Experiment And Numerical Simulation On Overcurrent Fault Of Copper Conductor

Over-current fault is the final manifestation of a variety of electrical faults.There are obstacles to heat dissipation in the current loop,stray current and ultra-high negative pressure,etc,which will cause overcurrent fault.In this paper,the evolution law of temperature characteristics when copper wire overcurrent fault is studied,and the microstructure of wire melt mark is found out.The research results provide reference and help for the identification technology of electrical fire material evidence,and further enhance the accuracy and scientific nature of fire investigation.The overcurrent faults of copper conductors at 128A,160A,192A and 224A are simulated by using electrical fault simulator.The experimental results show that the copper wire will be accompanied by red core,wire deformation,large amount of smoke precipitation,wire fusing and wire combustion when the copper wire overcurrent fault occurs.With the increase of current intensity,the wire heating rate becomes faster and the wire fusing time becomes shorter.When the current intensity is 128A,there is only one wire fuse point,and local combustion occurs.When the current intensity reaches 160A and above,multiple wire fuses will occur,and the whole line combustion phenomenon will occur.The temperature evolution law of PVC conductor and bare conductor is different in the pyrolysis process.Under the same current,the heating rate of the bare conductor is higher than that of the PVC conductor,and the fusing time is shorter than that of the PVC conductor.In addition,there will be a large number of CO,CH4,aromatic and aliphatic compounds generated in the pyrolysis process of PVC wires.The microstructure of the weld mark was analyzed by metallographic microscope.It is found that the microstructure of the weld mark is quite different under different current intensity.When the current is 128A,the grains are mainly slender dendritic and columnar.When the current is greater than 192A,the grain morphology changes into dendritic and cellular grains.The grain size was quantified by Image-Pro-Plus.The results show that with the increase of current,the average grain diameter of wire weld trace increases,and the insulation layer and cooling method have little effect on the grain morphology and size.By analyzing the phase structure of arc trace,it is found that the arc trace of copper wire is mainlyα-Cu base and Cu2O phase when the over-current fault occurs,and new phase will be formed with the increase of current.At the same time,the cooling rate also has a certain effect on the phase structure of the melt mark.By analyzing the microstructure and elemental composition of wire trace by SEM combined technology,it is found that the current intensity,wire type and cooling rate can affect the SEM morphology and elemental composition of the hole and grain boundary.Under different current intensity,wire type and cooling rate,there are great differences in element contents between grains and grain boundaries in the interior of the cavity and the surface of the weld mark.The data indicate that only elements of Cu,C and O can be detected under the current intensity of 128-192A.When the current reaches 224A,elements of Cu,C,O and Cl can be detected.Bare wires can’t detect Cl.Finally,the temperature field and microstructure in the solidification process of the wire were numerically simulated,and the temperature distribution of the copper wire in the solidification process was obtained.The microstructure simulation results were in good agreement with the experimental results.