F-Class DMD Composite Insulation Material in Dry-Type Transformers

F-Class DMD Composite Insulation Material F-class DMD composite insulation material, consisting of polyester (PET) f...

F-Class DMD Composite Insulation Material

F-class DMD composite insulation material, consisting of polyester (PET) film and polyester nonwoven fabric, plays a critical role in dry-type transformers, particularly in inter-layer insulation and end insulation of low-voltage windings. It combines the excellent electrical insulation properties of PET film with the mechanical strength of nonwoven fabric, maintaining stable performance at temperatures up to 155°C.

1. Applications of F-Class DMD in Dry-Type Transformers

Inter-layer insulation for low-voltage foil windings
Primarily used in low-voltage windings of copper or aluminum foil dry-type transformers.
DMD acts as an inter-layer spacer, effectively preventing short circuits between foil layers.
Pre-impregnated DMD applications
Often, DMD is pre-impregnated with epoxy resin.
After curing, it bonds tightly with the copper foil, forming a solid assembly that enhances mechanical strength and short-circuit resistance of the winding.
End insulation and padding
Used at the top and bottom ends of the transformer winding.
Prevents contact between the coil and core or clamping parts, providing reliable phase-to-phase and phase-to-ground insulation.
Slot insulation and layer insulation
In some medium- and low-voltage transformers, DMD is used as inner and outer layer padding as well as insulation spacers for the winding.

2. Application Requirements for F-Class DMD

Thermal rating
Must meet Class F standards, ensuring long-term use at 155°C without compromising insulation performance or mechanical strength.
High electrical performance
Should possess high dielectric strength, insulation resistance, and withstand voltage capacity to effectively prevent leakage currents during operation.
Excellent mechanical strength
Must withstand tension during winding and subsequent processing, ensuring foil layers remain tightly wound, flat, and free from delamination.
Good adhesion and curing properties
For pre-impregnated DMD, it should have a long shelf life at room temperature, low curing temperature, short curing time, and strong adhesion to copper or aluminum foils after curing.
Smooth and clean surface
The surface should be smooth and dust-free to prevent creepage distance reduction due to dust accumulation.

3. Common Issues and Limitations

Not suitable for oil-immersed transformers
Ordinary non-pre-impregnated DMD is mainly intended for dry-type transformer inter-layer insulation and may not be suitable for oil-immersed environments.
Temperature limitation
Although Class F, long-term operation above 155°C under overload conditions may accelerate aging of the DMD material.

Summary

F-class DMD insulation material, with its excellent electrical and physical properties, ensures safe and stable operation of dry-type transformers and is an indispensable auxiliary insulation material in modern dry-type transformer manufacturing.