If you've worked on power grid, substation or industrial power projects, you must have noticed a clear pattern: nearly all main transmission transformers for 110kV, 220kV and 500kV grids are Oil Immersed Power Transformer, while dry type power transformer only show up in distribution levels below 35kV. Can we build Large Power Transformer with dry cast resin transformers for high-voltage main station use? The short answer is technically not feasible for ultra-high voltage heavy-capacity main transformers, and today we will explain the three core reasons in plain, easy-to-understand language.
Firstly, the biggest limitation of dry cast resin transformers lies in insulation performance under high voltage. Dry type power transformer uses solid epoxy resin as the only insulating material wrapping around windings. For voltages above 110kV, strong electric field stress will gradually break down epoxy resin over long-term operation. Even reinforced high-grade casting resin cannot hold stable dielectric strength for 220kV or 500kV transmission standards. In contrast, Oil Immersed Power Transformer relies on special insulating oil as a liquid dielectric medium. The oil fills every tiny gap between coils and insulation paper, effectively suppressing partial discharge and resisting high voltage breakdown. This liquid insulation system has proven stable for decades of continuous operation in all large-scale power transmission projects, making it the only reliable choice for Large Power Transformer at high voltage levels.
Secondly, cooling efficiency creates a huge gap between oil immersed units and dry type power transformer. Heat generated by Large Power Transformer during full load operation is massive, and cooling directly decides long-term service life and safety. Dry cast resin transformers only rely on external air fans to blow cold air through coil gaps for heat dissipation, which is forced air cooling. Air has very weak heat carrying capacity, so dry type designs cannot take away massive heat fast enough when power capacity goes high. Overheating will trigger temperature rise alarms, accelerate insulation aging and even lead to unexpected shutdowns. On the other hand, Oil Immersed Power Transformer uses internal oil circulation cooling. Hot oil around windings rises naturally, flows to external radiators to release heat, then cold oil sinks back to cool coils. Liquid oil transfers heat far more efficiently than air, supporting stable continuous running of Large Power Transformer under heavy load, overload and long-hour operation conditions. No fan upgrade can match the natural liquid cooling cycle of oil immersed transformers.
Thirdly, overall manufacturing and project cost makes dry type power transformer an uneconomical pick for large main transformers. Dry cast resin transformers require precise vacuum casting processes, high-purity epoxy raw materials and larger structural frames to leave enough air flow space. For the same power rating, a dry type transformer costs far more than an Oil Immersed Power Transformer. When it comes to Large Power Transformer with tens of thousands of kVA capacity, the price gap expands dramatically. Power grid companies and industrial investors prioritize cost control for main station equipment, so oil immersed models become the default cost-effective solution. Dry cast resin transformers only make financial sense for small and medium distribution loads under 35kV, such as indoor office buildings, hospitals, metro stations and data centers, where fire safety and zero oil leakage risks are mandatory requirements.
This does not mean dry type power transformer has no market value at all. As a professional transformer supplier, Zhejiang Jiangshan Hengli Electrical produces both Oil Immersed Power Transformer and custom dry cast resin transformers to cover different client scenarios. Our dry type power transformer series work perfectly for low-to-medium voltage indoor projects with strict fire protection rules, while our full range of Oil Immersed Power Transformer serves high-voltage substations, large power plants, mining zones and renewable energy transmission stations that need Large Power Transformer with stable high-voltage and high-load performance.
If you are looking for reliable transformer solutions for your power project, Zhejiang Jiangshan Hengli Electrical offers one-stop technical consultation, custom design and global delivery service for both oil immersed and dry type transformers. Send us your voltage, capacity and installation environment requirements, and our professional engineers will recommend the most suitable transformer type for your project.
