铜包铝护套线过电流诱发短路故障过程及痕迹特征研究

Research on the process of short-circuit faults induced by overcurrent in copper-clad aluminum sheathed wire and the characteristics of weld marks

铜包铝护套线常被用于铜芯护套线替代线,但其承载能力差,易发生过电流故障诱发短路引发火灾。通过分析此类护套线发生过电流诱发短路故障时的典型现象及电压电流波动,研究短路发生所需时间、拉弧次数、燃烧持续时间等过程参量随过电流值变化规律,并得出典型痕迹特征。结果表明:5.50倍额定电流(rated current,I_(e))是此类护套线过电流故障诱发短路的最低电流;过电流诱发短路所需时间随着过电流值增加呈指数递减关系,由5.50I_(e)时的148.9 s,降至8.80I_(e)时的40.1 s,但短路引燃后平均燃烧持续时间呈先增高再降低的趋势,在7.15I_(e)时最长,达22.72 s;此种护套线过电流故障诱发短路均呈现多次反复拉弧的特征,拉弧次数最多可达55次,产生大量线芯电弧熔痕和短路迸溅熔珠,呈现珠状、叠加珠状,组织以树枝晶为主。研究结果对认定铜包铝护套线过电流诱发火灾及痕迹鉴定具有一定指导作用。

Copper-clad aluminum sheathed cables are commonly utilized as a cost-effective and lightweight alternative to copper-core sheathed cables.However,their lower carrying capacity renders them more vulnerable to overcurrent faults,which can induce short circuits and pose a fire hazard.This article aims to offer technical insights for comprehending and examining these fire-related incidents.This study investigates the characteristic patterns of fault occurrences,with a focus on voltage and current fluctuations during the process.It explores key process parameters such as the time to short circuit occurrence,number of arcing instances,and duration of combustion,across varying overcurrent values.Furthermore,the study identifies typical characteristics of melting marks and metallographic microstructures resulting from overcurrent-induced faults.The findings indicate that 5.50 times the rated current(denoted as I_e) represents the minimum current threshold at which overcurrent faults can induce short circuits in copper-clad aluminum sheathed cables.The time for a short circuit to occur decreases exponentially with higher overcurrent values,reducing from 148.9 s at 5.50I_(e) to 40.1 s at 8.80I_e.Notably,the duration of combustion after ignition of the short circuit initially increases and then decreases,with the longest duration of 22.72 s observed at 7.15I_e.Short circuits induced by overcurrent in these cables often involve multiple repeated arcing instances,with up to 55 arcs observed.The repeated arcing generates numerous wire core arc melting marks and short-circuit splattered melting beads.These marks typically manifest as bead-like or stacked bead-like shapes,often displaying dendritic crystal patterns in their internal structure.The findings of this study offer critical insights into identifying the origins of fires linked to copper-clad aluminum sheathed cables.Such understanding is essential for precise trace identification and can contribute to enhancing fire safety protocols and standards within the electrical industry.