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Comprehensive Guide to Insulation Materials for Oil Immersed Transformers

by:ZTELEC     Time: 2023-12-15

In the world of electrical engineering, transformers play a crucial role in transferring electrical energy from one circuit to another. Among the various types of transformers, oil-immersed transformers are widely used due to their efficient performance and reliability. One of the key components that ensure their smooth operation is the insulation material. In this blog post, we will dive deep into the world of insulation materials for oil-immersed transformers, exploring their types, properties, and applications.

Insulating materials for oil-immersed transformers

What materials are used in oil immersed transformers?

There are many types of insulation materials used in oil-immersed transformers. What are they and where are they used in the transformer? I will introduce them to you in detail next.

Diamond Dotted Paper:

Diamond dotted paper is a widely used insulation material in oil-immersed transformers. It is primarily utilized as a layer between the winding turns to enhance the mechanical and electrical strength of the insulation system. The diamond-shaped dots on the paper enable better oil impregnation, reducing the risk of partial discharges and improving overall insulation performance.

Oil Duct Strip:

Oil duct strips are crucial for ensuring proper oil circulation within the transformer. These strips, made of insulating material, are strategically placed in the winding structure to create channels for oil flow. They facilitate efficient cooling of the transformer, preventing excessive heat buildup and maintaining optimal operating temperatures.

Electrical Polyester Shrinkable Tape:

Electrical polyester shrinkable tape is commonly used for insulation and protection purposes in oil-immersed transformers. It provides excellent electrical insulation properties and acts as a barrier against moisture and contaminants. This tape is often used for securing winding leads, enhancing the overall insulation integrity of the transformer.

Electrical Cloth Tape:

Electrical cloth tape, also known as friction tape, is utilized in oil-immersed transformers for various applications. This tape provides excellent mechanical protection, acting as a barrier against abrasion, vibration, and physical damage. It is commonly used for securing and bundling cables, enhancing the overall durability and reliability of the transformer.

Unidirectional Binding Tape:

Unidirectional binding tape is employed for strengthening and reinforcing the winding structure of oil-immersed transformers. It is used to secure the windings and maintain their shape, preventing movement and potential damage during operation or transportation. This tape enhances the mechanical stability of the transformer, ensuring long-term performance.

Electric Insulation Phenolic Bakelite Paper Board:

Bakelite paper board is a key insulation material used in oil-immersed transformers. It is utilized for creating barriers and insulation supports within the transformer. Pressboard exhibits excellent electrical and mechanical properties, ensuring the insulation system’s integrity in critical areas, such as between windings and core laminations.

Densified Laminated Wood:

Densified laminated wood, also known as transformer board, is widely used in oil-immersed transformers for various applications. It provides excellent electrical insulation properties and mechanical strength, making it suitable for insulation barriers, support structures, and phase barriers within the transformer. Laminated wood ensures reliable insulation and prevents electrical breakdown.

Phenolic Paper Tube:

Phenolic paper tubes find applications in oil-immersed transformers as support structures and insulation barriers. These tubes offer excellent electrical insulation properties, high mechanical strength, and resistance to moisture and temperature variations. They are commonly used in bushings, coil forms, and other critical areas requiring reliable insulation.

Crepe Paper:

Crepe paper is extensively used for insulation wrapping and cushioning applications in oil-immersed transformers. It provides excellent dielectric strength, flexibility, and resistance to moisture. Crepe paper is commonly used to insulate individual windings, creating a barrier between the conductors and enhancing overall insulation performance.

Cable Paper:

Cable paper, also known as insulation paper, is utilized in oil-immersed transformers for various applications. It provides excellent electrical insulation properties and is often employed for insulating leads, connections, and other areas requiring reliable insulation. Cable paper ensures the safety and performance of the transformer’s electrical components.


Insulation materials are vital components in ensuring the reliable and safe operation of oil-immersed transformers. By understanding the different types, properties, and selection criteria, engineers can make informed decisions when choosing insulation materials for their transformer applications. If you have any technical questions, feel free to consult us. We are here to provide free technical guidance and assistance. We also welcome you to visit our factory or place an order with us.

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