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What's the Oil - Immersed Transformer?

Oil - immersed transformer is a kind of voltage conversion device which uses oil - cooled way to reduce transformer temperature. Unlike dry transformers, the body of oil-immersed transformers is mounted in a welded steel tank filled with insulating oil. When the oil-immersed transformer is in operation, the heat of the coil and core is first converted into insulating oil, and then into the cooling medium. And according to the capacity size, it can be divided into immersed natural cooling transformer and immersed forced air cooling transformer.

Detail of Oil - Immersed Transformer

An oil-immersed transformer consists of a core and coil assembly immersed in a fluid, usually mineral oil. The fluid must have both good heat transfer and electrical insulation properties. One advantage of liquid-immersion transformers is that they allow for compact design. Typically, transformers above 10 MVA and/or 34.5 kV are liquid-filled. Since oil is flammable, sufficient precautions must be taken when using liquid-immersion transformers to identify oil flammability. This poses challenges for indoor applications.

Advantages of Oil - Immersed Transformer

The primary and secondary windings used in oil-immersed transformers shall be made of electric-grade copper, with a minimum conductivity of 98% of the International Annealed Copper Standard (IACS) for copper used in electrical conductors. The conductor shall be wound by machine helix with several overlapping layers of insulating paper. This process should detect and eliminate conductor burrs that may affect the dielectric integrity of the winding. The winding shall be given no more than one varnish dip treatment, It should be used for mechanical protection, not to improve dielectric properties. However, under no circumstances should varnish or other adhesives be used to seal the coil and prevent air and water discharge and oil impregnation.