Oil Immersed Distribution Transformer VS Dry Type Cast Resin Transformer

Cooling Media

In oil-immersed distribution transformers, oil is used as a heat conductor, and heat is released through radiator fins. Since the mineral oil has a flash point of 160 to 180°C, oil-immersed transformers must be installed in separate locations to prevent fire hazards in public spaces.

In dry-type cast resin distribution transformers, the coils are exposed to air, allowing heat to be dissipated immediately. Heat dissipation is usually enhanced by fans mounted at the bottom of the transformer. The transformer uses fire-resistant resin materials, making it safe for installation inside buildings.

Maintenance

Oil-immersed distribution transformers require maintenance such as oil purification or periodic replacement, bushing packing replacement, checking bushing and connection torque, and changing silica gel in the breather.

Dry-type cast resin distribution transformers require only periodic torque checks on the busbar connections, with no risk of oil leakage.

Efficiency

Oil-immersed distribution transformers are generally more efficient than dry-type cast resin distribution transformers because they have more space for windings and cooling, whereas the size of dry-type cast resin transformers is limited by the cast resin molding dimensions.

Dry-type cast resin distribution transformers are more sensitive to overheating and high losses when subjected to overload.

Tianya Transformer has experience manufacturing dry-type cast resin distribution transformers up to 5000 kVA and oil-immersed distribution transformers up to 167 MVA, 275 kV (Power Transformers).

Noise

According to some literature, dry-type cast resin distribution transformers can produce more noise than oil-immersed transformers. This noise is caused by the magnetostriction phenomenon, which slightly changes the dimensions of the iron core during magnetization (stretching and shrinking). When the core is not magnetized, it returns to its original size, resulting in a buzzing sound.

However, based on our experience, the noise levels of both transformer types under normal load are relatively similar and do not exceed 60 decibels.

Dielectric

Advantages : Dry type cast resin distribution transformers have lower partial discharge than Oil immersed distribution transformer. Dry transformers are also more resistant to sort circuits, and have better resistant to lightning impact / impulse (lightning strike).

But the Dry type cast resin distribution transformers have more losses than Oil immersed distribution transformer.

Price

At the same capacity, dry-type cast resin distribution transformers generally have a higher price than oil-immersed distribution transformers. This price difference reflects the advantages offered by dry-type transformers, such as safety, fire resistance, and indoor installation suitability.

In practical applications, customers often choose a dry-type transformer for installation in high-rise buildings or public areas, while oil-immersed transformers are preferred for locations isolated from the public. For large transformer capacities above 5000 kVA, oil-immersed transformers are usually recommended due to their higher efficiency.