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DuPont™ Nomex® Paper and Pressboard |
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Nomex®: A family of insulation materials engineered to meet the diverse demands of the electrical industry
Wherever there's a need for electrical insulation, there's usually a product of DuPont™ Nomex® aramid to fill it. In it's various forms --primarily papers and pressboards--Nomex® products have the right balance of properties for use in transformers, motors, generators and other electrical equipment. This unique balance of properties has been providing reliability to users for over 25 years.
Nomex® is a synthetic aromatic polyamide polymer that provides high levels of electrical, chemical and mechanical integrity, when converted into its various sheet forms. Used properly, Nomex® products can extend the life of electrical equipment, reduce premature failures and repairs, and act as a safeguard in unforseen electrical stress situations.
Nomex® products have characteristics which make them ideally suited for electrical insulation application. These characteristics may vary slightly in the different forms and types of Nomex®.
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| A Unique Combination Of Properties Gives DuPont™ Nomex® Superior Characteristics |
Inherent dielectric Strength
In densified form, Nomex® aramid products withstand short-term electrical stresses of 450 to 1000 V/mil (18 to 40 kV/mm) depending on product type and thickness, with no need for further treatment with varnishes or resins.
Mechanical Toughness
Densified Nomex® products are strong, resilient and (in the thinner grades) flexible, with good resistance to tearing and abrasion.
Thermal Stability
Temperatures up to 200°C (390°F) have little or no effect on the electrical and mechanical properties of Nomex® products, and useful values are retained at considerably higher temperatures. Furthermore, these useful properties are maintained for at least 10 years of continuous exposure at 220°C (430°F).
Chemical Compatibility
Nomex® is essentially unaffected by most solvents, and is unusually resistant to attack by acids and alkalies. It is compatible with all classes of varnishes and adhesives, transformer fluids, lubricating oils, and refrigerants. Since Nomex® products are not digestible, they are not attacked by insects, fungi or molds.
Cryogenic Capabilities
Nomex® has found acceptance in a variety of cryogenic applications due to its unique polymeric structure. At the boiling point of nitrogen (77 0K), Nomex® Type 410 paper as well as Type 993 and Type 994 pressboard have tensile strengths in excess of room temperature values.
Moisture Insensitivity
In equilibrium at 95 percent relative humidity densified Nomex® papers and pressboards maintain 90 percent of their bone-dry dielectric strength while many mechanical properties are actually improved.
Radiation Resistant
Nomex® is essentially unaffected by 800 megarads of ionizing radiation (which causes polyester laminates to crumble), and still retains useful mechanical and electrical properties after eight times this exposure.
Non-Toxic/Flame Resistant
Nomex® products will not produce any known toxic reactions in humans or animals, or melt or support combustion in air. Nomex® products are available which meet UL94V-0 requirements. Material Safety Data Sheets (MSDS) are available upon request, by calling (800) 453-8527 or (800) 387-2122 (Canada).
| DuPont™ Nomex® Papers and Pressboards Provide Short and Long-Term Benefits in Transformers |
Transformers of all types can benefit from the superior performance of Nomex® aramid papers and pressboards. These include open ventilated dry-types, cast coil and liquid filled, in sizes from lighting ballasts up to 62.5-MVA, 35kVA mobile substations.
| DuPont™ Nomex® Offers Improved Performance in Open Ventilated Dry Type Transformers |
Open ventilated dry type (OVTD) transformers are growing in popularity worldwide. Nomex® aramid papers and pressboards permit major design improvements in this type of transformer. OVDT designs with Nomex® offer the following advantages.
Enhanced Safety
There are no liquids to spill, explode or burn, and Nomex® does not support combustion in air. In the case of a building fire, Nomex® products do not produce significant amounts of toxic smoke or dangerous particles. (For this reason, among others, Nomex® is used extensively in honeycomb structures for aircraft interiors).
Low Transmission Losses
Since dry type transformers insulated with Nomex® can be located close to their loads - inside factories, schools, hospitals and apartments - low-voltage lines can be shortened.
Reduced Cost, Size and Weight
150°C rise units insulated with Nomex® require less conductor and core steel, resulting in lower initial cost. This reduced size and weight contributes to ease of installation, especially since no vaults or catch basins are required. Smaller cores also mean lower no-load losses.
Increased Reserve Capacity
If transformers are to be operated continuously at or near their rated loads, efficiency is of prime importance. In this case, one could select 80°C rise units insulated with Nomex®, allowing these units to operate continuously at 133 percent of rated load (if needed, for example, due to unplanned expansions) at a much lower cost (in increased load loss) than that associated with adding an additional transformer.
Improved Reliability
Surveys published by IEEE show failure rates of modern open ventilated dry type transformers equivalent to conventional liquid-filled units in the same power and voltage classes. Repair time for dry type units is also considerably shorter.
Resistance to Humidity
Since the properties of densified Nomex® papers and pressboards are insensitive to moisture, open ventilated transformers insulated with Nomex® perform satisfactorily in the most humid environments. This allows the placement of OVDT units in many locations not considered in the past.
| DuPont™ Nomex® Offers Improved Performance in Liquid-Filled Transformers |
Nomex® aramid papers and pressboards in liquid-filled transformers offer some of the same advantages as in OVDT designs. These advantages can be realized either when building new units or repairing existing ones.
Improved Reliability
Insulation systems based on Nomex® maintain excellent electrical and mechanical characteristics over the transformer's service life. Negligible aging, resistance to shrinkage and compression, and the superior resilience of Nomex® help to assure coil structures will remain tight and able to withstand short circuit forces, even after years of service.
Increased Reserve Capacity
Transformers insulated with Nomex® have extra power capacity for emergency peak load situations and unanticipated expansions. This can result in substantial savings in redundancy planning.
Reduced Size and Weight
While maintaining top oil temperatures at constant levels, with only modest increases in average oil temperature, the weight of the transformer can be reduced up to 25 percent for a given kVA output. Conversely, the kVA rating can be increased up to 50 percent for a given size and weight. Use of a high-temperature liquid like silicone oil permits even greater savings in size and weight.
Reduced Size and Weight
While maintaining top oil temperatures at constant levels, with only modest increases in average oil temperature, the weight of the transformer can be reduced up to 25 percent for a given kVA output. Conversely, the kVA rating can be increased up to 50 percent for a given size and weight. Use of a high-temperature liquid like silicone oil permits even greater savings in size and weight.
This weight reduction allows mobile substations, for example to be designed with operating capabilities larger than ever before.
Manufacturing Economies
The mechanical toughness of Nomex® papers and pressboards reduces shop failures and repairs. Use of a single, versatile insulation for all types and classes of transformers can reduce inventory costs. The use of Nomex® versus other insulating materials has significantly reduced dry-out time prior to oil impregnation in several cases.
Specific Applications Where Nomex® is used in Transformers
- Conductor wrap
- Layer and barrier insulation
- Coil end filler
- Core tubes
- Section or phase insulation
- Lead and tap insulation
- Case insulation
- Radial and axial spacers and spacer sticks
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| DuPont™ Nomex® Papers and Pressboards Increase Reliability and Extend Life of Motors and Generators |
Nomex® aramid papers and pressboards in liquid-filled transformers offer some of the same advantages as in OVDT designs. These advantages can be realized either when building new units or repairing existing ones.
Improved Reliability
Nomex® aramid papers and pressboards find numerous applications in motors and generators. Nomex® is used in all types of rotating equipment from AC and DC to random and form-wound, in sizes from miniature servo motors to 13.6kV industrial drives and 150MW steam-turbine generators.
The use of Nomex® papers and pressboards provides significant advantages to users of motors and generators.
Better Thermal Protection
Use of Nomex® for ground insulation can prevent premature motor failure and equipment downtime. This is because Nomex® does not shrink, embrittle, soften or melt during short-term exposure to temperatures as high as 300°C (570°F) and maintains good insulating properties continuously at 220°C (430°F) for 10 years. Motors may encounter temperatures considerably above their design ratings due to:
- Overloads, caused by reduced speeds or stalled rotors
- Restricted cooling (especially in dirty environments)
- Reduced line voltage or unbalanced phases
- Frequent starts and stops
- Unusually high ambient temperatures
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Because of its superior thermal properties, Nomex® can enhance motor performance and reliability.
Boosted Mechanical Toughness
The strength and resilience of Nomex® papers and pressboards help extend rotating equipment life in severe operating conditions. These conditions include severe shock and vibration seen in steel mill drives and railroad traction motors, as well as the abrasion caused by thermal expansion and centrifugal forces in stand-by gas-turbine generators.
| DuPont™ Nomex® Papers and Pressboards offer Manufacturers of Motors and Generators many Advantages |
One Product Line For all Needs
The flexibility and formability of type 410 and 414 Nomex® aramid papers (7 to 15mils, or 0.18 to 0.38mm) facilitates their insertion (automatic or manual) as slot liners. Their resilience holds them in the slot.
The stiffness of thick grades of Nomex® papers (20 to 30mils or 0.51 to 0.76mm) makes them especially useful as slot wedges, topsticks and midsticks, inserted by machine or by hand. Thicker Nomex® papers are routinely hot-formed into permanent shapes such as slot wedges and V-ring segments. Additionally, Nomex® pressboards can be cut and shaped into sticks and other more complex shapes.
The high dielectric strength and cut-through resistance of Nomex® papers may permit replacement of thicker materials, thereby gaining additional space in the slot.
Reduced Slot Liner Damage
The tear resistance of Nomex® papers reduces slot liner damage during winding and shaping of the coils in random-wound motors. Under unusually severe conditions (high-fill-factor, hand-wound units), laminates of Nomex®-Mylar®-Nomex® can be counted on to provide a superior slot insulation barrier.
Reduced Tooling Costs
End lams of Nomex® pressboards can be punched using the same die sets used for metal laminations.
Specific Applications where Nomex® is used in Rotating Equipment
Some examples of how Nomex® papers and pressboards are used in rotating equipment include:
- Conductor wrap
- Coil wrap and interleaving
- Slot liners
- Wedges, mid-sticks and top-sticks
- Phase insulation
- End-lams
- Pole pieces and coil supports
- Cross over tubing and end caps
- Commutator V-Rings
- Bushings (for double insulation)
- Lead Insulation
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| Other Applications of DuPont™ Nomex® Products |
Other electrical applications include fire-resistant wrapper and marker tapes for cables, appliance switch covers, shields for printed circuit boards, thermal and static barriers, and speaker coils.
| DuPont™ Nomex®: A Family of Insulation Materials Engineered to Meet the Diverse Demands of the Electrical Industry |
Nomex® offers the following advantages over conventional wire enamels:
- Economical and quick application
- Low startup and processing waste
- No cleanup or disposal problems
- No pollution problems
- Compatible with all common electrical equipment materials
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Nomex® aramid papers and pressboards
Nomex® aramid papers and pressboards are made entirely of synthetic aromatic polyamide polymer in two forms:
Floc: short fibers that provide mechanical strength.
Fibrids: microscopic filmy particles that provide dielectric strength and act as a binder.
The floc and fibrids are combined to form sheet structures by specialized paper or board-making methods. During each process the fibrids join to form filmy webs between the fibers. In most cases, the paper sheet is then densified-or calendered-at high temperature and pressure to permanently lock the components together and produce a relatively impermeable structure with high levels of electrical and mechanical integrity.
Paper and pressboard are the most widely used forms of Nomex®. There is an appropriate type and thickness for each electrical insulation application.
| DuPont™ Nomex®: Aramid Paper |
Type 410
is the original form of Nomex® paper, and is widely used in a majority of electrical equipment applications. It is produced in 11 thicknesses (2 to 30 mils, or 0.05 to 0.76 mm) with specific gravities from 0.7 to 1.2. A calendered product, it has high inherent dielectric strength, mechanical toughness, flexibility and resilience. Type 410 is used in almost every known sheet insulation application.
Type 411
is the uncalendered precursor of Type 410. It is available in five thicknesses (5 to 23 mils, or 0.13 to 0.58 mm), with a specific gravity of 0.3 and correspondingly lower electrical and mechanical properties. It is used in applications such as motor phase insulation and transformer coil end filler, where high bulk and conformability are of prime importance. Type 411 offers increased impregnability and saturability when compared to Type 410.
Type 414
is electrically and thermally similar to Type 410, but is calendered under different conditions which produce a strong, but more flexible and conformable sheet. It is produced in five thicknesses (3.4 to 15 mils, or 0.09 to 0.38 mm) with specific gravities from 0.9 to 1.0. Type 414 was designed for use as slot insulation in hand-wound motors and for linear wrapping of wire, but is also used in other applications where its specific characteristics are desirable (such as folded or punched parts).
Type 418
also called Nomex® M aramid and mica paper is produced by adding 50 percent mica platelets, intimately blended with the floc and fibrids during papermaking. It is available in five thicknesses (3 to 14 mils, or 0.08 to 0.36 mm) and is designed for high-voltage applications, including motor conductor and coil wrap, and transformer ground and layer insulation. Type 418 is a calendered product with high inherent dielectric strength (750 to 1000 V/mil, or 30 to 40 kV/mm), but can also be readily impregnated with varnishes where this is desirable. Type 418 offers increased voltage endurance when compared to Type 410.
Type 418
also called Nomex® M aramid and mica paper is the uncalendered precursor of Type 418. It is available in two thicknesses (7 and 13 mils, or 0.18 and 0.33 mm) with a specific gravity of 0.5, for applications where conformance and saturability are required.
| DuPont™ Nomex®: Aramid Pressboards |
Increased thickness and rigidity set Nomex® aramid pressboards apart from the other forms of Nomex®. They are used for spacers and barriers in transformers, both liquid-filled and dry type, and as end-lams in motors. This family of products offers a range of mechanical properties which insures design flexibility in a variety of applications.
Type 992
is a low-density pressboard produced in two thicknesses (63 and 125 mils, or 1.6 and 3.2 mm) with a specific gravity of 0.5. This material's low density allows easy formation of complex shapes, and provides the highest saturability of the pressboard products.
Type 993
is a medium-density pressboard produced in eight thicknesses (40 to 240 mils, or 1.0 to 6.0 mm) with specific gravities of 0.7 to 0.9. This material provides a balance of rigidity and conformability along with outstanding saturability and excellent electrical properties in oil.
Type 994
is a densified version of Type 993, available in 11 thicknesses (40 to 380 mils, or 1.0 to 9.6 mm) with specific gravities from 1.1 to 1.2. It provides superior stability under compressive loads. Type 994 will also absorb oils and other fluids, but not as readily as Types 992 and 993.
Type 994
is a densified version of Type 993, available in 11 thicknesses (40 to 380 mils, or 1.0 to 9.6 mm) with specific gravities from 1.1 to 1.2. It provides superior stability under compressive loads. Type 994 will also absorb oils and other fluids, but not as readily as Types 992 and 993.
| Spunlaced fabrics of DuPont™ Nomex® Aramid |
Spunlaced fabrics of Nomex® aramid are the most recent addition to the family of Nomex® products. They were specifically designed for use with resins and varnishes, where the open, porous structure allows for a high degree of saturability.
These non-woven sheet products combine saturability with the superior thermal capability, chemical compatability, moisture insensitivity, radiation resistance and non-toxicity seen in all Nomex® products. Spunlaced products are lightweight and compatible with all types of resins and varnishes.
Type E-88C
is a calendered non-woven sheet with excellent saturability and conformability.
Type E-88HM
is a high density calendered non-woven sheet with less saturability than the E-88C, but with improved modulus for those applications requiring increased physical strength.
| DuPont™ Sontara® Spunlaced Fabrics |
Spunlaced fabrics of Nomex® aramid are also available as non-calendered styles in the DuPont™ Sontara® line of products. These non-calendered versions of spunlaced fabric offer bulk and conformability along with excellent saturability.
| Other Forms of DuPont™ Nomex® Aramid |
The unique thermal, chemical, and physical properties of Nomex® can be obtained in many forms. Trade-produced variations include: laminates of Nomex® and Mylar® polyester film or Kapton® polyimide film, needlepunched felts, quilts and woven fabrics of fiber of Nomex®, tie cords of continuous filament of Nomex®, spun yarns, and many others. If your insulation needs include these or any other variations, we can help you with your application and provide source lists for these materials, upon request. Available in a wide range of coated laminated, formed, punched and prefabricated parts
** DuPont™, Sontara®, Nomex®, Mylar® and Kapton® are registered trademarks or trademarks of E.I. duPont de Nemours and Company. DuPont Canada is a licensee.
Information on Nomex® and other DuPont products are available upon request!
| Call or e-mail us for copies of the following data: |
- Magnet Wire Insulation of Nomex® Aramid Paper
- Recommended grades of Nomex® paper
- General principles and practices for linear wrapping
- Coil winding techniques
- Recommended grades of Nomex® paper
- Application information
- Linear wire wrap of Nomex®
- Nomex® Aramid Paper Type 410 Typical Properties
- Nomex® Aramid Paper Type 411 Typical Properties
- Nomex® Aramid Paper Type 414 Typical Properties
- Nomex® Aramid Paper Type 418 & 419 Typical Properties
- Nomex® Pressboard Type 992 Typical Properties
- Nomex® Pressboard Type 993 Typical Properties
- Nomex® Spunlaced Fabrics Typical Properties
- 1.5 mil Nomex® Paper Type 910 Typical Properties
- Nomex® Paper Type E56 Typical Properties
- UL-Recognized 600 Volt Class Electrical Insulation Systems Based on Nomex®
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