Straygassing of insulating liquids - Manifestation and influence on diagnostics

The phenomenon of fault gas generation out of insulating fluids at moderate temperatures, based solely on their constituent and not related to an equipment failure is described with the term “straygassing”. Straygassing is not a new phenomenon, but it seems to be stronger manifisted with modern mineral oils. Especially the use of some additives, mainly passivators may accelerate strongly the straygassing production. This paper is an overview on: the possible mechanism of straygassing; the typical stray gas formation of mineral oil, as well as of further insulating liquids like synthetic or natural esters under various temperature conditions; examples of possible interference of the straygassing pattern with diagnostics; how to distinguish straygassing from fault cases in the DGA evaluation.