Proposta e avaliação de desempenho de um novo indicador para o diagnóstico do isolamento de cabos elétricos subterrâneos

Abstract

The search for electrical supplies, which offer quality, safety and reliability, is a challenging question that is still ever relevant in actuality. It is within this scenario that one finds the question surrounding non-programmed discontinuities, which are in themselves due to failures in numerous electrical devices encountered on the market today, within which isolated electric cables can be found. With the focus on such components, as it is recognized that they are in greater part responsible for the untimely interruptions that occur in installations, this thesis aligns itself towards the investigation with the view of establishing strategies and mechanisms, which in a predictive manner are capable of indicating the state of degradation present in a cable s isolation. Regarding the nature of the phenomena that may affect the useful working life of these components the authors emphasize the manifestations of socalled water- trees, which can cause damage to the dielectric material and as a result therefore cause the interruption of the electricity supply. It is within this context that the present thesis proposes the exploration of a technique for the analysis of such water-tree phenomena, which is aimed at extracting a new indicator concerning the operational status of the cables. Such a performance parameter is denominated as the non-linear coefficient and in line with the concept of such a magnitude, expresses the degree of correspondence between the voltages and leakage currents determined for a given stretch of cable. The underlying foundation of the proposition rests on the idea that such variables, under the action of the type of degradation in focus, characterize a nonlinear element.