Oil-immersed or cast-resin? How to choose between the two transformer types
Hermetically sealed oil transformers and cast-resin dry-type units solve the same task in different ways. A side-by-side comparison of cost, losses, fire safety, noise, maintenance and where each one belongs.
Both PNACHO series deliver the same voltages, the same ratings and the same Ecodesign Tier 2 losses. The difference is the insulation system – mineral oil in a sealed steel tank, or epoxy resin cast around the windings – and that difference decides where each transformer belongs.
Side by side
| Criterion | PNACHO-O (oil-immersed) | PNACHO-D (cast resin) |
|---|---|---|
| Ratings | 25 – 2500 kVA | 100 – 2500 kVA |
| Installation | Indoor and outdoor, IP00 tank, RAL 7033 C3 finish | Indoor, IP00 (enclosures IP21–IP44 optional) |
| Cooling | ONAN – oil natural, air natural | AN; AF fans add ~40 % capacity |
| No-load losses (630 kVA, Tier 2) | 540 W | 990 W |
| Load losses (630 kVA, Tier 2) | 4 600 W | 7 100 W |
| Noise (630 kVA) | ≈ 48 dB(A) | ≈ 47 dB(A) AN |
| Fire behaviour | Mineral oil (ester fluid optional) | Self-extinguishing, class F1, no fluid |
| Maintenance | Hermetic tank – no oil change, no breather | Dust removal, ventilation check |
| Mass (630 kVA) | ≈ 1 800 kg | ≈ 1 700 kg |
| Purchase price | Lower | Higher (typically +30–50 %) |
When oil-immersed is the right choice
Outdoor pad-mounted substations, compact kiosk substations, industrial sites, agricultural and rural networks, photovoltaic and wind plants, construction-site supplies – anywhere the transformer stands in its own room or outdoors. The hermetically sealed corrugated tank needs no conservator and no maintenance, losses are lower, and the price is the lowest of any technology. Over 30 years the lower no-load losses of an oil unit save several thousand euros per transformer.
When cast resin is the right choice
Inside occupied buildings: office towers, hospitals, shopping centres, data centres, underground car parks, tunnels, ships and anywhere fire load or water protection rules exclude oil. Cast-resin windings do not burn, do not leak and do not need an oil pit. Fans can be added later, which makes a PNACHO-D easy to upgrade when the IT load in a data centre grows.
If oil is acceptable for the site but the fire risk is a concern, an oil-immersed unit filled with a natural or synthetic ester (fire point > 300 °C, K-class fluid) is often cheaper than a cast-resin unit of the same rating – ask us for both prices.
Both series, one specification
Whatever the type, the data that matters is the same: rated power, voltage ratio (6.3, 10 or 21 kV to 0.42 kV, or 0.8 kV for PV), vector group Dyn11 (Dyn5 on request), short-circuit impedance, and the Tier 2 losses. Browse the oil-immersed range and the cast-resin range, or send us the site description and we will recommend the type.
Further reading: What is the difference between an oil transformer and a dry, cast-resin transformer? (energeks.com, EN) · Czym się różni transformator olejowy od suchego, żywicznego? (energeks.pl, PL)
Request a quote for your PNACHO transformer
Send us rated power, voltages and the site of installation – our engineers will select the right configuration and send a quote within 24 hours.