Influences of moisture content on insulation properties of vegetable insulating oil

Due to the fact that saturated moisture content of vegetable insulating oil is greater than that of mineral insulating oil, it is necessary to investigate the characteristics of moisture influencing the insulation properties of vegetable insulating oil. We analyzed the influence of moisture content in a refined rapeseed insulating oil on breakdown voltage of the oil, measured the relative permittivity and dissipation factor of the rapeseed insulating oil with various moisture contents by using a dielectric spectrometer, analyzed the characteristic of the two parameters versus frequency, and tested the volume resistivity of the rapeseed insulating oil specimens according to relevant standards. Measurement results show that the breakdown voltage of vegetable insulating oil are higher than that of insulating mineral oil at the same relative moisture content. With the increase of moisture content, the breakdown voltage of insulating vegetable oil declines more slowly than that of insulating mineral oil. The absolute moisture content of insulating vegetable oil is higher at the same relative moisture content, indicating that it has slight influences on breakdown voltage of vegetable insulating oil. When the relative moisture content is lower than 50%, the insulation properties of the rapeseed insulating oil are little affected. When the relative moisture content exceeds the saturated moisture content of the oil, the insulation properties of the rapeseed insulating oil are remarkably affected.