Dielectric properties of coconut oil impregnated pressboard samples

Coconut oil has been reported as a potential alternative for mineral oil when used as the power transformer liquid insulation. However, the information on dielectric properties of coconut oil impregnated transformer solid insulation i.e. paper and pressboard are still lacking. This paper presents variations of capacitance and dielectric losses of coconut oil and mineral oil impregnated pressboard samples during oven heating. First 24 pressboard samples having either 2% or 4% moisture contents were prepared. Then the samples were impregnated by coconut and mineral oil (half each) and the samples were dried inside two ovens over 800 hours at two different temperature (110 °C and 130 °C) levels. The dielectric properties were obtained by Frequency Domain Dielectric Spectroscopy (FDS) measurements. The results showed that in both coconut oil and mineral oil impregnated pressboard samples, capacitance and dielectric losses increased with heating time, temperature level and initial moisture content. Further the losses were relatively higher for coconut oil impregnated pressboard samples in comparison to mineral oil.