Understanding the Ageing Performance of Alternative Dielectric Fluids

Mineral oil has traditionally been used as a cooling fluid in power transformers, but its low biodegradability and fire point have motivated the search of alternatives. In this work, six different dielectric fluids studied, including four vegetable liquids, from sunflower, rapeseed, soybean, palm, one synthetic ester mineral for comparison. These oils were subjected to an accelerated thermal ageing glass vessels at 150°C weeks (672 hours) presence Kraft insulating paper. Different parameters measured during ageing, i.e. breakdown voltage, dissipation factor, permittivity, DC resistivity, density, kinematic viscosity, flash points, interfacial tension, acidity, dissolved gases; additionally, degree polymerisation (DP) paper was measured. Results showed that changes natural esters properties, except palm oil, similar along time. Palm results those whereas behaviour esters. The kraft degradation higher followed by oil. No significant differences found with