| The energy market faces great challenges derived from de-regulation process in North America. Operators are encouraged to minimize costs of operation while still keeping high indices of reliability and safety. Therefore, it is paramount for electrical operators to identify the best available tools to monitor and/or diagnose the condition of High-Voltage serial components within the electrical infrastructure, whether related to generation, transmission, or distribution of electrical energy.;Among High-Voltage serial components, High and Medium Voltage Current Transformers are seemingly simple electrical devices used for measurement and protection of other major electrical equipment and systems although their own protection has been disregarded so far. There is a growing interest in these components because their failure caused by electro-thermal breakdown of the high-voltage insulation may result in explosions whose intensity can damage nearby electrical apparatus, contaminate the surrounding soil, and cause serious injuries to on-site personnel.;This research work specifically investigates the ageing characteristics of Medium Voltage Oil-Immersed Current Transformers of the measurement type typically used in substations and proposes the use of thermal accelerated aging techniques by means of non-typical load profiles above rated specifications to age the combined insulation system and trace this aging process through state-of-the-art testing methods, capable of identifying changes in the physical, chemical, and dielectric properties of liquid and solid insulation.;The project started with the consideration of all factors involved in the aging process of the combined insulation. In this process, Pyrolysis was found to be the main one, which led the project into setting-up an experiment to replicate the thermal effect on the insulation system. A variety of sensors were strategically embedded in the Current Transformer to provide online information of the temperature variations on the transformer's hottest-spot within the insulation system. The thermal behavior turned out to be different for each type of Current Transformer, therefore, each type was independently modeled and its characteristics laid out.;Later on the research moved onto tracking the aging process and building the aging model by using electrical DC and AC techniques, dissolved in oil gas analysis, furanic compound concentration, and degree of polymerization. In particular, results showed the relevance of the furanic concentration for determining the life of the Current Transformer.;The final stage involved comparing the obtained values with previously published data and models. The results provided new models which, depending on the construction of the Current Transformer, can be used to estimate the age of the unit. The analysis of data determined that normal insulation life of Medium Voltage Oil-Immersed Current Transformers can go beyond standard limits to up to approximately 200,000 hours under a thermal acceleration factor equal to one. |
