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
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.Index Terms -Carbon monoxide, mineral oil, synthetic and natural esters, silicone fluids, catalytic influence of copper.
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