Possibility of blending sesame oil with field aged mineral oil for transformer applications

Different vegetable oils have been proposed over the last few years as an alternative to the mineral oil used in transformer liquid insulation applications. Previous studies on coconut, sesame and castor oil revealed that physical, chemical as well as electrical properties of these oils needs improvements to be used as liquid insulation in transformers. This paper presents an investigation of electrical, chemical and physical properties of blends of treated sesame and field aged mineral oil to identify the required improvements to use these oils for refilling of mineral oil filled transformers. The tested properties were polarization & depolarization current, dc conductivity, breakdown voltage, viscosity, acidity and color. Result shows that the conductivity should be the most important property when mixing treated sesame oil with aged mineral oil. Conductivity was varied hugely from the acceptable limit after mixing. Hence treating should be more precise to control the conductivity to the limits.