The Eskom Transmission Network experiences an exceptionally high number of line faults, the cause of which, may not be correctly identified. This thesis analyses a number of all the possible factors responsible for causing these faults. The objective is to assign probable causes of these faults and that the correct preventative or corrective measures may be planned. The percentage of unexplained line faults is estimated to be 35 % of the total system faults. It is important for the Transmission Group of Eskom to minimise the number of faults. Major efforts to minimise identified faults such as bird streamers, veld fires, sugar cane fIfes, lightning and a hypothesised light pollution, light wetting mechanism has been undertaken by the transmission grid authority. This thesis presents an analysis of the statistical data of the unknown faults (unknown faults is defined as lines that trip due to a reason which could not be identified) that has been undertaken. This analysis takes into account a number of categories of causes of line faults. The period, for which the performance of the lines was analysed for was the years inclusive of 1993 to 1997. The investigation has focused on the identification of the under-performing lines of the main Transmission Network. The identified poorly performing lines have been compared with each other from the perspective ofthe following variables: • Region • Voltage (System Voltage) • Climatic Data Line faults - Time ofDay analysis • Line Faults - Time of Year analysis. The analysis indicates that the majority of unexplained flashovers occur between 22 :00 and 07:00 the following morning (Britten et al, 1999). Almost all of the under performing lines in South Africa fall in the sub-tropical/humid climatic area. All the lines studied are insulated with standard glass disc insulators. The analysis indicated that most of the unexplained line faults occur during the months when the seasons change, e.g. from autumn to winter. The analysis further indicates that most unexplained line faults occurred during the months of April to May and August to September. Of note is that during the period of this investigation bird guarding was performed on some lines. Installing bird guards may reduce those line faults that are caused by bird streamers. However, the bird pollution (deposited on glass disc insulators) that is not washed off at the same time as the bird guard installation may cause the line to trip due to the combination of the pollution and wetting resulting in a pollution type flashover. This is a possible cause of some unexplained line faults that occur from April to May. Bird streamers are also identified as the most probable cause of the unexplained faults which occur during the late evening periods (22:00 - 00:00). Pollution (with wetting) during the early morning periods may result in faults for the period 00:00 to 02:00. Line faults in the early morning periods (04:00 - 7:00) could be due to bird streamers or pollution and wetting, depending on the time of year in which the faults occurs. / Thesis (M.Sc.)-University of Natal, Durban, 2003.

The management of parallel and series resonance conditions is important for ensuring that harmonic levels are managed on utility networks, and that shunt compensators are able to operate without constraints for various network conditions (states). For these and similar problems, harmonic impedance assessment of the ac network is required for the design of ac filter or shunt capacitor bank installations. This is particularly important for large installations connected to HV or EHV systems, because resonances at these voltage levels tend to be highly un-damped resulting in potentially damaging voltage and current amplification. The objective of this dissertation was to develop and demonstrate a design methodology which makes use of network impedance assessment methods to provide robust harmonic integration of large shunt compensators into a transmission and HVDC systems. The design methodology has two aspects. The first part considers network modeling, evaluation of different models and simulation of harmonic impedance. In the second part, methods of analyzing and assessing the simulated harmonic impedance are developed. A detailed step-by-step approach was taken in the development of the design methodology. The methodology was documented as a guideline and accompanied by the development of an Excel tool that can be used to assess the simulated harmonic impedance. The Excel tool permits a systematic assessment of the simulated network impedance where shunt compensators are integrated into transmission systems. The tool also ensures that the design of transmission and HVDC ac shunt compensation is optimally robust in terms of harmonic resonances. The theoretical and computational review has been tested and demonstrated on the existing Eskom Transmission system through several case studies. The results have shown the merits of the design methodology. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2013.

Für die Menschen zählen Gewitter mit Donner und Blitz zu den ältesten bekannten Phänomenen der Natur. Die Tatsache, dass Blitze dennoch bis heute nicht abschließend erforscht sind, liegt in dem äußerst komplexen, schnellen und stochastischen Verhalten der Blitzentladung begründet. Der Autor befasste sich in Rahmen dieser Arbeit u.a. mit der Entwicklung eines modernen Messsystems, durch das die Erfassung von sowohl elektrischen als auch optischen Parametern der im Nanosekundenbereich ablaufenden Prozesse der Entladungen möglich wurde. Es handelt sich um technisch anspruchsvolle Messungen von hohen Stoßspannungen und schwachen Vorentladungsströmen in einem großen Frequenzbereich. Außerdem gelang es durch eine geschickte Synchronisation, die Entladungsprozesse präzise und erstmalig in einer Fotosequenz aufzunehmen. Auf Grundlage der Messergebnisse konnte der Entladungsprozess in mehrere Phasen der Vorentladung unterteilt und beschrieben werden. Vor allem beweisen die Messergebnisse die Existenz einer kanalartigen Vorentladung, die nicht zwingend zu einem Durchschlag führt. Dieser Mechanismus, der bei langsam ansteigenden Spannungen als stabile Leaderentladung benannt und mit Thermoionisation gekennzeichnet ist, war bei Blitzstoßspannungen bisher umstritten. / The breakdown behavior of long air gaps by Lightning Voltages has been investigated and the results of a new measurement system are reported. A series of up to eight photos (made by a high-speed camera) have recorded the expansion of discharge activities during the breakdown process. The pre-discharge current and voltage have been measured as well. The modern measurement techniques have made possible the synchronization of the photos with the current and voltage measurements in nanosecond-ranges. The combination of the measured current, voltage, and photos can precisely explain the breakdown process. The experiments have been carried out with the lightning impulses up to 2.4 MV and the air gaps up to 4 m. Despite of such high voltages, the experimental system has been verified to be appropriate for measuring the pre-discharge current in mA-ranges.

Mémoire (M.Sc.A.)--Université du Québec à Chicoutimi, 1985. / Document électronique également accessible en format PDF. CaQCU

The HVDC, High Voltage Direct Current, is important when it comes to upgrading the energy system to a renewable, sustainable and efficient system. This master thesis is investigating what is happening during the most decisive fault cases when the HVDC station is operating with inherent overload. An inherent overload operating area is defined and simulations are performed in PSCAD/EMTDC to study the transient behavior of the fault currents and overvoltages.

No description available.

This diploma thesis deal with the description of electrical energy quality in low voltage. A test data model is created in the thesis which can automatically evaluate the state of the quality of electric energy in terms of higher harmonic voltages in the MATLAB programming environment. To verify the correct design of the model, two possible views of simulated data are created in the form of tables and graphical dependencies. An user interface is created for more complex control of each model states of the data being considered.

Indiana University-Purdue University Indianapolis (IUPUI) / This research introduces a new design of a converter modified from SEPIC converter (Single end primary inductive converter), capable of generating desired voltage levels and polarities. The new switching converter topology allows for boost and buck of the input voltage theoretically achieving infinite positive and negative voltage levels. The proposed topology utilizes single high frequency switch to perform the power conversion which simplifies the design of the gate driver, but meanwhile, it still retains the ability to provide a wide range of output voltage. Mathematical modeling of the converter and computer simulations are validated by experimental data. To verify its performance a prototype was designed and built. It is experimentally proven that the circuit can generate a desired voltage in the range of voltages up to ±170 V, delivering 480 Watts of power to a resistive load.

No description available.

As linhas de distribuição de energia estão frequentemente expostas a sobretensões causadas por descargas atmosféricas diretas e indiretas. As formas de onda dessas sobretensões podem diferir bastante do impulso atmosférico normalizado utilizado em ensaios para verificação da adequação dos projetos das isolações dos equipamentos frente a sobretensões atmosféricas (1,2/ 50 µs). Diferentes modelos têm sido propostos para se estimar o desempenho das isolações frente a impulsos não normalizados, sendo o modelo do efeito disruptivo (disruptive effect model) um dos mais utilizados. Este trabalho visa avaliar o comportamento de isoladores de média tensão quando sujeitos a sobretensões atmosféricas bipolares oscilatórias. Simulações realizadas usando o \"Extended Rusck Model\"(ERM) e resultados de medições demonstram que a ocorrência de sobretensões bipolares oscilatórias em linhas de distribuição não é um fato raro, pois descargas atmosféricas podem, sob certas condições, induzir tensões com tais características. Modificações realizadas no circuito de um gerador de impulsos de alta tensão convencional permitiram a geração de tensões bipolares de três períodos distintos: 2,2 µs, 4,1 µs e 6,0 µs. Este trabalho investiga o comportamento de um típico isolador de porcelana tipo pino de 15 kV sujeito a um impulso bipolar, representativo de uma tensão induzida por um raio. Mostra-se que uma modificação no método proposto por Savadamuthu et al. para estimar a suportabilidade do isolamento de pequenos (alguns milímetros) sistemas de isolamento submetidos a tensões oscilantes bipolares leva a resultados promissores em termos de previsão da ocorrência de descargas no isolador de classe 15 kV. / Power lines are often exposed to surges caused by direct and indirect lightning. The waveforms of these overvoltages may differ significantly from the standard lightning impulse used in tests to verify the adequacy of equipment insulation designs against atmospheric overvoltages (1.2/50 µs). Different models have been proposed to estimate the performance of the insulation against non-normalized impulses, with the disruptive effect model being one of the most used. This work aims at evaluating the behavior of medium voltage insulators when subjected to bidirectionally oscillating voltages. Simulations run using the Extended Rusck Model (ERM) and measurement results show that the occurrence of bipolar oscillating overvoltages are not rare on power distribution lines, as lightning strokes can induce, under certain conditions, voltages with such characteristics. Modifications performed in the circuit of a conventional high voltage pulse generator allowed the generation of bipolar voltages of three distinct periods: 2.2 µs, 4.1 µs and 6.0 µs. This work investigates the behavior of a typical 15 kV pin-type porcelain insulator subjected to bipolar impulses representative of lightning-induced voltages. It is shown that a modification on the method proposed by Savadamuthu et al. to estimate the insulation strength of small (a few mm) insulation systems subjected to bipolar oscillating voltages leads to promising results in terms of predicting the occurrence of flashovers on the 15 kV insulator.