Choose for the installation, not the label
Dry-type and oil-filled transformers can both be considered for suitable projects. Their cooling and insulation arrangements lead to different installation questions. Neither description, by itself, determines the correct rating, lifecycle cost or suitability for a particular room. The project engineer must assess the load, supply system, location and applicable requirements.
OSTL’s confirmed range is power and distribution transformers up to 10 MVA and 66 kV, and dry-type transformers up to 3 MVA. Those are range ceilings, not a guarantee that every possible voltage and rating combination is available. Dry-type voltage capability needs separate confirmation.
A practical comparison
| Decision area | Dry type | Oil filled |
|---|---|---|
| Insulation and cooling | No insulating oil around the active part; confirm the actual insulation system and cooling arrangement. | Uses insulating liquid; confirm the liquid, preservation system and cooling arrangement. |
| Installation space | Review ventilation, enclosure, heat removal, access and electrical clearances. | Review location, heat rejection, access and any required oil containment arrangements. |
| Fire and environmental planning | Do not assume zero fire risk or a particular fire-performance classification. | Assess liquid-related risks and the fire/environmental provisions required for the site. |
| Exposure | Specify dust, moisture, contamination, ambient conditions and enclosure requirements. | Specify ambient conditions, site exposure, corrosion requirements and liquid-system provisions. |
| Maintenance planning | Agree inspection, cleaning, ventilation and monitoring needs for the actual design. | Agree inspection, liquid-system checks and maintenance needs for the actual design. |
| Cost comparison | Compare the transformer and its complete installation requirements. | Use the same performance, installation and supply-scope basis before comparing costs. |
What to ask before deciding
- What load and operating duty have been used to select the rating?
- Can the proposed design meet the project’s environmental and installation conditions?
- Which requirements are part of the transformer supply, and which remain with the installer or site owner?
- Which losses, temperature conditions, enclosure details and acceptance documents are agreed?
- What are the access, transport and maintenance implications of each proposal?
Avoid shortcuts in a specification
Do not assume “dry type” means cast resin, VPI, a particular insulation class, an enclosure rating or maintenance-free operation. Likewise, do not infer ONAN cooling, a CRGO core or a particular oil arrangement from an oil-filled illustration. Specify requirements and obtain written confirmation. Copper and aluminium windings are available from OSTL; selection is confirmed for the proposed product.
If an enclosure, fire-performance classification or liquid-containment requirement matters to your project, ask for the applicable standard and supporting documentation. This comparison is general buying guidance, not a site safety assessment.
Continue with the right enquiry
Dry-Type Transformers
A confirmed OSTL product line. Define the installation and performance requirements before selecting the configuration.
↗PRODUCT LINEPower Transformers
A project-specific starting point for power transformers up to 10 MVA and up to 66 kV.
↗RFQ WORKSHEETPrepare a useful quotation brief
A practical technical and commercial checklist, plus a copyable/downloadable template.
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