Bulk Diamond Dotted Paper for Transformer Winding Insulation – Custom Sizes & Thickness Available

In dry-type transformers, interlayer insulation not only needs to meet standard requirements but also directly affects the transformer's service life and operational safety. Among various insulation materials, diamond dotted paper (DDP) is a commonly used and reliable choice.

This is because it prevents displacement between winding layers while maintaining good dielectric strength. If you are sourcing materials for large-scale transformer production, choosing a bulk supplier that can provide custom sizes and thicknesses is crucial.

This article introduces the advantages of diamond dotted paper, thickness selection, and how to make precise, customized bulk purchases.

Diamond dotted paper is a composite insulation material made from high-quality kraft paper or Nomex® paper as a base material, with a surface coated with thermosetting epoxy resin dots in a diamond pattern.

Working Principle:

Base Paper: Provides mechanical strength and dielectric insulation.

Epoxy Resin Dots: Forms controlled air gaps and an adhesive layer.

Diamond Pattern: Ensures uniform resin distribution and prevents lateral movement of winding layers.

When a transformer undergoes heat curing (during impregnation or drying), the epoxy resin melts, bonding adjacent layers together, and then re-cures. This results in a stable coil structure that is resistant to vibration and can withstand the electrodynamic forces generated by short circuits.

Key Features of Diamond Dotted Paper

Excellent Electrical Insulation

The diamond-shaped adhesive structure forms a stable insulating layer upon heating, increasing dielectric strength and reducing the risk of partial discharge.

High Mechanical Strength

After curing, the adhesive enhances interlayer adhesion, making the winding structure more compact and stable, reducing vibration and displacement.

Good Heat Resistance 

Suitable for transformer designs at various temperature levels, meeting the thermal stability requirements for long-term operation.

Improved Overall Winding Reliability 

Helps maintain winding shape during operation, extending transformer lifespan.

Key Advantages of Diamond Dotted Paper: Custom Sizes and Thickness

Standard rolls often fail to fully meet production requirements. Material waste and mismatched thickness are common challenges faced by transformer engineers. The following explains why customization is essential for bulk buyers.

Custom Width and Roll Length

Problem:

When a standard 1000 mm wide roll is used for small cores, about 150 mm of edge waste is generated on each side.

Solution:

Custom manufacturers can slit the material according to the exact width of your winding machine, ranging from 10 mm to 1500 mm. This eliminates edge waste and reduces the cost per transformer.

Custom Thickness

The total thickness includes the base paper thickness and the height of the epoxy resin dots. We offer four main ranges:

Custom thicknesses outside these ranges are also available upon request.

Custom Dot Coating Pattern

Dot Diameter: Standard options of 2 mm, 3 mm, or 4 mm 

Dot Spacing: Center-to-center spacing from 5 mm to 20 mm 

Bonding Strength: Adjustable resin content from 15 g/m² to 35 g/m² 

Diamond Dotted Paper Bulk Procurement Guide: Key Points for Supplier Selection

Diamond dotted papers produced by different manufacturers vary. When ordering bulk diamond dotted paper for transformer windings, please confirm the following four items:

1. Heat Resistance Rating

Ensure the material meets the transformer's temperature rating:

F-grade (155°C): Standard epoxy-coated kraft paper.

H-grade (180°C): Epoxy-coated Nomex® or modified PET film.

2. Resin Reactivity (Stage B)

The epoxy resin must be in a semi-cured (Stage B) state. It should feel dry to the touch at room temperature and melt and flow at 120–150°C. Over-cured (Stage C) dispensing will not bond.

3. Shelf Life and Storage

Minimum shelf life of 12 months in original packaging (20°C, <50% relative humidity).

Moisture-proof packaging—kraft paper absorbs moisture, reducing dielectric strength

4. Dielectric Strength Test Data

Test certificates are required, including:

Short-term breakdown voltage.

Partial discharge initiation voltage (PDIV) is crucial for medium and high voltage designs.

Large quantities of diamond dotted paper, as an important material for transformer winding insulation, play a vital role in improving equipment reliability and extending service life. With its excellent insulation properties, mechanical strength, and flexible customization capabilities, this material has become a commonly used key material in the power industry.

If you are looking for a supplier of diamond dotted paper with a stable supply, customization support, and high cost-effectiveness, please contact us for a quote and sample support.