In power systems, oil-immersed and dry-type transformers are two widely used types of transformers. Due to differences in cooling medium and structural design, they exhibit significant differences in performance and applicable scenarios. Choosing between the two requires precise matching based on actual needs.
The most significant difference lies in their core cooling method. Oil-immersed transformers use transformer oil (mineral or synthetic) as their cooling medium. Heat generated during operation is absorbed by the oil, which is then naturally cooled through the tank walls or heat sinks. Some high-power models also incorporate fans and oil pumps for enhanced heat dissipation. Dry-type transformers, on the other hand, rely on air cooling. Natural air cooling dissipates heat through direct heat exchange between the core and windings and the air, while forced air cooling uses fans to accelerate air flow and improve heat dissipation efficiency. In terms of structural design, oil-immersed transformers require a sealed oil tank to hold the transformer oil, which is typically fitted with a heat sink (or heat pipe). This results in a larger and heavier overall size and weight and requires monitoring components such as an oil level gauge and thermometer. Dry-type transformers, on the other hand, do not require an oil tank, and their windings are often encapsulated with epoxy resin (or fiberglass wound), resulting in a more compact and lighter structure. This eliminates the need for additional oil storage space during installation.
The difference in applicable scenarios is particularly crucial. Oil-immersed transformers, due to their excellent insulation and low cost, are more suitable for outdoor, open environments such as substations, high-voltage transmission lines, and industrial park distribution centers. They are particularly widely used for high-power power supply in remote areas. However, due to the risk of transformer oil leakage (potentially contaminating soil and water sources) and its flammable nature (flash point approximately 140°C), they are not suitable for crowded, explosive, or environmentally sensitive environments. Because they are oil-free, non-flammable, and pollution-free, dry-type transformers are the preferred choice for indoor applications such as shopping malls, hospitals, data centers, and high-rise building distribution rooms. They are also preferred by some factories with high fire protection ratings (such as chemical and textile mills). They are also quieter (typically operating at noise levels below 50 decibels), making them more suitable for noise-sensitive environments.
The maintenance requirements and safety features are also significantly different. Oil-immersed transformers require regular inspections of the oil level and quality (testing for dielectric loss and moisture content), with oil replacement every 3-5 years. They also need to prevent tank leaks and heat sink blockage, resulting in a higher maintenance frequency. In the event of a fault, oil handling and equipment repair are more difficult and pose a fire hazard. Dry-type transformers are easier to maintain, requiring only regular cleaning of the winding surface to prevent heat dissipation and inspection of the insulation for cracks. No oil-related maintenance is required, making troubleshooting more straightforward. Furthermore, because they contain no flammable media, they are less likely to cause fires in the event of a short circuit, providing a higher safety factor. Some models also feature a self-extinguishing feature to reduce the risk of an accident spreading.