Ivanka Atanasova-Höhlein

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.

Interpretation of carbon monoxide formation in liquid impregnated equipment

Carbon monoxide concentrations higher than reference values in international standards have been observed in fault free equipment in service. Since carbon oxides are being commonly considered as degradation products of solid insulation, it is important to find the source of these gases. In a number of cases it seems that it could be due to a higher oil oxidation rate due to moderate, however, continuous bulk oil temperature. Laboratory tests bring evidence that insulating fluids tend to produce higher amounts of carbon monoxide and sometimes also further hydrocarbon compounds (the so called stray gassing), especially under the catalytic influence of copper. Also degradation of passivator in oxidized oils may lead along further gases also to a higher amount of carbon monoxide. Field examples, as well as laboratory verification of carbon monoxide evolution at different temperatures and insulating liquids is presented.

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.