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Arc-Tracking and Wire INsulation Pyrolization - EPB of NASA GRC



 


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 Glenn 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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[Typical Arc Tracking Test Result on FCC]
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. [Typical Arc Tracking Test on Wire]
The above picture is a Typical Arc Tracking Test
result for a Sample of MIL-W-81381 American Wire Guage (AWG) 20.

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Curator:  Sandra.A.Zolo@nasa.gov  and NASA Official Responsible For Content:  Sharon.K.Miller@nasa.gov 
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Last Updated: 02/04/2014