Both meet the same standards and the same Tier 2 levels. So the choice is not about "which is better", but about your room, your fire risk and your operation. Here is the comparison, plainly.
The oil-immersed transformer cools its windings in a liquid dielectric (mineral oil or ester). The dry-type transformer encases its windings in resin (cast resin) and cools by air. Technically, both transform voltage the same way and are both designed to meet Tier 2 and EU compliance. The difference is the dielectric, and it drives everything else.
| Criterion | Oil-immersed (oil / ester) | Dry-type (cast resin) |
|---|---|---|
| Purchase cost | Generally more economical at equal power | Often more expensive, especially at higher ratings |
| Fire safety | Combustible dielectric: bund required. Ester = high fire point, biodegradable | Better fire behaviour (class F1), self-extinguishing, no liquid |
| Room & siting | Outdoor or dedicated room with containment | Indoor, close to the load, commercial / public buildings / high-rise |
| Maintenance | Oil monitoring (analysis, dissolved gases / DGA) | Virtually maintenance-free dielectric |
| Short overload | Good thermal inertia, handles peaks better | Less tolerant of sustained overload |
| Harsh environments | Sealed: robust in dust / humidity | Sensitive to humidity and pollution, unless classes E2 · C2 |
| Losses / efficiency | Comparable at equal Tier 2 level | Comparable at equal Tier 2 level |
| Natural fit | Grid / distribution, industry, outdoor, solar & wind | Data centers, hospitals, buildings, marine, sensitive indoor |
The first question is not price, but where the unit will live:
At Veltrium we design both families, and we start from your real constraint (siting, fire regulations, budget) rather than a catalogue. Describe your project in the configurator: we steer you to the right type and quote.
General selection guidance; the exact type is confirmed case by case according to the room, the applicable regulations and site constraints.
At equal power, an oil-immersed transformer is generally cheaper to buy than a dry-type (cast-resin) unit. But the right trade-off also weighs the room, fire safety and maintenance, not just the price of the unit.
Dry-type (cast resin) is often preferred indoors and in public buildings for its fire behaviour (class F1) and the absence of a liquid dielectric. Oil-immersed remains possible with a bund, or in ester to reduce the fire risk.
On the dielectric side, yes: no oil to analyse or treat. An oil unit needs oil monitoring (analysis, dissolved gases). In return, oil-immersed handles short overloads and some harsh environments better.
The type choice crosses with the dielectric, sizing and compliance.
Describe the room, the use and the budget: we recommend oil or dry, and quote, first reply within 48 h.
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