DMD Epoxy Prepreg Material in Dry-Type Transformers: Enhancing Thermal and Electrical Insulation

DMD epoxy prepreg is a flexible composite material made of polyester film and polyester fiber nonwovens, impregnated with a heat-resistant modified epoxy resin and then baked. This material cures quickly at high temperatures and exhibits exceptionally high bond strength with copper foil. During the drying and curing process, it produces no low-molecular-weight volatiles, resulting in an insulation structure with minimal shrinkage.

In industrial applications, DMD epoxy prepreg is widely used for interlaminar insulation in low-voltage coils of dry-type transformers, as well as slot insulation and phase insulation in Class F motors. Its excellent performance makes it an indispensable component in electronic equipment manufacturing.

Why does DMD epoxy prepreg significantly improve the performance of dry-type transformers? Dry-type transformers do not require oil for insulation or cooling, relying entirely on solid insulation materials. Therefore, they place extremely high demands on thermal and electrical properties. DMD epoxy prepreg perfectly meets these requirements in the following three aspects:

1. Enhanced Electrical Insulation

High Dielectric Strength: Polyester film inherently possesses extremely high dielectric strength (breakdown voltage). The three-layer composite structure of DMD forces the electric field to pass through different dielectrics, effectively suppressing the generation and propagation of electrical treeing, significantly improving the material's withstand voltage rating and reliability.

Uniform Insulation Barrier: After curing, the epoxy resin in the prepreg completely fills the voids in the fiber nonwoven fabric, forming a dense, bubble-free, and defect-free insulation layer. This characteristic eliminates potential discharge points and keeps partial discharge (PD) to extremely low levels, a key indicator of dry-type transformer life.

Excellent Arc and Tracking Resistance: The cured epoxy resin system exhibits excellent arc resistance, effectively preventing surface carbonization from forming conductive pathways.

2. Optimized Thermal Insulation and Thermal Stability

Excellent Thermal Resistance: DMD epoxy prepregs typically meet Class F (155°C) or Class H (180°C) thermal resistance standards. This means it can operate in high-temperature environments for extended periods without significant thermal aging or performance degradation, ensuring the transformer's overload capacity and long service life.

Good thermal conductivity: This property, seemingly contradictory to "thermal insulation," is actually crucial for transformer coils. Good thermal conductivity allows heat generated during coil operation to be more efficiently transferred to the outside through the insulation layer and dissipated, thereby reducing hotspot temperatures within the coil. Furthermore, after curing, the epoxy resin adheres tightly to the copper wire and iron core, reducing contact thermal resistance and optimizing the overall heat dissipation path.

Low thermal expansion coefficient: After curing, the epoxy resin exhibits excellent dimensional stability, closely matching the thermal expansion coefficient of copper conductors. During thermal cycling, it reduces internal stress caused by differential expansion and contraction, preventing insulation cracking and maintaining long-term insulation integrity.

3. Excellent Mechanical and Processing Properties

High Strength and Rigidity: The cured epoxy resin tightly bonds the DMD substrate to the coil, forming a solid "rigid structure" that significantly enhances the transformer's short-circuit resistance and can withstand significant electrical forces without deformation or damage.

Excellent Impregnation and Adhesion: As a prepreg, it already contains a fixed amount of resin, which allows for optimal compatibility and bonding with the impregnating varnish during the vacuum pressure impregnation (VPI) process, forming an integrated insulation system without the risk of delamination or shelling.

Moisture and Corrosion Resistance: The dense epoxy resin layer effectively blocks the intrusion of moisture and corrosive gases, maintaining a dry and stable insulation system, making it particularly suitable for harsh environments such as humid and dirty environments.

DMD epoxy prepreg, with its multiple advantages in electrical insulation, thermal performance, and mechanical processing, provides a core support for the safe and stable operation of dry-type transformers. Whether extending equipment life, enhancing environmental adaptability, or ensuring reliability under overload conditions, it has become the preferred insulation material for dry-type transformers and lays a crucial foundation for performance upgrades in electronic equipment manufacturing.