Abstract: China’s first fully domestic 110 kV transformer with aramid insulating paper and synthetic ester oil has been successfully commissioned. Catering to the trend of large capacity, compact design and high overload capacity for energy storage step-up transformers and data centre distribution transformers, North China Electric Power University has developed aluminium nitride (AlN)/boron nitride (BN) composite-modified high-thermal-conductivity aramid insulating paper. It effectively mitigates the winding hot-spot temperature rise issue caused by the poor thermal conductivity of conventional aramid paper and provides a high-temperature-resistant solid insulation solution for new-generation compact power transformers.

Following the successful commissioning of China’s first fully domestic 110 kV transformer adopting aramid insulating paper and synthetic ester oil, energy storage step-up transformers and data centre distribution transformers are evolving towards larger capacity, compact footprint and higher overload capability. Winding hot-spot temperature rise has become the core bottleneck limiting performance improvement of transformers.

Traditional meta-aramid insulating paper boasts favourable heat resistance yet low thermal conductivity. Under full-load operation, heat inside the windings cannot be dissipated quickly, which accelerates insulation ageing and restricts the short-time overload capability of the equipment.

The research team of North China Electric Power University has developed AlN/BN composite-modified aramid insulating paper. The team first performs surface modification on thermal conductive fillers to improve interfacial compatibility between fillers and the aramid matrix, then manufactures the composite insulating paper via the wet-laid process. The dielectric and thermal properties can be flexibly adjusted by changing the filler ratio:

• At an AlN‑BN ratio of 3:7, the breakdown strength reaches 186 kV/mm;
• At an AlN‑BN ratio of 7:3, the out‑of‑plane thermal conductivity is 213.6 % higher than that of pure aramid paper.

This new composite insulation material can effectively reduce winding hot‑spot temperature, improve short‑term overload capacity and extend the service life of the insulation system. It is compatible with eco‑friendly synthetic ester insulating oil.

This new material is currently at the laboratory sample stage. In the next phase, the team will carry out long‑term thermal ageing, oil immersion compatibility and other tests, as well as transformer prototype verification, to support the insulation system upgrade of new‑generation compact power transformers.

This R&D breakthrough offers a viable new approach for optimising the insulation system of large‑capacity transformers. Tianan’s R&D team continuously tracks cutting‑edge developments in insulating materials. Founded in 1969, Tianan has decades of experience in transformer R&D and manufacturing. Addressing the industry challenges of large capacity and high overload requirements for transformers for energy storage and data centres, we conduct continuous forward‑looking pre‑research. Focused on practical engineering implementation, we steadily promote the conversion and application of advanced material technologies in power equipment and meet industry demands with solid technical expertise.