Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The use of high voltage direct current (HVDC) applications has gained enormous popularity for long distance power transmission. This is due to the lucrative benefits offered by this type of power transmission technology when compared to the traditional high voltage alternative current (HVAC). This new shift in the paradigm of power system design has led to the increased interest in the research that focuses on issues relating to the reliability of power supply associated with HVDC. Amongst such issues, insulation coordination has increasingly become a challenging task that continues to receive renewed research focus. It has been convincingly demonstrated, both from field experience and laboratory research, that insulator contamination constitutes a multifaceted phenomenon, especially when transmission voltages ramp up into high operating voltage levels. More so, this is particularly interesting with reference to the increasing applications of high voltage direct current (HVDC). The recently commissioned HVDC power-line in Namibia is one of the major motivations upon which NamPower (Namibia‟s national power utility) has committed financial resources to research on insulator pollution performance. This project was a part of NamPower‟s research initiative – seeking to investigate the phenomena associated with insulator pollution performance under natural pollution environments when energized under both AC and DC excitation voltage types. The significance of this research is especially crucial for HVDC applications given the paucity of research conducted on the DC performance of insulators, under natural pollution environments. This study was conducted at the Koeberg Insulator Pollution Test Station (KIPTS) on the west coast of Cape Town in the Western Cape province of South Africa. KIPTS is an internationally recognized insulator pollution test facility, which is widely used by both insulator manufacturers and academic researchers from many parts of the world. STRI and ABB, both Swedish-based companies, are good examples of international subscribers to the KIPTS research facility. The first objective of this research was to design a suitable DC excitation voltage system for both DC+ and DC- to be used at KIPTS. This apparatus was designed and built at the University of Stellenbosch. The second objective was to conduct a comparative evaluation of the performance of high temperature vulcanized silicone rubber (HTV-SR) power line insulators under AC, DC+ and DC- when subjected to natural pollution conditions at KIPTS. All test insulators were made from the same material and sourced from the same manufacturer – having different creepage lengths. Five different creepage lengths were considered for each excitation voltage – summing up to fifteen HTV-SR test samples. A standard DC glass disc insulator was also installed on each excitation voltage as a control sample. It was therefore envisaged that this study would give rise to new research questions, leading to future explorations on the subject. With reference to weather monitoring and leakage current measurements (using an online leakage current monitoring device - OLCA), a correlation was found to exist between the variations in climatic conditions and the corresponding occurrence of leakage current on the insulator surfaces. High leakage current levels were recorded in summer due to the high pollution levels that were measured in that season (using the equivalent salt deposit density (ESDD) approach). Winter, in contrast, had lower levels of leakage current recorded. This corresponds to a high prevalence of rainfall in winter, which caused occasional natural washing of the insulator surfaces. The leakage current levels for the HTV-SR insulators were of a similar order of magnitude for AC and DC+ and lower for DC-. The harshest pollutants (with high conductivities, as measured with the directional dust deposit gauges (DDDG)) were found to have emanated largely from the south. As a result, most instances of erosion were observed in the southward direction on the test insulators. The electrical discharge activity observations, conducted at night, had revealed that dryband corona (DBC) and dryband discharge (DBD) prominently occurred on the terminating sheaths (both live and ground ends) and bottom side of HTV-SR and glass disc insulators, respectively. This justifies the dominance of erosion that was observed on the terminating sheaths and bottom side of HTV-SR and glass disc insulators, respectively. Flashover events were recorded on the shortest HTV-SR insulator installed on DC+ and the glass disc insulator installed on DC-. All flashover events occurred in summer (the harshest season at KIPTS). Two interesting observations, albeit unexplained, were observed: star-shaped erosion on the shed bottoms of the HTV-SR insulators installed on DC+ and material peel-off at the shed-to-sheath bonding interface of the HTV-SR insulators installed on DC-. These observations therefore require further investigation in order to establish possible explanations. / AFRIKAANSE OPSOMMING: Die gebruik van hoë gelykspanning (HSGS) het baie gewild geword vir kragtransmissie oor lang afstande. Dit is as gevolg van die uitstekende voordele wat hierdie tipe tegnologie teenoor die tradisionele hoë wisselspanning (HSWS) bied. Hierdie paradigmaskuif in die ontwerp van kragstelsels het tot verhoogde belangstelling in navorsing gelei wat betrekking het op aspekte wat verband hou met die betroubaarheid van kragvoorsiening deur HSGS. Van hierdie aspekte word isolasiekoördinasie toenemend ʼn uitdagende taak en navorsing word tans daarop toegespits. Daar bestaan oortuigende bewyse, gebaseer op laboratorium- en veldtoetse dat isolatorbesoedeling ʼn verskynsel met vele fasette is, veral wanneer hoër spannings gebruik word. Dit is in „n meerdere mate van belang met verwysing na toepassings van HSGS. Die onlangs inbedryfgestelde HSGS kraglyn in Namibië is een van die hoofmotiverings vir die verskaffing van geldelike steun deur NamPower (Namibië se nasionale kragvoorsiener) vir navorsing oor die besoedelingsprestasie van isolators. Hierdie projek is deel van NamPower se navorsingsinisiatief om verskynsels betreffende die besoedelingsprestasie van isolators in natuurlik-besoedelde omgewings te ondersoek, onder WS en GS-bekragtiging. Die betekenis van hierdie navorsing is veral belangrik vir die HSGS-toepassings in die lig van die skaarsheid van navorsing oor die GS-prestasie van isolators in natuurlik-besoedelde omgewings. Hierdie studie is gedoen by die Koeberg isolatorbesoedelingstoetsstasie (KIPTS) aan die weskus van die Wes-Kaap. KIPTS is 'n internasionaal-erkende toetsfasiliteit en word algemeen gebruik deur beide isolatorvervaardigers en akademiese navorsers uit baie dele van die wêreld. STRI en ABB, albei Sweeds-gebaseerde maatskappye, is die goeie voorbeelde van die internasionale gebruikers van die KIPTS navorsingsfasiliteit. Die oogmerk van hierdie navorsing was om eerstens 'n geskikte GS-kragbron vir beide die GS+ en die GS- vir gebruik by KIPTS te ontwerp. Hierdie apparaat is ontwerp en gebou deur die Universiteit van Stellenbosch. Tweedens is 'n vergelykende evaluering van die prestasie hoë temperatuur gevulkaniseerde silikoon (HTV-SR) kraglynisolators onder WS, GS+ en GS– onder natuurlike besoedeling by die KIPTS uitgevoer. Alle toetsisolators is van dieselfde materiaal gemaak en is afkomstig van dieselfde vervaardiger, maar het verskillende kruipafstande. Vyf verskillende kruipafstande is gebruik vir elke tipe spanning  'n totaal van vyftien HTV-SR toets monsters. 'n Standaard GS glasisolatorskyf is ook vir elke spanning as' n kontrolemonster geïnstalleer. Dit kan dus verwag word dat hierdie studie aanleiding sal gee tot nuwe navorsingsvrae, wat kan lei tot verdere toekomstige ondersoeke oor die onderwerp. Met verwysing na die monitering van die weer en die lekstroommetings (met behulp van 'n aanlyn-lekstroommoniteringstoestel - OLCA), is 'n korrelasie gevind tussen die variasie in klimaatstoestande en die ooreenstemmende voorkoms van lekstroom op die isolator- oppervlaktes. Hoë lekstroomvlakke is waargeneem in die somer, as gevolg van die hoë besoedelingsvlakke wat in daardie seisoen gemeet is (met behulp van die ekwivalente soutneerslag-digtheid (ESDD) metode). In die winter, in teenstelling, is die laagste vlakke van lekstroom aangeteken. Dit stem ooreen met 'n hoë voorkoms van reënval in die winter, wat die isolatoroppervlaktes van tyd tot tyd natuurlik gewas het. Die lekstroomvlakke op die HTV-SR isolators was van soortgelyke ordegrootte vir WS en GS+ maar laer vir GS-. Dit is bevind dat die ergste besoedelingstowwe, met 'n hoë geleiding, soos gemeet met die rigtingsensitiewe stofneerslagsmeters (DDDG), hoofsaaklik uit ʼn suidelike rigting kom. As gevolg hiervan, is die meeste gevalle van erosie aan die suidekant van die toetsisolators waargeneem. Die waarneming van elektriese ontladingsaktiwiteit in die nag, het aan die lig gebring dat droëbandkorona (DBC) en droëbandontladings (DBD) prominent voorgekom het op die skedes aan die uiteindes (beide lewende en grond kante) en onderste kant van HTV-SR en glasskywe, onderskeidelik. Oorvonkings is waargeneem op die kortste HTV-SR isolator op GS+ en op die glasisolator op GS-. Al die oorvonkings het in die somer (die ergste seisoen by KIPTS) voorgekom. Twee interessante, dog onverklaarbare, verskynsels is waargeneem: stervormige erosie aan die onderkante van die skerms van die HTV-SR isolators op GS+ en material-afskilfering by die skerm-skede tussenvlak van die HTV-SR isolators op GS-. Hierdie verskynsels vereis verdere ondersoek ten einde moontlike verklarings vas te stel.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The electromagnetic and mechanical design aspects of an optimally designed double-sided rotor radial flux permanent magnet wind generator with non-overlap iron-cored stator windings are analysed in this thesis. The generator topology proposed in this study aims to reduce the strength demand on the generator structural support, caused by the magnetic attraction forces between the rotor and stator iron components, and in so doing reducing the overall generator mass. The proposed design has very good cooling properties. Compared to a conventional iron-cored permanent magnet generator and an air-cored permanent magnet generator, the double-sided rotor iron-cored topology performs the best with reference to mass and efficiency. / AFRIKAANSE OPSOMMING: Die elektro-magnetiese en meganiese ontwerp-aspekte van ‘n optimal ontwerpte tweesydige rotor radial-vloed permanente magneet windgenerator met nie-oorvleulende ysterkern statorwindings word in hierdie tesis ontleed. Met die generator topologie wat in hierdie studie voorgestel word, word beoog om die strukturele materiaal wat vir die generator benodig is te verminder. Die magnetise aantrekkingskragte tussen die yster komponente van die rotor en stator word dus aangespreek in hierdie studie, om sodoende ook die algehele massa van die permanente magneet generator te verminder. Die voorgestelde tweesydige-rotor ontwerp het baie goeie verkoelings eienskappe en het ‘n kleiner massa en hoër effektiwiteit as beide ‘n konvensionele ysterkern generator met ‘n enkelsydige-rotor en ‘n tweesydige-rotor lugkern permanente magneet generator met dieselfde drywingsvermoë.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2005. / Although regenerative braking has been in used in railway systems for a long time already, the energy generated was dissipated in resistor banks. The rapid advances in the power electronics field, accompanied by the development of faster and higher power switching devices in recent years, now make it possible to convert the regenerated electrical energy from DC to AC, which can then be injected into the Eskom grid. A 1.5 MW full scale prototype system was built, installed and tested in a Spoornet DC traction substation. A seven level series-stacked converter topology was used along with a specially designed injection transformer. The system was controlled by the PEC 33 controller board, which was developed at the University of Stellenbosch. The primary function of the system is to function as a regeneration converter and as a secondary function act as an active power filter.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2007. / Electrification of rural areas is one of the biggest challenges faced by ESKOM and methods are required to extend medium voltage distribution lines to these often remote areas. As loads increase due to line-extension, in-fills and energy theft, maintenance cost and life expectancy of distribution and power transformers becomes more critical. The thesis addresses these two aspects with the development of a self regulated and protected electrification transformer that makes use of current, voltage and ambient temperature measurements to regulate voltage and protect hardware from overloading. The design of the hardware that allows the system to run at 200% load without decreasing the lifetime of the transformer is examined. Temperature estimation techniques are used to estimate the temperatures in the 16 kVA, 22 kV to 230 V, distribution transformer to run above nameplate ratings without causing damage. The control of the system is implemented on TMS320F2812 digital signal processor from TI that is DSP/BIOS compatible. The control software is implemented using DSP/BIOS, which allows real-time scheduling and monitoring of procedures. Furthermore a distribution transformer was fitted with temperature sensors and heat run tests were performed. The results of the temperature tests were used to verify the estimation techniques and to determine constants used for temperature estimation.

Thesis (MEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2009. / Autonomous rendezvouz and docking is seen as an enabling technology. It allows, among others, the construction of larger space platforms in-orbit and also provides a means for the in-orbit servicing of space vehicles. In this thesis a docking sequence is proposed and tested in both simulation and practice. This therefore also requires the design and construction of a test platform. A model hovercraft is used to emulate the chaser satellite in a 2-dimensional plane as it moves relatively frictionlessly. The hovercraft is also equipped with a single camera (monocular vision) that is used as the main sensor to estimate the target’s pose (relative position and orientation). An imitation of a target satellite was made and equipped with light markers that are used by the chaser’s camera sensor. The position of the target’s lights in the image is used to determine the target’s pose using a modified version ofMalan’s Extended Kalman Filter [20]. This information is then used during the docking sequence. This thesis successfully demonstrated the autonomous and reliable identification of the target’s lights in the image, and the autonomous docking of a satellite pair using monocular camera vision in both simulation and emulation.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2007. / Electrical energy is continuously transported across the world by high voltage transmission lines. These transmission lines are however subject to losses beside the inherent resistive and dielectric losses. This additional loss phenomenon is described as corona. The CSIR has developed an optical system to detect the radiation caused by the corona so that preventive measures can be taken to reduce these losses. The corona mechanism and how it results in measurable radiation is explored and the structure of the optical system is analyzed. The optical emissions detected by the present optical system offer no indication of the severity of the corona discharge. This issue is addressed in this thesis as correlations are sought between the illuminated pixels displayed on the camera’s display and physical quantities. A blackbody is employed to find a correlation between these illuminated pixels and radiation. Deviations from the correlation drawn is explored regarding the saturation mechanisms of the optical system and the distance from the blackbody. A corona cage is next employed to find a correlation between the illuminated pixels and electrical corona loss, a quantity indicative of the severity of corona losses on a transmission line. Further tests are also performed at a reduced gain as it was discovered that the optical system’s response is more linear at reduced gain than at full gain. It is also indicated that this usage of reduced gain does not have a detrimental effect on the sensitivity of the optical system. The corona cage measurement employs a small spheric source which is taken as a base measurement against which all other measurements can be compared. The deviation of this base analogy is explored against deviations in the corona discharge geometry used, the prevalent weather condition, and the saturation of the optical system itself. Both the corona cage and blackbodies used are quite bulky pieces of laboratory equipment. The use of a smaller, more portable calibration source is therefore also explored. A literature study is made of lasers, lamp sources, and laser diodes that can be employed as a more portable calibration source. The final choice of calibration source is shown to be a lamp source. Tungsten calibration lamps are explored in depth and a circuit is designed to keep the radiation from a lamp source constant in order to improve on its ability as a calibration source.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2005. / This thesis discuss an investigation into the applicability of modern high frequency power conversion technology in the plasma mineral processing industry. The physics governing the plasma in a processing environment are analysed to provide a clear understanding of this plasma as electrical load. This was done to create an electrical model for the plasma as load and gain understanding into the electrical supply requirements. Modern high frequency power conversion technology is contrasted with thyristor controlled line frequency technologies to provide a suitable starting point for the study. A 3 kW soft switched converter is proposed for application with a plasma load. This converter is designed and verified. The small-signal signature of the proposed converter under peak current mode control is investigated and a new model is proposed to describe this control configuration.

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.