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. |
