Characteristics of Epoxy Resin Insulated Dry-Type Transformers
The primary advantage of epoxy resin insulated dry‑type transformers lies in their solid insulation system. The windings are vacuum‑cast with epoxy resin, forming a dense solid insulation structure. The casting epoxy resin offers an insulation breakdown strength of 18–22 kV/mm, and the insulation thermal class generally reaches Class F (155°C) and Class H (180°C).
High‑quality epoxy resin combined with fiberglass provides high electrical strength, with partial discharge levels controllable to ≤5 pC. Low partial discharge means that the transformer will not develop cracks throughout its service life, and insulation performance will not degrade. Compared with traditional oil‑immersed transformers (oil immersed transformer), the epoxy resin casting process completely seals out moisture and dust, enabling normal operation even in 100% humidity environments, and the transformer can be re‑energised immediately after shutdown without drying or pre‑heating.
In addition, dry‑type transformers (Dry transformer) employing “thin‑insulation (1–3 mm)” technology can meet the requirements of low‑temperature, high‑temperature, and large‑temperature‑difference applications, effectively solving the cracking issues commonly associated with the older “thick‑insulation” approach.
Fire safety is one of the most prominent features of epoxy resin insulated dry‑type transformers (cast resin transformer). Unlike oil‑immersed transformers that use mineral oil as both insulation and cooling medium, cast resin transformers use flame‑retardant epoxy resin to fully encapsulate the windings, containing no flammable liquid.
Epoxy resin itself is inherently difficult to ignite and self‑extinguishing; even if exposed to fire, it will not cause explosions or secondary fires. Under high‑temperature open flames, the transformer produces almost no smoke, achieving a fire rating up to F1. This makes epoxy resin dry‑type transformers particularly suitable for locations with stringent fire safety requirements, such as hospitals, high‑rise buildings, commercial centres, airports, data centres, and subway stations.
By contrast, while oil immersed transformers offer better cooling efficiency, mineral oil poses leakage and fire risks. Especially in indoor installations or densely populated areas, the safety advantages of cast resin transformers are even more pronounced – they require no special fire‑proof oil pits or fire‑resistant compartments and can be installed directly at the load centre.
Epoxy resin is chemically extremely stable, offering outstanding moisture‑ and dust‑proof properties. Even in harsh environments with heavy atmospheric pollution, epoxy resin insulated dry‑type transformers operate reliably. This makes them suitable for the following challenging conditions:
High humidity and frequent condensation
Chemical plants with corrosive gases or dust
Offshore platforms and marine vessels
Tunnels, underground substations, and other space‑constrained locations
At the same time, cast resin transformers contain no insulating oil, completely eliminating the risk of environmental pollution from oil leaks. With increasingly stringent environmental regulations, this feature makes them an ideal choice for green buildings and sustainable development projects.
Another major advantage of epoxy resin insulated dry‑type transformers (Dry transformer) is their genuine maintenance‑free design. Because the windings are fully sealed and encapsulated by epoxy resin, there are no issues such as oil degradation, moisture ingress, or leakage. During operation, no oil testing, filtration, or replacement is required; routine maintenance is limited to simple cleaning and visual inspection.
This significantly reduces the total lifecycle operating cost of the transformer. For oil immersed transformers, regular oil sampling, gasket replacement, and radiator cleaning are necessary. In contrast, cast resin transformers, with their maintenance‑free nature, are especially suitable for installations where inspection is difficult or maintenance costs are high.
Xinhong Electrical, as a professional transformer manufacturer, offers epoxy resin dry‑type transformers covering capacity ranges from 50 kVA to 5000 kVA, meeting the distribution needs of diverse users.
Epoxy resin dry‑type transformers also perform excellently in overload capacity and short‑circuit withstand. The high‑voltage coils are resin‑cast, providing high mechanical strength; the low‑voltage coils use foil‑wound construction, resulting in low leakage flux and reduced axial mechanical forces. The overall structure employs tie‑rods and cushion blocks, making the core assembly stable and robust.
Thanks to the material properties of epoxy resin, the fully cast and heat‑cured winding assembly has high mechanical strength, making damage due to short‑circuits highly unlikely. With forced air cooling, the transformer can sustain long‑term cyclic overload or temporary emergency overload operation.
In terms of losses, by employing leakage flux calculations and optimising conductor transposition, stray losses and eddy‑current losses are effectively reduced. The products comply with IEC60076, GB/T10228, GB/T1094, and other domestic and international standards.
To better understand the characteristics of epoxy resin insulated dry‑type transformers, the following table compares them with traditional oil‑immersed transformers (oil immersed transformer):
| Aspect | Epoxy Resin Dry‑Type (Cast Resin) | Oil‑Immersed Transformer |
|---|---|---|
| Insulation / cooling medium | Epoxy resin solid insulation, air‑cooled | Mineral oil / ester fluid, oil‑circulation cooled |
| Fire performance | Flame‑retardant, self‑extinguishing, no fire risk | Mineral oil flammable, fire hazard exists |
| Environmental risk | No oil leakage, environmentally safe | Oil leakage pollution risk |
| Maintenance needs | Maintenance‑free, only cleaning and inspection | Regular oil testing, filtration, and replacement |
| Installation site | Indoors, load centres, safety‑sensitive locations | Outdoor substations, open areas |
| Insulation thermal class | Class F (155°C) / Class H (180°C) | Class A (105°C) |
| Overload capability | Strong (better with forced air cooling) | Excellent, large thermal inertia |
Overall, oil immersed transformers still hold advantages in large outdoor substations, applications requiring higher power density, and better heat dissipation. However, for indoor distribution and sites with strict safety and environmental requirements, cast resin transformers are undoubtedly the better choice.
Based on the above characteristics, epoxy resin insulated dry‑type transformers are widely used in the following scenarios:
High‑rise buildings and commercial centres – extremely high fire safety requirements and limited installation space
Hospitals and data centres – demanding high power supply reliability and no oil leakage risk
Subways and tunnels – space‑constrained with strict fire protection and environmental regulations
Chemical plants and offshore platforms – corrosive environments requiring excellent moisture and dust resistance
Airports and transport hubs – public spaces where fire safety is paramount
In these applications, Dry transformers can be installed directly at the load centre, reducing cable losses and improving power supply efficiency.
Epoxy resin insulated dry‑type transformers, with their superior insulation performance, outstanding fire safety, excellent environmental adaptability, genuine maintenance‑free operation, and strong overload and short‑circuit withstand capabilities, are playing an increasingly important role in modern power distribution systems. Whether in safety‑critical indoor locations or harsh environments with high humidity and contamination, cast resin transformers provide reliable, efficient, and safe power protection.
Jiangsu Xinhong Electrical Equipment Co., Ltd. (Xinhong Electrical), as a professional transformer manufacturer, is committed to developing and producing high‑quality epoxy resin dry‑type transformers as well as oil‑immersed transformer products. The company’s product range covers oil‑immersed transformers from 50 kVA to 3000 kVA (oil immersed transformer China) and advanced epoxy resin dry‑type transformer series, meeting different customisation needs. Whether you require an oil immersed transformer or a cast resin transformer, Xinhong Electrical provides safe, efficient, and energy‑saving power solutions with strict quality control and advanced manufacturing processes.
Choosing the right transformer type requires a comprehensive consideration of installation environment, safety requirements, maintenance capability, and budget. For more information about Dry transformers or oil immersed transformer products, please feel free to contact the technical team at Xinhong Electrical for professional advice.
