Thèse (D.Eng.) -- Université du Québec à Chicoutimi, 2007. / La p. de t. porte en outre: Thèse présentée à l'Université du Québec à Chicoutimi comme exigence partielle du doctorat en ingénierie. CaQQUQ Bibliogr.: f. 222-239. Document électronique également accessible en format PDF. CaQQUQ

Thèse (D.Eng.) -- Université du Québec à Chicoutimi, 2007. / La p. de t. porte en outre: Thèse présentée à l'Université du Québec à Chicoutimi comme exigence partielle du doctorat en ingénierie. CaQQUQ Bibliogr.: f. 222-237. Document électronique également accessible en format PDF. CaQQUQ

Mémoire (M.Sc.A.)-- Université du Québec à Chicoutimi, 1992. / Bibliogr.: f. 108-109. Document électronique également accessible en format PDF. CaQCU

Thesis (Ph. D.)--University of California, San Diego, 2000. / Vita. Includes bibliographical references.

Thesis (Ph. D.), Oregon Graduate Institute of Science & Technology, 1996.

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

Thesis (M.Ing.)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: The application of cycloaliphatic epoxide (CE) insulation in the Republic of South Africa is investigated within this thesis. There was a request from industry to evaluate the product and indicate its suitability for application within the various geographic and climatic zones typical of the RSA. An extensive survey was conducted into the historic origins of the material, and the experiences of international utilities applying the insulation medium in respect of polluted conditions. The properties of the Automatic Pressure Gelation (APG) CE insulator manufacturing process are discussed with reference to the manufacture of glass and porcelain insulation, and typical areas for concern are discussed with reference to insulators found to deviate from specification. Typical insulators were obtained from the manufacturers and utilities associated with the product, and were subjected to electrical, material and visual examination tests. The electrical tests included AC wet and dry, lightning impulse, clean fog, salt fog, mould release resiliency and the IEC 1109 voltage test. The material tests included the identification of the epoxide systems in use in the RSA, ultraviolet radiation aging simulation, water hydrolysis and salt deposit density tests. The main findings are: • CE insulation is sensitive to marine pollution and continuous-wetting pollution types. • The use of CE insulation is promoted in respect of inland and medium industrial pollution types. • Class B pin-type CE insulation is prone to partial discharge related failures. • Surface roughening on the insulator surfaces leads to reduced AC wet flashover voltages and increased pollution catch. Additionally: • A comprehensive aging hypothesis was developed detailing three independent aging stages/modes applying to CE insulation. • A hypothesis was developed for a new evaluation method for documenting changes on insulator surfaces due to the action of aging mechanisms: The Surface Area Index. / AFRIKAANSE OPSOMMING: Die aanwending van sikloalifatiese epoksied (SE) isolasie in die Republiek Van Suid Afrika word in hierdie skripsie ondersoek. Hierdie ondersoek is geloods op versoek van die elektrisiteitsbedryf om die toepaslike aanwending van die produk onder die verskeie heersende streeksweersomstandighede binne die RSA te evalueer. Breedvoerige navorsing is gedoen om die geskiedkundige oorsprong van die materiaal vas te stel, sowel as om die prestasie daarvan as insulasiemiddel te boekstaaf. Daar is veral gelet op die prestasie van die materiaal onder besoedelende omstandighede en ondervinding wat opgedoen is deur intemasionale ondememings. Die eienskappe van die automatiese drukjelvormings-vervaardigingsproses (APG) word behandel met verwysing na die maak van glas en porselein insulators. Tipiese probleemareas word bespreek van insulators wat afwyk van spesifikasie af. Verteenwoordigende isolators is vanaf vervaardigers en ondememings verkry wat met die produk bemoei is. Hulle is blootgestel aan elektriese, materiaal en visuele toetse. Die elektriese toetse het die volgende behels: nat en droog wisselstroom, skoon waterdamp, sout waterdamp en die IEe 1109 spanningstoets. Die effek van die verlies van die anti-kleefmiddel (gebruik tydens die gietproses) as gevolg van veroudering is ook in detail behandel. Die materiaaltoetse het ingesluit: die uitkenning van die epoksied stelsels in gebruik in die RSA, gesimuleerde veroudering deur ultravioletligbestraling, water hidroliese en soutlaag digtheids toetse. Die hoofbevindings is: • SE isolasie word bemvloed deur seelug besoedeling sowel as volgehoue benatting. Die gebruik van SE isolasie word voorgestel vir binnelandse gebruik sowel as in gebiede met mediumvlak nywerheidsbesoedeling. • Klas B pen-tipe SE isolasie is geneig tot deelontladings wat dan tot faling lei. • Oppervlakvergroffing lei tot In verminderde wisselstroom orvonksspanning onder nat toestande sowel as verhoogde vangs van besoedeling. Bykomend hiertoe is: • 'n breedvoerige SE verouderingshipotese ontwikkel wat drie onafhanklike stadia en modusse van die verouderingsproses uitgewys het. • 'n hipotese ontwikkel vir In nuwe evaluasiemetode om die verandering in die isolatoroppervlak as gevolg van veroudering te dokumenteer: Oppervlakte- Area Indeks (SAl).

Thesis (MScEng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: This project relates to the unexplained failure of 33kV porcelain line post insulators in ESKOM's Southern Region. An initial investigation suggested that the failures could probably be due to a combination of internal manufacturing flaws and the effects of lightning. The failures all occurred in insulators based on a new design that uses a metal spindle for mechanical attachment to a power line structure embedded in the insulator base. This thesis investigates the non-destructive detection of internal flaws in porcelain line post insulators. The research was structured as follows: • The examination of the manufacturing process and materials used to determine the cause, location and nature of internal flaws. • An electrical field simulation study to verify whether a void in the sulphur cement will experience discharge activity when exposed to systeni nominal voltage or lightning potential. • The identification of non-destructive techniques (NDT) that are potentially viable for determining the presence of insulator internal flaws. • The design of NDT experiments for X-ray, partial discharge (PD) detection and ultrasonic testing. These experiments were evaluated for their effectiveness in determining the presence of internal flaws and their usefulness as a quality control measure in the insulator manufacturing process. The main findings are: The major cause of insulator internal flaws is the fast setting sulphur cement used for cementing the metal spindle (mechanical attachment) to the porcelain body of the insulator. The field simulation study shows that a discharge in a 3mm diameter spherical void on the insulator's axis of symmetry will occur if the insulator is exposed to lightning potential. High energy X-raying is an effective technique for exposing the location, nature, size and number of flaws in the insulator, but is impractical due to the high Xraying cost and over-utilisation of the only high energy X-ray facility in the RSA. The PD experiment was effective in revealing the presence of internal flaws, but the location, nature, size and number of flaws cannot be determined. The experiment is time consuming and is therefore not suitable for quality control in the insulator manufacturing process. A preliminary investigation into the suitability of ultrasonic testing techniques encountered major technical difficulties. Further investigation into the use of ultrasonic 3D imaging techniques is recommended. / AFRIKAANSE OPSOMMING: Hierdie projek hou verband met die onverklaarbare faling van 33kV porselein staaftipe isolators in ESKOM se Suidelike Streek. 'n Aanvanklike ondersoek het daarop gedui dat die falings veroorsaak is deur 'n kombinasie van interne vervaardigingsfoute en die effek van weerlig. Die falings het almal plaasgeving op isolators waarvan die vashegtingsbout direk in die porselein versink is. Die doel van hierdie navorsingsprojek is om nie-vernietigende toetsmetodes (NVT) te ondersoek, teneinde interne foute in die tipe isolators op te spoor. Die tesis is soos volg gestruktureer: • Die ondersoek van die vervaardigingsproses en die materiale wat gebruik word, ten einde die oorsaak, posisie en aard van hierdie foute vas te stel. • 'n Simulasie van die elektriese veld om vas te stelof 'n holte in die swaelsement ontladings salondervind onder die invloed van nominale spanning en weerlig. • Die indentifisering van nie-vernietignde toetsmetodes wat gebruik kan word om die teenwoordigheid van interne foute te bepaal. • Die ontwerp van NVT eksperimente vir X-straal, gedeeltelike ontlading ("PD") deteksie en ultrasoniese toetsing. Hierdie eksperimente is geëvalueer om hul effektiwiteit om die teenwoordigheid van interne foute vas te stel, asook hul nuttigheid as 'n kwaliteitsbeheermaatreël in die iso latorvervaardigingsproses. Die hoofbevindinge is: Die hoofoorsaak van die interne foute is die vinnig-stollende swael-sement wat gebruik word om die metaalinsetsel aan die porselein te heg. Die veldsimulasies het getoon dat 'n ontlading in 'n 3mm sferiese holte op die isolator se simmetrie-as sal plaasvind as die isolator aan weerligpotensiaal onderwerp word. Hoë-energie-X-strale is 'n effektiewe tegniek om die posisie, aard, grootte en aantal foute in die isolator vas te stel. Dit is egter onprakties as gevolg van die hoë koste en oorbenutting van die enigste hoë-energie-X-straal-fasiliteit in die RSA. Die ontladingsdeteksie eksperiment was effektief om die teenwoordigheid van interne foute aan te dui, maar die posisie, aard; grootte en getal foute kan nie bepaal word nie. Die eksperiment is tydrowend en is daarom nie geskik vir kwaliteitsbeheer van die isolatorvervaardigingsproses nie. 'n Voorlopige ondersoek na die geskiktheid van ultrasoniese toetsmetodes het groot tegniese stuikelblokke opgelewer. Verdere ondersoek van die gebruik van ultrasoniese 3D-beeldtegnieke word aanbeveel.

M.Ing. (Electrical and Electronic Engineering) / Dissolved Gas-in-oil analysis (DGA) is used to monitor the condition of bushings on large power transformers. There are different techniques used in determining the conditions from the data collected, but in this work the Artificial Intelligence techniques are investigated. This work investigates which gases in DGA are related to each other and which ones are important for making decisions. When the related and crucial gases are determined, the other gases are discarded thereby reducing the number of attributes in DGA. Hence a further investigation is done to see how these new datasets influence the performance of the classifiers used to classify the DGA of full attributes. The classifiers used in these experiments were Backpropagation Neural Networks (BPNN) and Support Vector Machines (SVM) whereas the Principal Component Analysis (PCA), Rough Set (RS), Incremental Granular Ranking (GR++) and Decision Trees (DT) were used to reduce the attributes of the dataset. The parameters used when training the BPNN and SVM classifiers are kept fixed to create a controlled test environment when investigating the effects of reducing the number of gases. This work further introduced a new classifier that can handle high dimension dataset and noisy dataset, Rough Neural Network (RNN). This classifier was tested when trained using the full dataset and how it is affected by reducing the number of gases used to train it. The results in these experiments showed that ethane and total combustible gases attributes are core attributes chosen by the four algorithms as gases needed for decision making. The average results of the classification performance showed that the reduction of attributes helps improve the performance of classifiers. Hence the science of transformer condition monitoring can be derived from studying the relations and patterns created by the different gases attributes in DGA. This statement is supported by the classification improvements where the RNN classifier had 99.7% classification accuracy when trained using the three attributes determined by the PCA.

No description available.