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What Is an Oil-immersed Transformer?

Jul. 19, 2021


A transformer in which the magnetic circuit and windings are immersed in oil. Oil-immersed transformers are used in power distribution or substations. Their cores and coils are immersed in oil, thus cooling and insulating.

Why do transformers need oil?

Transformer oil is a mineral oil that is commonly used in transformers because of its chemical properties and dielectric strength. This oil in the transformer acts as an insulator and coolant. The acid will form deposits and settle on the windings of the transformer, resulting in reduced heat dissipation.


Structure of oil-immersed transformer

Oil-immersed transformers consist of a magnetic core, windings, and bushings. The core provides the path for the magnetic flow. The winding generates the magnetic field and consists of a conductor coil wound around the core and insulated with a cardboard barrier and screen. The thickness of the winding insulation increases as the voltage increases. The bushing connects the transformer windings to the substation. A feature of oil-immersed transformers is the oil storage cabinet. It simplifies operation by monitoring the oil level in the tank and providing space for the thermal expansion of the oil.

Oil-immersed Transformer

 Oil-immersed Transformer

Characteristics of oil-immersed transformers

Oil-immersed transformers are transformers that use transformer oil as the heat dissipation medium. Oil-immersed transformers have been used in power systems for centuries in transmission and distribution projects. Oil-immersed power transformers have become one of the most widely used electrical equipment in the world because of their simple structure, long history, rich manufacturing operation, and reliable operation. Most of the transformers operating in the power system are oil-immersed transformers. As the name suggests, a dry-type transformer is a transformer that uses air instead of transformer oil as the heat dissipation medium.


Transformer basic structure  

Transformer oil is used as the cooling medium for oil-immersed transformers. The heat generated during the operation of the transformer is transferred from the transformer oil to the metal casing and dissipated. It has the advantages of fast heat dissipation, uniform conduction, and recoverable insulating properties of the oil. However, the oil itself has low heat resistance, is flammable and easy to age, and other shortcomings, so there are many specific requirements when using transformer oil as a cooling medium.


For example, the building where the transformer is placed must meet the requirements of the fire resistance level specified in the fire code for buildings; measures must be taken to prevent the spread of fire caused by oil flow in case of fire; fire extinguishing measures must be available to put out oil fires; oil storage pool facilities must be available to prevent oil leakage from polluting the environment; daily work should monitor the aging of insulating oil and regular oil regeneration work, etc.


Moreover, there are strict distance requirements for the minimum net distance between the outer profile of the oil-immersed transformer and the walls and doors of the transformer room. The various civil structures, fire barriers, and storage tanks of oil-immersed substations are designed because of the flammability and fluidity of the oil. In addition, "when the substation room is located in a building, the door should be a Class A fire door". In this way, the construction investment of each substation designed for fire protection is naturally much larger.

If you want to get more information about the best oil-immersed transformer wholesale, welcome to contact us today or request a quote.

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