peak of the fundamental (cid:29)ux density by
13.5%. Theoverestimationwascausedbytheironreluctanceofthemain(cid:29)ux
path as well as saturation. Leakage was found to be a minor cause of this
overestimation.
Slot leakage and di(cid:27)erential leakage in machines having these windings
are studied. The analytical models were evaluated, with mostly good agree-
ments, compared to (cid:28)niteelement modeling as well as measurements.
Keywords: Windings, Leakage, Large machines, Induction motor construc-
tion.

v
Sammanfattning
Industrins(cid:246)keralltiddenmestkostnadse(cid:27)ektival(cid:246)sningnenp(cid:229)enmaskins
konstruktion. D(cid:228)rf(cid:246)r (cid:28)nns ett behov att bygga olika kunders maskiner, med
f(cid:246)ljaktligen varierande speci(cid:28)kationer, i samma maskinstomme och d(cid:228)rmed
anv(cid:228)nda en gemensam grundkonstruktion. Eftersom lindningen i en maskin
(cid:228)r avg(cid:246)rande f(cid:246)r prestanda samt dess utf(cid:246)rande (cid:228)r relativt billig att g(cid:246)ra
(cid:228)ndringar i, kan denanpassas till att uppfylla olika kunderskrav.
Denh(cid:228)rlicentiatavhandlingenutredergrundernaf(cid:246)renspeciellsortslind-
ning kallad delvarvslindning. Ett uttryckf(cid:246)r lindningsfaktorn f(cid:246)r vissa typer
avdessalindningarh(cid:228)rleds.Ber(cid:228)kningarvisarattvaletavlindningsf(cid:246)rdelning
p(cid:229)verkarstorlekenp(cid:229)deavlindningenproducerade(cid:246)verv(cid:229)gornailuftgapet.I
vissa fallkandenfemteochdensjundeordningens(cid:246)verv(cid:229)geliminerasgenom
anv(cid:228)ndandetavdelvarvslindning i kombination med h(cid:228)rvstegsf(cid:246)rkortning.
Byggetavendelvarvslindadasynkronmotorprototypdokumenteradesoch
beskrivs i dennalicentiatavhandling.
Vidare unders(cid:246)ks (cid:29)(cid:246)dest(cid:228)theten i luftgapet med sp(cid:229)rning av stator och
rotor i prototypen. En j(cid:228)mf(cid:246)relse med m(cid:228)tningar och (cid:28)nita elementmeto-
denvisarattdenanalytisktber(cid:228)knade(cid:29)(cid:246)dest(cid:228)theten(cid:246)verskattasmed13.5%
beroende p(cid:229) j(cid:228)rnreluktans och m(cid:228)ttning. L(cid:228)ckning visar sig endast p(cid:229)verka
resultatet marginellt.
Sp(cid:229)rl(cid:228)ckningochdi(cid:27)erentielll(cid:228)ckningimaskinermeddessalindningarun-
ders(cid:246)ks. Analytiska modeller utv(cid:228)rderas med mestadels goda resultat genom
j(cid:228)mf(cid:246)relse med (cid:28)nitaelementmetoden och m(cid:228)tningar.
S(cid:246)kord: Lindningar, L(cid:228)ckning, Stora maskiner, Konstruktion av asynkro-
nmotorer.

Acknowledgment
This project is conducted at the department of Electrical Machines and Power
Electronics at the Center of Excellence in Electric Power Engineering through the
High Performance Drives program.
First of all, I would like to thank my supervisor Assoc. Prof. Juliette Soulard
aswellasmyco-supervisorProf. ChandurSadaranganiforallhelpandinspiration
during the project. Secondly, I wish to thank all important people at ABB Au-
tomationProducts,DivisionMachineswhowereinvolvedintheproject. Especially
Holger Perssonfor suggesting the topic and Dr Marguerite Holmberg for supervis-
ing me at ABB in the beginning of the project. Further on, I am very grateful for
all support I got at ABB by Djordje Savinovic, Bj(cid:246)rn Lindberg, Magnus Lundin,
Dr Eva M(cid:229)rtensson, Hans ¯ke Eriksson, Bengt Eriksson and John Seppas. A spe-
cialthanks to Lars (cid:214)hrnwho I commuted with during the six months in V(cid:228)ster(cid:229)s.
Many thanks to all employees in the factory of ABB Machines, especially the sta(cid:27)
workinginthe winding factoryandthe test roomwhereIspentmanyjoyfulhours.
Thanks to all employees at the Department of Electrical Machines and Power
Electronics who have been very helpful and friendly. A special thanks to my of-
(cid:28)ce mate and friend Dmitry Svechkarenko, with whom I have solved the World’s
problems severaltimes but never remembersthe solution. Thanks to my colleague
and friend Alexander Stening for his inputs in discussions and also for his great
sense of humor. I am very happy having worked together with my colleague and
friend Rathna Chitroju. The department secretary Eva Pettersson has been very
helpful in administrative tasks, thank you for this. A huge thanks goes to Olle
Br(cid:228)nnvall for the many interesting discussions in the sauna and elsewhere, I hope
your shoulder will heal soon.
Iamverygratefultomymotherandfatherforalwaysbeingsupportivewhenever
I need.
Lastbutnotleast,IwouldliketothankKatharina,whohasbeenagreatpartner
and friend during these years.
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Contents
Acknowledgment vii
Contents viii
1 Introduction 1
1.1 AC-armature windings . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.3 Main contributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.4 Publications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.5 Outline of the thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2 Bene(cid:28)ts and issues associated with fractional conductor windings 9
2.1 Investigation of di(cid:27)erent phase group patterns. . . . . . . . . . . . . 11
2.2 Conclusions from the winding investigations. . . . . . . . . . . . . . 19
3 Winding factors for fractional conductor windings 21
3.1 Introduction of the coil factor . . . . . . . . . . . . . . . . . . . . . . 21
3.2 The coil factor for a simple winding . . . . . . . . . . . . . . . . . . 22
3.3 General expression of the coil factor for winding A . . . . . . . . . . 25
3.4 The coil factor for space harmonics . . . . . . . . . . . . . . . . . . . 27
3.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4 Modellingof air gap (cid:29)ux density at no load including stator and
rotor slotting 33
4.1 Air gap (cid:29)ux density in the prototype . . . . . . . . . . . . . . . . . . 33
4.2 In(cid:29)uence of slotting . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
4.3 Search coil measurements and comparison to analytical and FEM
models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
4.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
5 Stator slot and di(cid:27)erential leakage 47
5.1 The slot-model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
5.2 Veri(cid:28)cation of slot energy by FEM modeling. . . . . . . . . . . . . . 49
viii
CONTENTS ix
5.3 Di(cid:27)erential leakage . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
5.4 Measurements of slot leakage . . . . . . . . . . . . . . . . . . . . . . 62
5.5 Measurement details . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
5.6 Validation of FEM model . . . . . . . . . . . . . . . . . . . . . . . . 67
5.7 Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
5.8 Measurement Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
5.9 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
6 Construction of a full scale prototype 77
6.1 Punching of sheets . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
6.2 Stacking of sheets. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
6.3 Stator coils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
6.4 Winding the stator . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
6.5 Connection of the stator winding . . . . . . . . . . . . . . . . . . . . 81
6.6 Vacuum pressure impregnation (VPI) . . . . . . . . . . . . . . . . . 83
6.7 Insertion of rotor bars . . . . . . . . . . . . . . . . . . . . . . . . . . 84
6.8 Machine assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
6.9 Sensors and tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
6.10 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
7 Conclusions and Future Work 91
Appendices 92
A Derivation of the coil factor for winding A 93
Bibliography 97
List of Figures 100