Electrical Paper
Cellulose-based dielectric insulation for transformers, cables and electrical machines
Electrical Paper
Electrical paper is a pure-cellulose insulation material made from unbleached, additive-free sulphate kraft wood pulp. Its homogeneous fibrous structure delivers high dielectric strength, excellent compatibility with insulating oils and liquids, and enough mechanical strength to withstand winding stresses and in-service operation. The properties of electrical insulation paper are governed by IEC 60641.
In oil-filled transformer manufacturing, kraft paper covers copper or aluminium conductors, providing turn-to-turn and layer-to-layer electrical insulation. During vacuum impregnation (typically 60–80°C, minimum 72 hours), the paper absorbs oil up to 150–180% of its initial mass, significantly improving its dielectric and thermal properties. This paper-oil combination forms the main insulation system of the transformer.
In cable manufacturing, insulating paper acts as a separator between components and as a dielectric barrier in oil-impregnated medium- and high-voltage cables. Submarine cables, which operate at very high voltages, use insulating papers of 65 to 155 g/m² which — in addition to their dielectric function — contribute to water blocking in the event of outer-sheath failure thanks to their absorption and swelling capability.
The absence of metallic elements, sand or conductive substances ensures high resistance to folding and tearing, plus dimensional stability throughout the equipment's lifecycle. Electrical paper has no defined melting point, allowing it to withstand short-term thermal stresses up to 350°C without catastrophic degradation.
How to choose the right one?
Selection of the electrical paper depends on the application, the manufacturing process and the operating conditions. The main types differ in structure and mechanical properties.
Electrical paper types
| Type | Structure | Main application | Characteristics |
|---|---|---|---|
| Kraft paper | Smooth, long-fibre | Conductor covering, layer insulation | High tensile strength, good impregnation |
| Crepe paper | Crinkled surface | Irregular geometries, complex windings | High elongation (15–300%), conformability |
| Presspan paper | Calendered, high density | Structural separators, barriers | Greater thickness, mechanical stiffness |
| DDP paper | With epoxy resin dots | Power transformer windings | Layer bonding, short-circuit strength |
Selection by application
| Application | Recommended type | Typical grammage | Notes |
|---|---|---|---|
| Power transformers (oil) | Kraft, DDP | 25–120 g/m² | Impregnation with dielectric oil |
| Distribution transformers | Kraft, Crepe | 40–80 g/m² | Thermal class A (105°C) |
| MV/HV impregnated cables | Kraft | 65–155 g/m² | High dielectric strength |
| Motors and coils | Presspan | Variable | Thermal class B (130°C) available |
| Food packaging | Special kraft | Per application | Consult specific grades |
Technical specifications
Values indicated correspond to typical industry ranges per IEC 60641. Exact specifications available on request by reference.
Typical mechanical properties
| Property | Kraft paper | Crepe paper | Standard |
|---|---|---|---|
| Grammage | 25 – 180 g/m² | 25 – 180 g/m² | IEC 60641 |
| Thickness | 0.05 – 0.50 mm | 0.35 – 0.90 mm | IEC 60641 |
| Elongation | 2 – 5% | 15 – 300% | IEC 60641 |
| Tensile strength | High | Medium-High | IEC 60641 |
Typical electrical properties
| Property | Typical value | Notes |
|---|---|---|
| Dielectric strength | 10 – 12 kV/mm | Dry paper; improves with impregnation |
| Resistivity | High | Varies with moisture and impregnation |
| Dissipation factor | Low | Improves with oil impregnation |
Thermal properties
| Property | Value | Notes |
|---|---|---|
| Thermal class A | 105°C | Continuous service, standard kraft paper |
| Thermal class B | 130°C | Calendered presspan |
| Short-term resistance | Up to 350°C | No defined melting point |
Composition
| Property | Description |
|---|---|
| Base material | 100% sulphate cellulose (kraft pulp) |
| Bleaching | Unbleached |
| Chemical additives | No additives, sizing or fillers |
| Conductive particles | Free of metallic elements |
Degree of polymerisation (DP): The degree of polymerisation per IEC 450 characterises the paper's condition and remaining service life. New kraft paper shows DP between 1000 and 1500. During transformer operation, DP decreases progressively; end of service life is conventionally considered to occur at DP ≈ 200. Values shown are indicative. Consult exact specifications by reference and application.
Available variants
By paper type
- Plain kraft — conductor covering
- Crepe — high elongation for complex geometries
- Presspan — structural barriers and separators
By thermal class
- Class A (105°C) — standard applications
- Class B (130°C) — applications with higher thermal demand
Special formats
- DDP paper (Diamond Dotted Paper) — with epoxy resin dots for power-transformer windings
Delivery formats
Reels / Rolls
Slit tapes
Other formats and dimensions available on request. Custom slitting service available.
Application sectors
Agroalimentario
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Energía eólica
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Energía solar
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Fabricantes cable
View sectorAplicaciones típicas
| Aplicación | Función del producto |
|---|---|
| Oil-immersed transformers | Insulation of conductors and between layers |
| Impregnated MV/HV cables | Dielectric barrier, separation |
| Electric motors | Slot and inter-turn insulation |
| Coils and windings | Layer-to-layer separation, insulation |
| Capacitors | Impregnated dielectric |
Available transformation services
Custom slitting
Up to 1200 mm width, ±0.50 mm tolerance
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Spooling
Conversion to formats matched to the production line
View serviceWe process material from our stock or material supplied by the customer.
Need technical advice?
Our technical team is available to help you select the optimal material for your application.
Local stock in Barcelona · Availability on request