D. Gassing behavior
The low viscosity ester composition shows like most
insulating natural ester fluids a stray gassing behavior which is
connected with the oxidation stability of the fluid and is
influenced by temperature. Transformer materials like copper
have an influence on the gassing. This is probably connected to
the formation and destruction of peroxides.
Hydrolysis and oxidation reactions on natural esters can
have a high impact in the development of carbon oxides.
Carbon monoxide is produced by both mineral oils and natural
esters mainly through thermal degradation of the insulating
liquid itself. Its concentration is strongly dependent on the fluid
temperature. In mineral oil insulated transformers, carbon
dioxide derives mainly from the cellulose insulation. On the
other side, natural ester liquids show a carbon dioxide
formation through thermal endurance which derives from the
insulating liquid itself.
The ester composition develops in comparison to mineral
oil high ethane concentrations. The presence of copper has an
inhibitory effect in the formation of ethane, probably because
of the interruption of chemical reactions that produce
peroxides. Ethane is more likely a product of the oxidation of
ω-3 unsaturated fatty acids and is close related to the oxidation
stability of the insulating liquid. Thus ethane can be regarded
as a key-gas by the evaluation of the Dissolved-Gas-Analysis
of natural ester liquids. [2]