Pressboard is one of the most common insulation materials used in transformer production. This guide explains what it is, how it’s made, and where it’s used inside power equipment.
1.What Is Electrical Pressboard?
Electrical pressboard is a cellulose-based solid insulation material, made from high-purity kraft pulp processed under high pressure and temperature. Unlike resin-based materials, it provides strong mechanical and dielectric performance without synthetic additives.
The use of unbleached, high-purity kraft fibers ensures low conductivity and high oil affinity — a key reason it’s preferred for high-voltage insulation.
It is commonly referred to as:
- Transformer pressboard
- Pressboard insulation material
- Electrical insulation pressboard
➡️ As defined by IEC 60641, pressboard is standardized for use in electrical insulation systems.
2.Why Pressboard Is Used in Transformers
Pressboard plays a critical role in maintaining both electrical insulation and mechanical structure inside transformers. Key reasons include:
- High dielectric strength – Withstands up to 60 kV in oil-immersed environments
- Mechanical integrity – Supports coils and windings under operational stress
- Oil compatibility – Absorbs transformer oil efficiently, improving insulation life
➡️ That’s why pressboard in transformers is preferred in both high-voltage and medium-voltage applications.
3.Common Applications in Transformer Manufacturing
Pressboard is shaped into various profiles and parts used throughout transformer assembly:
- Cylinder insulation sleeves around windings
- End rings and axial spacers for layer separation
- Coil duct strips and barriers for airflow and insulation gaps
- Pressboard blocks, sheets, and strips for mechanical reinforcement
It is used in:
- Dry-type transformers
- Oil-filled transformers
- Reactor and choke coils
➡️ These components are essential to maintain thermal isolation, oil channeling, and mechanical spacing in transformer construction.
4. Key Technical Parameters
| Property | Typical Value |
|---|---|
| Thickness Range | 0.3 – 8.0 mm |
| Dielectric Strength | ≥ 60 kV (in oil) |
| Density | ~1.0 – 1.2 g/cm³ |
| Moisture Content | < 7% |
| IEC Standard | IEC 60641 |
These values make it highly reliable for Class A and Class E transformer designs.
5.Material Comparison Summary
| Material | Strengths | Use Case |
| Presspaper | Flexible, thin | Interlayer insulation |
| Densified Wood | Stronger, CNC-milled | Clamping, support beams |
| Pressboard | Moderate strength, flat & round shape formability | Cylinders, strips, barriers |
➡️ Pressboard is the best choice when you need oil-absorbent, formable, and layered insulation parts.
6.How to Source Quality Pressboard
When sourcing electrical insulation pressboard, consider:
✅ Certification: IEC 60641, ISO 9001, and RoHS/SGS testing
✅ Batch QC: Consistency in thickness, density, and fiber bonding
✅ Processing options: CNC pre-cutting, die punching, sheet lamination
Common supply formats:
- Rolls and flat sheets
- Custom pressboard blocks and duct strips
- High-density CNC-shaped profiles for core supports
➡️ We’ve helped over 50 OEMs across Asia and the Middle East cut procurement costs by 20% with our CNC-ready pressboard solutions.
7.Conclusion & CTA
Electrical pressboard remains essential in transformer design due to its unique combination of dielectric performance, mechanical support, and oil adaptability.
Email: jessie.feng@sidanm.com
📲 WhatsApp: +86-15958243831
✅ Response within 24 hours. Technical drawings and samples available on request.
