Electrical Insulating Paperboard: Application of T4 Insulating paperboard in Oil-Immersed Transformer Windings

The reliability of the insulation system in oil-immersed power transformers is directly related to operational safety, service life, and long-term stability. Electrical insulating paperboard is a core solid insulation material in oil-immersed transformer insulation systems and is widely used for internal winding structure insulation. Among these materials, T4 insulating paperboard has become a key and widely applied solution in medium- and high-voltage oil-immersed transformer windings, thanks to its excellent electrical properties, high mechanical strength, and strong compatibility with transformer oil.

This article provides a systematic analysis of the performance characteristics of T4 insulating paperboard, its typical application scenarios in oil-immersed transformer windings, and key selection considerations, helping transformer manufacturers and procurement professionals better understand its application value.

Fundamental Role of Electrical Insulating Paperboard in Oil-Immersed Transformers

Electrical insulating paperboard (also known as insulation board) is manufactured from high-purity raw materials through specialized processes, offering outstanding electrical insulation performance and mechanical strength. In oil-immersed transformers, its main functions are reflected in four key aspects:

Electrical Insulation: Isolates potential differences between windings, and between windings and the core, preventing insulation breakdown.

Mechanical Support: Secures the winding structure and withstands electrodynamic forces generated by short-circuit currents.

Thermal Management: Works together with transformer oil to form an oil–paper insulation system, improving heat dissipation efficiency.

Oil Duct Formation: Creates oil circulation channels to ensure effective cooling of the equipment.

T4 Electrical Insulating Paperboard Overview 

T4 electrical insulating board is a high-performance laminated insulation board manufactured from high-purity sulfate insulating wood pulp through specialized processing techniques. Its technical specifications comply with both international and domestic electrical insulation standards such as IEC and GB, and it is widely used in the manufacturing of oil-immersed transformers.

Key Characteristics of T4 Electrical Insulating Paperboard:

High dielectric strength

Good thermal stability

Low dielectric loss and high electrical resistivity

Uniform density with tight thickness tolerances

Good environmental performance and long-term durability

Typical Applications of T4 Electrical Insulating Paperboard in Oil-Immersed Transformer Windings

1. Interlayer Insulation of Windings

Between high-voltage and low-voltage windings, T4 electrical insulating paperboard is primarily used to manufacture interlayer barriers and turn-to-turn support components. Its stable dielectric performance effectively reduces the risk of partial discharge and helps prevent insulation breakdown.

2. End Insulation Structures of Windings

The winding end regions are areas with concentrated electric fields. T4 electrical insulating board can be processed into end insulation barriers and insulating spacers, helping to optimize electric field distribution and enhance the overall dielectric withstand level of the transformer.

3. Axial and Radial Oil Duct Support

T4 electrical insulating paperboard can be custom-processed into oil duct spacers and support strips in various specifications. While ensuring the mechanical strength of the windings, it forms stable oil circulation channels, thereby improving the transformer’s heat dissipation efficiency.

4. Load-Bearing and Short-Circuit Withstand Structures

Under short-circuit impact conditions, transformer windings are subjected to significant electrodynamic forces. Thanks to its high compressive and shear strength, T4 electrical insulating paperboard effectively supports the winding structure and prevents displacement or deformation. It is a critical material for enhancing a transformer’s short-circuit withstand capability.

Technical Considerations for Selecting T4 Electrical Insulating Paperboard

Thickness and Layer Design: Determine the appropriate board thickness and layer configuration based on the transformer’s voltage class.

♦ Pre-Treatment Process: Strictly implement drying and oil-impregnation procedures to completely remove internal moisture and air bubbles.

♦ Compatibility Testing: Verify long-term compatibility between the insulating board and the specified brand of transformer oil.

♦ Environmental Compliance and Certifications: Products should comply with international and national standards such as IEC, IEEE, and GB.

♦ Supplier Qualifications: Prioritize manufacturers with stable quality control and reliable supply capabilities.

The quality and application level of electrical insulating paperboard—especially T4 electrical insulating paperboard—directly affect transformer operating performance and service life. Proper selection of T4 insulating paperboard is a critical technical decision and an important measure to ensure both economic efficiency and operational safety. With the continuous advancement of materials science and insulation technology, T4 electrical insulating paperboard will continue to play a vital role in power equipment, supporting the stable and reliable operation of power grids worldwide.