In power distribution systems, dry-type transformers and oil-immersed transformers are the two most widely used types. However, during project selection, many people inevitably find themselves pondering: Which one should I choose—dry-type or oil-immersed?
Both have their strengths. Choose correctly, and you achieve both safety and cost-effectiveness; choose incorrectly, and later maintenance costs may multiply exponentially. Today, we will thoroughly clarify the differences between the two from three key dimensions: product construction, core performance, and application scenarios.
First, you can quickly distinguish them by appearance:
Dry-type Transformer: You can usually see the exposed windings, covered by a layer of noticeable red epoxy resin, giving it a compact and refined look.
Oil-immersed Transformer: It features a fully sealed metal tank filled with insulating oil. The tank is surrounded by vertical cooling fins that help dissipate heat from the internal oil.
The fundamental difference lies in the insulating medium, which leads to a series of distinct technical characteristics.
| Comparison Dimension | Dry-Type Transformer | Oil-Immersed Transformer |
|---|---|---|
| Construction & Insulation | Core and coils insulated by solid materials like epoxy resin, directly visible. | Core and coils immersed in insulating oil, completely sealed. |
| Cooling Method | Relies on air circulation (Air Natural AN / Air Forced AF). Fans at the bottom activate automatically when temperature rises. | Relies on oil circulation, where internal oil convection carries heat to the external cooling fins. |
| Voltage & Capacity | Typically used for 35kV and below, capacity mostly under 3150kVA. | Voltage level and capacity are virtually unlimited, covering high-voltage and large-capacity scenarios. |
| Overload Capacity | Relatively weak overload capacity, sensitive to overload operation. | Strong overload capacity, able to withstand high load impacts for short periods. |
| Manufacturing & Cost | Complex process, requires vacuum casting equipment, higher production cost. | Mature process, relatively lower cost, high cost-performance ratio. |
| Dimensions & Installation | Smaller footprint, can be installed side-by-side with switchgear, saving space. | Larger size for the same capacity, requires an oil containment pit, typically installed outdoors or in separate rooms. |
High Safety: Oil-free, completely eliminating risks of oil spray, leakage, and fire hazards, offering excellent fire and explosion protection.
Environmental Friendly: No risk of environmental pollution from oil leakage, zero emissions during operation.
Maintenance-Free: No daily checks of oil level or filtration needed; simple post-installation maintenance.
Strong Adaptability: The sealed structure makes them moisture-proof, dust-proof, and corrosion-resistant, ensuring stable operation in rain, snow, high temperatures, or harsh conditions.
Superior Overload Capacity: Oil has high thermal capacity and good heat dissipation, allowing short-term severe overloads, suitable for fluctuating loads.
High Performance Ceiling: Easily handles high-voltage and large-capacity requirements, making them the preferred choice for backbone power grids.
The core logic for selection is: Consider the installation location, safety requirements, and load characteristics.
Due to their oil-free nature, dry-type transformers are the absolute first choice for indoor installation. They are particularly suitable for locations with high demands for personnel and property safety:
Commercial & Residential: High-rise buildings, residential complexes, commercial plazas, office buildings.
Public Facilities: Hospitals, schools, stations, airports, convention centers.
Special Locations: Data centers, subways, tunnels, research laboratories.
With their strong environmental adaptability and overload capacity, oil-immersed transformers dominate outdoor and industrial applications:
Power Systems: Power plants, large substations, urban and rural power transmission/distribution.
Industrial Manufacturing: Heavy industries like steel, chemical, mining.
New Energy Fields: Outdoor power generation projects like wind and solar.
Harsh Environments: Outdoor installations, dusty, humid, or corrosive locations.
Simply put: Choose dry-type for indoors – safe and worry-free; choose oil-immersed for outdoors – durable and robust.
Choosing the right type is only the first step. Reliable manufacturing workmanship is the true cornerstone of a transformer's long-term safe operation.
