Insulation Materials for Oil-Immersed Transformers: Types& Selection Guide

Insulating Materials for Oil-Immersed Transformers Oil-immersed transformers play a crucial role in electrical engin...

Insulating Materials for Oil-Immersed Transformers

Oil-immersed transformers play a crucial role in electrical engineering as one of the core devices in power systems, primarily used for power transmission, distribution, and transformation.
There are many types of insulating materials used in oil-immersed transformers. Choosing high-quality insulation is essential for ensuring transformer safety, longevity, and operational stability. Today, Xujue Electrical engineers will guide you through the main types of insulation materials used in oil-immersed transformers and their applications.

Diamond Dotted Paper (DDP)

Diamond Dotted Paper (DDP), also known as diamond-pattern epoxy-coated insulating paper, is a composite insulating material formed by coating high-purity electrical insulation paper with epoxy resin dots.

In oil-immersed transformers, DDP is primarily used for insulation between the coil and the core, between layers, and between turns. Its double-sided epoxy resin coating ensures strong adhesion to conductors during transformer heating, drying, and vacuum-impregnation processes, forming a stable insulation system. DDP effectively prevents partial discharge and electrical breakdown, enhances dielectric strength and mechanical strength, and improves short-circuit resistance and heat tolerance, ensuring long-term operational safety and reliability.

Oil Duct Strip / Oil Strut Belt

Oil strut belts are made of electrical board strips adhered to DDP (Diamond Dotted Paper). They integrate closely with transformer coils, enhancing both mechanical and electrical performance. These belts are widely applied in oil-immersed transformers.

Electrical Pressboard

In oil-immersed transformers, pressboard is used for electrical insulation between windings, between windings and the core, and at tap changers and bushing locations. It can also be fabricated into support columns, spacers, and partitions to stabilize winding positions, reduce vibration, optimize oil flow, and improve cooling efficiency, thereby enhancing overall insulation performance and operational reliability.

Bakelite sheet (Phenolic Paper Sheet)

Bakelite sheets, or phenolic resin paper sheets, are hard, durable, electrically insulating materials made from phenolic resin reinforced with paper or fabric.
Bakelite sheets are key insulation components in oil-immersed transformers, forming barriers and supports within the insulation system. They exhibit excellent electrical and mechanical properties, ensuring reliable insulation in critical areas, such as between windings and core laminations.

Densified Laminated Wood

Densified laminated wood, also called transformer wood or electrical laminated wood, is widely used in oil-immersed transformers. It provides excellent electrical insulation and mechanical strength, making it suitable for insulation barriers, support structures, and phase separators. Laminated wood ensures reliable insulation and prevents electrical breakdown.

Phenolic Paper Tube

Phenolic paper tubes serve as support structures and insulation barriers in oil-immersed transformers. They offer excellent electrical insulation, high mechanical strength, and resistance to moisture and temperature fluctuations. Common applications include bushings, coil forms, and other critical areas requiring reliable insulation.

Crepe Paper

Crepe paper is widely used for insulation wrapping and cushioning in oil-immersed transformers. It provides excellent dielectric strength, flexibility, and moisture resistance, commonly used to insulate individual windings and enhance overall insulation performance.

Cable Paper

Cable paper, also known as insulation paper, is used in various transformer applications to provide reliable electrical insulation. It is commonly employed for insulating leads, connections, and other areas requiring high electrical performance, ensuring the safety and reliability of transformer components.

Electrical Polyester Shrinkable Tape

Electrical polyester shrinkable tape is used for insulation and protective purposes in oil-immersed transformers. It provides excellent dielectric strength and acts as a barrier against moisture and contaminants, often used to secure winding leads and enhance overall insulation integrity.

Electrical Cloth Tape

Electrical cloth tape, or friction tape, is employed in transformers for mechanical protection, shielding against abrasion, vibration, and physical damage. It is commonly used for securing and bundling cables, improving the durability and reliability of the transformer.

Conclusion

Insulating materials are a critical component for ensuring the safe and reliable operation of oil-immersed transformers. By understanding the different types, properties, and selection criteria, engineers can make informed decisions when choosing insulation materials for transformer applications.

Xujue Electrical, a professional manufacturer of electrical insulating materials since 1958, is one of China’s six major insulation production bases, equipped with automated production workshops and advanced insulation processing equipment.

For technical inquiries, Xujue Electrical provides free technical guidance and one-stop solutions for transformer insulation materials. We also welcome visits to our factory for long-term cooperation.