What is the difference between oil immersed and dry transformers?
Transformers are indispensable core components in power systems, performing critical functions such as voltage transformation, power distribution, and electricity transmission. Among the various types of transformers, Dry-Type Transformers and oil-immersed transformers stand out as two mainstream choices in power engineering design, distinguished by their structural characteristics and application scenarios. This article provides a comprehensive comparison of these two transformers across eight dimensions: construction principles, material composition, working mechanisms, performance characteristics, application fields, maintenance costs, safety and environmental considerations, and future development trends. The aim is to offer selection guidance and technical insights for professionals in related fields.
Dry-type transformers and oil-immersed transformers differ fundamentally in their physical structures, which directly influence their performance and applications. Dry-type transformers adopt an open or enclosed structure, with their cores and windings either exposed to air or encapsulated using solid insulating materials such as epoxy resin. This design gives dry-type transformers a relatively compact appearance, allows direct observation of their internal coil structure, and results in a volume that is typically 30%–40% smaller than oil-immersed transformers of the same capacity. The windings of dry-type transformers are usually made of copper or aluminum conductors, wrapped with high-grade insulating materials like epoxy resin or Nomex paper. Their protection rating is generally IP20, but this can be upgraded to IP54 by adding enclosures to accommodate humid or dusty environments.
The structure of oil-immersed transformers is notably different, characterized by an oil-tank system that serves as both protection and cooling medium. In these transformers, the core and windings are completely immersed in a sealed tank filled with transformer oil, making internal components invisible from the outside. Oil-immersed transformers have a more complex structure, incorporating auxiliary components such as an oil conservator (oil tank), pressure relief valve, oil level gauge, and radiators, in addition to the core and windings. The oil conservator adjusts for volume changes in the oil due to temperature fluctuations, while the pressure valve provides a safety release in case of excessive internal pressure. These additional features contribute to the larger overall size and significantly greater weight of oil-immersed transformers.
The two Transformer Types also differ markedly in lead design. Dry-type transformers predominantly use silicone rubber bushings as interfaces for high- and low-voltage leads. This material offers excellent insulation properties, mechanical strength, and seismic resistance, making it suitable for indoor installations. In contrast, oil-immersed transformers typically employ porcelain bushings as lead insulating devices. Porcelain materials better withstand the chemical effects of transformer oil and maintain stable surface insulation performance under atmospheric pollution conditions, making them particularly suitable for outdoor installations.
In terms of installation methods, dry-type transformers, with their compact structure and lighter weight, allow for versatile installation options. These include side-by-side placement with low-voltage distribution cabinets, wall-mounted installation, or even suspended mounting, significantly optimizing space utilization in distribution rooms. Oil-immersed transformers, due to their larger size, heavier weight, and requirement for an oil system, typically necessitate dedicated transformer rooms or outdoor platforms. They also demand higher load-bearing capacity for foundations, imposing greater limitations on installation flexibility.