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Transformer Pressboard is an essential solid insulation material in oil-immersed transformers. Different transformer types vary significantly in voltage level, short-circuit withstand capability, thermal requirements, and mechanical stress. Therefore, the selection of pressboard must be optimized according to the transformer’s structure and operating conditions.
This guide covers pressboard selection for distribution transformers, power transformers, special transformers, and dry-type transformers.
Lower voltage levels
Simpler structure
Cost-efficient and stable performance
Widely used in industrial, commercial, and municipal distribution networks
| Application | Suggested Specification |
|---|---|
| Interlayer & end insulation | 1–2 mm normal-density pressboard |
| Oil duct spacers & separators | 3–4 mm normal-density pressboard |
| Structural support components | 5–8 mm normal- or medium-density pressboard |
Electrical stress is relatively low; normal density is sufficient
A-class (105°C) insulation meets thermal requirements
Cost-effective for mass-production distribution transformers
High voltage levels
Requires strong short-circuit mechanical strength
Complex oil ducts and multi-layer insulation structures
Mainly applied in substations and heavy-industry projects
| Application | Suggested Specification |
|---|---|
| Interlayer/section insulation | 1–3 mm high-density pressboard |
| Coil end insulation | 3–5 mm high-density pressboard |
| Oil duct panels / spacers | 5–10 mm high-density pressboard |
| Press rings / structural components | ≥8 mm high-density pressboard |
High-density pressboard offers higher dielectric strength (≥60 kV/mm)
Superior mechanical stability under short-circuit forces
Minimal deformation after machining, suitable for precision oil duct design
Large currents and fluctuating loads
Strong electrical and mechanical impacts
High thermal variations
Harsh operating conditions
| Transformer Type | Recommended Pressboard |
|---|---|
| Rectifier / converter transformers | High-density, high-thermal-class pressboard (F-class 155°C) |
| Furnace transformers | High-density and thick pressboard (8–12 mm) for structural support |
| Traction / railway transformers | Vibration-resistant, high-temperature pressboard |
| PV and wind power transformers | Moisture-resistant high-density pressboard |
Requires excellent mechanical and thermal stability
Must withstand heavy short-circuit forces
Higher thermal class improves long-term reliability in unstable environments
Characteristics:
Air-cooled or forced-air-cooled
No insulating oil, full dependence on solid insulation
Frequent thermal shocks and localized hot spots
Recommended Pressboard Specifications:
1–3 mm boards: interlayer and section insulation
3–6 mm boards: structural supports and inner liners
F-class (155°C) or H-class (180°C) materials are preferred
Reasons:
Dry-type transformers experience higher temperature rises
High-density materials ensure dimensional stability in non-oil environments
| Transformer Type | Priority Material | Thickness | Density | Thermal Class |
|---|---|---|---|---|
| Distribution | Normal-density | 1–5 mm | Normal/Medium | A-class |
| Power | High-density | 1–10 mm | High density | A or F-class |
| Special | High-thermal, high-density | 3–12 mm | High density | F-class or above |
| Dry-type | High-thermal, high-density | 1–6 mm | Medium/High density | F/H-class |
Check short-circuit withstand capability (determines density)
Select thickness based on oil duct structure
Control moisture content ≤ 7% (pre-dry before assembly)
CNC or laser-cut parts are recommended for high-end transformers
For outdoor or high-humidity areas, choose moisture-resistant high-density board
