Distribution transformers

Power transformers serve transmission and generation networks at voltages up to the 800 kV insulation class and ratings from roughly 30 MVA to over 1,300 MVA and are designed for continuous full-load transmission duty. Distribution transformers operate at medium voltage — usually up to 36 kV on the primary side — and step power down for delivery to end users, or step decentralized generation up into the local grid. Because they run mostly at partial load, they are optimized for high efficiency in exactly that regime.

A cast-resin unit like the GEAFOL uses vacuum-cast solid insulation and air cooling — no insulating liquid — which makes it the standard choice for indoor and fire-sensitive locations such as buildings, data centers, and enclosed substations; its F1 fire class means it is flame-resistant and self-extinguishing. A fluid-immersed unit keeps its active part in a sealed, welded tank where the insulating liquid doubles as the coolant, supporting compact high-power-density designs with strong overload and thermal reserves for outdoor and utility duty. Compare the keySpecs and the Mechanical & environment spec groups on DT-O and DT-CR to match your installation constraints.

Fluid-immersed units can be filled with conventional mineral oil or with synthetic or natural ester liquids. The ester option is readily biodegradable (OECD 301), carries a K-class rating per IEC 61039 with a fire point above 300 °C, tolerates more moisture, and improves tank-rupture prevention by up to 20 % — which is why it is favored in environmentally sensitive locations and in the ester-filled 66 kV nacelle-mounted wind variant.

Start from the rating and voltage: the DT-O fluid-immersed family covers 50 kVA–5 MVA at up to 36 kV (REN variants up to 20 MVA / 145 kV Um for renewables), while the DT-CR cast-resin family runs up to 50 MVA / 52 kV, with the GEAFOL Neo series up to 6.3 MVA / 40.5 kV. Then check the variant tables on each product page — DT-CR lists per-rating losses, impedance, sound level, weight, and order number for the 100–3150 kVA Tier 2 series — and the environment rows (climate, fire, and protection classes) against your site conditions.

The essentials are rated power (kVA/MVA), primary and secondary voltages, frequency (50 or 60 Hz), impedance requirement, cooling mode (ONAN or KNAN for fluid-immersed, AN or AN/AF for dry-type), the installation environment (indoor/outdoor, IP class, climate class, altitude above 1000 m), and any regulation or monitoring options such as on-load tap changing or Sensformer®. If a listed type designation already fits — for example a GEAFOL Neo order number like 4GX6064-3EY from the DT-CR ordering table — quoting it directly makes the request unambiguous.

Yes. DT-CR lists GEAFOL Neo order numbers (4GB…/4GX… series) together with losses, sound power level, and weight per rating, plus the reconnectable HV tapping range of ±2 × 2.5 %; DT-O lists representative designations for the fluid-immersed family. The downloads on each page — the GEAFOL Neo catalog, the GEAFOL operating instructions, and the 66 kV FITformer® WIND flyer — carry the full ordering data and dimension drawings.

Both families are designed to be largely maintenance-free, and the catalog lists orderable accessories and spares by material number — PT100 sensors, PTC thermistor trigger devices, fan control units, and COMPACT-series spare parts on DT-CR, plus monitoring retrofits like SITRAM® H2Guard Lite on DT-O. Beyond parts, our transformer services cover preventive maintenance, diagnostics such as oil analysis, and repair across the asset's operating life.