A dry type transformer is a core component in modern industrial power distribution, especially where fire safety, indoor installation, and low maintenance are priorities. Unlike oil-immersed units, dry type transformers use air or cast resin insulation instead of liquid dielectric, making them suitable for commercial buildings, hospitals, data centers, and manufacturing plants. As a transformer manufacturer serving export markets, FIJ TECH supplies dry type and oil-immersed transformers that meet IEC, IEEE, and GB standards. This guide explains how to specify, compare, and apply dry type transformers in real projects.
What Is a Dry Type Transformer?
A dry type transformer transfers electrical energy between voltage levels without using oil as a cooling or insulating medium. The windings are either cast in epoxy resin or impregnated with special varnish, and cooling is achieved by natural air circulation (AN) or forced air (AF). This design eliminates the risk of oil leakage and reduces fire load, which is why many facility engineers choose dry type units for indoor substations.
FIJ TECH manufactures the SG(B)13 / SC(B)13 Dry-Type Transformer, designed for 6kV to 35kV systems and 30kVA to 2500kVA standard capacities. For larger projects, custom designs up to 31500kVA are available. The transformers comply with IEC 60076-11 for dry type transformers, GB 1094, and ISO 9001:2015 quality management.
Key Technical Parameters to Specify
When selecting a dry type transformer, engineers should define voltage ratio, capacity, frequency, cooling method, and efficiency class. The table below summarizes typical ranges for FIJ TECH dry type and oil-immersed distribution transformers.
| Parameter | Dry Type Transformer | Oil-Immersed Transformer |
|---|---|---|
| Voltage levels | 6kV, 10kV, 11kV, 20kV, 33kV, 35kV | 6kV, 10kV, 11kV, 20kV, 33kV, 35kV |
| Capacity range | 30kVA – 2500kVA standard; up to 31500kVA custom | 30kVA – 2500kVA standard; up to 31500kVA custom |
| Cooling | AN / AF | ONAN / ONAF |
| Typical impedance | 4% – 6% | 4% – 6% |
Efficiency standards vary by market. For China, GB 20052-2020 defines energy efficiency grades. For the EU, EcoDesign Tier 2 limits no-load and load losses. In the US, DOE 2016 sets minimum efficiency for distribution transformers. FIJ TECH can supply dry type transformers that meet these regional requirements, with test reports and certification documents provided for project approval.
Dry Type vs Oil-Immersed Transformer: Which to Choose?
The choice between dry type and oil-immersed transformers depends on installation environment, fire safety requirements, and maintenance capability. Dry type transformers are preferred for indoor locations, underground substations, and areas with strict fire codes. Oil-immersed transformers, such as the S20 Energy Efficiency Stage 2 Oil-Immersed Transformer, are often used outdoors or in dedicated transformer rooms where oil containment is available.
- Fire safety: Dry type transformers use self-extinguishing epoxy resin, reducing fire risk in occupied buildings.
- Maintenance: Dry type units require less routine maintenance because there is no oil to test or replace.
- Environmental impact: No oil leakage risk, making dry type transformers suitable for sensitive areas.
- Cost: Oil-immersed transformers typically have lower initial cost for the same capacity, but dry type units may reduce civil works and fire protection costs.
For a complete overview of both categories, visit our product catalog or explore the dry transformer and oil transformer ranges.
Factory Case Study: 11kV S13 Oil Immersed Distribution Transformer for Southeast Asia Textile Mill
Although this case study focuses on an oil-immersed transformer, it illustrates how transformer selection affects energy costs and production reliability. A textile mill in Vietnam operated with old S9 oil-immersed transformers that caused frequent voltage fluctuations and high no-load losses. The plant faced rising energy costs and unstable motor operation.
FIJ TECH supplied an S13-M-2000/11 transformer (11kV / 0.4kV, 2000kVA) designed to IEC 60076 and GB 1094. The S13 energy-efficient design reduced no-load loss by approximately 30% compared with the old S9 units. The transformer was delivered within 35 days, minimizing production downtime.
According to the customer, “After upgrading to S13 transformers, our monthly energy cost dropped by approximately 18%. The delivery was completed within 35 days.” This project demonstrates how selecting the right transformer—whether dry type or oil-immersed—can deliver measurable operational savings.
Voltage Drop & Short-Circuit Impedance Check
Proper voltage drop and impedance verification ensure that the transformer coordinates with switchgear and maintains acceptable voltage at load terminals. Follow these steps for a typical dry type transformer application:
- Verify transformer impedance voltage (uk%) matches switchgear breaking capacity. A mismatch can lead to inadequate fault current limitation or unnecessary oversizing.
- Typical 10kV distribution transformer: uk = 4%. For dry type transformers, impedance may range from 4% to 6% depending on design.
- Calculate voltage drop under load: ΔU = β × uk × (cosφ + sinφ × tanθ), where β is load factor, cosφ is power factor, and θ is the phase angle between voltage and current.
- Ensure voltage drop at full load stays below 5% at motor terminals. If the calculated drop exceeds 5%, consider a larger conductor size, lower impedance transformer, or tap adjustment.
This calculation is especially important for dry type transformers feeding motor loads, because starting currents can cause significant voltage dips. FIJ TECH provides technical support and test data to help engineers validate their designs.
Standards and Certifications for Dry Type Transformers
Compliance with international standards is essential for export projects. FIJ TECH dry type transformers are designed and tested according to:
- IEC 60076-11: Dry type transformers
- IEC 60076: Power transformers
- IEEE C57.12.00: General requirements for distribution, power, and regulating transformers
- GB 1094: Chinese national standard for power transformers
- GB/T 17467: Compact substations
- ISO 9001:2015: Quality management system
- CE marking for European conformity
- VDE (Germany) applicable for project basis
These certifications give procurement managers and EPC contractors confidence that the transformers will pass local inspections and perform reliably over their service life.
Applications and Selection Tips
Dry type transformers are widely used in:
- Commercial buildings and shopping centers
- Hospitals and healthcare facilities
- Data centers and telecom rooms
- Industrial plants with indoor substations
- Renewable energy projects (solar and wind)
When selecting a dry type transformer, consider altitude, ambient temperature, humidity, and seismic requirements. For high-altitude or high-humidity environments, specify appropriate insulation class and cooling method. FIJ TECH offers AN and AF cooling options to match load profiles and space constraints.
Request a Quote for Dry Type Transformers
Whether you need a standard 1000kVA dry type transformer for a commercial project or a custom 31500kVA unit for an industrial plant, FIJ TECH can provide a solution that meets your technical and certification requirements. Our engineering team supports voltage drop calculations, impedance checks, and documentation for project approval. Contact us today to request a quote and discuss your next power distribution project.
For more information, visit our dry transformer category or browse the full product catalog.