Stray gassing cases of insulating liquids in HV equipment

The phenomenon of fault gas generation out of insulating fluids at moderate temperatures, based solely on their constituents and not related to an equipment failure is described with the term “stray gassing“. Stray gassing is not a new phenomenon, but it seems to be stronger manifested with modern mineral oils. Also the use of some additives, mainly passivators may accelerate strongly the stray gassing production. This paper is a short overview on testing possibilities for stray gassing and suggestion for the influencing factors, typical stray gas patterns in mineral oil, as well as in further insulating liquids like synthetic or natural esters under various temperature conditions, examples of possible interference of the stray gassing pattern with fault and possibilities to distinguish between them, and some experiences in preventing stray gassing.