Liquid Immersed Transformers

Demanding Liquid Immersed Transformer Applications Rely on Nomex®

The use of DuPont™ Nomex® 900 Series papers and pressboards in liquid immersed transformer applications helps reduce lifecycle costs and provide safety benefits for the power utility, industrial and railway markets.

From helping to save space and weight in high-speed trains and in wind turbine nacelles—both onshore and offshore, to improving the reliability and high-temperature capability of power transformers in nuclear power plants, Nomex® insulation plays a key role in building a better liquid immersed transformer.

What makes Nomex® an ideal insulation solution for liquid immersed transformers is its unique combination of thermal stability, mechanical toughness, chemical compatibility, flame resistance and inherent dielectric strength. 

Specifically designed for liquid immersed transformers, the Nomex® 900 Series helps enable long-term reliability; reduced size and weight with greater power density; and the ability to take load variations and severe overloads.

Long-term Reliability

Insulation systems based on Nomex® maintain excellent electrical and mechanical characteristics over the service life of a liquid immersed transformer. 

Nomex® papers offer exceptional resistance to shrinkage and compression.  Nomex® pressboards provide superior stability under compressive loads. This superior resilience helps to ensure that coil structures will remain tight and able to withstand short circuit forces—even after years of service—so that liquid immersed transformers continue to operate reliably over an extended lifetime.

Reduced Size and Weight

Using Nomex® insulation helps enable the weight of a liquid immersed transformer to be reduced by as much as 25% for a given kVA output, while maintaining top oil temperatures at constant levels with only modest increases in average oil temperatures.  Conversely, it can help  kVA ratings increase by up to 50% for a given size and weight. 

The use of high-temperature liquids, such as silicone oil or ester liquids, helps enable even greater savings in size and weight.  Nomex® is compatible with commonly used dielectric fluids and transformer oils.

Increased Reserve Capacity

Liquid immersed transformers insulated with Nomex® papers and pressboards can be designed to have extra power capacity for emergency peak load situations.  This increased reserve capacity can result in substantial savings in redundancy planning.

Typical Uses in Liquid Immersed Transformers

Nomex® papers and pressboards are used in liquid immersed 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 Liquid Immersed Transformer Applications

Nomex® papers and pressboards are used in a wide variety of liquid immersed transformer applications, including:

  • Mobile transformers
  • Traction transformers
  • Wind turbine generator step-up (GSU)
  • Rectifier transformers
  • Furnace transformers
  • Distribution transformers (<36 kV)
  • Power transformers (>36 kV)
  • Rail trackside transformers
  • HVDC transformer/reactors
  • Underground/submersible transformers



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