Made with grain oriented magnetic laminations cut at 45° and assembled with the step lap method.


Filled with PCB-free oil that has been dried and degassed, and complies with IEC standards.


Made with oval or circular cross-section, with pure cellulose paper or double enamel conductor insulation.


Made in-house, either corrugated or with radiators made from stamped cold-rolled steel.


The primary and secondary windings of oil transformers are made from aluminium and/or copper with pure cellulose paper conductor insulation, or double enamel insulation for small diameter wires. These windings have an oval or circular cross-section, are concentric and coaxial with the core columns.

Transformers up to 6300 kVA can have a flexible corrugated tank, but an oil expansion vessel is recommended for powers exceeding 3150 kVA. For higher powers, radiators made from galvanized stamped cold-rolled steel can be provided on request.

The transformer can be provided with a protective casing on the LV side and/or on the MV side, with or without any busbars and a disconnector/switch on both the MV and LV sides.

The tanks are made in-house and the surfaces are treated with suitable preparation processes, phosphate coated, washed and painted with RAL 7033 water-based coatings using the flow coating method, which ensures excellent resistance in all environments. The standard coating cycle is C3, but for industrial or coastal areas with high humidity and corrosive atmospheres, GBE guarantees C4 and C5 cycles.

The transformers can be hermetic, with an air/nitrogen cushion or with a conservator.

Hermetic oil transformers normally have sealed corrugated tanks that allow the oil to expand as the temperature varies. The tank is sealed up to 0.5 Bar. This type of transformer is the most widely used worldwide. In a hermetic transformer, the oil does not come into contact with the air and its electrical properties are therefore not compromised, ensuring a long service life. For powers exceeding 3150 kVA, or for transformers with radiators, the transformer can still be made hermetic by means of a nitrogen cushion.

Non-hermetic transformers are equipped with a cushion under the cover or a conservator to allow the oil to expand as the temperature varies. Since they are not hermetic, the oil is always in contact with the air through salt filters to capture the moisture. The tank can be corrugated or can have radiators. This design applies to all powers, but especially from 4000 kVA up. For higher powers and to avoid contact between the oil and air, a rubber separator (rubber bag) or nitrogen cushion is used.

up to 6300 kVA
Voltage class
up to 36 kV
CRGO or amorphous
Winding material
aluminium or copper
Oil type
mineral, Midel 7131, vegetable, silicone
no-load, on-load (OLTC)
Ambient temperature
-60°C to +60°C
Overpressure valve, thermometer, oil level, vibration damping, protective casing and more
Strong points
Outdoor installation even in aggressive environmental conditions; no insulation level limits, excellent resistance to resonant overvoltages

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oil transformers? Contact us