Diamond Dotted Paper (DDP)

Diamond Dotted Paper Introduction

Diamond dotted paper (DDP) is an electrical insulation presspaper partially coated with heat-curable epoxy resin dots arranged in a diamond pattern. During coil drying / oven heating, the resin dots soften and cure to bond adjacent layers, helping improve winding mechanical stability in transformer manufacturing.

DDP insulation paper is commonly used as interlayer insulation between coils in oil-immersed transformers, where controlled bonding is needed without sacrificing oil impregnation and drying efficiency.
Chengrui Insulation can provide DDP insulation paper in rolls with different thicknesses, widths, and slitting options according to production requirements. Our team can help confirm roll size, resin dot pattern requirements, packing method, sample availability, and bulk order delivery schedule. In additional, we can also provide diamond dotted DMD, diamond dotted AMA, Thermally Upgraded Diamond Dotted Paper (TU DDP) etc

Product Structure

• Base paper: electrical grade insulation paper (presspaper/kraft-type)

• Resin dots: heat-curable epoxy resin, applied on one side or both sides

• Dot pattern: diamond layout (typical reference pattern: 9.5 mm × 9.5 mm diamonds, 15.9 mm center spacing)

Working Principle in Transformer Manufacturing

DDP is designed to remain dry and non-tacky at room temperature, making it easy to handle and wrap.

During the transformer coil process (e.g., drying/heating), the resin dots soften, flow locally, and then cure, creating permanent bonding points between paper layers and conductors.

Why the "dotted" pattern matters:

Discrete resin dots create bonding while still leaving channels for air/moisture evacuation during vacuum drying and for oil impregnation flow, which helps reduce insulation defects and supports stable transformer performance.

Key Benefits

• Improves winding mechanical stability and helps resist layer displacement under short-circuit forces

• Controlled bonding: adhesion points form only after heat activation

• Supports efficient drying & oil impregnation due to the dotted pattern and channels

• Good compatibility with transformer oil after curing

Diamond Dotted Paper Applications

Diamond dotted paper is widely used in oil-immersed transformers as:

Interlayer insulation between coils

Layer insulation in windings

Insulation structures where bonding is required during drying/heating

Diamond Dotted Insulation Paper Storage

Store in a dry and clean room, without being pressed, and keep away from wire or heat or wet, or in the sun.

FAQ

Q1:What is diamond dotted paper used for?

A: It is used as insulation presspaper in transformer windings, especially for interlayer insulation where heat-activated bonding is required.

Q2:How does DDP bond during manufacturing?

During heating/drying, epoxy resin dots soften and cure, creating permanent bonding points between insulation layers.

Q3: Why is it a "dotted" pattern instead of full coating?

Discrete dots provide bonding while maintaining channels for vacuum drying and oil impregnation, supporting reliable insulation quality.

Related Transformer Insulation Materials

Diamond dotted paper is commonly used together with other transformer insulation materials in winding systems. Depending on the transformer design and insulation structure, the following materials are often used in combination:

Insulation presspahn paper – used for general layer and structural insulation in transformer windings.

Transformer crepe paper – applied for conductor wrapping and oil-immersed insulation systems.

Transformer pressboard – used for structural insulation components and mechanical support inside transformers.

Using the correct combination of insulation paper and pressboard materials helps ensure long-term transformer reliability and mechanical stability