Experimental investigation on breakdown performance of coconut oil for high voltage application

Abstract

• Dielectric breakdown performance of RBD and virgin coconut oil was studied as against standard natural ester. • After thermal aging, viscosity of coconut oil remained steady like the other natural ester. • No significant drop in AC or impulse breakdown voltage of RBD coconut oil due to thermal aging. • Most importantly, resistivity of RBD coconut oil did not decline rapidly with aging, unlike the standard natural ester. • Differences in the molecular structure in natural esters may be attributed to the differences in their dielectric strength. This paper investigates the electrical breakdown performance of coconut oil, viz. refined, bleached, and deodorized (RBD) and virgin grade. The primary objective is to determine whether they can perform equivalent to natural ester, e.g., MIDEL eN1215, commonly developed for transformers, so electric utilities can use coconut oil in tropical countries. Experimental results show that after aging in a sealed environment, the viscosity of coconut oil remained steady like the other natural ester. Most importantly, its resistivity (especially for RBD coconut oil) did not decline rapidly with aging, unlike the standard natural ester. Furthermore, it was demonstrated that thermal aging at 130°C, which is capable of lowering the AC breakdown strength in virgin coconut oil or MIDEL eN1215, did not result in a significant drop in the case of RBD coconut oil. Further, no measurable effect of oil moisture was detected upon the AC breakdown strength of RBD coconut oil. Overall, it is shown that RBD coconut oil is the most encouraging, whether subjected to AC or impulse voltage, as it shows the highest breakdown performance.