A Comprehensive Review on Recent Advances in Insulation Materials and Pressboard Technologies for Power Transformers

Power transformers are essential components of electrical transmission and distribution networks and their long-term reliability depends extensively on the performance of their insulating systems. Mineral oil and cellulose-based paper have always served as the primary liquid and solid insulating materials. However, the rising need for greater efficiency, environmental compliance and operational safety has motivated thorough research into innovative insulation solutions. This review article summarizes research achievements from 2021 to 2025 focused on liquid and solid dielectric innovations for power transformer applications. Significant advances have been made in the field of liquid insulation using natural and synthetic esters, nanofluids and bio-based oils. Compared to traditional mineral oils, these materials provide higher biodegradability, increased fire safety, more dielectric strength and superior thermal conductivity. Innovations in solid insulating materials such as cellulose nanocomposites, aramid-infused pressboards and biomaterials infused with polymers are reviewed highlighting improvements in mechanical strength, moisture resistance and thermal durability. It also focuses on diagnostic approaches, predictive maintenance and testing methodologies. The study emphasizes the role of nanoparticles and environmentally suitable replacements in power transformer insulating systems. Improved material compatibility, greater modeling of flashover behavior, and uniform test protocols are also recommended.