Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: With the current worldwide energy problems electric vehicles are set to replace conventional combustion engine vehicles. Electric vehicles with gearless in-wheel mounted brushless permanent magnet motors provide a more flexible and efficient means of vehicle propulsion but the electric motors, particularly the non-overlap stator winding type have not been fully researched. This study focuses on the selection and design of suitable in-wheel hub drive machine. Several machine topologies are evaluated and the single-sided axial flux machine is chosen. The average vehicle requirements are determined and design optimisations are carried with the aid of finite element analysis and an optimisation algorithm. A comparison of torque quality between single-layer and double-layer machines is carried out and it is found that double-layer machines have the least torque ripple and single-layer machines with un-equal teeth the best torque per ripple characteristics. A 16 kW, 30-pole 27-slot prototype machine optimised for power density is built, and it is found fitting for the application meeting the design requirements. The prototype machine is extensively tested and good agreement is found between finite element and measured results. The well known axial flux attraction forces are encountered in the prototype machine and they are overcome by suitable bearing selection and mechanical design. It is found that theoretical and measured cogging torques are inconsistent, the reason for this is that practical machines are not absolutely ideal due to material and manufacturing tolerances. Excessive rotor losses are found in the prototype machine and appropriate methods for their reduction are presented. This work does not aim to find the best in-wheel hub drive solution, but instead looks to uncover some of the technical available solutions. / AFRIKAANSE OPSOMMING: Met die huidige wêreldwye energie probleme, is elektriese voertuie bestem om konvensionele binnebrandenjin voertuie te vervang. Elektriese voertuie met ratlose binnewiel-geleë borsellose permanente magneet motors, voorsien „n meer aanpasbare en effektiewe metode van voertuig aandrywing, maar die elektriese motors, veral die oorvleulende stator winding tipe is nog nie ten volle nagevors nie. Hierdie studie fokus op die keuse en ontwerp van „n binnewiel aandryf masjien. Verskeie masjien uitlegte word geëvalueer en „n enkelkant aksiaalvloed masjien is gekies. Die gemiddelde voertuig behoeftes word bepaal en ontwerp optimalisering word uitgevoer met behulp van eindige element analise en „n optimaliserings algoritme. Enkellaag en dubbellaag masjiene se draaimoment kwaliteit word vergelyk. Die bevinding is dat dubbellaag masjiene die laagste draaimoment rimpel toon terwyl die enkellaag masjiene, met oneweredige tande, die beste draaimoment per rimpel karakteristieke toon. „n 16 kW, 30 pool, 27 gleuf prototipe masjien, wat vir drywingsdigtheid ge-optimaliseer is, is gebou en is geskik vir die toepassing en die vereistes. Die prototipe masjien is getoets en goeie vergelykings word getref tussen die eindige element analise en die gemete resultate. Die alom bekende aksiaal vloed aantrekkings kragte word in die prototipe masjien gesien en word oorkom deur die regte rollaer keuse en meganiese ontwerp. Nog „n bevinding is dat die teoretiese en gemete waardes vir die vertandings draaimoment nie ooreenstem nie. Die rede hiervoor is dat die praktiese masjien nie ideaal is in terme van materiaal en vervaardigings toleransies nie. Groot rotor verliese in die prototipe masjien is gevind en goeie metodes vir die minimering daarvan word voorgestel. Hierdie werk is nie „n soektog na die beste binnewiel aandrywings oplossing nie, maar mik eerder om sommige van die tegniese beskikbare oplossings te onthul.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Energy efficiency and the move to renewable energy resources are of vital importance in growing profitable and sustainable economies. In recent years, greater emphasis has been placed on institutions, companies and individuals to reduce their electrical energy demand through energy management. In an attempt to reduce the demand, the electrical power utility in South Africa, Eskom, has introduced Demand Side Management programs and substantial increases in electricity tariffs. In addition to these, tax incentives have been offered to help off-set the capital costs associated with the investments made in replacing old electrical equipment with new electrically efficient equipment. Thus the need for accurate Measurement and Verification of electrical energy demand reduction, to substantiate fiscal claims, has become imperative. The main purpose of Measurement and Verification is to investigate the actual monetary performance of an energy savings project. Energy savings assessments, based on purely deterministic baseline demand, do not adequately represent the statistical nature of the savings impacts of many practical load systems, as disclosed in a reporting period. This thesis presents the development of a generic probabilistic methodology to determine the demand profiles of preand post-Energy Conservation Measures (ECMs) for practical load systems. The difference between the simulated demand of the pre- and post-ECMs for a particular set of variables represent the electrical demand impact. The electrical demand of the pre- and post-ECMs is defined in terms of Probability Density Functions, and derived using a multivariate kernel density estimation algorithm. The approach is tested using a simulation model of a waterheating geyser implemented in MATLAB. Three different ECMs are simulated using the geyser model and demand density estimation. The results of the demand impacts of the ECMs are presented and evaluated. With regards to possible future research this methodology could be applied to the evaluation of the demand impacts of heat pump technologies and solar water heaters. / AFRIKAANSE OPSOMMING: en die skuif na hernubare energiebronne is van deurslaggewende belang vir die ontwikkeling van winsgewende en volhoubare ekonomieë. Onlangs is meer klem geplaas op instansies, maatskappye en individue om hul aanvraag na energie te verminder met behulp van energiebestuur. In ‘n poging om die aanvraag te verlaag, het Eskom, Suid-Afrika se elektrisiteitsverskaffer, aansienlike elektrisiteitstariefverhogings ingelyf en Aanvraagbestuursprogramme van stapel gestuur. Bykomend hiertoe is belastingaansporings ook aangebied, waarteen kapitale kostes, geassosieer met die vervanging van ou elektriese toerusting met nuwe elektries doeltreffende toerusting, afgeset kan word. Derhalwe het die behoefte aan akkurate Meting en Verifikasie van elektriese energie aanvraagvermindering, om finansiële eise te staaf, noodsaaklik geword. Die hoofdoel van Meting en Verifikasie is om die werklike finansiële prestasie van energiebesparingsprojek te ondersoek soos bekend gemaak word tydens ’n verslagdoeningstydperk. Energiebesparingassesserings wat slegs gebaseer word op die suiwer deterministiese basislyn aanvraag na elektrisiteit, verteenwoordig nie die werklike statistiese aard van die besparingsimpakte van baie praktiese lasstelsels nie. Hierdie tesis stel die ontwikkeling van generiese waarskynlikheids-metodologie voor, om die voor- en na- Energiebesparings-maatreëls se aanvraagprofiele vir sulke praktiese lasstelsels, vas te stel. Die verskil tussen die gesimuleerde aanvraag van die voor- en na- Energiebesparings-maatreëls vir spesifieke stel veranderlikes verteenwoordig die elektriese aanvraag impak. Die voor- en na- Energiebesparings-maatreëls van die energieverbruik profieldata word gedefinieer in terme van Waarskynlikheidsdigtheidsfunksies en afgelei deur gebruik te maak van meerveranderlike kerndigtheidafskattingsalgoritme. Die benadering is getoets deur gebruik te maak van simuleringsmodel van warmwaterstelsel geïmplimenteer in MATLAB. Drie verskillende voor- en na- Energiebesparings-maatreëls is gesimuleer met behulp van die warmwaterstelselmodel en aanvraag digtheidafskatting. Die resultate van die elektriese aanvraag impakte van die voor- en na- Energiebesparings-maatreëls word vervolgens bespreek en geëvalueer. Met betrekking tot moontlike toekomstige navorsing kan hierdie metodologie toegepas word om die aanvraag impakte van hittepomp- en sonwaterverwarmingstegnologieë te evalueer.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The use of power electronic converters provides a more efficient, accurate and dynamic solution to reactive compensation. In this thesis the application of power electronic converters to shunt reactive compensation will be discussed. In particular voltage dips and voltage unbalance are considered as both can be mitigated by means of shunt reactive compensation. A pre-existing uninterruptible power supply is adapted to operate as a shunt reactive compensator. The uninterruptible power supply consists of a 250 kVA three phase voltage source inverter. The modifications are limited to software and control algorithms that do not alter the normal operation of the uninterruptible power supply. Control algorithms are designed and discussed in detail. A typical double loop control strategy is implemented on the power electronic converter. The inner loop consists of a dead-beat current controller. The outer loop consists of three proportional and integral controllers controlling the DC-bus voltage, AC voltage and voltage unbalance respectively. Voltage dips and unbalance are compensated for using only reactive power. Focus is placed on producing a result can be used easily in practice. / AFRIKAANSE OPSOMMING: Drywings elektroniese omsetters wat gebruik word vir newe reaktiewe kompensasie lewer meer effektiewe, akkurate en dinamiese resultate. In hierdie tesis word die toepassing van drywings elektroniese omsetters vir newe reaktiewe kompensasie bespreek. Daar word meer spesifiek na spannings duike en spannings wanbalans gekyk aangesien albei met newe reaktiewe kompensasie verminder kan word. ’n Bestaande nood kragbron is aangepas om as n newe reaktiewe kompenseerder te funksioneer. Die nood kragbron bestaan hoofsaaklik uit ’n 250 kVA drie fase omsetter spanningsbron. Die aanpassings is beperk tot sagteware en beheer algoritmes wat nie die oorspronklike funksionaliteit van die nood krag bron beinvloed nie. Beheer algoritmes word ontwerp en deeglik bespreek. ’n Tipiese dubbel lus beheer strategie word op die drywings elektroniese omsetter toegepas. Die binnelus bestaan uit ’n voorspellende stroom beheerder. Die buite-lus bestaan uit drie proportioneel en integraal beheerders wat onderskeidelik die GS-bus spanning, WS spanning en spanning wanbalans reguleer. Spannings duike en wanbalans is verminder deur slegs reaktiewe drywing te gebruik. Die doel was ook om ’n prakties bruikbare resultaat te lewer.

This thesis describes a new method of constructing a real-time interactive software system for a minicomputer to enable the interactive facilities to be extended and improved in a multitasking environment which supports structured programming concepts. A memory management technique called Software Virtual Memory Management, which is implemented entirely in software, is used to extend the concept of hardware virtual memory management. This extension unifies the concepts of memory space allocation and control and of file system management, resulting in a system which is simple and safe for the application oriented user. The memory management structures are also used to provide exceptional protection facilities. A number of users can work interactively, using a high-level structured language in a multi-tasking environ=ment, with very secure access to shared data bases. A system is described which illustrates these concepts. This system is implemented using an interpreter and significant improvements in the performance of interpretive systems are shown to be possible using the structures presented. The system has been implemented on a Varian minicomputer as well as on a microprogrammable micro= processor. The virtual memory technique has been shown to work with a variety of bulk storage devices and should be particularly suitable for use with recent bulk storage developments such as bubble memory and charge coupled devices. A detailed comparison of the performance of the system vis-a-vis that of a FORTRAN based system executing in-line code with swapping has been performed by means of a process control Case study. These measurements show that an interpretive system using this new memory management technique can have a performance which is comparable to or better than a compiler. oriented system. / Thesis (Ph.D.)-University of Natal, 1978.

This dissertation describes the role played by bird streamers in transmission line faults under HVDC conditions. The research was initiated due to the lack of knowledge of these faults under HVDC conditions. An explanation as to what bird streamers faults are, the role they play in the breakdown of air-gaps and a means of preventing bird streamer caused faults from occurring is made Experimental work has been carried out in order to gain an understanding of these faults under HVDC conditions. The overall aim of the experiments was to find a horizontal distance (protected zone) on an HVDC tower top, in order to prevent birds from perching around the centre of the tower. This will lead to a reduction of bird streamer caused faults. A brass rod was used as the artificial streamer in the experiments, under both negative and positive polarity (voltages in the range 0 to 220 kV DC were applied). Later in the experimental phase, a string soaked in a saline solution was used as a more realistic simulation of a bird streamer. QuickField™, an FEM package, was used to simulate the electric field in the region of the live conductor fitting and the tip of the bird streamer, to assess the degree of distortion of the electric field caused by the introduction of the bird streamer. These simulations served as means of verifying the laboratory experiments. This dissertation has proposed a relationship between the breakdown voltage and the protected zone length, based on the air-gap breakdown voltages for both I-String and V-String insulator configurations in the air-gap range 0 to 350 mm. These curves can be used in the design of transmission lines, as a means of reducing bird streamer faults. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2007.

Low-voltage switchgear and controlgear assemblies with a rated short-circuit withstand strength above 10 kA, are required, by law, to conform to the South African standard, SANS 1473-1 (Low Voltage Switchgear and Controlgear Assemblies: Part 1: Typetested, partially type-tested and specially tested assemblies with rated short-circuit withstand strength above lOkA). Standard SANS 1473-1 stipulates three categories of assemblies i.e. type-tested, partially type-tested and specially tested assemblies. The specially tested assembly is unique to the South African market, while the other two categories are stipulated in standard SANS IEC 60439-1 (Low Voltage Switchgear and Controlgear Assemblies: Part 1: Type-tested and partially type-tested assemblies), which is internationally accepted in many countries as the applicable low-voltage assembly standard. Standard SANS 1473-1 specifies seven type-tests for certification as a type-tested assembly (TTA), but specifies, at most, three type-tests for certification as a specially tested assembly (STA). The underlying purpose of a technical standard is to provide for the safety of people and property, with the purpose of the research being twofold: 1. To investigate if the testing requirements specified for a specially tested assembly (STA), in accordance with standard SANS 1473-1, are correctly applied, and do not pose any safety risks. 2. To investigate any safety risks that stem from the fact that four type-tests are excluded for verification as a specially tested assembly (STA), as opposed to the seven type tests required for verification as a type-tested assembly (TTA). The document highlights the technical inadequacies of an assembly that is certified as a STA, in accordance with standard SANS 1473-1, and the potential safety risks associated with this type of assembly classification. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2004.

Modern networks carry a wide range of different data types, each with its own individual requirements. The scheduler plays an important role in enabling a network to meet all these requirements. In wired networks a large amount of research has been performed on various schedulers, most of which belong to the family of General Processor Sharing (GPS) schedulers. In this dissertation we briefly discuss the work that has been done on a range of wired schedulers, which all attempt to differentiate between heterogeneous traffic. In the world of wireless communications the scheduler plays a very important role, since it can take channel conditions into account to further improve the performance of the network. The main focus of this dissertation is to introduce schedulers, which attempt to meet the Quality of Service requirements of various data types in a wireless environment. Examples of schedulers that take channel conditions into account are the Modified Largest Weighted Delay First (M-LWDF), as well as a new scheduler introduced in this dissertation, known as the Wireless Fair Largest Weighted Delay First (WF-LWDF) algorithm. The two schemes are studied in detail and a comparison of their throughput, delay, power, and packet dropping performance is made through a range of simulations. The results are compared to the performance offour other schedulers. The fairness ofM-LWDF and WFLWDF is determined through simulations. The throughput results are used to establish Chernoff bounds of the fairness of these two algorithms. Finally, a summary is given of the published delay bounds of various schedulers, and the tightness of the resultant bounds is discussed. / Thesis (M.Sc. Eng.)-University of Natal, Durban, 2003.

Fires generate heat and propel burning material into the air above and around the core of the fire. Fires under power lines reduce the breakdown strength of the air insulation due to the influence the heat and particles have on the electric field surrounding the conductors. The result can be flashovers and undesirable power supply interruptions in the electrical transmission network with a considerable impact on Eskom's 275 kV and 400 kV MTS (main transmission system) networks. Eskom typically experiences a loss in sales, a reduction in the quality of the power supplied to consumers and disgruntled consumers who in turn experience financial losses due to a loss in production. In this thesis, the high frequency characteristics of corona and electrical discharges generated by the fire phenomena are studied. The influence of the operating voltages on the electric fields, the potential of different media to initiate ionisation and comparison of conductor construction (bundling and diameter) are all considered in the measurement of high frequency signals in the range of frequencies available in the tuned circuits connected to power lines. The propagation of these high frequency signals is studied both in isolation of other sources of high frequency signals (within controlled laboratory conditions) and in the real environment adjacent to all other interfering sources. Finally the fingerprinting of the varying high frequency signal patterns associated with fires is considered with a view to implementing an operational early detection device. Early detection of a fire allows the utility to understand the source of a system fault, manage it effectively and if possible pre-empt possible failure by means of appropriately applied standard operating guidelines (SOG) to minimise the impact. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2003.

In order to sustain transmission grid availability and reliability it is imperative that the condition of vital and costly high voltage equipment is ascertained on a continuous or regular basis. It is necessary to establish the effective diagnostic tools or surveillance devices that can be used to assess equipment condition. Emphasis has been placed on refining well-established and more novel but developing condition assessment techniques. It is important to note that condition assessment of equipment also allows the opportunity to predict failure. Based on a complete and systematic assessment, the failure of defective equipment may be evident or predicted in time, thus preventing a forced outage and loss of valuable 'system minutes'. It has also become necessary to extend the life of existing equipment since most of them are reaching the end of their useful life. Replacement strategies have proven to be ineffective due to financial and resource constraints experienced by utilities. Life extension is the work required to keep equipment operating economically beyond its anticipated life, with optimum availability, efficiency and safety. One of its principal components is condition assessment, with the possibility of predicting remnant life. As a result, refurbishment projects are then raised. Refurbishment by replacement, uprating, modifications or change of design of certain key components to extend the life usually requires a substantial amount of capital to be invested. These projects must be economically justified. This thesis focuses on establishing condition assessment techniques for major power equipment such as power transformers. Assessment techniques for instrument transformers and circuit breakers are included, since these are commonly replaced or modified under refurbishment projects. An experimental investigation was carried out to determine the effectiveness of integrating data of two diagnostic techniques i.e. dissolved gas analysis (on-line) and acoustic detection of partial discharges. It was found that there is a correlation between data obtained from an acoustic detection system and an on-line single gas (Hydrogen) analyser. By integrating the data of both on-line monitoring systems, the diagnostic process is further enhanced. In addition, the location of a fixed discharge source was verified by using an acoustic detection system. Further, the sensitivity of the acoustic technique to partial discharge inception voltage, relative to the established electrical detection technique was determined for the experimental arrangement used. The results obtained indicated that this is an effective technique for the evaluation of activity within a transformer structure. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2004.

Load growth projections on South Africa's electricity demand indicate that Eskom's spare capacity will be eroded by the year 2005. In the late 1960s South Africa experienced electricity shortages and Eskom embarked on a program to build large coal fired power stations, to ensure that South Africa would have sufficient electricity capacity to meet the envisaged high growth rate. With sanctions being imposed on South Africa, the demand was much less than predicted and in the late 1980s South Africa had an excess of generating capacity, which resulted in some power stat ions being mothballed. Due to the increased economic growth after the 1994 elections and Eskom's electrification drive, there has been an increase in demand and the excess capacity has diminished. From past experiences, the lead time to build a power station varies with the type of power station. For large fossil, nuclear and hydro plants, the lead time is in excess of six years. Gas fired stations can have a lead time of less than three years. An option to defer the building of new power stations to meet this expected shortfall in demand is Demand Side Management (DSM). Eskom has already begun initiating a DSM program to try and defer the expected demand shortfall. From a university perspective there have been cutbacks in funding from government. For this reason tertiary institutions have been forced to review the way in which they manage their operating costs. A large tertiary institution spends a substantial portion of their facilities budget providing utility service to the campus. At most universities, 20 % or more of the annual utility budget is for electricity. In many facilities operations, tremendous potential exists to improve on energy efficiency and resource conservation and to reduce electricity costs. The management of energy tended not to feature very high on the list of priorities of tertiary institutions. Therefore targeting electricity for cost reductions in a campus environment makes sense. Additionally the historically low electricity price in South Africa, coupled with economic isolation meant that there is a proliferation of inefficient energy technologies present. The University of KwaZulu-Natal campuses (Medical, Pietermaritzburg, Howard College and Edgewood) spend about R 8 million per year in electricity expenditure. This constitutes about 5.8 % of the annual operational costs for the above mentioned centres (excluding salaries and capital expenditure). Not only is energy consumption a significant cost to the university, but energy use at the university also contributes to the depletion of natural resources and environmental problems associated with energy production and processing. The work presented in this thesis is the first step towards the establishment of what has become the formal energy management program at the University of KwaZulu-Natal. A comprehensive energy audit was conducted and metering of the mini substations was subsequently introduced. The readings from these meters, together with the results of the energy audit, are analysed. A successful case study involving energy efficient lighting technology implemented on the campus main library is also discussed. Energy savings of approximately R 220 000 per annum has been realised from the implementation of this case study. Conservative estimates to retrofit all the existing luminaires, with more modem efficient luminaires, show that the lighting system demand component can be reduced by approximately 600 kW. The audit has revealed loads that can be potentially shifted without adversely affecting regular campus activities. The air-conditioning load has been identified as an area where considerable savings can be attained. The ability to conservatively reduce the base load will realise savings in excess of R 100 000 per annum (2002 costs) and merely requires an awareness campaign to be instituted at minimal cost. The specific objectives of the study are given in the table below: 1. To conduct an energy audit to identify major energy users on campus. Object achieved: YES. 2. To establish a database of historical energy consumption data for each building on the Howard College campus. Object achieved: YES. 3. To further investigate the larger users of energy and quantify their energy consumption, and identify trends, where possible. Object achieved: YES. 4. To make recommendations where possible, for savings to be made. Object achieved: Yes. 5. To implement a case study demonstrating that energy management is a viable option. Object achieved: YES. As can be seen from the above table, all of the objectives were met. This analysis forms the basis of future efforts in the energy management program at the University of KwaZulu-Natal. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2005.