DMD Insulation paper — Important Insulation Material for Oil-Immersed Transformers

Selection and Application of DMD in Oil-Immersed Transformers As power equipment continues to develop toward higher ...

Selection and Application of DMD in Oil-Immersed Transformers

As power equipment continues to develop toward higher reliability, higher thermal class, and longer service life, oil-immersed transformers require insulation materials with superior performance. DMD Insulation paper  (Polyester Non-woven – Polyester Film – Polyester Non-woven Composite) has become one of the most widely used flexible insulation materials in transformer windings due to its excellent mechanical strength, dielectric properties, and thermal class (Class B/F).
This article introduces the characteristics, typical applications, and selection principles of DMD in oil-immersed transformers.

DMD Insulation paper (white/red)

1. Structure and Performance Characteristics of DMD

DMD consists of three composite layers:
Outer Layer: Polyester non-woven fabric (Dacron)
Middle Layer: Polyester film (PET)
Inner Layer: Polyester non-woven fabric

Key Advantages:

High mechanical strength: Withstands winding compression, binding, and electromagnetic force.
Excellent dielectric properties: Maintains stable breakdown resistance under strong electric fields.
Good oil impregnation performance: Compatible with transformer oil to enhance thermal stability.
High thermal class: Standard Class B (130°C), enhanced versions available in Class F (155°C).
Great flexibility & easy processing: Easy to cut, shape, and wrap.

2. Typical Applications of DMD in Oil-Immersed Transformers

DMD is widely used in 10 kV, 35 kV, 110 kV oil-immersed power transformers, including:
Turn-to-turn insulation
Used for wrapping both LV and HV windings
Provides mechanical support and electrical isolation
Enhances short-circuit withstand capability
Layer and section insulation
Placed between winding layers
Prevents partial discharge, tracking, and sliding
Applicable to round coils, helical coils, and continuous windings
End padding and reinforcement
Used as cushioning pads at winding ends
Improves anti-vibration and short-circuit strength
Lead protection and wrapping
Provides flexible insulation protection for leads and taps
Enhances anti-corona performance

3. Key Factors for Selecting DMD in Oil-Immersed Transformers

Selection should consider transformer capacity, voltage level, and insulation system design:

Thermal Class (B/F)

General 10–35 kV transformers: Class B (130°C)
High-load or high-temperature environments: Class F (155°C)

Thickness Options

Common thicknesses: 0.15, 0.20, 0.23, 0.25, 0.30, 0.35 mm
Selection guidelines:
Turn insulation: 0.15–0.20 mm
Layer insulation: 0.23–0.30 mm
Structural pads: 0.30–0.35 mm

Mechanical strength requirements

For large-capacity transformers (20 MVA+), enhanced-strength DMD is recommended (higher fiber density).

Oil compatibility

DMD is fully compatible with insulating oil, but ensure:
Environmentally compliant, low-acid oil is used
Material meets IEC/GB insulation system standards

4. Comparison of DMD with Other Flexible Insulation Materials

5. Manufacturing & Installation Precautions

Storage :Keep dry (humidity < 60%),Avoid sunlight; use moisture-proof packaging

Processing：Use clean cutting tools,Avoid bends, tears, or sharp folding

Installation:Do not overstretch,Ensure proper compression with windings,Perform oil impregnation & drying after assembly

6. Conclusion:

DMD Is the Mainstream Insulation Material for 10–35 kV Oil-Immersed Transformers

With its high strength, excellent oil compatibility, stable dielectric performance, and cost-effectiveness, DMD plays an essential role in transformer insulation systems. Whether for turn-to-turn wrapping, layer insulation, or lead protection, DMD offers a reliable and mature solution for power transformer manufacturers.

DMD manufacturer

XUJUE ELECTRICAL has over 65 years of experience in producing transformer DMD insulation materials, ensuring reliable quality and stable performance. Throughout customer service, Xujue’s professional team can provide suitable specifications and models of 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.