This study uses natural fibre, which is moisture absorbent, as an innovative and economical filler for insulating oil. Rice husk (RH) is a natural fibre known to have water-absorbing properties and used as a supplementary cementitious material. This research utilises the water-absorbing properties of RH to improve the physicochemical and dielectric properties of insulating oil. RH was refined into a fine powder at a diameter of less than 63 µm. Palm oil (PO) was synthesised with RH at concentrations of 0 g/L, 0.01 g/L, and 0.1 g/L. The moisture-absorbent properties of RH were analysed by using Fourier-transform infrared (FTIR) spectroscopy. The particle size and distribution of RH in PO were also obtained using a scanning electron microscope (SEM) and a Zeta particle analyser. The breakdown voltage (BDV) strength of PO with RH was measured according to IEC 60156, and the dielectric frequency response was investigated in the range of 102–105 Hz. RH is proven to absorb moisture from PO, as the O–H band intensity at the 3350 cm−1 is increased from the experimental results. Therefore, the mean BDV and dielectric insulation properties of PO dispersed with RH also increased accordingly.

This study aims to analyse the effect of natural fibres on the breakdown strength and stability of natural ester as liquid insulating material. Breakdown voltage test is performed to determine the breakdown strength of natural esters. In contrast, the stability of natural esters after the incorporation of natural fibre is determined by comparing the initial spectra of natural esters with the spectra of natural esters after several days. Natural ester used in this study is refined, bleached, deodorised palm oil (RBDPO). A natural fibre, rice husk, is used in the sieved form (63 microns) and is dispersed in palm oil. The breakdown voltage test is studied according to IEC 60156 using Megger OTS100AF oil tester. Then, the results are analysed by using Weibull statistical analysis. For the stability of samples, optical spectroscopy test is carried out by using UVVis spectrometer. The obtained spectra are compared with Day 1 and Day 8 of the samples to determine the filler dispersion stability in palm oil. As a result, the breakdown voltage of natural ester is improved when rice husk is added, which is expected due to the nature of rice husk as a moisture scavenger. The stability of natural esters decreased after a few days due to the agglomeration of fillers.

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