Electro -Physics Branch, NASA Glenn Research Center
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Introduction:
Momentary short-circuit arcs between a defective polyimide insulated wire
and another conductor may thermally char (pyrolize) the insulating material.
The charred polyimide, being conductive, is capable of sustaining the
short-circuit arc. The sustained arc may propagate along the wire through
continuous pyrolization of the polyimide insulation (arc tracking). If
the arcing wire is part of a multiple wire bundle, the polyimide insulation
of other wires within the bundle may become thermally charred and start
to arc track (flash over). Therefore, arc tracking may lead to complete
failure of an entire wire bundle or harness. Due to the popular use of
polyimide insulated wires, such as MIL-W-81381, for use in aerospace vehicles,
a program has been initiated by the NASA Office of Safety and Mission
Assurance (Code Q) to identify candidate wire insulation types for aerospace
applications that are not susceptible to arc tracking. Arc tracking tests
conducted by the Electro-Physics Branch, Power and On-Board Propulsion
Technology Division at the NASA Lewis Research Center have been performed
to evaluate candidate wire insulation's susceptibility to arc tracking.
A unique test procedure has been designed to aid in the selection of a
candidate insulation type least susceptible to arc tracking. Tests have
conducted in the following three environments:
Air at atmospheric pressure and 1 gravitational (g) force.
vacuum (2.67E-3 Pa) and 1g.
air at atmospheric pressure and microgravity (< 0.04g).
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Abstracts
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The above picture is a Typical Arc Tracking Test Result for a Sample of
The Proposed Flexible Current Carrier (FCC) for the International Space
Station.
The above picture is a Typical Arc Tracking Test
result for a Sample of MIL-W-81381 American Wire
Guage (AWG) 20 (Kapton).
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curator and official responsible for content: Bruce.A.Banks@grc.nasa.gov
Privacy Statement
Electro-Physics Branch, NASA Glenn Research Center
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Evaluation of Kapton Pyrolysis, Arc Tracking,
and Arc Propagation on the Space Station Freedom (SSF) Solar Array Flexible
Current Carrier (FCC)
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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Evaluation of Kapton Pyrolysis, Arc Tracking, and
Flashover on SiOx-Coated Polyimide Insulated Samples of Flat Flexible
Current Carriers for SSF
Kapton polyimide wiring insulation has been found to be vulnerable to
pyrolization, arc tracking, and flashover when momentary short-circuit
arcs have ocurred 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 alse 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.
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Evaluation of Pyrolysis and Arc Tracking on Candidate
Wire Insulation Designs for Space Applications
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 are presented.
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Comparison of Arc Tracking Tests in Various Aerospace
Environments
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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Performance of Partially Fluorinated Polyimide
Insulation for Aerospace Applications
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.
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64 Cases of Shuttle Wiring Failure (and a Close Call) |
curator and official responsible for content: Bruce.A.Banks@grc.nasa.gov
Privacy Statement
Comparison of Arc Tracking Tests in Various Aerospace Environments
AUTHOR(S):
Thomas J. Stueber, Ahmad Hammoud, and David McCall
REPORT DATE:
March 1996
FUNDING NUMBERS:
WU-323-15-03 C-NAS3-27186
PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES):
NYMA Inc. 2001 Aerospace Parkway Brook Park, Ohio 44142
PERFORMING ORGANIZATION REPORT NUMBER:
E-10149
SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES):
National Aeronautics and Space Administration Lewis Research Center Cleveland,
Ohio 44135-3191
REPORT TYPE AND DATES COVERED:
Final Contractor Report
SPONSORING/MONITORING AGENCY REPORT NUMBER:
NASA CR-198463
SUPPLEMENTARY NOTES:
Prepared for the 1996 International Symposium on Electrical Insulations
cosponsored by the Institute of Electrical and Electronics Engineers and
the Dielectrics and Electrical Insulation Society, Montreal, Canada, June
16-19, 1996. Thomas J. Stueber and Ahmad Hammoud, NYMA Inc., 2001 Aerospace
Parkway, Brook Park, Ohio 44142 (work funded by NASA Contract NAS3-27186);
David McCall, Cleveland State University, Cleveland, Ohio. Project Manager,
Ronald Cull, Space Power Technology Division, organization code 5430,
(216) 433-3948.
ABSTRACT:
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 wires or to neighboring
wires leading to complete failure of the wire bundle. Wire insulation
susceptibility to arc 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 1 gravitational (g) force, 2) Vacuum
(2.67x10-3 Pa) and 1g, and 3) Air at atmospheric pressure and microgravity
(<0.04g).
SUBJECT TERMS:
Arc tracking
NUMBER OF PAGES:
07
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