DuPont Nomex 910 Engineered Cellulose
Insulation Thermal Aging Analysis
®
Summary
As previously announced, DuPont has been conducting
long-term thermal aging studies of new Nomex® 910
engineered cellulose insulation. These studies are based
on the recently revised IEEE C57.100™-2011,
the “IEEE Standard Test Procedure for Thermal
Evaluation of Insulation Systems for Liquid Immersed
Power and Distribution Transformers.”
After more than 10 months of aging work, DuPont has
established that the thermal performance of new
Nomex® 910 insulation is at least 10°C better than the
industry standard thermally upgraded kraft paper (TUK)
in mineral oil systems.
These studies also indicate that new Nomex® 910 insulation
may provide an additional 10°C performance enhancement
in natural ester liquids. Based on Table 1 of the new
IEEE C57.154™-2012, this performance enhancement
translates to a system Thermal Class of 130 in mineral oil
and 140 in natural ester liquids.
Background
Researchers at DuPont have developed a unique
technology that combines Nomex® aramid ingredients
with cellulose, using the superior thermal capability
of Nomex® to improve the thermal capability of the
combined product. Because the majority of the insulation
is made from cellulose, the thermal improvement comes
at a small increase in the price of the insulation, providing
users with an attractive cost/performance ratio.
The introduction and final issuance of the two new IEEE
standards noted above have helped lead the way to a new
portfolio of insulation materials for the liquid transformer
industry. Nomex® 910 insulation is the first of those to be
introduced by DuPont.
In what may be the first published report of aging results
based on the new IEEE C57.100™-2011, an extensive
evaluation was conducted of the industry standard system
and new candidate systems using Nomex® 910 insulation.
These reported results are based on sealed tube aging of
more than 100 aging cells, involving at least six different
system combinations, including systems with mineral oil
and biodegradable liquids.
Due to the unpredictability of the thermal capability
of this new material, DuPont conducted aging tests at
seven different temperatures vs. the minimum three
temperatures required by the standard.
Sealed tube aging of the industry standard system of TUK
and mineral oil at three temperatures resulted in an endof-life target of approximately 16.3% of the original tensile
strength. This system has an industry accepted thermal
index of 110°C when projected to 180,000 hours and
120°C when projected to 65,000 hours.
Using this base point, the individual cell combinations
were aged from four to six timeframes, with failure points
beyond the base point. The data were then interpolated for
each system temperature to arrive at the end-of-life times
at the 16.3% target. Once these data were obtained, the
life (Arrhenius) curve was then plotted with end-of-life vs.
temperature. These curves were then projected to 180,000
hours to arrive at the thermal index of each system.
Conclusions
The Arrhenius curve for the Nomex® 910 insulation and
mineral oil system is shown in Figure 1. The curve projects
to a thermal index of 120°C at 180,000 hours for a thermal
class of 130°C.
DuPont Nomex 910 in Mineral Oil
™
®
10
8
Ln Life (hours)
™
6
y = 16980x - 31.073
R = 0.94545
2
4
2
0
0.0021 0.00215 0.0022 0.00225 0.0023 0.00235 0.0024
1/Temp (1/K)
Figure 1.
of Nomex® 910 insulation were at least as good as those of
the 7-mil (0.18-mm) thickness of Nomex® 910 insulation
paper previously tested in the distribution transformer
ratio. The interpolated time to 16.3% tensile strength at
180°C was nearly 50% higher (611 vs. 414 hours) in this
aging experiment (see Figure 3). Based on these results,
DuPont believes this shows at least equivalent performance.
For a comparison of these results to those for the
industry-proven system (control), refer to Figure 2.
DuPont Nomex 910 in Mineral Oil
™
®
10
y = 16980x - 31.073
R = 0.94545
2
8
DuPont Nomex 910 in Mineral Oil - 180˚ C
™
7
Percent Tensile Strength
Ln Life (hours)
9
y = 14993x - 27.048
6
5
4
0.0021 0.00215 0.0022 0.00225 0.0023 0.00235 0.0024
1/Temp (1/K)
Nomex 910
®
150
100
50
0
0
100 200 300 400 500 600 700 800 900
Hours
Power - 3 mil
Industry-Proven System
Figure 2.
Dist - 7 mil
Figure 3.
This initial study was based on the distribution system
material ratios found in Table B.1 of the IEEE C57.100™2011. A 7-mil (0.18-mm) thickness of Nomex® 910
insulation was used in this study because this thickness is
representative of a common layer insulation used in
the distribution industry.
Future Studies
Additional thermal aging analysis of Nomex® 910
insulation in several biodegradable liquids is in progress.
Due to the superior thermal capability of Nomex® 910
insulation and the enhancement of the liquids over
mineral oil, the end-of-life of these systems has far
exceeded DuPont projections when the aging studies
began. As a result, more testing at higher temperatures
will be required to determine the thermal index in a
reasonable amount of time.
Sealed tube materials ratios
Transformer Type
Material
®
Power
Distribution
Insulating Liquid
200 cm
0.05 to 0.10 mm
conductor insulation
6.4 cm
3
200 cm
3
3
0.13 to 0.38 mm
layer insulation
11.2 cm
1.00 to 3.00 mm
low-density pressboard
1.2 cm
An example of this is shown in the results from testing
Nomex® 910 insulation in FR3® natural ester liquid.
The calculated life of Nomex® 910 insulation in FR3®
at 195°C was 1,120 hours, which is more than five times
the life in mineral oil. In addition to aging at 195°C,
DuPont also conducted aging at 180°C and 165°C.
In both of these cases, the end-of-life target of 16.3% was
not reached, even after more than twice the life of
Nomex® 910 insulation in mineral oil.
3
3
2.00 to 8.00 mm
high-density pressboard
16.4 cm
Ratio–liquid to solid
8.8 to 1
3
16.3 to 1
Reprinted with permission IEEE, Copyright 2011. All rights reserved.
To verify these results with a 3-mil (0.08-mm) thickness
of Nomex® 910 insulation (a thickness that would be
more commonly used as wire wrap insulation in power
transformers), DuPont performed a single-point aging
test at 180°C, using the sealed tube material ratios
representative of a power system.
Assuming the same Arrhenius slope, and considering the
doubling factor of material life in 7°C increments, this
initial data suggests that the thermal index of Nomex®
910 insulation is at least 10°C greater in FR3® than in
mineral oil, and probably much more. This results in at
least a 20°C increase over the standard system of TUK in
mineral oil.
Despite the fact that more solid material is in the same
volume of liquid, the aging results with the 3-mil thickness
For more information:
Mexico 52.55.5722.1000
US 1.800.221.2960
Canada 1.800.663.7027
www.nomexpaper.dupont.com
www.nomex610.dupont.com
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experimentation. It is not intended, however, to substitute for any testing you may need to conduct to determine for yourself the suitability of our products for your particular purposes.
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