When selecting core equipment for power distribution systems, oil-immersed transformers and dry-type transformers are the two most common choices. As a professional manufacturer of high-quality power transformers, Xinhong Electrical often receives the same question from customers: What are the key differences between these two types, and which applications are they best suited for? In this article, we provide a clear technical and practical comparison.
Oil-immersed transformers use transformer oil as both the insulating and cooling medium. The core and windings are completely submerged in insulating oil, which removes heat through natural convection or forced circulation. Common types include fully sealed and oil-immersed self-cooling designs.
Dry-type transformers use air, epoxy resin, or other solid materials as the insulation medium. The windings are either directly exposed to air or vacuum-cast with epoxy resin to form a robust insulating layer. Typical examples include the SCB series epoxy resin cast dry-type transformers.
This fundamental difference determines their distinct structures, performance characteristics, and application scenarios.
Oil-immersed transformer: Contains mineral oil with a risk of leakage. Caution is required in locations with high fire hazards or strict environmental requirements. However, fully sealed designs significantly reduce the probability of oil leakage.
Dry-type transformer: Oil-free, leak-proof, and non-flammable. Xinhong Electrical dry-type transformers have passed Class F1 flame-retardant tests, making them ideal for environments with high fire safety requirements.
Oil-immersed transformer: Oil has a high specific heat capacity and excellent heat dissipation, providing strong short-term overload capacity. It can typically withstand 130–150% rated load without immediate damage.
Dry-type transformer: Air heat dissipation is much weaker than oil, resulting in lower overload capacity. It is generally recommended to operate at 100% load or less. Forced air cooling can be added to improve heat dissipation.
Oil-immersed transformer: Requires space for oil ducts and cooling fins, making it larger and heavier. Generally needs a dedicated transformer room or outdoor installation.
Dry-type transformer: Compact structure, small size, and light weight. Can be installed directly at the load center or even integrated into low-voltage switchgear assemblies. Ideal for space-limited indoor locations.
Oil-immersed transformer: Requires periodic oil level checks, oil dielectric strength tests, and replacement of aged insulating oil. Maintenance costs are higher, but design life can reach 30–40 years.
Dry-type transformer: Virtually maintenance-free – only requires good ventilation and cleanliness. Although initial investment is slightly higher, the total life-cycle operating cost is lower. Xinhong Electrical dry-type transformers use Class H or Class C insulation materials and also achieve a design life of over 30 years.
Oil-immersed transformer: Strong resistance to pollution, humidity, and salt spray. Suitable for outdoor and harsh industrial environments.
Dry-type transformer: Sensitive to ambient cleanliness and humidity. Typically requires indoor use with at least IP20 protection. Optional IP40 or higher enclosures allow semi-outdoor use.
| Application Scenario | Recommended Transformer Type | Main Reason |
|---|---|---|
| Residential complexes, commercial buildings | Dry-type | Safe, oil-free, can be installed in indoor basements |
| High-rise buildings, hospitals, schools | Dry-type | Strict fire codes, oil-filled equipment not allowed |
| Factory workshops, mines | Oil-immersed | Harsh environment, high overload capacity, cost-effective |
| Outdoor substations, pole-mounted transformers | Oil-immersed | Weather-resistant, no indoor enclosure needed |
| Data centers, precision electronics workshops | Dry-type | Low noise, low fire risk, clean environment |
| Temporary construction power | Oil-immersed (basic type) | Low cost, convenient for outdoor use |
| Wind and solar PV power stations | Dry-type or specialized oil-immersed | Depends on grid connection location and fire codes |
In actual projects, we recommend focusing on three key factors when selecting between an oil-immersed transformer and a dry-type transformer:
Installation location – Indoor or outdoor? Is a dedicated transformer room available?
Fire safety requirements – Is the site a densely occupied area or a high fire protection class zone?
Budget and maintenance capability – Prioritize initial cost or total life-cycle cost?
As a professional power transformer manufacturer, Xinhong Electrical offers a full range of both oil-immersed transformers (S11, S13, S20 series, etc.) and dry-type transformers (SCB10, SCB12, SCB14, SCB18 series), and we can customize according to IEEE/IEC standards. Whether for urban distribution networks, industrial plants, or renewable energy projects, we will provide the most suitable product solution for your needs.
About Xinhong Electrical
Xinhong Electrical specializes in the R&D and manufacturing of medium and low voltage power transformers. Our products include oil-immersed transformers, dry-type transformers, and prefabricated substations, exported to Southeast Asia, the Middle East, Africa, and South America. Guided by the design philosophy of "safe, energy-saving, reliable," we provide high-quality power solutions to customers worldwide.
For further technical selection support or to request a quote, please visit our official Google-indexed website or contact our sales team directly.
