Abstract
Arc beads are high-temperature luminous electric discharges that form across a gap between two bodies, which is one of the vital forensic pieces of evidence for the evaluation of electrical fires. In this study, based on an actual electrical fire, the microstructure of arc beads from a copper wire that experienced an overcurrent fault was investigated by optical microscopy and scanning electron microscopy. Moreover, the effects of the overcurrent intensity on the grain morphology, trace elements, and microstructure of the arc beads were analyzed. The results showed that the simulated metallographic structure of the arc beads is mainly dendrite at four times the rated current, which is consistent with the fire scene. With an increase in the overcurrent, the average diameter, perimeter, and area of the grains increased, while the dendrite growth was inhibited by the overcurrent. In addition, the main trace elements were Cu, C, O, and Cl. When the current increased, the Cu content gradually decreased and tended to be stable, while the C content gradually increased. The conclusion of this research provided a scientific reference for identifying the melting trace in a copper conductor under overcurrent fault.
Highlights
Electrical fire is one of the main causes of most urban building fires
In this paper, based on a machinery plant fire that occurred in Xi’an city, China, the characteristics of the traces of the fire scene were analyzed by optical microscopy (OM) and SEM-EDS, and the results were compared with experimental simulation traces to identify the cause of the fire
Our aim in this study was to obtain the microstructural characteristics of arc beads with various overcurrent faults and to provide a scientific reference for fire investigation
Summary
Electrical fire is one of the main causes of most urban building fires. From the statistics of the Emergency Management Department Fire and Rescue Bureau in China [1], in 2018 electrical fires accounted for 36.6% of the total number of fires in China. Wu et al [19,20] compared the distribution of the substances of Cu and Cu2 O by x-ray photoelectron spectrometry (XPS) These studies focus on the study of trace characteristics in short-circuit electrical fires, which is fundamentally different from overcurrent faults, and the studies are not shared. He et al [8] and Si et al [21] investigated the molten thermoplastic drip and microstructure under an overcurrent fault. In this paper, based on a machinery plant fire that occurred in Xi’an city, China, the characteristics of the traces of the fire scene were analyzed by OM and SEM-EDS, and the results were compared with experimental simulation traces to identify the cause of the fire. Our results provide clear scientific evidence to identify the melting trace in a copper conductor under overcurrent fault
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