Electrical Pressboard: Density Classification and Specifications

Introduction to Electrical Paperboard Electrical paperboard is a high-quality insulating material made from speciall...

Introduction to Electrical Paperboard

Electrical paperboard is a high-quality insulating material made from specially processed cellulose fibers. It is widely used in electrical equipment for its excellent dielectric, mechanical, and thermal properties.

Classification of Electrical Pressboard by Density

Electrical pressboard is usually categorized according to its density (g/cm³), as different densities provide different mechanical and electrical properties:

Low-density pressboard
Density: 0.70–0.90 g/cm³
Features: Soft, flexible, easy to bend; suitable for low-stress areas and curved insulation.

Medium-density pressboard
Density: 0.90–1.00 g/cm³
Features: Balanced mechanical strength and flexibility; most widely used, applied in layer insulation and spacers of oil-immersed transformers.

High-density pressboard
Density: 1.00–1.20 g/cm³
Features: High mechanical strength, excellent compressive resistance; mainly used for structural components (spacers, end rings, clamping parts) in large-capacity transformers.

Ultra-high-density pressboard
Density: ≥1.20 g/cm³
Features: Very high strength, low shrinkage, good dimensional stability; used in critical parts of high-voltage and large-scale transformers.

Common Standards

Both international and national standards define density and performance requirements for electrical pressboard:

IEC 60641 – Pressboard and presspaper for electrical purposes

Defines classification, density, oil absorption, dielectric strength, etc.

High-density pressboard generally requires density ≥1.0 g/cm³.

IEC 60763 – Specification for laminated pressboard for electrical purposes

Mainly specifies laminated pressboard.

GB/T 5019-2008 – Electrical pressboard (China National Standard)

Provides detailed requirements on density, oil absorption, dielectric strength, and moisture content.

DIN 7733 (German Standard)

Specifies density ranges and mechanical strength classification.

Application & Selection Guidelines

Low-density: for flexible, bendable insulation parts.

Medium-density: the most commonly used, suitable for general transformer insulation.

High/Ultra-high-density: for components under high mechanical stress and voltage, such as end rings, spacers, and clamping boards.

Classification and Selection of Electrical Pressboard by Density

Selection Summary

By mechanical stress: Low/medium density for low-stress areas; high/ultra-high density for heavy-load structural parts.

By voltage level: The higher the voltage, the higher the density required.

By processing needs: Low/medium density for parts requiring bending and cutting; high/ultra-high density for compression-resistant structural components.