D.Ing. / This study describes the technology of the Nonlinear Resonant Pole Converter. The NLRP is a soft switching topology that has different advantages.over other power electronic converters. This study describes the evolution, analysis, application and design of the NLRP. An introduction and background section with operating principles are provided. Detail analysis with operational limits is given ...

Includes bibliographies. / This study resulted from a perception held by the author that more attention is afforded to complying with the procedural elements of Environmental Impact Assessment (EIA) in South Africa, than to ensuring the validity of its technical content. The routing of high voltage overhead transmission lines provides a relevant field of study in which to address this perception. An initial literature review to contextualise the perceived problem showed that the questionable validity of the technical content of EIA was one of six shortcomings identified. To address the problem, an inductive approach was adopted to focus on the interpretation and prediction activities of EIA and two propositions, stated as research questions for discussion, were developed. These referred to the theoretical question of whether methods are specified for high voltage overhead transmission line EIAs, and to the practical question of whether the environmental impacts that are known to result from transmission line projects are effectively addressed in such EIAs in South Africa. Investigating these questions provides insights into whether the technical content of transmission line EIA is sufficiently rigorous in South Africa. The method of study takes the form of a sequentially more focused examination of the literature on EIA, from the strategic level, to the sectoral level and culminating at the project level. EIA methods specified for linear developments were identified at the sectoral level, while at the project level the known environmental impacts that result from high voltage overhead transmission lines were determined. A theoretical background was compiled in this way, which allowed for comparison with the practice as determined from benchmark and case study Environmental Impact Reports (EIRs).

Achieving electrostatic control of quantum phases is at the heart of condensed matter physics allowing us to interface fundamentally different electronic orders and observe their interplay with one another. Recent investigations have revealed emergent superconductivity tuned by the electric field effect in two-dimensional (2D) semimetals and moiré heterostructures. Through electrical transport measurements, we investigate superconductivity in few-layered Td - MoTe2 in this dissertation. Given its sensitivity to the ambient, a process to encapsulate and simultaneously electrically contact the material is developed to preserve the innate properties of MoTe2. At the outset, we observe a dramatic enhancement of superconducting critical temperature (Tc) in few-layered MoTe2. Monolayer’s Tc of ∼ 7.5 K is about 60x higher than the bulk. Reflecting its relatively small Fermi surface, superconductivity is tunable with electrostatic gating andresponse to in-plane magnetic fields reveals a tilted Ising spin texture. Some 2D crystal systems exhibit a polar crystal structure resulting in a robust, nonvolatile and bistable interlayer polarization giving rise to electric-field tunable ferroelectricity. Remarkably, we show that noncentrosymmetric bilayer Td - MoTe2 exhibits such ferroelectric switching while simultaneously being a superconductor, two electronic orders conventionally thought to be incompatible with one another. Further, electrostatic doping unveils a superconductingdome. It is found that the maximum Tc is concomitant with compensated electron and hole carrier densities and vanishes when one of the Fermi pockets disappears with doping pointing towards a pairing mechanism mediated by Fermi surface nesting between electron and hole pockets. Finally, in-plane magnetotransport measurements reveal a two-fold symmetric superconductivity around the crystal axes for bilayer MoTe2. Superconductivity is maximized when magnetic field is parallel to the ?-axis of the crystal and minimized for b-axis. Although unsurprising given the ?2 crystal symmetry, these results lend further credence to the tilted Ising spin texture, as unveiled from Hc2|| measurements on the monolayer.

In this thesis case studies have been made to study the impact ofSMES system on power system transmission with a decoupled Optimal Power Flow program. Linear Programming (LP) and Quadratic Programming (QP) storage scheduling methods including transmission security have been developed, LP method is suitable for single storage system and QP method is capable of solving multiple storage scheduling problem. Results on single storage system is compared with Load Shaving method, which indicate that three methods have approximately the same storage schedule and daily fuel cost. Results on two storage system with QP method suggest that the coordination between storage units can help to transfer more power from base units and reduce total fuel cost in peak hours. / Master of Science

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.

This dissertation investigates the role that is played by high temperatures of air gaps on the breakdown voltage levels under DC positive and negative polarity applied voltages. Due to past experience of AC transmission lines tripping as a result of sugar-cane fires that occur under these lines during cultivation seasons, this study was initiated to investigate this effect under DC applied voltages. Results were obtained from laboratory work conducted and these were closely analysed to understand the behaviour of air gaps under these conditions. A 17mm2 square-cut brass rodrod electrode configuration was used to carry out these tests at the various air gap temperatures. These were induced by a gas burner for both the positive and negative polarities at 200C – 3000C for the 10 mm – 150 mm air gap range and 200C – 1500C for the 200 mm – 500 mm air gap range. Later particles were introduced into the air gap to determine the subsequent behaviour. These were introduced vertically from the top into an air gap via a vibrating micro sieve mechanism to regulate the consistency of the introduction of these particles in the air gap. A reduction of 55% and 50% was observed on the breakdown voltage under positive and negative polarity applied voltages respectively from ambient conditions to 3000C. Additionally the breakdown behaviour of both negative and positive DC was found to be linear which is similar to the AC case. However, air gaps subjected to positive DC applied voltages were found to portray an inferior dielectric strength as opposed to the equivalent negative DC polarity. The study found that the effect of particles in the air gap is practically negligible and that for practical purposes, only the temperature effect plays a role due to the reduced air density at high temperatures. Empirical models for both the positive and negative DC polarities have been proposed by the study that incorporate the effect of the temperature in the air gap to enable the determination or prediction of the breakdown voltage level at various temperatures. These models may be utilised for DC transmission line design for servitudes in areas that are known to be prone to fires. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2012.

Thesis (PhD)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: Accurate load models are required for the computation of load flows in MV distribution networks. Modem microprocessors in recent times enable researchers to sample and log domestic loads. The findings show that they are stochastic in nature and are best described by a beta probability distribution. . In rural areas two different load types may be present. Such loads are domestic and pump loads, the latter may be modelled as constant P - Q loads. An analytical tool for computing voltage regulation on MV distribution networks for rural areas feeding the mentioned loads is therefore required. The statistical evaluation of the consumer voltages requires a description of load currents at the time of the system maximum demand. To obtain overall consumer voltages at any specified risk for the two types of the loads, the principle of superposition is adopted. The present work deals with conventional 22kV three-phase distribution (te:. - te:.) connected networks as used by ESKOM, South Africa. As the result of the connected load, MV networks can experience poor voltage regulation. To solve the problem of voltage regulation, voltage regulators are employed. The voltage regulators considered are step-voltage regulators, capacitors and USE (Universal Semiconductor Electrification) devices. USE devices can compensate for the voltage drops of up to 35% along the MV distribution network, thus the criteria for the application of the USE devices is also investigated. The load currents are treated as signals when assessing the cost of distribution system over a period of time due to power losses. The individual load current signal is modelled by its mean and standard deviation. The analytical work for developing general expressions of the total real and total imaginary components of branch voltage drops and line power losses in single and three-phase networks without branches are presented. To deal with beta-distributed currents on MV distribution networks, new scaling factors are evaluated at each node. These new scaling factors are derived from the distribution transformer turns ratio and the deterministic component of the statistically distributed load currents treated as constant real power loads. In the case of an individual load current signal, the transformation ratio is evaluated from the distribution transformer turns ratio and the average value of the· signal treated as constant real power load. The evaluation of the consumer voltage percentile values can be accurately evaluated up to 35% voltage drop. This is possible by the application of the expanded Taylor series, using the first three terms. The coefficients of these three terms were obtained using a search engine imbedded in the probabilistic load flow. The general expressions for evaluating the overall consumer voltages due to statistical and non-statistical loads currents are also given. These non-statistical currents may be due to constant P - Q loads, line capacitance and the modeling of voltage regulators. The Newton-Raphson algorithm is applied to perform a deterministic load flow on singlephase networks. A backward and forward sweep algorithm is applied to perform a deterministic load flow on single and three-phase systems. A new procedure for modelling step-voltage regulators in three-phase (te:. - te:.) connected networks is outlined. Specifying a transformation ratio of 1.1 and 1.15 respectively, identifies the open-delta or closed-delta configuration for three-phase networks. The algorithms and the developed general expressions for single and three-phase networks without branches are presented in this work. A new algorithm is developed to enable the developed general expressions to be applied to practical MV distribution networks. The algorithms were tested for their accuracy by comparing the analytical results with Monte Carlo simulation and they compared well. An illustrative example to show the application of the present work on a practical MY distribution networks is presented. A criterion for the application of the USE devices is outlined. It is anticipated that, the work presented in this thesis will be invaluable to those involved in the design of MY distribution systems in developing countries. / AFRIKAANSE OPSOMMING: Akkurate lasrnodelle word benodig vir drywingsvloei analises in MV distribusiestelsels. As gevolg van nuwe digitale verwerkers is dit deesdae moontlik om huishoudelike laste te monitor. Die lasdata dui daarop dat laste stochasties is en kan met behulp van die Beta verdeling beskryf word. In landelike gebiede is daar twee tipes laste. Hulle is eendersyds huishoudelike laste en andersyds pomp-tipe laste wat as konstante P-Q laste beskou kan word. Dit is dus belangrik om toepaslike analitiese metodes te gebruik om die spanningsvalle by hierdie laste te bereken met inagname van die las-tipes. By die statistiese berekening van die verbruiker se spanning moet 'n statistiese model van die lasstroom verskaf word op die tydstip van maksimum aanvraag. Daarna moet die prinsiep van superposissie gebruik word om die spannings by verskeie nodes by 'n gespesifiseerde vertrouensinterval te bepaal. Hierdie proefskrif is gebaseer op konvensionele 22kV, drie fase distribusie (delta na delta) netwerke, soos deur Eskom, Suid Afrika gebruik. Hierdie stelsels ondervind dikwels nadelige spanningsvlakke en spanningsreëlaars word derhalwe aangewend. Hierdie reëlaars is gewoonlik van tap-tipe of daar kan ook gebruik gemaak word van kapasitore en ook elektroniese reëlaars soos die USE tipe toestelle. Laasgenoemde kan op LV vir spanningsvalle tot 35% kompenseer. In hierdie werk word die werkdrywing verliese in die geleiers bereken met behulp 'n seinmodel van die lasstrome. Die individuele lasstrome word by wyse van gemiddeldes en variasies beskryf. Om die algemene algoritmes vir die berekening van die reële en imaginêre spanningsvalle, asook die verliese in enkelfase en driefase stelsels daar te stel word aanvanklik gebruik gemaak van stelsels sonder vertakkings. Om die statistiese lasbeskrywing op die laagspanningskant na die MV vlak oor te dra word van nuwe skaalfaktore gebruik gemaak. Hierdie faktore word bereken op die basis van die transformator se verhouding en die deterministiese komponent van die statistiese verspreide lasstrome, as konstante reële drywingslaste beskou. Met die ontwikkelde metode kan die verbruiker se spanning by 'n gegewe vertrouensinterval akkuraat bereken word vir spanningsvalle tot 35%. Dit word moontlik gemaak deur die Taylor-reeks tot drie terme toe te pas. Daar moet egter gebruik gemaak word van toepaslike koëffisiënte wat bepaal word deur 'n geprogrammeerde soektog. 'n Algemene stel vergelykings om die spanning by enige verbruiker te bereken, ongeag die topologie van die netwerk, word ook gegee. Die Newton-Raphson metode word aangewend om die deterministiese drywingsvloei op enkelfase stelsels te bereken. A truwaartse-voorwaartse metode is gebruik om die drywingsvloei te bepaal vir driefase stelsels. 'n Nuwe prosedure is ontwikkel vir die modellering van die spanningsreëlaars in driefase, delta-delta netwerke. Deur gebruik te maak van 'n transformatorverhouding van 1.1 of 1.15 kan die oop-delta of toe-delta netwerke voorgestel word. 'n Nuwe algoritme is ontwikkelom multi-vertakkings in 'n netwerk te hanteer. Al die prosedures is deeglik met behulp van Monte Carlo simulasies getoets en die resultate is heel bevredigend. Om die metodes te illustreer word 'n gevallestudie ingesluit waar die metodes gebruik word om 'n netwerk te evalueer met en sonder die sogenaamde USE toestelle. Kriteria vir die aanwending van hierdie toerusting word voorgestel. Daar word verwag dat die werk soos in hierdie proefskrifuiteengesit is die ontwerp van MV distribusiestelsels, veral in ontwikkelende lande, heelwat sal verbeter.

Thesis (MScIng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: This thesis covers the development of a transformerless series dip compensator. Of all known power quality problems, voltage dips are the greatest reason for concern. Series injection dip compensators offer the advantage of only having to compensate for the decrease in supply voltage during a dip. This results in significant reduction in converter ratings and energy storage requirements. The aim of this thesis was to take up previous developments and combine them with new technologies to maximize their functionality. The new design was implemented with ultracapacitors to offer a maintenance-free device lifespan of 20 years. As they are very expensive, a new topology was introduced in this thesis to maximize their use so that they become viable for industry. Furthermore, a new method of daisy chaining switches was introduced to minimize costs involved in controlling them. A single-phase compensator, with this new topology and the new way of controlling switches, was designed and built according to specifications stated by Eskom. This ultracapacitor-based dip compensator was tested with a dip generator, developed by the University of Stellenbosch for different load currents. The experimental results confirmed simulations made with identical parameters. This thesis presents a reliable and cost effective solution for dip compensation. / AFRIKAANSE OPSOMMING: Hierdie tesis dek die ontwikkeling van ’n transformatorlose duik kompenseerder. Van al die bekende toevoerkwaliteit probleme wek duike in die spanning die meeste kommer. Serie-injeksie kompenseerders het die voordeel dat hulle net kompenseer vir die verlies in die toevoerspanning tydens die duik. Dit het ’n beduidende vermindering in die omsetterkenwaardes en energiestoorvereistes tot gevolg. Hierdie tesis mik om vorige soortgelyke ontwikkelings op te volg en te verbeter met nuwe tegnologie om die funktionliteit te maksimeer. Die ontwerp is geimplementeer met ultrakapasitore wat die onderhoudsvrye toestel ‘n leeftyd van 20 jaar toelaat. Omdat ultrakapasitore so duur is moes ‘n nuwe topologie onwikkel word om die gebruik van ultrakapasitore meer ekonomies aantreklik te maak. Daar is ook ‘n nuwe manier van skakelaar beheer ontwikkel wat toelaat dat baie skakelaars oor een optise veesel beheer kan word. ‘n Enkel fase dip kompensaeerder is toe onwikkel en gebou volgens Eskom se spesifikasies. Die ultrakapasitor gebaseerde omsetter is getoets met ‘n dip generator wat deur die Universiteit van Stellenbosch ontwikkel is. Die praktiese resultate bevestig die simulasies wat gedoen is met dieselfe parameters. Hierdie tesis lei tot ‘n betroubaare en ekonomiese oplossing vir duik kompensasie.

Thesis (MScIng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: The optimal placement of different types of compensators on electrical networks is a complex task faced by network planners and operations engineers. The successful placement of these devices normally involves a large number of power flow studies and relies heavily on the experience of the engineer. Firstly the operation and application of the different types of compensators must be clearly understood. Secondly the application of combinations of different compensators on a specific network must be investigated. Then the dynamics of the network and interaction between the network and the compensator/s must be studied under a wide variety of network conditions and load levels. This task is further complicated by the non-linear nature of the mathematical equations that govern the power flow and voltage distribution on an electrical network. Yet another complication is the fact that some of the variables that describe an electrical network can be non smooth or discrete. For instance, the discrete value of a tap position of a power transformer can only assume an integer value. To simplify the problem of compensator placement, advanced software tools are available that are capable of solving power flows of networks containing compensators. To a large degree, however, these tools still rely on the user to make intelligent decisions as to the configuration of networks and the placement of compensators. In many cases trial and error is the only way to find a good solution. The purpose of this thesis is to show the different techniques available to implement intelligent algorithms capable of finding optimal solutions specific to the placement of voltage regulators. State of the art algorithms are implemented in Matlab that can place voltage regulators on sub transmission, reticulation and low voltage networks. The sub transmission and reticulation placement algorithm is a combination of an SQP technique and a simple combinatorial algorithm. The low voltage placement program is based on a simple genetic algorithm with a few customized features that has been developed to ensure fast convergence. The programs developed were used to do optimal voltage regulator placement on a number of networks. As far as possible real world networks were used. Where real world networks were not available test networks were used that closely resemble real networks, as they exist on typical networks owned by Eskom Distribution. It was found that SQP is a very efficient algorithm for optimising large non-linear problems such as the placement of a Step Voltage Regulator on a large electrical network. This algorithm however does not handle discrete variables very well and is also limited in handlingany reconfiguration of the network due to the placement of series devices such as voltage regulators. To cater for reconfiguration, it is necessary to combine the SQP algorithm with a combinatorial algorithm. The genetic algorithm used to do optimal placement of multiple Electronic Voltage Regulators on low voltage networks was found to be very efficient and robust. This can be attributed to the simplicity of the algorithm as well as the fact that it does not rely on the availability of derivative and second derivative information to move towards an optimal solution. Instead, it only uses fitness values obtained from function evaluations to optimise the placement problem. Another useful feature of using a genetic algorithm is that the algorithm does not get stuck in sub optimal areas in the solution space. Both the placement programs developed are relatively simple and do not consider all the factors involved in the placement of voltage regulators. However, the addition of any number of factors is however possible with further development of the programs as presented in this thesis. / AFRIKAANSE OPSOMMING: Die optimale plasing van verskillende kompenseerders op elektriese kragstelsels is ´n moeilike probleem vir beplanners en operasionele personeel. Die plasing van kompenseerders gaan gewoonlik gepaard met ´n groot hoeveelheid netwerk studies en die sukses daarvan berus gewoonlik op die ondervinding van die ingenieur. Eerstens moet die werking en toepassing van elke kompenseerder behoorlik verstaan word. Tweedes moet die plasing van ´n enkele asook kombinasies van verskillende kompenseerders ondersoek word. Dan moet die dinamika van die netwerk en interaksie met die kompenseerder/s bestudeer word vir al die moontlike netwerk konfigurasies en belasting vlakke. Die taak word verder bemoeilik deur die nie-liniêre vorm van die wiskundige vergelykings wat die netwerk vrag en spanning verspeiding beskryf. Nog ´n komplikasie is die feit dat van die veranderlikes wat die probleem beskryf, diskreet is. Byvoorbeeld die tap posisie van ´n transformator kan slegs ´n heel getal aanneem. Om die plasing van kompenseerders te vergemaklik is gevorderde sagteware beskikbaar wat simulasies kan doen van netwerke wat kompenseerders bevat. Tot ´n groot mate is die sagteware nog steeds afhanklik van intellegente besluitneming deur die gebruiker. In die algemeen moet ´n groot hoeveelheid studies nog steeds gedoen work om ´n goeie oplossing te vind. Die doel van hierdie tesis is om die verskillende tegnieke te wys wat beskikbaar is om intelligente algoritmes te implementeer wat optimale oplossings kan vind vir spesifiek die plasing van spanning reguleerders. Moderne algoritmes is in Matlab geimplementeer wat spanning reguleerders op sub transmissie, retikulasie en laag spanning netwerke kan plaas. Die sub transmissie en retikulasie plasings algoritme is gebaseer op ´n kombinasie van ´n sekwensieële kwadratiese programmering metode en ´n eenvoudige kombinatoriese metode. Die laag spanning plasings program is gebaseer op ´n eenvoudige genetiese algoritme met ´n paar unieke verstellings om vinnige konvergensie te verseker. Die twee programme wat ontwikkel is word dan gebruik on spanning reguleerders te plaas op ´n paar netwerke. So ver moontlik is bestaande netwerke gebruik. Waar bestaande netwerke nie beskikbaar was nie is toets netwerke saamgestel wat gebaseer is op bestaande Eskom netwerke. Daar is gevind dat sekwensieële kwadratiese programmering ´n effektiewe algoritme is om groot nie liniêre optimerings probleme, soos die plasing van spanning reguleerders, op te los. Hierdie algoritme is egter nie geskik om diskrete veranderlikes te hanteer nie. Dit is verder ook nie geskik om enige netwerk rekonfigurasie te hanteer tydens die plasing van seriesgeskakelde kompenseerders soos spanning reguleerders nie. Om die rekonfigurasie moontlik te maak is dit nodig om die sekwensieële kwadratiese programmering te kombineer met ´n kombinatoriese algoritme. Daar is verder gevind dat die genetiese algoritme wat gebruik is om elektroniese spanning reguleerders te plaas op laag spanning netwerke baie effektief en robuust is. Dit is as gevolg van die eenvoudigheid van die algoritme en die feit dat dit nie afhanklik is van afgeleide en tweede afgeleide informasie om na die optimale oplossing te beweeg nie. Die algoritme gebruik slegs fiksheid waardes bereken van funksie evaluasies om die probleem te optimeer. Nog ´n voordeel van genetiese algoritmes is dat dit nie in sub optimale gebiede van die oplossing ruimte stil staan nie. Beide die programme wat ontwikkel is, is redelik eenvoudig en neem nie al die faktore in ag wat gepaard gaan met die plasing van spanning reguleerders nie. Addisionele faktore kan egter maklik ingesluit word deur verdere ontwikkeling van die bestaande programme.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2005. / Spoornet is one of South-Africa’s largest railway companies. It is very important to operate the railway system as cost effectively as possible. A large portion of the railway operates from 3 kV DC traction supplies. One method of cost saving is to utilise the regenerative braking mechanism of the electric trains.