Analysis of excessive hydrogen generation in transformers in service

Abstract

The paper concerns the case study of a group of oil power transformers in which, on the basis of the measurements of concentration of gases dissolved in oil, excessive generation of hydrogen was noticed. Analysis performed using the ratio method proposed by IEC 60599 standard, and the Duval triangle method, identified partial discharge (PD) generation in the transformer units considered. Deepened analysis indicated however that such a diagnosis may by false and excessive hydrogen generation is a result of stray gassing. Additional studies such as the measurements of partial discharge intensity using acoustic emission method as well as internal inspection and factory tests (including PD measurements using electrical method) of selected units seem to confirm this hypothesis. However, taking into account the recommendations described in CIGRE brochure 296, lack of compatibility of constructional materials with the oil used in the analyzed group of transformers is also probable. Finally, this may be concluded that assessment of the results of the DGA needs to be carried out carefully when an increase in the concentration of hydrogen in the transformers in service is observed. An unambiguous determination of the cause of the fault cannot be indicated only on the basis of basic analysis. Some other, more specific analyses and tests should be used.