Standard Pressboard: Foundation Insulation for General Applications
Standard pressboard represents the baseline insulation grade manufactured from unbleached sulfate softwood pulp through conventional wet-forming and pressing processes. This material typically achieves densities of 0.90-1.00 g/cm³ with dielectric strengths of 35-45 kV/mm when oil-impregnated, suitable for structural components and insulation barriers in distribution transformers up to 35 kV class.
The manufacturing process involves sheet formation on fourdrinier machines, mechanical pressing to achieve target thickness, and controlled drying to 4-6% moisture content. Standard grades offer excellent dimensional stability and cost-effectiveness for applications including transformer oil duct spacers, end insulation blocks, and core lamination insulation where moderate mechanical loads apply.
Pre-Compressed Pressboard: Enhanced Density for High-Voltage Systems
Pre-compressed pressboard undergoes additional mechanical compaction during manufacturing, achieving densities of 1.10-1.25 g/cm³—approximately 15-25% higher than standard grades. This increased density translates to superior mechanical strength (compressive strength 80-120 MPa) and improved dielectric performance (45-60 kV/mm), making it essential for high-voltage power transformers and interleaved winding structures.
The enhanced rigidity minimizes compression set under mechanical clamping forces, maintaining stable winding pressure throughout the transformer lifecycle. Pre-compressed grades also exhibit reduced oil absorption rates, facilitating faster vacuum drying cycles while maintaining excellent oil compatibility. For critical insulation applications in transformer manufacturing, this grade provides the structural integrity required for 66-500 kV equipment.
Formable Pressboard: Conformability for Complex Geometries
Formable pressboard incorporates specialized fiber treatment and reduced density (0.75-0.90 g/cm³) to achieve exceptional flexibility and moldability. This grade accommodates complex three-dimensional shapes including rounded corners, cylindrical coil forms, and contoured end packs without cracking or delamination, eliminating the need for machined components in irregular geometries.
The material undergoes controlled hydration during processing that allows it to be molded at room temperature or slightly elevated temperatures (60-80°C), then sets to rigid form upon drying. Applications include shaped lead exits, formed angle rings, and specialized pressboard components for compact transformer designs where space constraints preclude rigid machined parts.
Comparative Analysis and Selection Guide
| Grade | Density (g/cm³) | Dielectric Strength | Best Applications |
|---|---|---|---|
| Standard | 0.90-1.00 | 35-45 kV/mm | Distribution transformers, duct spacers |
| Pre-Compressed | 1.10-1.25 | 45-60 kV/mm | HV power transformers, structural barriers |
| Formable | 0.75-0.90 | 30-40 kV/mm | Complex shapes, lead exits, angle rings |
Selection depends on electrical stress calculations, mechanical load requirements, and geometric complexity. Pre-compressed grades command 20-30% price premiums over standard materials, while formable grades typically cost 15-25% more due to specialized processing. SIDA provides comprehensive technical guidance on pressboard selection for specific transformer designs.
Frequently Asked Questions
How do I determine whether standard or pre-compressed pressboard is required for my transformer design?
Specify pre-compressed grades when mechanical compressive loads exceed 5 MPa or operating voltages surpass 66 kV. Standard grades suffice for distribution transformers and structural components subject to moderate mechanical stress. Always consider safety factors for short-circuit forces that may temporarily increase mechanical loads.
Can formable pressboard replace machined components in high-voltage applications?
Formable grades suit complex geometries in low-to-medium voltage applications (≤35 kV) where dielectric stress permits reduced density. However, high-voltage barriers (>66 kV) typically require pre-compressed machined components to ensure adequate dielectric strength and dimensional precision under oil pressure.
What moisture content is acceptable for pressboard at installation?
All grades should arrive at 4-7% moisture content and be processed to <0.5% before oil impregnation. Pre-compressed grades absorb moisture more slowly than standard grades due to reduced porosity, requiring extended vacuum drying cycles for large cross-sections.
Where can I source certified pressboard meeting IEC 60641 standards?
SIDA supplies certified standard, pre-compressed, and formable pressboard grades meeting IEC 60641 specifications. Visit SIDA官网 or contact via WhatsApp. Email jessie.feng@sidanm.com or call +86-15958243831 for quotations.
