A newly developed oil-impregnated densified wood material delivers record electrical insulation, superior heat management, and enhanced mechanical strength, potentially improving the reliability and lifespan of next-generation power transformers.
A new approach to power transformer insulation
Power transformers are indispensable components of modern electrical systems, performing critical functions related to voltage conversion, transmission efficiency, load distribution, and renewable energy integration.
These specialized devices form the backbone of power infrastructure, ensuring reliable and efficient electricity delivery to homes, businesses, and industries. Because they operate under extremely high voltages, they require highly effective insulation systems to prevent short circuits, fires, and catastrophic failures.
One of the most widely used insulating materials is oil-impregnated lignocellulosic paper. First developed in 1890, it remains popular due to its low cost and favorable physical properties. However, traditional Kraft paper has several limitations. It tends to retain heat rather than dissipate it, while its insulating performance is constrained by microscopic oil pockets that form within its internal structure.
Heat exposure also gradually degrades the cellulose fibers, reducing long-term durability. In addition, Kraft paper offers limited resistance to significant mechanical stress.
Several alternatives are already available, including synthetic papers based on aramid polymer fibers and dry-type transformers with windings fully encapsulated in epoxy resin. Yet a multidisciplinary team of researchers in the United States sought to improve insulation performance while continuing to rely on renewable raw materials.
Oil-impregnated densified wood
Instead of conventional cellulose paper, the researchers started with natural wood veneer. The material was chemically treated to remove lignin and hemicellulose, then immersed in insulating oil and compressed to increase its density.
The resulting material was named oil-impregnated densified wood (ODW).
āDuring the densification process, the original micrometer-sized oil-filled channels shrink into isolated one-dimensional nanoscale channels,ā researchers at Yale University explained. āThese channels are separated by dense, highly aligned cellulose walls.ā
Record-breaking performance
Unlike conventional insulating paper, the engineered wood contains a continuous three-dimensional oil network that eliminates the issues associated with isolated oil pockets.
The technical performance is remarkable. ODW achieved a record dielectric strength of 105 kilovolts per millimeter, mechanical strength of up to 384 megapascals, and thermal conductivity of 0.33 watts per meter-kelvin. The material also demonstrated greater durability during accelerated thermal aging tests conducted at 150Ā°C for six weeks.
In practical terms, the material combines strong electrical insulation with improved thermal management and structural robustness.
Researchers also built a planar transformer using ODW as the insulating enclosure. Under load conditions, the prototype operated at temperatures approximately 10Ā°C lower than a comparable transformer using conventional polymer-based insulation.
āAlthough this multidisciplinary research was motivated by the global need to improve transformers,ā said Robert Hebner, who coordinated the testing, āthe thermal, mechanical, and electrical properties of this unique material suggest potential benefits across a much broader range of applications.ā
Scalable production from renewable materials
An additional advantage of the technology is its manufacturing potential. The material can be produced using roll-to-roll processing and can be derived from multiple wood species, offering both scalability and material flexibility.
The study, āOil-impregnated densified wood veneer with high electrical insulation enabled by nanosized oil channels,ā was published in Science Advances in 2026 (DOI: 10.1126/sciadv.aed5744).
