Experimental study of spontaneous ignition of overloaded electrical wires under transverse wind

Spontaneous ignition of electrical wire caused by the Joule heat generated in core due to overloading or a short circuit is common, and is significantly influenced by wind velocity, but has been very limited addressed yet. This paper, for the first time, presents an experimental investigation in spontaneous ignition of over-loaded wire under transverse wind (perpendicular to wire). Polyethylene (PE)-insulated wires with a NiCr core diameter of 0.8 mm and the insulation layer thickness of 0.3 mm and 0.15 mm are employed as sam -ples. It can be found that with the increase of transverse wind velocity, the ignition delay time demonstrates a non-monotonic tendency (firstly decreases then increases, and decreases again, finally increases) until ignition limit, where four regimes are clarified according to different controlling mechanisms. The ignition delay time declines with the increase of electrical current. One of the most noteworthy findings is that the ignition delay time declines as the insulation thickness increases, which shows an opposite trend with the results of piloted ignition for thermally thin materials. In order to distinguish the ignition and non-ignition zones, an ignitabil-ity map considering both the gas phase kinetic effects and the solid phase heat loss effect is established based on two non-dimensional parameters [Damkohler number ( Da ) and Rloss]. A theoretical ignition model com-bining the effects of pyrolysis time, mixing time and chemical time is established, which well interprets the variation trend of ignition delay time and verifies the significant role of the chemical time in spontaneous ig-nition. This work provides essential knowledge on spontaneous ignition of overloaded electrical wires under practical transverse wind.& COPY; 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

This paper presents an experimental investigation on the spontaneous ignition of overloaded electrical wires under transverse wind. The results show that the ignition delay time has a non-monotonic trend with the increase of wind velocity. A significant finding is that the ignition delay time decreases as the insulation thickness increases, contrary to the results for thermally thin materials.