A state-of-the-art review on green nanofluids for transformer insulation.

• Vegetable insulating liquids are potential alternative to mineral insulating oil. • Application of nanoparticles enhances the properties of vegetable insulating liquid. • The utmost problem of nanofluids is long-term stability. • Enhancing nanofluid stability through steric and electrostatic approaches. • Physicochemical and dielectric properties of nanofluid from different nanoparticles. The utilization of nanotechnology to enhance the properties of liquids has been underway for several decades. The systematic incorporation of nanoparticles into the base liquids has demonstrated its effectiveness in improving the thermoelectrical properties of insulating liquids. Vegetable-based liquids have emerged as potential alternatives to mineral-insulating oil due to the environmental concerns associated with the latter, despite their excellent electrical properties. Despite the environmental friendliness and health safety attributes of vegetable-based liquids, there are yet some limitations like low ionization resistance, high dielectric losses, low volume resistivity, and poor oxidation stability. These limitations are currently being addressed using different nanoparticles by the addition of an appropriate concentration to the base liquids. Though there is development in the synthesis of nanofluids using different nanoparticles for transformer insulation, no nanoparticle has been declared as one with ultimate performance. This review presents a comprehensive examination of recent findings in the literature concerning the use of nanofluids for transformer insulation, focusing specifically on the challenge of long-term stability. The review addresses various aspects including the characterization of nanoparticles, types of nanoparticles employed for enhancing insulating liquids, methods for preparing nanofluids, strategies for improving nanofluid stability, the impact of nanoparticles on vegetable-based insulating liquids, and the existing challenges associated with nanofluids. The report investigates these topics extensively, presenting a thorough analysis of the subject matter. It aims to provide valuable insights to researchers in this field and to encourage the exploration of sustainable and environmentally friendly insulating liquids suitable for green transformers. [ABSTRACT FROM AUTHOR]