Dielectric characteristics comparison of insulating babaçu's grain vegetable oil and transformers mineral oil
Insulating mineral oils have been used for more than a century as an insulating and cooler medium in electrical equipment. Its consolidation as the most used insulating fluid in the world is due to good insulation and cooling capacities. In addition, it has physical-chemical properties that guarantee the chemical compatibility with other materials present in the equipment. Moreover, it is widely available and low cost when compared to other insulating oils, such as silicone oils and synthetic esters. The mineral oils are derived from petroleum, therefore it has characteristics such as low flash point and poor biodegradation rate. These characteristics can origin safety problems and serious environmental damage, such as explosions and contamination of groundwater. In addition, the fact that petroleum is a non-renewable resource justifies the search for alternatives to insulating mineral oils that are renewable and biodegradable and have similar or superior properties than mineral oils. Vegetable oils are strong candidates for substitute mineral oils as insulating medium. They meet dielectric requirements and are highly biodegradable and renewable due to their production process from vegetable grains. However, there are studies for the development of vegetable oils from different base oilseeds, such as dendê, andiroba, rice, and others. The studies aim to produce oils that meet the specifications of an insulating fluid, as well as reduce the cost of vegetable oils and explore the biodiversity of grains in several regions of the world. The objective of this paper is to evaluate the dielectric stiffness of the vegetable oil made of babaçu’s grains (Orbignya Phalerata), present mainly in the Brazilian Northeast, and a conventional mineral oil through laboratory tests performed according to the standards established by IEC 60156. The experiments were made using an oil analyser for both oils under two different conditions: before and after laboratory treatment. The treatment consists in the use of a hot air oven and a compressor in order to reduce the presence of moisture and gases, respectively, contained in the oil. The presence of these factors results in the reduction of the oils dielectric strength, as verified during the execution of the experiments. The final dielectric strength obtained for babaçu oil presented a result close to that obtained by mineral oil and higher than the minimum limit established by ABNT NBR 15422 for new insulation vegetable oils. This result encourages other tests required by the standard, such as neutralization index, dielectric loss factor, flash points and fluidity. These tests must be performed to prove the applicability of babaçu oil as an insulating fluid for transformers. Concerning the test performed on the samples before treatment, the vegetable oil had an average dielectric strength higher than the value found for the mineral oil.
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