PVC护套线过电流诱发短路过程及绝缘燃烧速率研究

Study on overcurrent-induced short circuit process and burning rate of PVC sheathed wires

为深入研究护套线过电流诱发短路过程及绝缘燃烧特征与引发火灾危险的关系,搭建电源护套线过电流诱发短路故障电路,统计初次短路的发生时间和位置,借助高速摄像机获取短路发生的过程,分析绝缘燃烧特征。结果表明:护套线在受到过电流作用后,其绝缘层逐渐失效,诱发短路故障,短路电弧引起绝缘层燃烧;短路后绝缘发生燃烧的最低概率为62.5%,发生在24 A时,48 A时燃烧持续时间最长为51 s,持续时间约为24 A时的2倍,最大火焰蔓延速率为2.08 mm/s,燃烧持续时间与火焰蔓延速率均随电流增大呈指数递增。

To further study the process of short circuits induced by overcurrent and the characteristic of wire insulation combustion,it is necessary to simulate the short circuit fault induced by the overcurrent of sheath wire.The process of the short circuit was captured by a high-speed camera.The time when the first short circuit occurred could be calculated from the video.Moreover,the probability of wire insulation burning after a short circuit fault was analyzed.The video was processed by the video frame cutting technology,thereby recorded the changes of sheath wire at key time points,and measured the location of the initial short circuit.The insulation combustion duration and flame spread situation after the short circuit were accurately analyzed.The mathematical models of insulation combustion duration and flame spread rate respectively were established to predict the characteristic parameters of energized wire combustion under overcurrent without experimental verification.The results suggest that the core temperature continues to increase after overcurrent.The gradual failure of the insulation induces the short circuit fault.The short circuit arc can ignite the premixed gas produced by the insulation pyrolysis at the fault point.Consequently,the insulation layer burns with a flame.Under all experimental conditions,the maximum distribution range of the initial short circuit points appears at 48 A,which is 60-250 mm.When I=24 A,the minimum ignition probability of insulation is 62.5%,which combustion duration range is 4-18 s.besides,the range of maximum flame spread rate is 1.37-1.58 mm/s.When I=48 A,the probability is 100%,and the burning duration range is mere twice that at 24 A.In this condition,the maximum flame spread rate is 2.08 mm/s.The mathematical models show that the duration of insulation combustion and flame spread rate increases exponentially with rising the current value.