HD 397 S1:1979

Interpretation of the analysis of gases in transformers and other oil-filled electrical equipment in service

Electrical discharges or thermal stresses in the oil or solid insulation, for example paper pressboard etc, of an oil-filled transformer cause degradation of these materials with the formation of gases of various types - To some extent these gases dissolve in the oil but using techniques described in IEC Publication 567, Guide for the Sampling of Gases and of Oil from Oil-filled Electrical Equipment and for the Analysis of Free and Dissolved Gases, they may be removed from a sample of the oil and analyzed quantitatively by gas chromatography - This standard describes how the concentrations of dissolved gases or of free gases may be interpreted to diagnose the condition of a transformer in service and suggest future action - The methods of interpretation have been developed for power transformers wound with copper conductors insulated with cellulosic paper or pressboard-base solid insulation and filled with hydrocarbon mineral oil in service on power networks; until further experience has been gained, the methods should be applied with caution in relation to other materials - The methods may also apply in principle to instrument transformers oil-filled cables, switchgear, etc. but insufficient experience is available to formulate suitable interpretation and limits. In any case, the indication obtained must be viewed only as a guide, any resulting action must be undertaken with proper engineering judgement