Regeneration of Spent Transformer Oil Using Coconut Shell Derived Activated Carbon

Abstract

The reliability of power transformers depends on the insulating oil, which performs the critical dual role of dielectric medium and coolant. Degradation from thermal and oxidative stress produces harmful contaminants like acids and moisture which severely reduce the dielectric strength of the oil, thus necessitating sustainable regeneration to rejuvenate its functionality. The need for sustainable alternatives as adsorbent abounds because conventional adsorbents such as activated alumina are non-renewable and expensive. This study investigated the regeneration of spent transformer oil using activated carbon derived from coconut shells as a low-cost and eco-friendly adsorbent. The coconut shells were carbonized at 800 °C and chemically activated with 1 M sodium bicarbonate to enhance porosity and surface area. The degraded transformer oil was treated under controlled conditions, and its physicochemical properties including moisture content, viscosity, acid number, color, and dielectric breakdown voltage were analyzed before and after regeneration. The regeneration performance was assessed at varied temperatures of 60,80 and 100 ⁰C at constant time of 30 min. Also, regeneration performance was assessed at contact time of 45 and 60 min at a constant temperature of 80 ⁰C. The results revealed a significant improvement in oil quality: Acid number reduced from 4.21 mg KOH/g to 2.11 mg KOH/g (49.8 % performance recovery), viscosity decreased from 9.19 cP to 8.67 cP (5.66 % recovery) and dielectric breakdown voltage increased from 7.8 kV to 25.2 kV (223 % recovery). These findings confirm that coconut shell–based activated carbon effectively restores the properties of spent transformer oil, providing a sustainable, economical, and environme.