Th 51st AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference was held on January 2010 and included presentations of a wide range of technical papers. From the perspective of EWIS, authors McCabe and Cyphers reported on A Study of Over-Current Protection, Electrical Arcing, and Fire Protection. Their research objective was to gather data for ballistic threats to EWIS, particularly the likelihood of igniting a fuel spray.
Testing was performed at normal atmospheric pressure and at a pressure representing an altitude of 30,000ft. In addition to examining fuel ignition of EWIS components, tests were performed to evaluate different circuit protection device effectiveness and the ignition potential of fuel spray. The testing was carried out using 270VDC and 28VDC electrical systems.
The tests were initiated by one of three different arcing initiation methods (only two will be discussed here). This included (#1) open circuit to shorting condition (connection with ground after limiting resistors) and (#2) pulling the wire away from the ground connection to draw out an arc. During the test performance, a fuel spray was directed at arcing wires.
The following figure shows a simplified representation of the test circuit.
The authors do report the results of their work and show a number of scenarios in which the fuel may be ignited by the arcing wires. However, reviewing the results may lead some to assume that the likelihood of initiating a fire with a 28VDC power supply and a 22AWG wire is difficult. One critical part of their test circuit is that the test was performed after the current limiting resistors. The currents tested in this work were rather low and do not represent the fuel ignition hazard of a fault occurring in the circuit before the electrical load.
For those interested in the risks posed by electrical arcing and the process for assessment of electrical arc damage, this paper does provide a good overview of the subject area. For those new to electrical arcing, Lectromec’s EWIS Failure and the process of Electrical Arcing article is a good starting point to learn about the failure process.
If you are interested in arc damage assessments or the risk failed EWIS components may pose to your platform, contact Lectromec.