Study of the Dielectric Properties of Castor Oil as an Electrical Insulating Medium

Castor oil, produced extensively in Kano and Jigawa states in North West Nigeria, has attracted interest as a biodegradable alternative to mineral oil for use in electrical power transformers and high-voltage cable insulation systems. The dielectric properties of an insulating liquid, including relative permittivity, dielectric loss tangent, and breakdown voltage, determine its performance and safety margin in high-voltage applications. This study characterises the dielectric properties of commercially refined castor oil samples obtained from processors in Kano State. Relative permittivity and loss tangent are measured from 50 Hz to 100 kHz using an LCR bridge and parallel plate capacitor cell at temperatures of 25, 40, and 60 degrees Celsius. Dielectric breakdown voltage is determined using the ASTM D1816 sphere-plate electrode method at 2.5 mm electrode gap. Results indicate that castor oil exhibits a relative permittivity of 4.23 at 50 Hz and 25 degrees Celsius, with a dissipation factor of 0.0013. The breakdown voltage of 42.3 kV per mm exceeds the IEC 60156 minimum requirement of 30 kV per mm for new insulating oil. Thermal ageing at 80 degrees Celsius for 72 hours causes a 23 percent reduction in breakdown voltage. The findings support further investigation of castor oil as a locally sourced transformer insulating medium for Nigeria's power sector. Keywords: dielectric properties, castor oil, insulating oil, breakdown voltage, transformer