A transmissão de grandes blocos de energia elétrica por longas distâncias é uma tecnologia cujo domínio é de bastante interesse para o Brasil, devido às suas características de grande dimensão territorial, com uma distância considerável entre geração e centros de carga, e com um grande potencial energético ainda não explorado. A solução mais utilizada na transmissão em corrente alternada convencional, que é a compensação, ao longo da linha, da reatância série e paralela, se torna dispendiosa quando aplicada em distâncias muito longas. Sabe-se que a transmissão em corrente continua é uma solução viável para este tipo de transmissão. Outra opção, que é objeto deste trabalho, é a transmissão em linhas de \"pouco mais de meio comprimento de onda\", cujo principal atrativo é o fato de as distâncias entre as gerações na Amazônia e os centros de carga no Sudeste brasileiro serem bastante próximas do meio comprimento de onda das tensões e correntes alternadas em 60 Hz. Neste trabalho, serão descritas etapas de definição de condutor economicamente mais adequado e projeto da geometria da torre. Com base nesses dados, serão avaliados algumas propriedades das linhas de meia onda, durante operação normal, curtos-circuitos e energização. Serão também analisadas as perdas resistivas. / Bulk power transmission over long distances is a technology of much interest to Brazil, due mainly to the large territory owned with considerable distances between generation and the load centers; to which, it can be added the large amount of energetic potential still unexplored. When conventional AC power transmission is used, usually it is necessary to provide series and shunt compensation, solution that becomes expensive when applied to very long distances. It is known, though, that DC power transmission is still a viable solution to this type of transmission. In this work, differently of the above alternatives, it will be addressed another type of transmission, the so-called half-wavelength transmission lines (HWLL). One interesting requirement of this technology is the fact that these lines should be about 2500 km long, which is approximately the same distance between the generation area (Amazon region) and the load centers located in the Southeast region of the country. In this work, it will be suggested some steps to define the most suitable conductor cross section resulting from the compromise between line components acquisition and installation costs as well as power loss costs. Subsequently, a suitable geometry for the tower that could be used will be selected. Some of the properties of HWLL will be assessed for normal operation, short circuits and line energization. Finally, Joule losses will also be examined.

The objective of the proposed research is to develop a cost-effective power flow controller to improve the utilization and reliability of the existing transmission, sub-transmission, and distribution networks. Over the last two decades, electricity consumption and generation have continually grown at an annual rate of around 2.5%. At the same time, investments in the Transmission and Distribution (T&D) infrastructure have steadily declined. Further, it has become increasingly difficult and expensive to build new power lines. As a result, the aging power-grid has become congested and is under stress, resulting in compromised reliability and higher energy costs. In such an environment it becomes important that existing assets are used effectively to achieve highest efficiency. System reliability is sacrosanct and cannot be compromised. Utility system planners are moving from radial towards networked systems to achieve higher reliability, especially under contingency conditions. While enhancing reliability, this has degraded the controllability of the network, as current flow along individual lines can no longer be controlled. The transfer capacity of the system gets limited by the first line that reaches the thermal capacity, even when majority of the lines are operating at a fraction of their capacity. The utilization of the system gets further degraded as the lines are operated with spare capacity to sustain overloads under contingencies. Market efficiency is also sub-optimal, with congestion on key corridors restricting the low-cost generators to connect to the end users, resulting in higher electricity prices for the consumers. The proposed technology offers the capability to realize a controllable meshed-network, with the ability to utilize static and dynamic capacity of the grid to provide system-wide benefits, including- increased line and system-capacity utilization, increased reliability, improved operation under contingencies, and rapid implementation. It would allow a broadening of the energy market, permitting owners to direct how energy flows on their wires, and making it easier to connect to new sources of generation.

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.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / This thesis investigates the compensation of voltage flicker in an industrial environment. Industrial loads draw progressively less sinusoidal currents. These currents cause non-sinusoidal voltage drop over the line impedance, causing a distorted line voltage. The light output of incandescent electric lighting systems is quadratically proportional to the line voltage, and thus variations in the line voltage cause irritating variations in the output of such systems. Two tools to analyse flicker problems are developed: A USB data logger is built to log measured waveforms to computer hard disk. These data are analysed using a MATLAB implementation of the IEC-specified flicker meter. A converter-based flicker compensator is found to be the only compensator capable of compensating general flicker loads. Such a compensator is developed using the synchronous reference frame filtering technique. Several aspects of the compensator are dealt with in detail including selection of a current control strategy, calculation and implementation of the converter duty cycles and compensation of the various non-idealities in such a controller. Full compensation is contrasted to reactive compensation – the second option being less expensive but also less effective in the compensation of certain loads. The effectiveness of reactive compensation is found to be dependent not only on the type of load, but also on the type of line feeding the flicker load. Three industrial flicker loads are measured and analysed: a three-phase welder, a sawmill and a rock crusher. These loads are simulated, and the compensation proposed confirmed via these simulations. The compensation of the three-phase welder is tested using a hardware scale model. This verified the operation of the proposed flicker compensator in practice.

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.

published_or_final_version / abstract / Electrical and Electronic Engineering / Master / Master of Philosophy

published_or_final_version / abstract / Electrical and Electronic Engineering / Master / Master of Philosophy