Heat-Resistant Insulation Paper for Transformer Winding Insulation | DDP, DMD, Nomex Options

In the design and manufacturing of dry-type transformers, oil-immersed transformers, and special motors, the selection of winding insulation materials directly impacts equipment lifespan, heat resistance rating, and operational safety. As electrical equipment develops towards higher voltage, larger capacity, and miniaturization, related industries are placing increasingly stringent requirements on the high-temperature resistance of insulation materials.

Currently, the mainstream high-temperature resistant insulating papers on the market are DDP, DMD, and Nomex. They differ significantly in material composition, temperature resistance rating, mechanical properties, and cost. This article will detail the characteristics of these three insulating materials to help you make the appropriate selection in transformer winding design.

DDP (Diamond Dotted Paper) Insulating Paper

DDP (Diamond Dotted Insulating Paper) is made by coating the surface of cable paper or insulating paper with diamond-shaped epoxy resin dots, which achieve self-adhesion after heat treatment.

1. Main Characteristics

Excellent bonding performance.

Improves overall winding mechanical strength.

Good oil immersion compatibility.

Suitable for automated winding processes.

2. Applications

Oil-immersed distribution transformers.

Reactor winding fixing.

Coil structures requiring high mechanical strength.

DMD Composite Insulation Material

DMD consists of three layers: two layers of polyester fiber nonwoven fabric (Dacron) and a middle layer of polyester film (Mylar).

1. Performance Characteristics

Good electrical insulation performance

Excellent mechanical strength and flexibility

Temperature resistance rating is typically Class B (130°C) or Class F (155°C)

Moderate cost, offering high cost-effectiveness

2. Application Areas

Dry-type transformer windings

Motor slot insulation and phase-to-phase insulation

Medium and low voltage electrical equipment

Nomex Insulation Paper

Nomex is a high-performance aramid insulation material developed by DuPont.

1. Core Advantages

Extremely high temperature resistance rating, reaching Class H (180°C and above).

Excellent aging resistance.

Excellent flame retardancy and chemical stability.

High reliability, suitable for extreme operating conditions.

2. Application Scenarios

High voltage and ultra-high voltage transformers

Dry-type transformers (especially Class H)

Rail transportation, electric vehicles, power electronic equipment

How to Select Insulation Materials Based on Transformer Operating Conditions?

When selecting transformer winding insulation paper, price should not be the sole consideration. Factors such as heat resistance rating, mechanical stress, and operating environment must also be taken into account.

1. Selection Based on Heat Resistance Rating

Class B (130℃) and below: For conventional air-cooled dry-type transformers or ordinary oil-immersed transformers, if the temperature rise requirement is not high, DDP or DMD can meet the requirements and offer high cost-effectiveness.

Class F (155℃): This is the common heat resistance rating for industrial dry-type transformers. DMD is the preferred choice, as it meets the 155℃ temperature resistance requirement and has good impregnation performance. It is suitable for interlayer insulation in epoxy-cast dry-type transformers.

Class H (180℃) and above: For special transformers, traction transformers, mining explosion-proof transformers, or equipment that needs to operate for extended periods in high-temperature environments, Nomex must be selected. Only Nomex paper can ensure no thermal breakdown during long-term operation above 180℃.

2. Selection Based on Structural Strength and Processing Technology

If the transformer windings need to withstand significant electromagnetic force impacts (such as short-circuit conditions), DMD and Nomex exhibit superior tear strength compared to ordinary DDP.

If a vacuum pressure impregnation process is used, Nomex, due to the porosity of its fiber structure, has excellent adsorption of insulating varnish, resulting in a denser insulation structure and eliminating the risk of partial discharge.

3. Choosing Based on Cost Budget

DDP is suitable for small transformers, appliance transformers, or cost-sensitive products.

DMD is currently the most widely used insulating paper in the dry-type transformer industry. It boasts mature technology, stable supply, and comprehensive performance suitable for most industrial scenarios.

Nomex is suitable for high-speed rail traction transformers, wind power transformers, and building power supply systems with extremely high fire protection requirements. Although the cost per sheet is higher, it reduces the insulation layer thickness, thereby reducing the transformer size, and the overall cost may not increase significantly.

In transformer winding insulation systems, DDP, DMD, and Nomex each have their advantages and are suitable for different scenarios. Choosing the right insulation material can not only improve equipment performance but also extend transformer lifespan and reduce maintenance costs.

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