Electro-insulating Paper Degradation in Various Electro-insulating Fluids

The durability and safe operation of electrical equipment and devices with mixed insulation systems (solid/fluid - electro-insulating paper/oil) is determined by the insulation aging under simultaneous and synergic actions of electrical, thermal and chemical stress factors etc. In this context, degradations of insulating paper exposed to thermal aging in 5 different types of electro-insulating fluid have been studied experimentally. Liquid chromatography determinations have shown that the total content in furan products (resulting from cellulose degradation) in mineral oils is substantially higher than in electro-insulating fluid sorts based on of synthetic ester and/or natural ester (vegetable oil). This is due to the temperature between 90 degrees C and 130 degrees C when the activation energy of the furans formation process is up to 7.5 times lower in mineral oils than in ester-based oils. Degree determinations of cellulose polymerization (viscosimetric method) before and after exposure to heat treatment indicated that mineral oils degrade the electro-insulating paper much more strongly than ester-based oils (both synthetic and natural). Obtained results by liquid chromatography and by viscosity are in accordance with the images obtained by optical microscopy (at X 100).