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Oil Filled and Dry Type Transformers Compared
Liquid-filled units are more efficient, handle overload better and live outdoors on a pad. Dry type units avoid the fluid entirely, which is why they go indoors and in vaults where a spill or a fire load is unacceptable. They are not interchangeable, and a quote comparing one against the other is comparing two different products.
The real differences
| Liquid filled | Dry type | |
|---|---|---|
| Location | Outdoors on a pad | Indoors, vaults, rooftops |
| Efficiency | Higher | Lower |
| Overload capacity | Better, the fluid buffers heat | Limited |
| Life | Typically longer | Shorter at equal loading |
| Fire and spill | Needs containment and clearance | No fluid to contain |
| Footprint | Smaller for the same kVA | Larger |
| Noise | Quieter | Louder |
They are not substitutes
A pad-mounted liquid-filled unit and a dry type of the same kVA solve different problems. If a quote comes back materially cheaper, check which one you are being offered. It is the most common apples to oranges comparison in this market.
Where ester fluid fits
Natural ester, sold as FR3, is a less flammable fluid with a much higher fire point than mineral oil. It permits shorter clearances in some jurisdictions and is more forgiving environmentally. It costs more and not every manufacturer offers it on every rating.
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