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 (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, 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 (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.

Submitted in fulfillment of the requirements for the degree of Master of Engineering in Electrical Power Engineering, Durban University of Technology, Durban, South Africa, 2017. / Voltage instability and increased power loss on transmission lines are major challenges in power transmission due to ever increasing load growth. This work investigates the effect of Static Synchronous Compensator (STATCOM) to mitigate power losses and enhance the voltage stability of a transmission system. STATCOM, a shunt-connected power electronic device, operate as a Voltage Source Converter (VSC) to improve power transfer capacity of transmission lines by injecting a set of three-phase balanced sinusoidal current with controllable magnitude and phase angle into the transmission lines to regulate the line voltage and compensate for reactive power at the Point of Common Coupling (PCC). To validate the capacity of STATCOM in this light, a modified model of IEEE 14 bus test system was simulated using DIgSILENT PowerFactory v15. Four different load profiles were included by increasing the base load in a step of 10%. In each case, power flow was run with and without STATCOM incorporated in the network with a view to determine the impact of STATCOM on bus voltage and transmission line losses. The simulation results are obtained were recorded and analyzed. It is noted that there was sufficient improvement in the new voltage profile obtained for the weak buses of the system, the active and reactive power losses were mitigated by 17.73% and 24.80% respectively when STATCOM was incorporated at normal load. The results showed that STATCOM could give quick voltage support to reduce the likelihood of voltage collapse and mitigate power losses along the transmission lines. Reduction of reactive power losses along the lines is higher than the active power losses resulting in the improvement of the voltage profile as the device is connected to the system. / M

No description available.

Embedded generation (EG) provides many benefits in terms of reduction of system technical losses and increased load carrying capacity. In this study the sustainable EG carrying capacity permutations in a medium voltage distribution system, will be determined. Using these results, the financial investment recovery potential of EG will be studied and the impact on the cost recovery by the Utility as a result of compensating the EG at the current system marginal price, will be analysed. The study was done to show what capitalisation can be done on a medium voltage distribution system, by the owners of EG plant receiving revenue from the Utility, at the system margin price with the anticipated inflationary increases. The study will also cover the effect on the revenue stream of the Utility as a result of voltage changes caused by the EGs to the loads being supplied. The electrical system used in the study consisted of a radial system with distributed load and generation. The distributed loads were modelled using the average load capacity supplied by the Utility in medium voltage system. The average volume of sales lost as a result of non-technical losses was included in the load model so that the overall accuracy of the revenue effect by EG on the Utility, could be increased. The amount of capitalisation that is achievable by the owners of the EG was tested against various practical permutation scenarios, including variation of location, system impedance (different X/R ratios), time of operation and changing load volume and type. The extent of successful penetration of EG into the distribution system was found to be between 20% and 60% of the load carrying capacity of the system. The simulated results revealed “bathtub curve” behaviour for the cost of energy losses and this reconciled with the theoretical analysis of other studies done in this area. Lower volume penetration of EG results in higher investment potential of up to ten million rand per MW with a 5% MARR per year. This is very low when compared to the levelised cost of the expensive renewable energy technologies that are currently available in the market. With higher penetration of EG on low impedance systems, the gross contribution of the Utility is negatively affected which would introduce instability in the SMP yearly increases. / M. Sc. Eng. University of KwaZulu-Natal, Durban 2013.

Thesis (Ph.D.) -- Mississippi State University. Department of Electrical and Computer Engineering. / Title from title screen. Includes bibliographical references.

Thesis (Ph.D.)--University of Wollongong, 2008. / Typescript. Includes bibliographical references: page 150-155.

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