| Power transformers are the key components of electrical networks. Any failure or unexpected outage of these major asset scan cause damage in power system and lead to important financial losses. Their reliability is so important that they require special monitoring. The major faults inside the transformer can be related to the reduction in the insulation dielectric strength and in the mechanical and thermal integrities.;The main problem of the insulation system is the uncertainty of its reliability due to poorly understood mechanisms of aging and degradation under various stresses, including electrical, mechanical, environmental and thermal. Thus, a complete understanding of aging phenomena is essential to achieve a more reliable prediction of life expectancy and to develop more effective methods for monitoring insulation's conditions. An accurate assessment of the condition of any component of the electric network will help predicting the optimal replacement time.;The aim of this research project is to develop and evaluate procedures, techniques and diagnostic tools to assess the condition and remaining life of transformers approaching their end of life. For this purpose, various techniques have been used to study the deterioration and aging insulation, in order to identify the fundamental phenomena that are involved, and to establish the relationship between the degradation of insulation properties and aging byproducts.;The Canada Research Chair ISOLIME is equipped with diagnostic tools (electrical and physicochemical) at the leading edge of technology to perform tests according to international standards (ASTM and IEC...). In this research project, several types of equipment were used. Some of them helped in preparing samples and performing aging under different conditions; while others were used to assess different dielectric parameters and chemical and mechanical properties of the insulation samples.;The results of the evaluation of the insulation quality with the new techniques are shown in this thesis. Also, the assessment of these techniques and the methods of interpretations associated with it was made during the analysis of aging. Various aspects of aging were analyzed, such as comparison between the aging of mineral oils and esters, the influence of oxygen, etc.;Another part of the thesis aimed to build a 3D impedance network to simulate a mixture of dielectrics. Dielectric responses of mineral oil, ester oil impregnated pressboard were simulated. The results obtained from the measurement demonstrated the validity of the electric model. |
