In modern power systems, the prefabricated substation – which integrates high-voltage switchgear, transformers, and low-voltage distribution into a single, factory-assembled enclosure – has become a core infrastructure element in urban power grids, industrial parks, commercial buildings, and renewable energy projects.
Among all the components of a prefabricated substation, the transformer is undoubtedly the most critical. When it comes to transformer selection, the two main categories are dry-type transformers (Dry transformer) and oil-immersed transformers (oil immersed transformer). This article explores the roles, technical characteristics, and suitable applications of both types within prefabricated substations, providing a practical guide for informed decision-making.
As a professional power equipment manufacturer, Xinhong Electrical is committed to delivering high-quality oil immersed transformer products, cast resin transformer solutions, and complete prefabricated substation systems to customers worldwide.
An oil-immersed transformer has its core and windings completely submerged in a sealed tank filled with transformer oil. The oil serves a dual purpose: it acts as both an insulating medium and a cooling medium. During operation, heat generated by the windings is transferred through natural circulation (ONAN) or forced circulation (ONAF) of the oil to the tank walls and radiators, where it is dissipated into the surrounding air.
(1) Superior Heat Dissipation and Overload Capacity
Oil-immersed transformers possess excellent thermal inertia and cooling efficiency, making them particularly suitable for high-capacity, high-load applications. Compared with dry-type transformers, they offer significantly higher overload capability and can better withstand instantaneous load surges.
(2) Notable Cost Advantage
For the same capacity rating, oil-immersed transformers are considerably less expensive than dry-type transformers. This makes them a more cost-effective choice for large-scale distribution projects.
(3) Wide Capacity and Voltage Coverage
Oil-immersed transformers are available from a few tens of kVA up to several thousand kVA, and voltage levels can range from low voltage to extra-high voltage. Xinhong Electrical offers three-phase oil-immersed power transformers with rated capacities from 50 kVA to 3000 kVA, meeting a broad spectrum of application needs.
Oil-immersed transformers are primarily used in outdoor standalone substation sites. Within prefabricated substations, they are the more economical and practical choice when the project is located in open outdoor areas, municipal roadsides, heavy industrial plants, urban and rural distribution networks, wind power, and solar PV installations.
As a professional oil immersed transformer manufacturer, Xinhong Electrical has supplied its oil-immersed transformer products to numerous outdoor power distribution projects with proven reliability.
A dry-type transformer (Dry transformer) does not use any liquid as an insulating or cooling medium; instead, it relies on air for cooling. Among dry-type transformers, the cast resin transformer is the most common type – its windings are completely encapsulated under vacuum with epoxy resin, forming a solid, rigid insulation structure.
(1) Excellent Fire Safety
Dry-type transformers contain no flammable liquid, eliminating the risk of oil leakage or spray. The epoxy resin encapsulation of cast resin transformers effectively prevents flame propagation and, in the event of a fault, does not generate oil fires. This makes them the preferred choice for locations with stringent fire and explosion protection requirements.
(2) Environmentally Friendly
Dry-type transformers pose no environmental risk of oil leakage. In green buildings and projects with strict environmental regulations, cast resin transformers are increasingly specified to meet sustainability standards.
(3) Low Maintenance
Dry-type transformers require no oil sampling, filtering, or other routine oil-related maintenance. Day-to-day upkeep is limited to regular cleaning, significantly reducing lifecycle operational costs.
(4) Flexible Installation
Dry-type transformers can be installed in indoor spaces, basements, intermediate floors, and rooftops – areas where space is constrained. They can be placed close to load centers, effectively reducing voltage drops and electrical losses.
Cast resin transformers are widely used in high-rise buildings, commercial centres, hospitals, airports, subway stations, tunnels, and underground substations – environments with extremely high safety and environmental demands. In prefabricated substations, when the project is located in densely populated urban cores, residential communities, or commercial complexes, dry-type transformers are generally the safer option.
To help customers make informed choices, the following table systematically compares oil immersed transformer and cast resin transformer across multiple dimensions:
| Comparison Aspect | Oil-Immersed Transformer | Cast Resin Transformer (Dry-Type) |
|---|---|---|
| Cooling / Insulation medium | Mineral oil / ester oil; liquid insulation | Air cooling; epoxy solid insulation |
| Fire safety | Mineral oil is flammable; ester oil offers higher safety | No flammable liquid; flames do not spread |
| Suitable location | Outdoor, standalone substations | Indoor, basements, occupied spaces |
| Overload capability | Excellent | Moderate |
| Maintenance needs | Requires periodic oil testing, filter changes | Essentially maintenance-free |
| Capacity range | Covers all capacity levels | Typically up to 2500 kVA |
| Unit cost | Lower | Higher |
| Environmental risk | Risk of oil leakage | No liquid leakage risk |
When evaluating oil immersed transformer vs cast resin transformer, the key factors are the project’s environment, safety requirements, and budget constraints.
As a large-scale power equipment enterprise integrating R&D, manufacturing, trading, and services, Xinhong Electrical possesses deep expertise in power transformers, high and low voltage switchgear, and prefabricated substations.
Xinhong Electrical’s core product portfolio includes:
Oil immersed transformer: Capacities from 50 kVA to 3000 kVA, voltage levels covering 10kV, 20kV, and 35kV, with customisation options available.
Cast resin transformer / Dry transformer: Designed for indoor and high-safety applications.
Prefabricated substation: European-type, American-type, and other styles, integrating high-voltage switchgear, transformers, and low-voltage distribution into a single, factory-assembled enclosure.
High-voltage switchgear and low-voltage distribution assemblies.
Whether your project requires an oil immersed transformer or a cast resin transformer, Xinhong Electrical provides professional selection guidance and high-quality power equipment solutions.
In the design and selection of prefabricated substations, both dry-type and oil-immersed transformers offer irreplaceable value. Oil-immersed transformers, with their superior heat dissipation, strong overload capacity, and significant cost advantages, dominate outdoor, high-capacity distribution scenarios. Meanwhile, dry-type transformers (especially cast resin types), with their outstanding fire safety, environmental friendliness, and maintenance-free operation, are the preferred choice for indoor and densely occupied spaces.
Understanding the core differences in the oil immersed transformer vs cast resin transformercomparison, and making a science-based selection according to project-specific needs, is the key to ensuring safe, stable, and efficient power system operation. Xinhong Electrical will continue to provide trustworthy power equipment and services to customers worldwide with professional technical expertise and reliable product quality.
