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Oil-Type Hermetic Transformers

STD Transformer > Oil-Type Hermetic Transformers
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General Features

Oil-type hermetic transformers are manufactured in a power range of 25 – 5000 kVA and up to 36 kV high voltage levels, three-phase, oil-immersed, naturally cooled through corrugated walls (ONAN with mineral oil / KNAN with vegetable oil) or fan-cooled (ONAF/OFAF). They can be designed with off-load tap changers or on-load automatic tap changers (OLTC) and can be used both indoors and outdoors. Hermetic oil-immersed distribution transformers are produced based on the principle of vacuum oil filling, ensuring that the oil does not come into contact with the atmosphere by balancing oil and atmospheric pressure at the desired temperature. While transformers above 5000 kVA and 36 kV are generally classified as power transformers, upon customer request, hermetic transformers can be produced up to 16 MVA and 72.5 kV.

Hermetic-type transformers are widely used in distribution networks for residential areas, industrial facilities, electric vehicle charging stations, commercial centers, and public areas. In transmission lines, they are particularly preferred in renewable energy projects.

Unlike standard distribution and transmission transformers, the use of hermetic relays is recommended for transformers of 630 kVA and above. For other power levels, a hermetic relay or double-contact thermometer can be added upon customer request.

The mechanical design of hermetic oil-type distribution transformers is structured to control internal heat by allowing the natural expansion and contraction of the transformer’s corrugated walls in response to changes in oil pressure due to temperature fluctuations.

Compared to expansion tank transformers, hermetic-type transformers have a lower height as they do not require an expansion tank, making them more suitable for cabinet installations. Additionally, since the oil is vacuum-pumped and does not come into contact with the atmosphere, periodic oil changes required in expansion tank transformers are not necessary for hermetic-type transformers.