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Dry-type and oil-immersed transformers are not actually just a matter of preference for indoor power projects, data centers, industrial plants, commercial complexes, and substations. Safety, code-compliance, and fire-protection decisions will be scrutinized during the design approval and fire acceptance inspection stages.
Ryan Electric's product range includes dry-type and oil-immersed transformers, ranging in size up to 10 MVA and from 3.3 kV to 132 kV. This actually enables us to provide fair and objective comparison based on standards in indoor spaces.
Indoor Layout and Clearance Requirements
Dry-type transformers (such as VPI type, cast-resin type) are usually used in the interior of the building, and there is no flammable liquid. They can also be mounted closer to loads and in buildings where separation distances are reduced, provided adequate ventilation and maintenance access are available.
Oil-immersed transformers, on the other hand, have a tendency to need designated fire rated space, oil containment (bunding), blast relief, and greater space clearance from walls, doors and living quarters. Local codes and IEEE/IEC standards typically require more space for indoor applications.
To help designers optimize space usage indoors while maintaining safety, Ryan Electric actually offers both cast resin and VPI dry-type transformers, as well as compact substation configurations.
Fire Rating and Fire Resistance Duration
The main difference is with regard to fire performance. Class H or higher insulation systems are used in dry-type transformers, and in normal circumstances they are basically non-combustible. They do not generate oil reservoirs that are prone to fire, standard fire resistance durations are actually achieved through enclosure ratings and wall ratings rather than by oil containment.
Oil-immersed transformers contain an inventory of flammable liquid. For indoor installations, walls, doors and cable penetrations are usually required to meet a 1-to-3 hour fire resistance rating to inhibit fire spread. Ryan Electric's oil-immersed power and distribution transformers will meet IEEE, IEC, GB standards, and be able to be installed in fire-rated substation enclosures.
Ester Liquid vs. Mineral Oil: The Indoor Trade-Off
Where oil-immersed technology is still needed, the selection between ester liquids and mineral oil is very important for indoor projects. Ester liquids (natural or synthetic) offer a higher flash and fire point, biodegradability and a greatly decreased fire risk. They are becoming more and more popular inside and in sensitive spaces.
Mineral oil is still relatively inexpensive and popular, but requires more stringent fire protection measures, spill containment and smoke management. Ryan Electric provides both ester-filled and mineral-oil transformers, and our R&D team tailors solutions according to the environmental and operational requirements.
Accident Oil Spill and Smoke Management
For indoor transformers, it is important to coordinate the transformer location with the appropriate spill containment system and fire suppression method—such as water mist, CO₂ or foam.
Dry-type transformers eliminate oily smoke and oil spill concerns, greatly reducing complexity of indoor ventilation and fire suppression design. This makes Ryan Electric’s cast resin transformers and VPI transformers popular in data centers, renewable energy applications, and underground substations.
Documents Required for Fire Acceptance Inspection
It is usual for fire acceptance inspections to include the following:
- Routine test certificates, transformer type test reports.
- Fire resistance rating certificates for enclosures and walls
- Oil containment and spill calculation documents (for oil-immersed units)
- The smoke exhaust and ventilation design calculations are provided.
- The project has been designed for compliance with IEEE, UL, CE, ASTA, DEKRA, CNAS, ISO, IEC, CSA, and GB standards.
Ryan Electric has two 35 kV/110 kV test labs and a CNAS-accredited test lab. We offer UL, ASTA, CSA, CE, DEKRA, CNAS certificates and our transformers are thoroughly inspected from raw material sourcing to delivery.
Conclusion and Call to Action
Power projects inside the buildings require transformer selection which is based on safety. From dry-type, ester-filled or mineral-oil solutions, Ryan Electric offers reliable, efficient and fully customized transformers that are used by top clients including Microsoft and State Grid in more than 50 countries.
Call our technical staff now to discuss your indoor project needs, or to ask for a bespoke solution and quotation. Contact Ryan Electric to ensure your project is safe, compliant with fire code and will pass an acceptance inspection.