Propriedades físico-químicas e dielétricas de óleos vegetais para uso como isolante em transformadores.

Abstract

The vegetable oil has been shown as promising candidate for the insulating fluid for electrical equipment to replace the mineral oil, traditionally used, as an agricultural product and easy biodegradability. Enjoying the great potential in the Brazilian production of oil, for this study were selected five varieties of commercial origin of refined oils: soybean, maize, sunflower, babassu and cotton. Density tests were performed at 20°C, viscosity at 20, 40 and 100°C, the presence of sulfur compounds, breakdown voltage, loss factor at 100° C, thermal stability by thermogravimetry in atmosphere of nitrogen and oxidative stability by the aging under air flow at 110°C. It was found that the oils of soybean, maize, sunflower and cotton density and viscosity are higher than those of mineral oil, however pass in the test NBR 15422. The babassu oil paste is even a temperature of 25°C, however at temperatures of 40 and 100°C has better viscosity than the other. The five species evaluated had high water content and low levels of breakdown voltage for electrical isolation and, moreover, index of acidity than the limit set by the standard above. After neutralization was possible to establish values of acidity within the recommended. The neutralized oil showed improvement in breakdown voltage and loss factor when compared to the originals. Only corn oil neutralized presented recommended minimum breakdown voltage for use as insulation. The vegetable oils tested have adequate thermal stability for use in electrical transformers for presenting the decomposition temperature above 200°C, and the oils of corn and cotton showed, respectively, the best and worst thermal stability. For resistance to oxidation took place the following order of stability: cotton <soybean <maize <sunflower <babassu.The vegetable oil has been shown as promising candidate for the insulating fluid for electrical equipment to replace the mineral oil, traditionally used, as an agricultural product and easy biodegradability. Enjoying the great potential in the Brazilian production of oil, for this study were selected five varieties of commercial origin of refined oils: soybean, maize, sunflower, babassu and cotton. Density tests were performed at 20°C, viscosity at 20, 40 and 100°C, the presence of sulfur compounds, breakdown voltage, loss factor at 100° C, thermal stability by thermogravimetry in atmosphere of nitrogen and oxidative stability by the aging under air flow at 110°C. It was found that the oils of soybean, maize, sunflower and cotton density and viscosity are higher than those of mineral oil, however pass in the test NBR 15422. The babassu oil paste is even a temperature of 25°C, however at temperatures of 40 and 100°C has better viscosity than the other. The five species evaluated had high water content and low levels of breakdown voltage for electrical isolation and, moreover, index of acidity than the limit set by the standard above. After neutralization was possible to establish values of acidity within the recommended. The neutralized oil showed improvement in breakdown voltage and loss factor when compared to the originals. Only corn oil neutralized presented recommended minimum breakdown voltage for use as insulation. The vegetable oils tested have adequate thermal stability for use in electrical transformers for presenting the decomposition temperature above 200°C, and the oils of corn and cotton showed, respectively, the best and worst thermal stability. For resistance to oxidation took place the following order of stability: cotton <soybean <maize <sunflower <babassu.