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Titles:
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Stueber, T.J., Hammoud, A., and McCall,
D., "Comparison of Arc Tracking Tests in Various Aerospace
Environments", presented at the 1996 International Symposium on
Electrical Insulation, Montreal, Quebec, June 16-19, 1996, NASA
Contractor Report 198463.
Momentary short-circuit arcs between a polyimide insulated
wire
with defective insulation and another conductor may cause pyrolization
of
the Insulation resulting In a conductive path capable of sustaining the
arc.
These sustained arcs may propagate along the wire or to neighboring
wires
leading to complete failure of the wire bundle. Wire Insulation
susceptibility
to art tracking may be dependent on Its environment. Because all wire
Insulation types tested to date arc track, a test procedure has been
developed to
compare different insulation types with respect to their arc tracking
susceptibility. This test procedure Is presented along with a
comparison of arc tracking in the following three environments: 1) Air
at atmospheric pressure and I gravitational (g) force, 2) Vacuum
2.67E-3 Pa) and 1g, and 3) Air at atmospheric pressure and microgravity
(< O.04g) .
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Hammoud, A., Stavnes, M., Suthar, J., and
Laghari, J., "Effects of Thermal and Electrical Stressing on the
Breakdown Behavior of Space Wiring", presented at the IEEE
Conference on Electrical Insulation and Dielectric Phenomena, Virginia
Beach, Virginia, October 1995, NASA CR 198360.
Effects of Thermal and Electrical Stressing on the Breakdown Behavior
of Space Wiring
Several failures in the electrical wiring systems of many aircraft and
space vehicles have been attributed to arc tracking and damaged
insulation. In some instances, these failures proved to be very costly
as they have led to the loss of many aircraft and imperilment of space
missions. Efforts are currently underway to develop lightweight,
reliable, and arc track resistant wiring for aerospace applications. In
this work, six wiring constructions were evaluated in terms of their
breakdown behavior as a function of temperature. These hybrid
constructions employed insulation consisting of Kapton, Teflon, and
cross-linked Tefzel. The properties investigated included the 400 Hz AC
dielectric strength at ambient and 200° C, and the lifetime at high
temperature with an applied bias of 40, 60, and 80% of breakdown
voltage level. The results obtained are discussed, and conclusions are
made concerning the suitability of the wiring constructions
investigated for aerospace applications.
Hammoud, A. N., Stavnes, M. W., Ide, J.
R., and Muegge, E., "Performance of Partially Fluorinated Polyimide
Insulation for Aerospace Applications", prepared for Glenn Research
Center Under Contracts NAS3-27186 and NAS1-18580, NASA Contractor
Report 198372.
Polyimide has been used extensively as the primary wiring insulation in
commercial planes, military aircraft and space vehicles due to its low
weight, high service temperature, and good dielectric strength. New
failure modes, however, have been associated with the use of polyimide
because of the susceptibility of the insulation to pyrolization and arc
tracking. A new wiring construction utilizing partially fluorinated
polyimide insulation has been tested and compared with the standard
military polyimide wire. Electrical properties which were investigated
include AC corona inception and extinction voltages (sea level and
60,000 feet), time/current to smoke and wire fusing time. The two
constructions were also characterized in terms of their mechanical
properties including abrasion resistance, dynamic cut through and notch
propagation. In this paper, these test efforts and the results obtained
are presented and discussed.
Stueber, T.J., Hammoud, A., Stavnes,
M.W., and Hrovat, K., "Evaluation of Pyrolysis and Arc Tracking on
Candidate Wire Insulation Designs for Space Applications",
presented at the
1994 IEEE International Symposium on Electrical Insulation, Pittsburgh,
Pennsylvania, June 6-8, 1994, NASA Contractor Report 195332.
Polyimide wire insulation has been found to be vulnerable to
pyrolization and arc tracking due to momentary short-circuit arcing
events. This report compares arc tracking susceptibility of candidate
insulation configurations for space wiring applications. The insulation
types studied in this report were gauge 20 (O.8l mm dia.) hybrid wiring
constructions using polyimide, tetrafluoroethylene (TFE), cross-linked
ethylene tetrafluoroethylene (XL-ETFE) and/or polytetrafluoroethylene
(PTFE) insulation. These constructions were manufactured according to
military wiring standards for aerospace applications. Arc track testing
was conducted under DC bias and vacuum (1OE-6 torr).
The tests were conducted to compare the various insulation
constructions
in terms of their resistance to arc tracking restrike. The results of
the
tests arc presented.
Hammoud, A. N., Stavnes, M. W.,
Dickman, J. E., Burkhardt, L. A., Woodford, L. M., Ide, J. R., and
Muegge, E.,
"Evaluation of Wiring Constructions for Space Applications",
presented
at the 1994 IEEE International Symposium on Electrical Insulation,
Pittsburgh,
Pennsylvania, June 5-8, 1994.
A NASA Office of Safety and Mission Assurance (OS&MA) program to
develop lightweight, reliable, and safe wiring insulations for
aerospace applications is being performed by the NASA Glenn Research
Center (GRC). As part of this effort, a new wiring construction
utilizing high strength PTFE (Poly Tetrafluoroethylene) as the
insulation has been tested and
compared with the existing military standard polyimide-based
MIL-W-81381
wire construction. Electrical properties which were investigated
included
ac corona inception and extinction voltages (sea level and 60,000
feet),
time/current to smoke, and wire fusing time. The two constructions were
also characterized in terms of their mechanical properties of flexural
strength, abrasion resistance (23ēC and 150ēC), and dynamic cut-through
(23ēC and 200ēC). The results obtained in this testing effort are
presented
and discussed in this paper.
Stueber, T.J. and Mundson, C., "Evaluation
of Kapton Pyrolysis, Arc Tracking, and Flashover on SiOx-Coated
Polyimide Insulated Samples of Flat Flexible Current Carriers for SSF",
presented at the 38th International SAMPE Symposium and Exhibition,
Anaheim, California, May 10-13, 1993, NASA Contractor Report 191106
Kapton polyimide wiring insulation has been found to be vulnerable to
pyrolization, arc tracking, and flashover when momentary short-circuit
arcs have occurred on aircraft power systems. Short-circuit arcs
between wire pairs that pyrolyize the polyimide resulting in a
conductive char
between conductors that may sustain the arc (arc tracking).
Furthermore,
the arc tracking may spread (flashover) to other wire pairs within a
wire
bundle. Polyimide Kapton will also be used as the insulating material
for
the flexible current carrier (FCC) of Space Station Freedom (SSF). The
FCC,
with conductors in a planer type geometric layout as opposed to
bundles,
is known to sustain arc tracking at proposed SSF power levels. Tests
were
conducted In a vacuum bell jar that was designed to conduct polyimide
pyrolysis,
arc tracking, and flashover studies on samples of SSF's FCC. Test
results
will be reported concerning the minimal power level needed to sustain
arc
tracking and the FCC susceptibility to flashover Results of the FCC arc
tracking
tests indicate that only 22 volt maps were necessary to sustain arc
tracking
(proposed SSF power level Is 400 watts). FCC flashover studies indicate
that
the flashover event is highly unlikely.
Stueber, T.J. "Evaluation of Kapton
Pyrolysis, Arc Tracking, and Arc Propagation on the Space Station
Freedom (SSF) Solar Array Flexible Current Carrier (FCC)",
presented at the 22nd IEEE
Photovoltaic Specialist Conference, Las Vegas, Nevada, October 7-11,
1991, NASA Contractor Report 189056.
Recent studies conducted by the Air Force Materials Laboratory and
Lockheed Missiles and Space Company involving the use of polyimide
Kapton coated wires indicate that if a momentary electrical short
circuit occurs between two wires, sufficient heating of the Kapton can
occur to thermally char (pyrolyze) the Kapton. Such charred Kapton has
sufficient electrical conductivity to create an arc which tracks down
the wires and possibly propagates to adjoining wires. These studies
prompted an investigation to ascertain the likelihood of the Kapton
pyrolysis, arc tracking, and propagation phenomena, and the magnitude
of destruction conceivably inflicted on Space Station
Freedom's (SSF) Flexible Current Carrier (FCC) for the photovoltaic
array.
The geometric layout of the FCC, having a planar-type orientation as
opposed
to bundles, my reduce the probability of sustaining an arc. An
experimental
investigation has been conducted to simulate conditions under which an
arc
can occur on the FCC of SSF, and the consequences of arc initiation.
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