11 Characteristics of Nomex for electrical insulation

Nomex paper

11 Characteristics of Nomex for electrical insulation

For over 50 years, designers and manufacturers of transformers, generators, motors and other electrical equipment have relied on the unique combination of properties of Nomex paper to help optimize performance, increase reliability and extend the life of their products. Products of the DuPont brand Nomex offer high electrical, chemical and mechanical integrity. This makes them ideal for a wide range of electrical insulation applications, such as slot insulation, slot closure and phase insulation in electric motors and generators, layer insulation in transformers and moulded parts as housing insulation in other electrical equipment.

11 properties distinguish Nomex papers:

  • Inherent dielectric strength
  • Mechanical strength
  • High temperature resistance
  • High chemical compatibility
  • High radiation resistance
  • Flame Resistance
  • Insensitivity to moisture
  • Suitable for low temperatures
  • good punchability
  • good coatability
  • good formability

Inherent dielectric strength of Nomex papers

At a high density, Nomex allows for short-term electrical loads from 18 kV/mm to 34 kV/mm (460 V/mil to 870 V/mil), depending on product type and thickness.

Mechanical strength of Nomex papers

Nomex high density products have high mechanical toughness, tensile strength and abrasion resistance and are also flexible (with a lower thickness).

Nomex Paper High Temperature Resistance

Temperatures up to 200 °C have little or no effect on the electrical and mechanical properties of Nomex products. The useful properties of Nomex paper are retained at much higher temperatures. These useful properties of Nomex paper are also maintained in continuous operation for at least 10 years at temperatures up to 220°C.

High chemical compatibility of Nomex papers

Nomex products are virtually unaffected by most solvents and are exceptionally resistant to acids and bases. They are compatible with all classes of paints and adhesives, transformer fluids, lubricating oils and refrigerants. Since Nomex products are not digestible, they are not attacked by insects, fungi or mold.

High radiation resistance

Nomex paper is virtually unaffected by 800 MegaGray ionizing radiation and retains its useful mechanical and electrical properties after eight exposures to this level of radiation.

Flame Resistance

Nomex products do not cause toxic reactions in humans or animals. Nomex products do not melt, and with an LOI value of over 20.8 at 220°C (the critical value for combustion in normal air) they do not support the combustion process. Nomex products that meet the requirements of Underwriters Laboratories Standard (UL) 94 V-O are available.

Moisture Insensitivity

In equilibrium at 95% relative humidity, Nomex papers and high density pressboards retain 90% of their dielectric strength when dry, while many of their mechanical properties are actually improved.

Suitable for low temperatures

Nomex products are used in a variety of cryogenic applications due to their unique polymer structure. At the boiling point of nitrogen (77 K) Nomex 410, Nomex 993 PSB and Nomex 994 PSB have a tensile strength higher than the value at room temperature.

Good punchability of Nomex papers

All Nomex papers and Nomex boards can be processed with the usual punching techniques. Boards can be milled into parts for high-voltage transformers on CNC machining centers.

Good coatability

Nomex papers can be coated with common adhesive systems to form adhesive tapes. Nomex papers can also be coated with epoxy resin systems to form prepregs.

Good formability

Nomex can be used to produce molded and formed parts for applications in transformers and electric motors.


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