Pre-Impregnated DMD paper in Dry-Type Transformers Selection

Application and Selection of Pre-Impregnated DMD in Dry-Type Transformers In dry-type transformer manufacturing, the...

Application and Selection of Pre-Impregnated DMD in Dry-Type Transformers

In dry-type transformer manufacturing, the reliability of the insulation system directly determines operational safety and service life. Pre-impregnated DMD Paper (Pre-Impregnated Dacron-Mylar-Dacron) is a cost-effective composite flexible insulation material widely used in medium- and low-voltage dry-type transformer winding systems. This article provides a systematic analysis from three perspectives: material characteristics, typical applications, and key selection criteria.

I. What Is Pre-Impregnated DMD insulation paper?

Pre-impregnated DMD paper  is based on conventional DMD insulation material, which is pre-impregnated with heat-resistant insulating resin (such as epoxy or polyester resin) and semi-cured (B-stage) during manufacturing.

Key characteristics include:

Stable and uniform resin distribution,Softening again when heated, enabling integral curing with the winding
Significantly improved mechanical strength and thermal endurance of the winding
In dry-type transformers, pre-impregnated DMD is a critical material for winding forming and overall curing processes.

II. Main Applications of Pre-Impregnated DMD in Dry-Type Transformers

Interlayer Insulation of Windings

Used between conductors of high- and low-voltage windings
Prevents turn-to-turn and layer-to-layer electrical breakdown
After resin curing, forms an integral structure that reduces partial discharge risk

Typical locations:

Interlayer insulation of high-voltage coils and low-voltage foil windings

Section and Phase Insulation

Separates windings of different voltage levels or phases
Enhances resistance to short-circuit mechanical stresses
During short-circuit events, cured pre-impregnated DMD effectively restricts winding displacement and deformation.

End-Winding Insulation and Binding

Used for shaping and fixing coil end sections
Reduces mechanical fatigue caused by vibration during transportation and operation

Compatibility with Vacuum Casting / VPI Processes

Applied in VPI (Vacuum Pressure Impregnation) or dry-type resin curing processes
Exhibits excellent compatibility with transformer resin systems
Improves consistency and reliability of the entire insulation system

III. Advantages of Pre-Impregnated DMD Compared with Conventional DMD

IV. Key Selection Criteria for Pre-Impregnated DMD

Thermal Class Selection

Dry-type transformers typically require higher thermal endurance:
Class F (155°C):
Most commonly used, suitable for dry-type transformers up to 10kV
Class H (180°C):
For high-temperature environments or long-term high-load operation
Selection principle:
Thermal class ≥ the designed insulation system class of the transformer

Thickness Selection (Typical Range)

Thickness should be determined by a combination of:
Voltage level + electric field strength + winding compactness

Resin System Compatibility

Confirm compatibility between the pre-impregnated resin and the epoxy resin system used in the transformer
Avoid incomplete curing or delamination issues
Especially critical for VPI processes

Process Compatibility

Before selection, confirm:
Softening temperature range of the pre-impregnated DMD
Suitability for existing winding forming and baking processes
Compatibility with automatic winding or molding operations

V. Application Recommendations

Standard 10kV dry-type transformers:
Class F pre-impregnated DMD with epoxy resin system

High-reliability / renewable energy / data center projects:
High-resin-content, Class H pre-impregnated DMD

Cost–performance balanced projects:
Standard Class F pre-impregnated DMD with optimized thickness selection

VI. Conclusion

Through material pre-treatment and process integration, pre-impregnated DMD paper significantly improves the dielectric strength, mechanical stability, and long-term operational reliability of dry-type transformer windings. In practical selection, manufacturers should comprehensively evaluate voltage level, insulation system design, production processes, and operating conditions, rather than relying solely on initial material cost.

Manufacturer consultation and quotation

XUJUE ELECTRICAL has over 65 years of experience in producing transformer pre-impregnated  DMD insulation materials, ensuring reliable quality and stable performance. Throughout customer service, Xujue’s professional team can provide suitable specifications and models of pre-impregnated  DMD insulation materials based on the specific requirements and application scenarios of transformer manufacturing. Whether for small batches or large-scale production, Xujue responds promptly, offering attentive service and high-quality products.

If you are looking for Dry transformer insulation paper, Please contact Xujue Electrical and provide the product specifications, thickness and purpose you need, you can get detailed product information and quotation, and also send samples free of charge