Ignition of silicone rubber sheaths by series arcs at different currents and durations

Understanding the igntion of combustibles by electric arc is important for the electric fire safety in energy systems. In this work, the ignition of a polymer sheath by series arcs with different supplied currents and arc durations was studied by a unique facility. Results show that the ignition process by different arcs can be categorized as one of three modes, including without ignition, with one-stage flaming ignition and with two-stage flaming ignition. Meanwhile, the ignition probability distribution versus current and duration was divided into three zones with different hazards levels (zone Ⅲ>Ⅱ>Ⅰ). The function of igntion probability with arc energy was established, obtaining the upper and lower limits of arc energy in zone Ⅱ, from 630 to 1515 J. Further, by comparing the test conditions where arc energy casued same ignition probability, it was found that the higher the supply current a lower arc energy was needed for ignition. Based on a quantitative analysis of the ignition time heated by sustained arcs and the arc current, the minimum ignition arc current (about 3 A) was in good agreement with experiment as predicted.