Dissolved gas analysis of a thermally overloaded oil-immersed current transformer

Sophisticated monitoring technologies have emerged to provide technical and analytical support to the condition assessment and diagnosis of high voltage electrical apparatus. As these technologies are being improved, on-line monitoring systems have a special role to prevent failure of major components of the electrical system. The behavior of evolving gases and their critical values have been published in the relevant international standards (IEEE C57.104-1991 and IEC 60599-1999). In this paper, authors address the analysis of the dissolved in oil gases in an oil-immersed 69kV 1200/600:5 current transformer (CT) that was put under thermal accelerated ageing stress. An on-line monitoring system is adapted to the CT and the data is evaluated under standard diagnostic techniques. A correlation between a dynamic gas evolution in the oil and the estimation of Loss-of-life of the CT has been attempted. Results of a constant load up to 3 times the rated value of the CT indicate a weak correlation between DGA and the life of the CT.