Aging markers for in-service natural ester-based insulating fluids

In this work, the degradation process of natural ester-based insulating fluids was evaluated through laboratory aging tests. Two distinct aging methodologies were used: natural ester-based insulating fluids were placed in sealed flasks at 120°C in the presence of Kraft insulating paper containing about 1.5 and 5 wt% moisture; and natural ester-based insulating fluids were aged with and without Kraft insulating paper containing 1.5 wt% moisture in an open system, adding oxygen at different temperatures. The results indicate that viscosity, acid number and dissipation factor are important markers to consider in monitoring service-aged natural ester fluids.