Transformer oil is commonly used in electrical insulation, cooling and lubrication of sliding components. There are many factors that negatively affect the electrical insulation properties of power transformers in its operation. Due to the increasing need to replace the petroleum-based mineral oil, there is an interest in replacing the oil with biodegradable vegetativebased oil. The properties of alternative oils that can be used to replace the existing mineral oil are described. Firstly, the vegetable oil was analyzed using computational simulation to investigate the dielectric characteristic and compared to the existing mineral oil. Then, a comparative experimental study concerning the ageing of vegetative-based oil, namely palm fatty acid ester (PFAE) and FR3 by comparing them with the commercially available mineral oil was conducted. Several important properties such as breakdown voltage, the dielectric dissipation factor (tan δ) and the capacitance of PFAE and FR3 oils have been measured. Varying ageing time have been applied during experimental process. Based on the experimental results, both oils show higher breakdown voltage compared to the mineral oil. In addition, both of the vegetative-based oils have lower value of dielectric dissipation factor and higher value of capacitance. Therefore, both oils are good insulating oils for transformer applications.

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The world's energy requirement has been dominated by petroleum-based oil for centuries in many application fields, including transportation, household, and electricity. Mineral oil as one of petroleum-based product; an important insulating material in power system has been used more than 150 years. Mineral oil application in power system equipment can be potentially hazardous to the environment especially when there are any incidents during operational time like transformer explosion, which may cause a spill of oil to the soil or water stream. Due to the concerns about the reducing petroleum resources and the environmental issues, the alternative insulating oil with biodegradable characteristics has been attracted lots of attentions for a couple of decades. The purpose of this research work is to investigate the partial discharge characteristics of palm-based oil, namely palm fatty acid ester (PFAE) as biodegradable oil for power transformer oil application. The characteristics then compared to other biodegradable oil, namely soybean-based oil and commercially available mineral oil for further analysis. The effect of electrical stress and ageing time on the oil samples were performed in this work. The results revealed that the partial discharge characteristics of PFAE are similar with commercially mineral oil. Particularly, PD magnitudes of PFAE are slightly lower than those of mineral oil samples during the ageing time. Therefore, PFAE has a good potential to be used as power transformer oil in electrical power system application.Keyword-partial discharge characteristics; alternative insulating oil; biodegradable oil; palm-based oil; mineral oil; power transformer oil.

This paper describes the properties of refined, bleached, deodorized palm oil (RBDPO) as having the potential to be used as insulating liquid. There are several important properties such as electrical breakdown, dielectric dissipation factor, specific gravity, flash point, viscosity and pour point of RBDPO that was measured and compared to commercial mineral oil which is largely in current use as insulating liquid in power transformers. Experimental results of the electrical properties revealed that the average breakdown voltage of the RBDPO sample, without the addition of water at room temperature, is 13.368 kV. The result also revealed that due to effect of water, the breakdown voltage is lower than that of commercial mineral oil (Hyrax). However, the flash point and the pour point of RBDPO is very high compared to mineral oil thus giving it advantageous possibility to be used safely as insulating liquid. The results showed that RBDPO is greatly influenced by water, causing the breakdown voltage to decrease and the dissipation factor to increase; this is attributable to the high amounts of dissolved water.