Dry Type Transformer Insulation


Nomex®--Proven Performance as Dry Type Transformer Insulation

For more than 45 years, DuPont™ Nomex® has been the material of choice for dry type transformer insulation. That’s because Nomex® brand insulation helps provide proven performance and enhanced safety. 

From lighting ballasts and uninterrupted power supplies (UPS) to medium-voltage substations (>1.2 kV), a critical key to success is the use of Nomex® papers and Nomex® based laminates as dry type transformer insulation.

Outstanding thermal stability, mechanical toughness, inherent dielectric strength, flame resistance and chemical compatibility make Nomex® papers and Nomex® based laminates ideal as dry type transformer insulation.

Ventilated dry type transformers (VDT) and cast resin transformers continue to grow in popularity around the world.  The use of Nomex® insulation is contributing to this trend by helping enable major design improvements in these types of transformers.

Enhanced Safety

Dry type transformers insulated with Nomex® offer enhanced safety because there are no fluids to spill, explode or burn, and Nomex® 400 Series papers do not support combustion in air.  And, in the case of a building fire, this series of Nomex® insulation does not produce amounts of toxic smoke or dangerous particles.

Low Transmission Losses

Because dry type transformers insulated with Nomex® can be located close to their loads—inside factories, schools, hospitals and apartments— it helps to shorten low-voltage lines with a consequent reduction of the related losses.

Reduced Cost, Size and Weight

Dry type transformers insulated with Nomex® can be designed with a temperature rise up to 150K, requiring less conductor and core steel, which can result in a lower initial cost.  The reduced size and weight contribute to ease of installation and the smaller cores result in lower no-load losses.

Increased Overload Capabilities

When dry type transformers operate continuously at or near their rated loads, efficiency is critical.  Nomex® insulation meets the challenge.  For example, an 80K temperature rise VDT transformer insulated with Nomex® can operate continuously at 133% of the rated load.

Improved Capability for Harmonic Loading

Dry type transformers supplying loads with heavy harmonic content frequently experience high hot spot temperatures.  This is no problem for dry type transformers insulated with Nomex® because they have a large reserve temperature capability to accommodate these hot spots.

Resistance to Humidity

Because the properties of densified Nomex® papers, such as Nomex® 410, are insensitive to moisture, dry type transformers insulated with Nomex® perform in humid environments, such as those found in marine applications.

Typical Uses in Dry Type Transformers

Nomex® papers, particularly those in the Nomex® 400 Series, and Nomex® based laminates are used in dry type transformers as:

• Turn and Conductor insulation

• Layer and barrier insulation

• Core insulation

• Lead and tap insulation

• End filler

• Channel and Washer

• Radial and axial spacers

Typical Dry Type Transformer Applications

Nomex® papers, particularly those in the Nomex® 400 Series, and Nomex® based laminates are used in a wide variety of dry type transformer applications, including:

• Large power, medium voltage and high voltage (>1.2 kV)

• Medium voltage, general purpose (>1.2 kV)

• Medium voltage, substation (>1.2 kV)

• Low voltage, general purpose/specialty (<1.2 kV)

• UPS/data center/converter

• Lighting ballast

• Traction

• Welding

• Mining

• Power conversion


Dupont brands

Nomex® Electrical Insulation
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Information & ideas

Nomex® Product Line Overview
Nomex® Paper Properties
Impact of DOE 2016 Regulation

Case studies

ABB’s Rapid Recovery Transformer Initiative

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Industry segments

Power Generation and Distribution 

DuPont offers a wide range of high-performance products that help optimize the performance and extend the service life of power generation and distribution equipment.

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