Online DGA – State of the Art and Influencing Parameters

For a holistic assessment of the condition of transformers, many factors and components have to be taken into account in connection with statistical failure properties. The analysis of gases dissolved in the insulating liquid represents an essential part of the condition assessment of transformers. However, not all influencing variables on the dissolved gas analysis (DGA) have been sufficiently researched yet. In particular, these are primarily the degassing of the transformers and the associated distortion of the basis of interpretation. Furthermore, the estimation of the criticality of a defect for the evaluation of the remaining service life is important.
In this paper, the online dissolved gas analysis (DGA) is reviewed and discussed in detail. Furthermore, results of laboratory tests with typical electrical and thermal defects in mineral oil (Nynas Nytro 4000A) are presented. Particular attention is paid to the parameters which influencing the degassing of transformer oil. In addition, experimental results regarding the gas formation of artificial electrical and thermal defects, the degassing behavior of various arrangements and their influencing parameters are shown.