Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Voltage regulation on distribution networks has so far been done by means of mechanical tap changers. However, these tap changers are plagued by high maintenance costs due to the arcing caused while switching, which degrades both the contacts and transformer oil. The major advances made during the last decade with regard to semiconductor technology have led to the development of high power IGBTs. These high power IGBTs are capable of conducting currents up to 1 000 A, while the voltage over the IGBT reaches well over 3 000 V. Using these high power IGBTs to design and build a solid-state tap changer allows the tap changer to regulate the output voltage with higher accuracy and speed. The supporting hardware is also discussed, while the design is verified by the use of simulations and practical measurements conducted on a scale-model of the IGBT-based solid-state tap changer. / AFRIKAANSE OPSOMMING: Spannings regulasie op distribusie netwerke word hedendaags verrig deur meganiese tap geskalde spanning reguleerders. Maar hierdie tap skakelaars word konstant beïnvloed deur oorvonking wat plaasvind tussen die kontakte wat hierdie kontakte beskadig en die transformator olie degradeer. Die laaste dekade het groot vordering getoon in halfgeleier navorsing wat gelei het tot die ontwikkeling van hoë drywing halfgeleiers. Die halfgeleiers of IGBTs kan strome so groot soos 1 000 A gelei terwyl die spanning oor die halfgeleier 3 000 V kan oorskry. Die gebruik van die hoë drywing halfgeleiers maak die pad oop vir die ontwerp en bou van ’n tap geskakelde reguleerder wat die uitree spanning akurater en vinniger kan reguleer. Die aanvullende hardeware is ook bespreek en die ontwerp is geverifieër deur middel van simulasies en deur praktiese metings wat geneem is op ’n skaal model van die hoogspanning spannings reguleerder.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The world is increasingly being faced with the challenge of effectively exploiting available renewable energy resources, not only to meet an ever growing energy demand, but also to preserve the available amount of fossil fuels and to reduce the amount of carbon dioxide emissions released into the atmosphere by fossil fuelled power stations. Hence, every available renewable energy resource, even small rivers has a contribution to make in the attempt to reduce the amount of fossil fuel generated electricity. The focus of this study is the design and installation of a low cost grid-connected 10 kW micro hydro power system (MHPS). The process to determine the potential of the available water resource is first to be presented. The environmental aspects of these systems, based on the study that is undertaken for the implementation of the landmark example, are discussed. The complete design of a micro hydro power system for a specific site is presented. This design is based on using commercially available components and equipment in an attempt to minimise the total cost of a micro hydro power system. The designed micro hydro power system is installed in-field and the predicted performance of the designed system is verified with measured results of the implemented system. Based on the results of the micro hydro power system landmark example, it is shown through a complete economic study, that this investment is very worthwhile. / AFRIKAANSE OPSOMMING: Die wêreld word daagliks meer en meer uitgedaag om beskikbare alternatiewe energiebronne effektief te benut, nie net om in die groeiende elektrisiteits aanvraag te voorsien nie, maar ook om die beskikbare fossiel brandstowwe te beskerm en ook om die hoeveelheid koolstofdioksied gasse wat deur fossiel brandstof kragstasies vrygestel word, te verminder. Dus het elke beskikbare alternatiewe energiebron, selfs klein riviertjies, ‘n bydrae om te lewer tot die poging om die hoeveelheid elektrisiteit wat deur fossiel brandstowwe opgewek word, te verminder. Die fokus van hierdie studie is op die ontwerp en implementering van ‘n lae koste netwerk gekoppelde 10 kW mikro hidro kragstelsel. Eerstens word die proses om die potensiaal van die beskikbare waterbron te bepaal, bespreek. Al die omgewings aspekte van hierdie mikro hidro kragstelsels word dan bespreek. Dit is ten volle gebaseer op die studies wat gedoen is vir die implementering van hierdie landmerk voorbeeld. Die volledige ontwerp van ‘n mikro hidro kragstelsel, vir ‘n spesifieke terrein, word bespreek. Hierdie ontwerp is hoofsaaklik gebasseer op die gebruik van kommersieel beskikbare komponente met die doel om die totale koste van die stelsel te minimeer. Die stelsel wat ontwerp is, is geïnstalleer op die terrein en die verwagte prestasie van die stelsel is toe geverifieer met gemete resultate van die geïnstalleerde stelsel. ‘n Volledige ekonomiese studie wat gebaseer is op die resultate van die geïnstalleerde stelsel, word dan bespreek en daar is gevind dat hierdie stelsel werklik finansieel die moeite werd is. / Centre for Renewable and Sustainable Energy Studies

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The electromagnetic and mechanical design aspects of optimally designed doublesided rotor radial flux permanent magnet wind generators with non-overlap aircored (iron-less) stator windings are analysed in this thesis. The wind generator is implemented in a battery charging system for use in rural settlements and farms. The optimal generator and system design is based on an accurate analytical model and is confirmed with finite element analysis. It is shown, amongst other things, that the electromagnetic design and surprisingly not the mechanical design, determines the rotor yoke dimensions and, hence, largely the mass and cost of the generator. Alternative battery charging systems are also considered and discussed. / AFRIKAANSE OPSOMMING: Die elektromagnetiese en meganiese ontwerp aspekte van optimaal ontwerpte dubbel-kant rotor radiale vloed permanente magneet windgenerators met nieoorvleuelende lug kern (sonder yster) statorwindings word in hierdie tesis ontleed. Die windgenerator word geplaas in 'n battery-laai stelsel vir gebruik in landelike nedersettings en plase. Die optimale generator en die stelsel ontwerp is gegrond op 'n akkurate analitiese model en is bevestig met eindige element analise. Daar word onder andere getoon dat die elektromagnetiese ontwerp, en nie die meganiese ontwerp, die rotor juk dimensies en dus grootliks die massa en die koste van die generator, bepaal. Alternatiewe battery-laai stelsels word ook oorweeg en bespreek.

Thesis (PhDEng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: The advent of new high energy product permanent magnet materials has opened great opportunities for novel electrical machine topologies with advantageous features such as high efficiency and high power/weight ratio. Amongst others, axial field permanent magnet (AFPM) machines with ironless stators are increasingly being used in power generation applications. Because of the absence of the core losses, a generator with this type of design can operate at a substantially high efficiency. Besides, the high compactness and disc-shaped profile make this type of machine particularly suitable for compact integrated power generation systems. Due to construction problems, the generator application of this type of machine has been limited to quite a low power range. There is a need to investigate the performance capability of this type of AFPM machine in the upper medium power level. The focus of this thesis is on the design optimisation of the air-cooled AFPM generator with an ironless stator. A design approach that directly incorporates the finite element field solution in a multi-dimensional optimisation procedure is developed and applied to the design optimisation of a 300 kW (at unity power factor) AFPM generator. To enable an overall design optimisation of the machine, different design aspects, such as the cooling capacity, the mechanical strength and eddy loss, are also studied in this research. To enable the free movement of the rotor mesh with respect to the stator mesh, the air-gap element originally proposed by Razek et. al. is derived for Cartesian coordinate systems. For minimising the large computation overhead associated with this macro element, a number of existing time-saving schemes have been utilised together with the derived Cartesian air-gap element. The developed finite element time-step model is applied to calculating the steadystate performance of the AFPM machine. Since the flux distribution in an AFPM machine is three dimensional by nature, calculating the eddy current loss by merely using a simple analytical method may be subject to a significant error. To overcome this problem, the two dimensional finite element field modelling is introduced to perform accurate field analysis. To exploit the full advantages of the twodimensional finite element modelling, a multi-layer approach is proposed, which takes into account the variation of the air-gap flux density in the conductors with regard to their relative positions in the air-gap. To account for the radial variation of the field, a multi-slice finite element modelling scheme is devised. The thermal analysis is an important aspect of the design optimisation of AFPM machines. From a design point of view, it is preferable to have a simple but effective method for cooling analysis and design, which can easily be adapted to a wide range of AFPM machines. In this thesis a thermofluid model of the AFPM machine is developed. The fluid flow model is needed for calculating the air flow rate, which is then used to find the convective heat transfer coefficients. These are important parameters in the subsequent thermal calculations. Experimental investigations have been carried out to verify each of the above-mentioned models/methods. With these models implemented, the design optimisation of an air-cooled ironless stator 300 kW (at unity power factor) AFPM generator is carried out. The performance measurements done on the fabricated prototype are compared in this thesis with predicted results. The study shows that the proposed design approach can be applied with success to optimise the design of the AFPM machine. The advantages of high power density, high efficiency, no cogging torque and good voltage regulation make this type of AFPM machine very suitable for power generator applications. The optimum steady-state performance of the AFPM machine shows that this machine with an ironless stator is an excellent candidate for high speed power generator applications, even in the upper medium power level. The good cooling capacity of this type of machine holds the promise of its being a self-cooled generator at high power ratings. / AFRIKAANSE OPSOMMING: Die uitvinding van nuwe hoë energiedigtheid permanent magneet materiale het groot geleenthede vir nuwe elektriese masjien topologië laat ontstaan met voordelige eienskappe soos hoë benuttingsgraad en hoë drywing/gewig verhouding. Onder andere word die aksiaalveld permanente magneet (AVPM) masjiene met kernlose stators toenemend gebruik vir elektriese generator toepassings. As gevolg van die afwesigheid van kernverliese kan 'n generator met hierdie tipe ontwerp teen 'n aansienlik hoë benuttingsgraad werk. Daarbenewens maak die hoë kompaktheid en skyfvorm-profiel die masjien in besonder geskik vir die ontwikkeling van kompak geïntegreerde drywing generator stelsels. As gevolg van konstruksie probleme is die toepassing van hierdie tipe masjien as generator beperk tot redelik lae drywingsgebiede. Dit is nodig om die werkverrigtingsvermoë van hierdie tipe AVPM masjien in die boonste medium drywingsgebied te ondersoek. Die fokus van hierdie tesis is op die ontwerp-optimering van 'n lugverkoelde AVPM generator met 'n kernlose stator. 'n Ontwerpsbenadering wat die eindige element veldoplossing in 'n multi-dimensionele optimeringsprosedure insluit, is ontwikkel en toegepas op die ontwerpsoptimering van 'n 300 kW (by eenheidsarbeidsfaktor) AVPM generator. Om 'n globale ontwerpsoptimering van die masjien te kan doen is verskillende ontwerpsaspekte soos die verkoelingskapasiteit, meganiese sterkte en werwelverliese ook in hierdie navorsing bestudeer. Om die vrye beweging van die rotormaas ten opsigte van die statormaas te verseker is die lugspleet-element, soos oorspronklik deur Razek et al voorgestel, afgelei vir Cartesiaanse koórdinaat stelsels. Om die lang berekeningstyd geassosieer met hierdie makro-element te minimaliseer is 'n aantal bestaande tydbesparende metodes saam met die ontwikkelde Cartesiaanse lugspleet-element gebruik. Die ontwikkelde eindige element tydstapmodel is toegepas om die bestendige werkverrigting van die AVPM masjien te bereken. Aangesien die vloedverspreiding in 'n AVPM masjien van nature drie-dimensioneel is, kan die berekening van die werwelstroomverliese tot aansienlike foute lei as eenvoudige analitiese metodes gebruik word. Om hierdie probleem te oorkom is twee-dimensionele eindige element modellering gebruik om akkurate veld-analise te doen. Om die volle voordele van die twee- dimensionele eindige element modellering te eksploiteer is 'n multi-laag benadering voorgestel wat die variasie van die lugspleetvloeddigtheid in die geleiers met betrekking tot hulle relatiewe lugspleetposisies in ag neem. Om voorsiening te maak vir die radiale variasie van die veld, is 'n multi-skyf eindige element modelleringstegniek ontwikkel. Die termiese analise is 'n belangrike aspek van die ontwerpsoptimering van AVPM masjiene. Vanuit 'n ontwerpsoogpunt is dit verkieslik om 'n eenvoudige maar tog effektiewe metode van verkoelingsanalise en -ontwerp te hê wat maklik toegepas kan word op 'n wye reeks van AVPM masjiene. In hierdie tesis word 'n termovloeimodel van die AVPM masjien ontwikkel. Hierdie vloeimodel is nodig vir die berekening van die lugvloeitempo, wat op sy beurt weer nodig is om die konveksie hitte-oordrag koëffisiënte te bepaal. Hierdie is belangrike parameters in die opvolgende termiese berekeninge. Eksperimentele ondersoek is uitgevoer om elkeen van die bogenoemde modelle en metodes te verifieer. Nadat hierdie modelle geïmplimenteer is, is die ontwerpsoptimering van 'n 300 kW (by eenheidsarbeidsfaktor) lugverkoelde kernlose stator AVPM generator uitgevoer. Die werkverrigtingmetings gedoen op 'n vervaardigde prototipe masjien, word in hierdie tesis vergelyk met voorspelde resultate. Daar word getoon dat die voorgestelde ontwerpsbenadering met sukses toegepas kan word om die ontwerp van die AVPM masjien te optimeer. Die voordele van hoë drywingsdigtheid, hoë benuttingsgraad, geen vertandingsdraaimomente en goeie spanningsregulasie maak hierdie masjien baie aantreklik vir generator toepassings. Die optimum bestendige werkverrigting van die AVPM masjien toon dat hierdie masjien met 'n kernlose stator 'n goeie kandidaat is vir hoë spoed generator toepassings, selfs in die boonste medium drywingsgebied. Die goeie verkoelingskapasiteit van hierdie tipe masjien hou die belofte in van'n selfverkoelde generator by hoë drywing aanslae.

Thesis (MScIng)--University of Stellenbosch, 2008. / ENGLISH ABSTRACT: The behaviour of induction motors at a petrochemical plant under transient conditions was investigated with the view to improve plant immunity to voltage fluctuations. The benefits of using a phase-variable induction motor model rather than the simpler d-q models usually employed are investigated. A simplified model of the plant electrical distribution system was derived. Phase variable and d-q induction motor models were implemented as well as a synchronous generator model. Practical considerations precluded the use of commercial software for the simulation of transient conditions and a basic simulation program was developed using Matlab to evaluate the behaviour of the dynamic machine models and distribution system. It was established that the configuration of the installed re-acceleration system can be optimised to reduce the possibility of plant outages as a result of voltage fluctuations. It was found that the use of more detailed induction machine models provide valuable insight into system behaviour and is justified if accurate motor parameters are available or can be estimated. The simplified plant model yielded useful results and enabled the identification of incorrect system data. The investigation showed that Matlab is suitable for the rapid development of a basic transient simulation program that can be used to study the behaviour of different interconnected dynamic machine models. / AFRIKAANSE OPSOMMING: Die gedrag van induksiemotors in 'n petrochemiese aanleg onder oorgangstoestande is ondersoek ten einde die immuniteit van die aanleg vir spanningsfluktuasies te verbeter. Die voordele van die gebruik van 'n fase-veranderlike induksiemotor model eerder as die eenvoudiger d-q modelle wat normaalweg gebruik word is ondersoek. 'n Vereenvoudigde model van die aanleg se elektriese distribusiestelsel is afgelei. Faseveranderlike en d-q induksiemotor modelle is geimplementeer sowel as 'n sinkroongenerator model. Praktiese oorwegings het die gebruik van kommersiële programmatuur vir die simulasie van oorgangstoestande verhoed en 'n basiese program is in Matlab ontwikkel om die gedrag dinamiese masjienmodelle en die distribusiestelsel te evalueer. Daar is vasgestel dat die konfigurasie van die geinstalleerde herversnellerstelsel geoptimeer kan word om die moontlikheid van aanleg onderbrekings as gevolg van spanningsfluktuasies te verminder. Daar is gevind dat die gebruik van meer gedetaileerde induksiemasjien modelle waardevolle insig in die gedrag van die stelsel lewer en geregverdig is indien akkurate motorparameters beskikbaar is of afgeskat kan word. Die vereenvoudigde model van die aanleg het bruikbare resultate gelewer en die het die identifikasie van foutiewe stelseldata moontlik gemaak. Die ondersoek het getoon dat Matlab geskik is vir die snelle ontwikkeling van 'n basiese oorgangsimulasie program wat gebruik kan word om die gedrag van verskillende gekoppelde dinamiese masjienemodelle te bestudeer.

Thesis (MScEng)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: The main objective of this research project was to develop a methodology which can be used to assist in developing an insulator pollution severity application map (INSMAP), more particularly for South Africa. The techniques must be able to assist in determining pollution severity levels. At the inception of this project a phase one insulator pollution severity application map was available; this map was based on an existing corrosion map, climatic maps and dust gauge measurements. The phase one map was conservative and did not highlight localised pollution. To confirm and possibly improve on this map, a phase two map was developed, which was based on feedback from Eskom field personnel via an electronic insulator pollution questionnaire survey (based on IEC 60815 guidelines).Jhe questionnaire was incorrectly completed in most cases due to a lack of understanding by field personnel of environmental pollution and the impact on insulator performance. This resulted in an unrealistic map with exaggerated contamination levels. To confirm the findings of the phase one map, a phase three approach was followed, which was focused on an investigation into pollution measurement techniques and methodologies. Based on the phase one map, a need was identified to confirm by measurements the impact of distance-to-coast. Also, the validity of installing a dust gauge at 3 metres above ground level, while insulators are at a height of 8 to 40 meters, had to be investigated. Two pollution monitoring programmes were established: a distance-to-coast and height-above-ground environmental pollution study. Various test methods are described with a complete testing procedure, descriptive equations and related pollution severity classifications for insulator pollution (DDG and ESDD) and corrosion (CLIMAT and metal specimens). The distance-to-coast test results confirm the phase one map, while the height-aboveground measurements justify the installation of dust gauges at 3 metres above ground level. Good correlations were found for the distance-to-coast study between insulator pollution severity and corrosion rates. From the height-above-ground study, a slight (insignificant) decrease in pollution levels was found for increase in height for insulator pollution and corrosion tests. Recommendations are made on setting up a basic pollution monitoring station. Key words: Insulator pollution, Corrosion, Distance, Height. / AFRIKAANSE OPSOMMING: Die hoofoogmerk van hierdie navorsingprojek was die ontwikkeling van 'n metodiek om 'n isolator besoedelingskaart saam te stel, meer spesifiek vir Suid Afrika. Die tegnieke moet die besoedelingsvlakke en impak-afstand van elke besoedelingvlak aandui. 'n Fase een isolator besoedelingskaart het reeds bestaan by die aanvang van hierdie projek, hierdie kaart was gebaseer op 'n bestaande korrosiekaart. Die fase een kaart was baie konserwatief en het nie lokale besoedeling aangedui nie. Dit was besluit om die fase een kaart te verbeter en 'n fase twee kaart was ontwikkel wat gebaseer was op 'n elektroniese isolator-besoedeling vraelys wat deur Eskom se tegniese veldpersoneel voltooi is. Die vraelys is in baie gevalle verkeerdelik ingevul, as gevolg van 'n gebrek aan die kennis oor besoedeling en die impak daarvan op isolatorprestasie. Dit het tot 'n onrealistise kaart gelei met onakurate besoedelingsvlakke. 'n Fase drie ontwikkeling is begin, waar 'n ondersoek gekyk het na metingstegnieke en metodiek vir besoedelingsmetings. 'n Volledige toetsprosedure, beskrywende vergelykings en besoedelingklassifikasies is ontwikkel vir die isolator-besoedeling (DDG en ESDD) en korrosietoetse (CLIMAT en metaal monsters). Toetsstasie seleksiekriterea vir die geografiese plasing van 'n toetsstasie is vasgestel. Twee toetsprogamme is vasgestel: 'n afstand-van-see en 'n hoogte-bo-grondvlak besoedelingsstudie. Die afstand-van-see studie het 'n impak-afstand vir elke besoedelingsvlak vir beide isolatorbesoedeling en korrosietoetse vasgestel. 'n Goeie korrelasie is vasgestel tussen isolator-besoedeling en korrosievlakke. Vir die hoogte-bo-grondvlak studie was gevind dat daar 'n klein (weglaatbare) vermindering in besoedelingsvlakke met toename in hoogte bo grondvlak vir isolatorbesoedeling- en korrosievlakke onstaan. 'n Goeie korrelasie bestaan tussen isolatorbesoedeling- en korrosievlakke. Aanbevelings word gemaak vir die opstel van 'n basiese besoedelingsmetingstasie. Sleutelwoorde: Isolator besoedeling, Korrosie, Afstand, Hoogte.

Thesis (MEng)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: This thesis deals with the design and optimisation of medium power traction switched reluctance machines with tapered and straight stator poles. Only the prototype of the tapered stator pole machine is constructed and evaluated in this study. A non-commercial finite element package is used in the design and optimisation of the machines. The finite element method is applied directly in the optimisation procedure to optimise the design of the machines in multi-dimensions. The lumped circuit analysis method is used only for the purpose of verifying some of the finite element calculated. It is not used in the optimisation procedure. The performance characteristics of the tapered and straight stator pole machines are compared and discussed and the tapered stator pole machine is found to have better torque performance. Also the calculated and measured static torque versus rotor position characteristics of the tapered stator pole machine are compared and discussed. / AFRIKAANSE OPSOMMING: Die tesis beskryf die ontwerp en optimering van medium drywing trekkrag geskakelde reluktansie masjiene met tapse en reguit stator pole. Slegs 'n prototipe van die tapse stator pool masjien is gebou en geëvalueer. Die masjiene is ontwerp en geoptimeer met behulp van 'n nie-kommersiële eindige element metode pakket. Die eindige element metode is direk in die optimerings algoritme gebruik vir die optimering van die masjiene in multi-dimensies. Die gekonsentreede parameter stroombaananalise is slegs gebruik om sommige van die eindige element berekenings te verifeer. Die vermoës van die tapse en reguit stator pool masjiene is vergelyk en bespreek. Die resultate toon dat die tapse stator pool masjien se draaimoment vermoë beter is as die van die reguit stator pool masjien. Die berekende en gemete statiese draaimoment teenoor rotorposisie van die tapse stator pool masjien is ook vergelyk en bespreek.

Thesis (MEng)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: A desire to increase the efficiency of the comminution process in mineral process systems has led to the need of determining the size distribution of ore particles at various stages in the system. The objective of this research is to investigate the feasibility of the use of an acoustic sensor for measuring particle size distribution. The acoustic signal generated when the particles impact on a cantilever bar is analysed using digital signal processing techniques. As rocks fall onto a metal bar, the bar vibrates. The vibrations contain information th a t is extracted to determine the size of particles tha t impacted on the bar. The bar is modelled as a linear system which is excited by impulses (impact of particles). The response of the bar is deconvolved from the acoustic signal to obtain an impulse whose amplitude is proportional to the energy of the impact. In order to improve size estimates, deconvolution is performed using a statistical model of the impulse sequence (Bernoulli-Gaussian) and then estimated using MAP estimation. Size estimates are not only a function of the mass of particles, but also on the exact position of impact on the bar. Since there is always a variation in the position of impact, size estimates are erroneous. It was found that the position of impact can be determined as to reduce variances dramatically. Due to physical sampling in space, the sensor has a bias towards larger particles. We show how this can be represented mathematically and removed. This project is mainly concerned with rocks in the +8-25mm (+0,7-22 gram) size range. / AFRIKAANSE OPSOMMING: Vergruising van erts in die mineraalbedryf verg groot hoeveelhede energie. Daar is ’n behoefte gei'dentifiseer orn hierdie proses meer effektief te maak. Aangesien die effektiwiteit van ’n meul ’n funksie is van die ertsgroottes wat gemaal word, kan partikel grootte inligting aangewend word om effektiwiteit te bevorder. Die doel van hierdie tesis is om die lewensvatbaarheid van ’n akoestiese sensor vir die doel van partikelgrootte estimasie, te ondersoek. Erts partikels wat val vanaf ’n vervoerband op ’n kantelbalk, veroorsaak dat die balk vibreer. Deur hierdie vibrasies te meet en verwerk, kan inligting aangaande partikel grootte verkry word. Die stelsel word gemodelleer as ’n lineere sisteem met impulse as intree. Die geobserveerde sein is die konvolusie tussen die intree impulse en die impulsweergawe van die sisteem. Deur gebruik te maak van ’n statistiese model en MAP-estimasie, word die effek van die sisteem gedekonvuleer vanaf die geobserveerde sein om ’n benadering van die intree impuls sein te verkry. Die amplitudes van die impulse word gebruik as ’n aanduiding van partikel massa. Partikelgroottes soos benader deur die stelsel, is ’n funksie van die die posisie waar die partikel die balk tref. Deur van patroonherkenning tegnieke gebruik te maak, word die posisie van impak bepaal om sodoende grootte benaderings aan te pas en die variansie van grootte verspreidings te verminder. As gevolg van die feit dat partikels gemonster word deurdat slegs ’n klein persentasie van die hele omvang van partikels ondersoek word, onstaan daar ’n oorhelling ( “bias” ) na groter partikels. Die kans dat groter partikels die balk tref is groter as vir klein partikels. ’n Wiskundige model vir hierdie verskynsel word voorgestel en gewys hoe die die oorhelling geneutraliseer kan word. Hierdie projek het te doen met ertsgroottes +8-25mm (+0,7-22 gram).

Thesis (MScEng)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: Once more opportunities exist for innovative technologies to be applied on MV and LV power distribution networks to meet the new challenges set by government through its National Electrification Programme (NEP) to electrify a further 2,5 million households of which a large majority are in low-density rural areas. Electronic means of voltage compensation of long MV and LV networks supplying these low-density rural areas are now possible in the form of electronic voltage regulators mounted on the secondary side of distribution transformers and service connection boxes along the LV feeders. Furthermore, it is now possible to provide remote rural agricultural customers with singlephase supplies supported by end-use technologies in the form of electronic phase converters that eliminate the need for three-phase supplies. This hybrid of supply- and end-use technologies together with Eskom's "self-build" policy has made the dream of Eskom grid power a reality. / AFRIKAANSE OPSOMMING: Nuwe geleenthede het na yore getree vir die toepassing van innoverende tegnologie op medium- en laagspannings netwerke in antwoord op die uitdagings gestel deur die regering in die vorm van die Nasionale Elektrifiseringsprogram (NEP). Die elektrifisering van 'n verdere 2,5 miljoen huishoudings waarvan die grootste gedeelte in yl bevolkte plattelandse gebiede is, word in vooruitsig gestel. Spanningskompensasie van lang laag- en mediumspannings netwerke word nou moontlik gemaak deur middel van elektroniese spanningsreguleerders, gemonteer aan die sekondere kant van distribusie transformators en in diensaansluitingskaste op laagspannings voerders. Verder is dit ook nou moontlik om afgelee landelike plase met enkelfase krag, gerugsteun deur eindverbruik tegnologie in die vorm van elektroniese fase omsetters, te voorsien. Die beskikbaarheid van hierdie tegnologie elimineer die vraag na drie-fase krag. Hierdie hibriede kombinasie van toevoer- en eindverbruik tegnologie in kohesie met die selfbou beleid van Eskom, maak dit moontlik dat 'n droom van Eskom voorsiende elektrisiteit, in 'n werklikheid omskep word.

Thesis (MEng)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: This thesis deals with different design aspects of the multi-flux barrier rotor of the reluctance synchronous machine (RSM). The effect of the different designs on the performance of the RSM is investigated by means of two-dimensional finite element analysis. The finite element analysis is also directly used in the optimum design of the rotor of the RSM. The importance of the use of the finite element analysis in the design and performance calculations of the RSM is illustrated in this thesis. The design aspects of the RSM which are focussed on in this thesis are, amongst other things, the chording of the stator winding, the skewing of the rotor and the ratio of the number of rotor flux barriers to the number of stator slots of the RSM. The effects of these design aspects on the average torque and torque ripple of the RSM are investigated and general design directives are given. The occurrence of flux pulsations in the stator teeth and rotor iron segments of the RSM are also studied to some extent. The finite element optimum design of a4-pole RSM-rotor with a high number of flux barriers is described in the thesis. This optimum designed rotor is built and the RSM with this rotor is tested in the laboratory. Its calculated and measured performances are studied and compared with a conventional, low number rotor flux barrier RSM. It is found, amongst other things, that the RSM with the high number of rotor flux barriers has a slightly higher average torque with a significantly lower torque ripple. / AFRIKAANSE OPSOMMING: Hierdie tesis handeloor verskillende ontwerp-aspekte van die reluktansie sinchroonmasjien (RSM) met 'n multi-vloedversperringsrotor. Die effek van die verskillende ontwerpe op die vermoë van die RSM is met behulp van twee-dimensionele eindige element analise ondersoek. Die eindige element analise is ook direk in die optimum ontwerp van die rotor van die RSM gebruik. Die belangrikheid van die gebruik van die eindige element analise in die ontwerp en vermoë-berekening van die RSM word in die tesis geïllustreer. Die ontwerp-aspekte van die RSM waarop in hierdie tesis gefokus word, is onder andere die spoelsteekverkorting van die statorwikkeling, die skuinsing van die rotor en die verhouding van die getal rotor-vloedverperrings tot die getal statorgIeuwe van die RSM. Die effek van hierdie ontwerpaspekte op die gemiddelde draaimoment en draaimoment-rimpel van die RSM word ondersoek en algemene riglyne vir die ontwerp van die RSM word gegee. Die voorkoms van vloedpulsasies in die statortande en rotor yster segmente van die RSM word ook deels ondersoek. Die eindige element optimum ontwerp van 'n 4-pool RSM-rotor met 'n hoe getal vloedversperrings word in die tesis beskryf. Hierdie optimum ontwerpte rotor is gebou en die RSM met hierdie rotor is in die laboratorium getoets. Die berekende en gemete vermoë is bestudeer en vergelyk met die vermoë van 'n RSM met 'n konvensionele, lae getal vloedversperrings rotor. Dit is onder andere gevind dat die RSM met die hoë getal rotor-vloedversperrings 'n effens hoër gemiddelde draaimoment het met 'n behuidende laer draaimoment-rimpel.