Electrical Insulation Papers
High-purity cellulose-based dielectric paper. Manufactured from 100% sulphate wood pulp — zero chemical additives, zero sizing agents. Delivers consistent breakdown voltage, superior oil absorption and dimensional stability across full roll width.
Four primary grades cover every transformer and motor insulation need: Kraft paper, Crepe paper, Press paper (Pressphan), and Diamond Dotted Paper (DDP). All grades conform to IEC 60554 and IEC 60641 standards.
Four Core Product Grades
Each grade solves a distinct engineering challenge. Select by application, voltage class and impregnation method.
Kraft Paper
Flat, high-density cellulose paper. Maximum dielectric strength per unit thickness. Ideal for layer insulation and inter-winding barriers in oil-immersed transformers.
IEC 60554-3-5 · Class 5B2 H1Crepe Paper
Mechanically crinkled; 15–300% elongation. Conforms to irregular shapes. Used for lead wrapping, terminal insulation and coil end protection.
High Elongation · Oil-CompatiblePress Paper (Pressphan)
Dense, calendered kraft. High mechanical strength and dimensional stability. Functions as structural spacers, duct barriers and inter-layer insulation.
IEC 60641-2 · High DensityDiamond Dotted Paper (DDP)
Press paper partially coated with epoxy resin dots. Bonds winding layers under heat — resists short-circuit displacement forces. Minimises partial discharge risk.
Epoxy Resin · Foil Wound TxGrade Comparison at a Glance
| Property | Kraft | Crepe | Press Paper | DDP |
|---|---|---|---|---|
| High Dielectric Strength | ||||
| Flexibility / Elongation | ||||
| Structural / Load-Bearing | ||||
| Winding Layer Bonding | ||||
| Oil Impregnation Speed | ||||
| Short Circuit Resistance |
Technical Overview
Electrical insulation papers operate at the core of every oil-immersed transformer, motor slot and HV switchgear assembly. High cellulose purity — ash content below 1.0% — ensures no metallic contamination reaches the insulating fluid. Relative permittivity of ~4.4 pairs with oil (permittivity ~2.2) to create a graded dielectric barrier that suppresses partial discharge initiation.
Cellulose fibre refining controls density, porosity and inter-fibre bonding. Denser grades (press paper) resist mechanical deformation under electromagnetic stress. Open-structured grades (kraft, crepe) maximise capillary oil uptake — fully impregnated papers achieve dielectric strength above 60 kV/mm versus ~15 kV/mm dry.
All papers remain chemically inert in mineral oil (ASTM D 3487), alkyl benzene and synthetic ester (MIDEL) fluids. No sulphur compounds that trigger sulphidation of copper conductors.
Key Features
- 60 kV/mm dielectric strength when fully oil-impregnated — consistent breakdown voltage across full sheet area
- 100% sulphate wood pulp — zero chemical additives, low ionic contaminants, low power factor
- Low ash content (<1.0%) — no metallic particles that degrade oil or create conductive paths
- High oil absorption (wicking) — enables rapid vacuum impregnation in oil-filled transformer tanks
- Thermal Class A (105°C) — stable performance at rated operating temperature per IEC 60085
- Custom slit rolls from 40 mm — burr-free edges, consistent reel tension for CNC winding machines
- Fire-retardant grades available for dry-type transformer and switchgear applications
- Moisture content <8% at 50% RH — stable in tropical climates and humid storage environments
Applications by Industry
- Oil-immersed power transformers (11 kV–132 kV): Layer insulation, conductor wrapping, inter-winding barriers, lead insulation and duct spacers. Kraft and DDP used in distribution transformer coils.
- Dry-type transformers: Press paper structural components, crepe paper lead insulation, fire-retardant grades for indoor/cast-resin units.
- Motor and generator winding: Slot insulation, phase-to-phase separation, coil end protection in AC and DC machines (Class A and Class E).
- HV switchgear and current transformers: Capacitance grading, dielectric shielding, bushing insulation and oil-impregnated instrument transformer wrapping.
- Power and film capacitors: Primary dielectric spacer in oil-impregnated paper capacitors — uniform thickness prevents localised field intensification.
- Paper-insulated cables: Conductor wrapping for PILC and mass-impregnated oil cables in MV underground distribution.
Technical Specifications
| Standard Physical & Electrical Properties | |
|---|---|
| Thickness Range | 0.025 mm to 12 mm |
| Density (by grade) | 300 to 1200 kg/m³ |
| Thermal Conductivity | 0.035 to 0.07 W/mK |
| Dielectric Strength (dry) | 15 kV/mm to 25 kV/mm |
| Dielectric Strength (oil-impregnated) | Up to 60 kV/mm |
| Relative Permittivity | ~4.4 (dry) / ~3.5 (oil-impregnated) |
| Moisture Content | < 8% (at 50% relative humidity) |
| Ash Content | < 1.0% (high purity grades) |
| Crepe Elongation (crepe paper) | 15% to 300% |
| Thermal Class | Class A — 105°C (IEC 60085) |
| Standard Compliance | IEC 60554-3-5, IEC 60641-2, IS 1576 |
| Custom Roll Widths | 40 mm upwards — precision slit, burr-free edges |
Engineering Tools Suite
Calculate dielectric safety margins, oil impregnation rates and thickness requirements for transformer design. Interactive tools — no login required.
Frequently Asked Questions
Kraft paper — flat, high-purity, maximum dielectric strength per mm. Use for layer insulation and inter-winding barriers in oil-immersed transformers.
Crepe paper — mechanically crinkled, 15–300% elongation. Use for wrapping transformer leads, terminal connections and coil ends where conformability matters.
Press paper (Pressphan) — dense, calendered, high mechanical load capacity. Use as structural duct spacers and inter-layer barriers that must resist electromagnetic deformation forces.
Diamond Dotted Paper (DDP) — epoxy-coated press paper. Use in foil-wound transformers — bonds winding layers under heat, resists short-circuit displacement, speeds vacuum impregnation via open channels.
Yes. Kraft paper conforms to IEC 60554-3-5 Class 5B2 H1. Press paper and pressboard conform to IEC 60641-2. Diamond Dotted Paper conforms to IEC 60554-3-5 Class 5B2 H1 base with epoxy coating per Hitachi/Weidmann reference standards. Zero chemical additives — 100% sulphate wood pulp ensures compliance with transformer fluid compatibility requirements.
All grades stay chemically inert in mineral transformer oil (ASTM D 3487), alkylbenzene and synthetic ester (MIDEL) fluids. Excellent capillary oil absorption enables rapid vacuum impregnation. Fully impregnated dielectric strength exceeds 60 kV/mm. No sulphur compounds, no metal elements, no conductive acidic substances that contaminate insulating fluid or corrode copper conductors.
In-house slitting and rewinding equipment provides widths from 40 mm upwards — any increment to match CNC winding machines. Burr-free edges, consistent reel tension. Core diameter matched to customer equipment. Contact our technical team for MOQ and lead time based on grade and quantity.
