DMD Insulation Material in Oil-Immersed Transformers: Applications and Selection

1.DMD Insulation Paper Introduction DMD inulation paper  (Polyester Film + Non-woven Fabric) is a flexible composite...

1.DMD Insulation Paper Introduction

DMD inulation paper  (Polyester Film + Non-woven Fabric) is a flexible composite insulation material, usually composed of polyester non-woven fabric / polyester film / polyester non-woven fabric in a three-layer structure.

Key Features:

Excellent electrical properties: polyester film ensures high dielectric strength.

Good mechanical flexibility: non-woven fabric provides softness and fold resistance.

Good impregnation: allows full oil impregnation in oil-filled environments, ensuring reliable insulation.

Common thermal classes: Class B (130℃) and Class F (155℃).

2. Applications of DMD in Oil-Immersed Transformers

Interlayer Insulation

Used as insulation between low-voltage and high-voltage windings.

Thin DMD is suitable for interlayer insulation in small transformers.

Turn-to-Turn Insulation and Wrapping

Applied as conductor wrapping insulation to prevent turn-to-turn breakdown.

Excellent flexibility makes it suitable for corners and edges of windings.

Cushioning and End Insulation

Used as spacers and liners for mechanical support and electrical isolation.

Enhances safety and reliability of end insulation in windings.

3. Selection Guidelines for DMD

Thickness

Common range: 0.10mm, 0.15mm, 0.20mm, 0.25mm, 0.30mm, 0.35mm, 0.40mm

Small-capacity/low-voltage transformers: choose thin grades (0.10–0.20mm) for better flexibility and impregnation.

Medium/large-capacity or medium-high voltage transformers: choose thicker grades (0.25–0.40mm) for higher mechanical strength.

Thermal Class

Class B (130℃): widely used in general power transformers.

Class F (155℃): recommended for high-temperature rise or harsh long-term operation.

Structural Requirements

Balanced type (equal thickness of fabric/film/fabric) → balanced electrical and mechanical properties.

Film-reinforced type (thicker middle film) → higher dielectric strength, suitable for higher voltage.

Fabric-reinforced type (thicker non-woven layers) → better flexibility and impregnation, ideal for bending areas.

4. Selection Recommendation Table

Summary:

DMD is mainly used for interlayer insulation, turn-to-turn insulation, and end insulation in oil-immersed transformers. The selection should consider thickness, thermal class, and structural characteristics, matched to the transformer’s capacity, voltage level, and operating conditions.