Experimental Study On Characteristics Of Flame Spread Over Electrical Wires And Cables With Thermoplastic Insulation

The development of social and economic is inseparable from the support of electricity.The high incidence of electrical fires poses a huge threat to the safety of people’s lives and property.It is of great practical significance to conduct research on the behavior of flame propagation over electrical wires and cables to prevent and control the danger of electrical fires.The purpose of this thesis is to study the flame propagation over electrical wires and cables with thermoplastic insulation.A series of experiments were carried out to study the fire propagation characteristics of polyethylene(PE)insulated wires at different inclination and space.According to experimental data,the influence of relevant parameters on flame propagation characteristics could be revealed.In addition,the fire characteristics and smoke stratification rules of vertically-arranged PVC insulated cables in restricted cabins are explored to better understand the development process of thermoplastic cable fires,so as to effectively prevent and control the fire hazard of thermoplastic wires.Firstly,PE insulated wires with different thicknesses of insulation were selected as the research objects.The experiment of flame propagation over inclined wires was conducted.The angle of inclination and the size of the wire under molten dripping effects on the rate of flame propagation,flame shape,and insulation temperature were studied.The results show that the fire spread rate has an “L” shape change with the increase of the tilt angle,and two control modes for the flame spread behavior of the inclined wires are obtained,namely the flowing preheat control mode and the flame preheat control mode.Finally,the accuracy of the two control modes was verified through the heat transfer process of the insulation.In addition,the research also found that the drop frequency and drop fraction of the wire at a small angle of fire spreading are related to the insulation thickness.And the dripping behavior will cause the flame height to increase suddenly,and the flame width will also change periodically depending on the dripping frequency;Then,based on the single wire experiment,the flame propagation behavior of the twin wires under the coupling effect of the inclination and spacing were studied.By changing the gaps between the two wires and the inclination angle of the wires,it was found that except for the inclination angle of-90 °,the flame spread rate,average flame height,and mass loss rate of the twin wires with a spacing arrangement are higher than the average value of a single wire burning,but are lower than the average value of a single wire when it is tightly arrangement;based on the change of flame shape,the interaction of two flame with the change of spacing could be divided d into three stages,namely the flame merging stage,the intermittent merging stage,and the flame separation stage.In addition,it can be seen from the results of the mass burning rate that when the inclination angle increases,the mass burning rate can reach a peak at a smaller gap;Finally,according to the results of previous study,the research on the fire characteristics and smoke stratification of vertical cables in confined cable compartment was conducted.By analyzing the combustion process of vertical cable in the compartment,the burning process of cables can be divided into the ignition stage,the acceleration stage and the attenuation stage,and the corresponding fire characteristics also show corresponding changes.At the same time,for the high-temperature and toxic smoke generated by the cable combustion,based on the fire three-layer zone model,three smoke interface stratification methods were developed and verified with experimental data.The results show that the three methods can reasonably stratify the smoke regions,and the temperature changes obtained from the inversion of the smoke interface fits well with the experimental values.