Thesis (PhD (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Certain types of electric machines are particularly susceptible to the proliferation of eddy
currents flowing within the solid conducting regions in the rotor. Single-layer, non-overlapping
windings within uneven open slots are some stator properties that can produce damaging,
asynchronous magnetic field harmonics which manifest in the rotor as eddy currents. The
ohmic losses caused by these eddy currents are a source of inefficiency and can cause a marked
increase in the temperature of the rotor. This temperature rise can be dangerous for the
magnets, which have to be kept within temperature limits to avoid partial or full
demagnetization.
The research work presented here is concerned with reducing the effect of eddy currents in the
rotor magnets and solid rotor yoke of an electric machine. The work presents analytical
methods to calculate the magnetic fields, eddy currents and solid loss in an electric machine due
to current in the winding and due to the interaction of the permeance variation in the stator
with the magnets in the rotor. A method is also suggested where the analytical theory can be
used with a magnetostatic finite element solution to produce a transient solid loss result. The
research work also investigates a method for optimal segmentation in both level and
penetration, and provides some design suggestions.
The work presents the method of partial magnet segmentation, which is a technique whereby
thin incisions are made into the magnet material from one or both sides. Another method of
partial rotor segmentation is also presented where the incisions are made into a portion of the
magnet-facing solid yoke. These methods attempt to interrupt the flow of eddy currents and
increase the resistance ‘seen’ by the eddy currents, while also keeping construction difficulty
and cost to a minimum. The methods are verified using finite element calculations which are
compared to measured results.
The result is that partial magnet segmentation is a very useful, effective and practical method of
segmenting magnets. The loss reduction profile can be similar to that of traditional full
segmentation. The method of partial rotor segmentation also shows a large reduction in rotor
power loss. With implementation of these methods on a test machine, one can expect an
efficiency increase of more than 4 % / AFRIKAANSE OPSOMMING: Sekere tipes van elektriese masjiene is veral sensitief vir die vloei van werwelstrome in solied
geleidende gebiede in die rotor. Enkellaag, nie-oorvleuelende wikkelings in oneweredige oop
gleuwe is enkele stator eienskappe wat skadelike, asinchrone magneetveld harmonieke tot
gevolg kan hê, wat as werwelstrome in die rotor manifesteer. Die ohmiese verliese wat deur
hierdie werwelstrome teweeg gebring word is 'n bron van ondoeltreffendheid en kan lei tot 'n
merkbare toename in die temperatuur van die rotor. Hierdie temperatuur styging hou gevaar in
vir die magnete en moet binne temperatuur limiete gehou word om gedeeltlike of self volle
demagnetisering te vermy.
Die navorsing vervat in hierdie document is gemoeid met die vermindering van die effek van
werwelstrome in die rotor magnete en in die soliede rotor juk van 'n elektriese masjien. Die
werk bied analitiese metodes aan vir die berekening van die magneetvelde, werwelstrome en
soliede verliese in ’n elektriese masjien as gevolg van strome in die wikkelings en die interaksie
van die permeansie variasie van die stator met die magnete in die rotor. ’n Metode word ook
voorgestel waar die analitiese teorie saam met ’n magnetostatiese eindige element oplossing
gebruik word om ’n resultaat vir die oorgang soliede verliese te verkry. Die
navorsingswerk ondersoek ook ’n metode vir die optimale segmentering in beide vlak sowel as
penetrasie, en verskaf sekere ontwerp voorstelle.
Die werk bied die metode aan van gedeeltelike magneet segmentering, wat 'n tegniek is
waarvolgens dun insnydings gemaak word aan een of beide kante van die magneet materiaal.
Nog ’n metode van gedeeltelike rotor segmentering word beskou waar die insnydings in in ’n
gedeelte aan die magneetkant van die soliede rotor juk gemaak word. Hierdie metodes poog om
die vloei van werwelstrome te onderbreek en die weerstand soos "gesien" deur die
werwelstrome te verhoog, terwyl konstruksie kompleksiteit en koste tot ’n minimum beperk
word. Die metodes word bevestig deur eindige element berekeninge wat met gemete resultate
vergelyk word.
Die gevolg is dat gedeeltelike magneet segmentering 'n baie nuttige, doeltreffende en praktiese
metode van die segmentering van magnete is. Die verliesverminderingsprofiel van gedeeltelike
segmentering kan soortgelyk wees aan dit van tradisionele volle segmentering. Die metode van
gedeeltelike rotor segmentering toon ook 'n groot afname in rotor drywingsverlies. Met die
implementering van hierdie metodes op ’n toetsmasjien, kan ’n mens ’n verhoging in
benuttingsgraad verwag van meer as 4 %
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/4014 |
| Date | 03 1900 |
| Creators | Wills, Dominic |
| Contributors | Kamper, M. J. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 93 p. ; ill. |
| Rights | University of Stellenbosch |
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