In modern power systems, the reliability of oil-immersed transformers directly depends on the performance of their internal insulation materials. Among these materials, High Density G4 Pressboard has become one of the most widely used and trusted solid insulation solutions for medium- and high-voltage transformers.
This article explores its material composition, key properties, typical applications, and why G4 remains the preferred insulation pressboard in the transformer manufacturing industry.
G4 Transformer Pressboard is a high-density cellulose-based insulation material made from 100% sulfate wood pulp. It is manufactured through a purification, layering, pressing, and drying process that ensures excellent mechanical strength and dielectric performance.
G4 pressboard is specifically designed for use in oil-immersed transformers, where it must maintain stability under mechanical stress, electrical load, and thermal aging.
Key Features & Advantages of G4 Pressboard
1. Excellent Dielectric Strength
G4 pressboard has high electrical insulation capability, providing stable dielectric strength in transformer oil. This ensures safe operation of the transformer under high voltage stress.
2. High Density & Mechanical Strength
With its dense fiber structure, G4 pressboard can withstand:
• High compressive forces
• Bending stress
• Long-term clamping pressure inside windings
This makes it suitable for structural insulation such as spacers and support blocks.
3. Outstanding Compatibility with Transformer Oil
The material absorbs transformer oil quickly and uniformly, improving its electrical insulation properties. It also has excellent oil resistance and does not produce harmful substances during long-term oil immersion.
4. Good Thermal Stability
G4 pressboard maintains mechanical integrity and insulation performance under elevated temperatures, making it reliable for continuous operation.
5. Dimensional Stability
Even after long operation cycles, G4 pressboard maintains its thickness and shape, contributing to the transformer’s overall structural stability.
Typical Applications in Transformers
High Density G4 Pressboard is widely used in power transformers, distribution transformers, and reactor insulation systems. Common applications include:
• Coil spacers & key spacers
• End insulation rings
• Strips and package blocks
• Barriers and partitions
• Winding cylinder reinforcement
• Molding parts & CNC-machined components
Because of its high density and stability, G4 pressboard is ideal for CNC machining to create custom insulation parts with tight tolerances.
Transformer environments demand materials that can endure electrical stress, high temperature, oil immersion, and mechanical impact. G4 pressboard fulfills all these requirements with consistent quality and long-term durability.
Compared with lower-grade pressboard, G4 provides:
• Higher density
• Stronger mechanical performance
• Better purity and fiber bonding
• Lower moisture content
• Higher dielectric strength
This makes it a preferred choice for high-reliability and high-voltage transformer designs.
Special sizes and custom machining available upon request.
We also offer:
• CNC-machined insulation blocks
• Spacer strips
• Oil-duct components
• Molding parts
Insulation kits for transformer winding assemblies
Our products comply with IEC 60641 standards and are widely used in global transformer factories.
High Density G4 Pressboard plays an essential role in ensuring the safety and reliability of oil-immersed transformers. With strong mechanical properties, excellent dielectric performance, and perfect compatibility with transformer oil, it remains one of the core insulation materials in the transformer industry.
For transformer manufacturers and EPC contractors looking for stable supply and high-quality insulation solutions, G4 pressboard is a proven and cost-effective choice.
