单芯铜线过电流故障电弧熔痕的微观特征研究

Study on microcosmic characteristics of arc melting trace caused by overcurrent fault of single-core copper wire

为准确认定电气火灾中过电流故障,模拟4~7倍额定电流(Ie)条件下单芯铜导线过电流故障,利用光学显微镜和扫描电子显微镜(SEM)分析过电流故障电弧熔痕的组织特征,并结合Image-Pro Plus软件测定晶粒直径、周长和面积,探究金相组织的量化判据和变化规律。结果表明:当I=4Ie时,过电流故障电弧熔痕的金相组织主要为方向性较强的树枝晶;当I=5Ie,6Ie时,金相组织内树枝晶占比减小,胞状晶占比升高;当I=7Ie时,方向性较弱的胞状晶占主导。随着电流增加,晶粒的平均直径、周长和面积均呈增长趋势。通过火灾案例分析可知,实验结果与现场的电弧熔痕组织特征基本相符,验证火灾事故原因为过电流故障。

In order to accurately identify the overcurrent faults in the electrical fires,the overcurrent faults of single-core copper wire under the conditions of 4~7 times rated current(Ie)were simulated.The optical microscopy and scanning electron microscopy(SEM)were used to analyze the structural characteristics of arc melting trace caused by the overcurrent fault,and the Image-Pro Plus software was used to determine the grain diameter,circumference and area,then the quantitative criteria and changing laws of metallographic structure were explored.The results showed that when I=4Ie,the metallographic structure of arc melting trace caused by overcurrent faults was mainly the dendrites with stronger directivity.When I=5Ie or 6Ie,the proportion of dendrites in the metallographic structure decreased,while the proportion of cellular crystals increased.When I=7Ie,the cellular crystal with weaker directivity was dominated.As the current increased,the average diameter,circumference and area of the grains increased.Through the fire case analysis,it was found that the experimental results were basically consistent with the structure characteristics of on-site arc melting trace,and the fire accident was verified to be caused by overcurrent fault.