Oil Immersed Transformer | MBT Transformer

Oil-immersed transformer definition, composition, and design features

Power transformers are the most important components of an electrical grid. Transformers designs differ by the cooling and electrical insulation systems used. There are dry transformers and oil-immersed transformers. Most of the transformers in service are oil-immersed. So let's find out through the article below.

Table of contents

1. What is an Oil Immersed Transformer?

2. Structure and operation principle of Oil-immersed transformer

3. Types of Oil-immersed transformer

a. One-phase oil-filled transformer

b. Three-phase Oil Immersed Transformer

4. Purpose of using Oil Immersed Transformer

5. Cautions when using an Oil-immersed transformer


1. What is an Oil Immersed Transformer?

An oil-immersed transformer, also called Oil filled transformer, is a kind of voltage transformation device utilizing the oil cooling method to reduce the transformer temperature. Unlike the dry type transformer, the body of the Oil-immersed transformer is installed in the welded steel oil tank filled with insulation oil. When an Oil-immersed transformer in operation, the heat of the coil and iron core firstly is transformed into the insulation oil and then to the cooling medium. And according to the capacity sizes, it can be divided into an immersed natural cooling transformer and an immersed forced air cooling transformer.

2. Structure and operation principle of Oil-immersed transformer

An Oil-filled transformer is structurally similar to that of a transformer. It's one of the types of transformers classified according to the form of core insulation. Hence, it has the identifiable feature of oil-immersed coils to lower the heat map of the devices within it. 

The basic elements of an oil-immersed are consist of the magnetic core, windings, and bushings. The magnetic core provides a path for magnetic flow. Windings create a magnetic field and consist of a conductor coil, wrapped around the core and insulated with pressboard barriers and screens. The thickness of the winding insulation increases with voltage. Bushings connect transformer windings to a substation. 

Oil-type transformers are used in power distribution or electrical substations. Their core and coils are immersed in Oil, which cools and insulates. Oil circulates through ducts in the coils and around the coils and core assembly, moved by convection. The Oil is cooled by the outside of the tank in small ratings, and by an air-cooled radiator in larger ratings.

Structure and operation principle of Three-phase transformer

3. Types of Oil-immersed transformer

The Oil-immersed transformers have two main types as 1-phase transformer and 3-phase transformer.

a. One-phase oil-filled transformer


One-phase Oil-immersed transformer 50KVA-25KVA-15KVA


b. Three-phase Oil Immersed Transformer

Open-type 3-phase oil-mmersed transformer (left) and Closed-type 3-phase oil-immersed transformer(right)

4. Purpose of using Oil Immersed Transformer

Oil-type transformers can be ground-, pad- or pole-mounted for use outdoors. They deliver efficient performance in diverse applications, including transmission and distribution networks, renewable energy generation, and small industries.

The oil transformer has a huge capacity, so it will save a lot of electrical energy, minimize power loss, save energy sources, and reduce costs for users. More than that, the Oil in the machine cools the internal wire cores to contribute to the durability and electrical properties of the transformer equipment.

5. Cautions when using an Oil-immersed transformer

  • An Oil-filled transformers use Oil to operate, so the quality of the Oil will significantly affect the transformer's life and safety.
  • During use, it is necessary to regularly check and maintain the transformer system to ensure the machine works well and safely. If not, it is very easy to cause problems and extremely dangerous risks.
  • The waste from Oil is easy to pollute the environment, affecting the surrounding people's lives. Therefore, the gradual waste treatment is also very important.

=> For more information and support from a team of leading experts in transformer manufacturing and manufacturing. Please contact immediately +84913 006 538 or email:  [email protected].

Best regard,
Hanoi Electric Power Transformer Manufacturing Joint Stock Company (MBT)


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