Electrical paper pressboard is one of the core solid insulation materials used in oil-immersed power transformers. Known for its excellent dielectric strength, mechanical rigidity, and oil compatibility, pressboard ensures the long-term stability and reliability of transformer operation. As global demand for higher-efficiency and longer-lifespan transformers grows, high-quality electrical pressboard has become essential in transformer manufacturing and refurbishment.
Electrical pressboard is a cellulose-based insulation material made from 100% sulphate wood pulp or cotton-linter pulp. Through a mechanical pressing and drying process, the fibers form a dense and uniform structure. Its insulation performance is further optimized by high-temperature curing, making it suitable for harsh electrical and thermal environments inside power transformers.
Pressboard is typically used in combination with transformer insulating oil, forming a complete solid–liquid insulation system.
High Dielectric Strength
Good cellulose purity and dense fiber structure give pressboard a dielectric strength of ≥70 kV/mm in oil, ensuring strong resistance to electrical stress.
Excellent Mechanical Strength
Pressboard maintains dimensional stability under high compression. Even in oil-filled conditions, it:
• Resists deformation
• Endures mechanical shock
• Withstands tightening forces in winding structures
Strong Oil Compatibility
During long-term immersion, the pressboard absorbs transformer oil, improving insulation and extending service life. No chemical reactions or degradation occur with qualified mineral oil or synthetic oils.
Thermal Class A (105°C)
Electrical pressboard can operate continuously at 105°C, and withstand short-term thermal stress during overload or short circuits.
Low Moisture & Dehydration Stability
Moisture significantly affects insulation performance. High-quality pressboard has:
• Initial moisture content below 10%
• Ability to reach <1% moisture after vacuum drying
This gives transformers higher dielectric reliability.
Electrical pressboard is used throughout the insulation structure of power and distribution transformers, including:
Spacer blocks
Keep proper distance between low- and high-voltage winding layers.
End rings and cylinders
Provide mechanical support and insulation to winding ends.
Clamping and supporting parts
Enhance structural stability under short-circuit forces.
Oil duct spacing
Ensure smooth oil circulation and better heat dissipation.
Lead insulation and barrier boards
Prevent electrical breakdown between conductors.
Laminated structures
Made into 3-ply or multi-ply pressboard components for high-voltage insulation.
Its versatility makes it key to transformer performance, especially in medium and high voltage levels.
A stable insulation system directly affects the life expectancy of a transformer. Using certified pressboard ensures:
• Reduced dielectric failures
• Lower partial discharge risk
• Better heat distribution
• Long-term mechanical stability
• Reliable service life up to 30+ years
For OEM transformer factories and maintenance companies, choosing high-grade cellulose pressboard significantly reduces failure rates and after-sales problems.
When selecting pressboard for oil transformers, consider the following:
Thickness:
Common sizes range from 0.5 mm to 30 mm based on application.
Density and rigidity:
Higher density improves compression resistance and mechanical strength.
Certification:
Ensure compliance with IEC 60641
Moisture content:
Lower moisture means higher dielectric performance.
Processing capability:
Pressboard should be suitable for CNC machining, punching, and bending.
As a manufacturer specializing in transformer insulation materials, XuJue supplies:
• High-density electrical pressboard
• 100% high purity sulphate wood pulp
• Precision-machined pressboard components
• Custom transformer insulation kits
We offer fast delivery, stable quality, and technical support for OEM transformer factories worldwide.
