Ageing and Dissolved Gas Assessments of Rice Bran Oil and Palm oil for Power Transformer Application

Natural ester insulating oils (NEO) have high fire points and excellent biodegradable characteristics. As a result, there is an increasing demand for NEO as transformer insulating oils. Among the promising NEOs are Palm Oil (PO) and Rice Bran Oil (RBO). Since the failure of in-service transformers could be costly, it is essential to understand the oil characteristics; this can be carried out through accelerated thermal ageing study. The ageing characteristics of Mineral oil (MO) knowledge is well established as it has been researched extensively. On the other hand, the ageing studies on NEOs are currently ongoing. According to the findings of these studies, the ageing characteristics and compositions of the NEO were slightly different compared to conventional MO. Thus, there are differences in the variety and proportion of gas production during ageing and fault conditions especially PO and RBO. In this thesis, the ageing behaviour of presence and absence of Kraft paper insulation in MO, PO, and RBO and as well as DGA were investigated. All physicochemical, mechanical, dielectric, and electrical properties were measured at different ageing times of 2, 30, 90, and 180 days and temperatures of 90°C, 110°C, and 130°C. For DGA study, the simulated thermal fault and electrical fault were studied, and the sample of gasses produced due to the faults were taken and analysed. Based on the results, the moisture content in RBO impregnated paper is lower than in MO, which slower the paper ageing in RBO. Moisture content in oil, vegetable-based oils have higher values because they can absorb more moisture from the paper by the effect of hydrolysis. The acid value of PO and RBO are bigger than mineral oil because the triglyceride molecule in the vegetable oil is easy to hydrolyse to produce a large amount of high molecular acid. Relative permittivity and dielectric dissipation factor (DDF) for PO and RBO were higher (1.59 and 2.02) compared to the MO. The higher DDF value of PO and RBO is due to the molecular structure which has a slightly more polar character compared to MO. The RBO has the highest resistivity compared to PO and MO and this is reflected well with the result of the AC breakdown voltages. For DGA study, it could be identified that the main fault gases of thermal fault for PO and RBO are CH4, C2H4, C2H6, H2 and C2H6. The DGA analysis for both faults for NEO might be inaccurate due to different interpretation. Therefore, for PO and RBO, the DGA analysis needs further improvement before it can be used as transformer oil.