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NOMEX Type 410
NOMEX® Type 410 is a calendered insulation paper which offers high inherent dielectric strength, mechanical toughness, flexibility and resilience. NOMEX® Type 410 is the original form of NOMEX® paper, and is widely used in a majority of electrical equipment applications. Available in 12 thicknesses (0.05 to 0.76 mm) (2 to 30 mil), NOMEX® Type 410 is used in almost every known electrical sheet insulation application.

To read the full DuPont NOMEX Type 410 PDF, please click here.

Electrical Properties
The typical electrical property values for NOMEX® Type 410 paper are shown in Table 1. The AC Rapid Rise dielectric strength data of Table 1, representing voltage stress levels, withstood 10 to 20 seconds at a frequency of 60 Hz. These values differ from long-term strength potential. DuPont recommends that continuous stresses in transformers not exceed 1.6 kV/mm (40 V/mil) to minimize the risk of partial discharges (corona). The Full Wave Impulse dielectric strength data of Table 1 were generated on flat sheets, such as in layer and barrier applications. The geometry of the system has an effect on the actual impulse strength values of the material. The dielectric strength data are typical values and not recommended for design purposes. Design values can be supplied upon request.

Temperature has a minor effect on dielectric strength and dielectric constant, as shown in Figure 1.

Variations in frequency up to 104 Hz have essentially no effect on the dielectric constant of NOMEX® Type 410 paper. The effects of temperature and frequency on dissipation factor of dry NOMEX® Type 410 – 0.25 mm (10 mil) paper are shown in Figure 2. The 60 Hz dissipation factors of thinner papers are essentially the same as those for 0.25 mm (10 mil) at temperatures up to 200°C. At higher temperatures and frequencies, the thicker papers have somewhat higher dissipation factors than those shown for the 0.25 mm (10 mil).

Surface and Volume Resistivities of dry NOMEX® Type 410 – 0.25 mm (10 mil) paper are shown in Figure 3 as functions of temperature. The corresponding values for other thicknesses of NOMEX® Type 410 are very similar.

The relatively minor effects of moisture (humidity) on the electrical properties of NOMEX® Type 410 – 0.25 mm (10 mil) are shown in Table II.

Like other organic insulating materials, NOMEX® paper is gradually eroded under attack by corona discharges. Corona intensity is a function of voltage stress, which, in turn, depends almost entirely on design parameters such as spacing between circuit elements, smooth vs. sharp contours, etc. Although corona does not occur during normal operation of properly designed electrical equipment, any device may be subject to occasional overvoltages which produce brief corona discharges; and it is important that the insulation not fail prematurely under these conditions. The voltage endurance (time to failure under corona attack) of NOMEX® Type 410 paper is superior to other commonly used organic insulations and even compares favorably with some inorganic compositions, as shown in Figure 4. These data were obtained in all cases on single layers of 0.25 mm (10 mil) materials at room temperature, 50% relative humidity, and 360 Hz frequency. Times to failure at 50-60 Hz are approximately 6–7 times as long as indicated.

Mechanical Properties
The typical mechanical property values for NOMEX® Type 410 paper are shown in Table III. The effects of high temperatures on tensile strength and elongation are illustrated in Figure 5. NOMEX® sheet structures also retain good mechanical properties at very low temperatures. At the boiling point of liquid nitrogen (minus 196°C or 77K) the tensile strength of NOMEX® Type 410 – 0.25 mm (10 mil) paper exceeds its room-temperature value by 30 to 60% (depending on direction), while elongation to break is still greater than 3% (better than most inorganic materials at room temperature). This allows NOMEX® Type 410 to work well in cryogenic applications.

Water is a mild plasticizer for NOMEX® paper. The effects of moisture (humidity) on tensile strength and elongation are shown in Figure 6. Like elongation, the tear strength and toughness of NOMEX® Type 410 paper are also improved at higher moisture contents.

The dimensions of bone-dry NOMEX® Type 410 paper exposed to 95% relative humidity conditions will increase at most 1% in the machine direction and 2% in the cross direction (due to moisture absorption). This swelling is largely reversible when the paper is redried. The rate of change in dimensions will depend, of course, on paper thickness and configuration (for example, individual sheets versus tightly wound rolls). Variations in environmental humidity will usually produce dimensional changes which will be less than 1%. However, even small dimensional changes, especially if they are non-uniform, can cause or accentuate non-flatness (sag, puckers, etc.) in the sheet, which can cause problems in critical operations like laminating or creping. Therefore, NOMEX® paper intended for these applications should be kept sealed in its protective polyethylene wrapper, to maintain uniform moisture content, until just before use.

Thermal Properties
The effects of long-time exposure of NOMEX® Type 410 – 0.25 mm (10 mil) to high temperature on important electrical and mechanical properties are shown in figures 7, 8 and 9. These Arrhenius plots of aging behavior are the basis for the recognition of NOMEX® paper as a 220°C insulation by Underwriters Laboratories, the U.S. Navy, and others, and are confirmed by more than 35 years’ commercial experience. These curves can also be extrapolated to higher temperatures. Measurements show, for example, that NOMEX® paper Type 410 will maintain 12 kV/mm (300 V/mil) dielectric strength for several hours at 400°C, which is the performance predicted by the Arrhenius plot.

The thermal conductivity of NOMEX® Type 410 – 0.25 mm (10 mil) paper is shown in Figure 10. These values are similar to those for cellulosic papers, and, as with most materials, are primarily determined by specific gravity (density). Therefore, thinner grades of NOMEX® Type 410 paper, which are somewhat less dense, will have slightly lower conductivity, and thicker grades, which are denser, will have higher conductivities, as is seen in Table IV. The total system construction may affect the overall thermal conductivity, therefore, care should be taken in applying individual sheet data to actual situations. For example, two sheet insulations with identical thermal conductivities may have quite different effects on heat transfer from a coil, due to the differences in stiffness or winding tension which affect the spacing between the insulation layers.

Chemical Stability
The compatibility of NOMEX® paper and pressboard with virtually all classes of electrical varnishes and adhesives (polyimides, silicones, epoxies, polyesters, acrylics, phenolics, synthetic rubbers, etc.), as well as other components of electrical equipment, is demonstrated by the many UL-recognized systems comprising NOMEX,® as well as longstanding commercial experience. NOMEX® papers are also fully compatible (and in commercial use) with transformer fluids (mineral and silicone oils and other synthetics) and with lubricating oils and refrigerants used in hermetic systems. Common industrial solvents (alcohols, ketones, acetone, toluene, xylene) have a slight softening and swelling effect on NOMEX® Type 410 paper, similar to that of water. These effects are mainly reversible when the solvent is removed.

The Limiting Oxygen Index (LOI) of NOMEX® paper Type 410 at room temperature ranges between 27 and 32% (depending on thickness and density), and at 220°C, from 22 to 25%. Materials with LOI above 20.8% (ambient air) will not support combustion. NOMEX® Type 410 must be heated between 240°C and 350°C (again depending on thickness) before its LOI declines below the flammability threshold. The LOI data for Type 410 – 0.13 mm (5 mil) is shown in Figure 11.

The effect of 6400 megarads (64 Mgy) of 2 MeV beta radiation on the mechanical and electrical properties of NOMEX® Type 410 paper is shown in Table V. (By comparison, a laminate of polyester film and polyester mat of the same thickness, 100% epoxy-impregnated, crumbled after 800 megarads, or 8 Mgy). Similar results were obtained on exposure to gamma radiation. The outstanding radiation resistance of NOMEX® paper has led to its use in critical control equipment for nuclear power installations.

To read the full DuPont NOMEX Type 410 PDF, please click here.

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