DDP Insulation Paper in Transformers Applications and Selection

1. Introduction to DDP Insulation Paper Full Name: Diamond Dotted Paper (DDP) Structure: Made of electrical insulat...

1. Introduction to DDP Insulation Paper

Full Name: Diamond Dotted Paper (DDP)

Structure: Made of electrical insulating paper as the base material, with diamond-shaped epoxy resin dots evenly coated on the surface (typically covering 25%–50% of the area).

Features: During the hot-press or vacuum drying process in transformer manufacturing, the epoxy dots soften and bond the windings together. After cooling, they solidify to form a stable and robust insulation structure, while maintaining oil or air channels for effective cooling.

2. Main Applications in Transformers

Layer Insulation in High-Voltage Windings

Placed between layers of oil-immersed or dry-type transformer high-voltage windings to prevent breakdown and enhance short-circuit resistance.

End Insulation and Reinforcement

Used at the ends of high-voltage windings in conjunction with clamping rings and spacers to reduce the risk of partial discharge and creepage.

Turn-to-Turn Insulation

Certain high-voltage conductors are wrapped with DDP to improve dielectric strength and mechanical shock resistance.

Winding Wrapping in Dry-Type Transformers

Used in combination with glass cloth or polyester film to increase mechanical strength and moisture resistance.

3. Key Selection Factors

Base Paper Type and Thickness

Common thicknesses: 0.05 mm, 0.08 mm, 0.13 mm, 0.17 mm;

Greater thickness offers higher mechanical strength but reduced flexibility, suitable for different transformer capacities and voltage levels.

Coating Density and Specifications of Epoxy Dots

Coverage Rate: Commonly 25%, 35%, 50%; higher coverage offers stronger bonding but slightly less cooling efficiency.

Dot Shape: Standard diamond, rectangular, or customized;

Dot Thickness: Affects bonding strength and insulation gap after hot pressing.

Thermal Class:

Commonly Class A (105°C) and Class B (130°C);

For high-load or high-temperature applications, a higher thermal class is recommended.

Compatibility with Transformer Types

Oil-immersed transformers: Focus on insulation stability in oil and mechanical strength.

Dry-type transformers: Focus on moisture resistance and full wrapping integrity.

Processing Dimensions

Standard widths from 10 mm to 1000 mm; available in rolls or sheets according to coil size.

4. Advantages of Using DDP

Reliable Insulation: Maintains high dielectric strength and reduces partial discharge;

Structural Integrity: Improves winding cohesion after curing, preventing displacement during short-circuits;

Moisture Resistance: Epoxy coating seals paper fibers, reducing moisture absorption;

Efficient Cooling: Gaps between epoxy dots allow oil or air circulation, lowering hot-spot temperatures.

5. Recommended Selection Table (Example)