Regeneration of Spent Transformer Oil Using Bentonite Clay and Palm Kernel Shell

Abstract

The reliable operation of power transformers is critically dependent on the quality of insulating oil, which degrades over time due to thermal, electrical, and chemical stresses. This study explores an innovative, sustainable approach using bentonite clay and palm kernel shell-activated carbon (PKS-AC) for regenerating spent transformer oil. The adsorbents were chemically activated at 7N sulfuric acid concentrations and characterized using FTIR, SEM, and physico-chemical analyses. Regeneration experiments were carried out using a transformer oil-to-palm kernel shell-to-bentonite base ratio of 30:3.4:3.8 (mL/g/g), at a temperature of 77 °C, for 77 minutes, with continuous stirring at 744 rpm. Density decreased from 0.975 to 0.8342 g/cm³, kinematic viscosity from 18.3 to 10.34 mm²/s, acidity from 0.821 mg KOH/g to 0.003 mg KOH/g, and water content from 35.42 ppm to 10.254 ppm, while the breakdown voltage increased from 10 to 60 kV, flash point from 144 °C to 150 °C and fire point from 156 °C to 160 °C. The regenerated oil met standard acceptable limits, with significant improvements in the transformer oil properties. These findings indicate successful restoration of dielectric strength and thermal stability of transformer oil.  Based on the result obtained, bentonite and palm kernel shell are veritable adsorbents for regeneration of used transformer oil, thus contributing to sustainable energy practices.