Study On The Influence Of The Fire-Retardant Coating On The Cable Ignition Characteristics And The Temperature Distribution Of Overloaded Cable

With the development of economy and society and the advancement of urbanization,industrialization and informatization in China,the power network develops and expands quickly both in scope and depth and people gradually rely heavily on the power system.In addition,the fragility of city's dependence on energy and information also gradually increases.The installation method of burying high-voltage cable system under ground is gradually promoted,which places greater demands and deeper challenges on the safe and optimal design of power system.As for the high-voltage live cables,they can be abstracted as a kind of physical structure of wrapping the heating metal in the outer polymer.In recent years,the cases reveal that the local overheating and outer heat source caused by various reasons play an important role in the cable fault and fire.The design and installation standard of cables in China stipulate the rated load of cable in detail and single out the importance of safety margin.This project is mainly about the cable.Based on the layered material distribution structure of cables in the axial direction,a calculation model for the coupling heat transfer inside and outside the cable is established.It calculates and analyzes the characteristics of the inner and outer temperature distribution of cables under the conditions of different loads and environment.The results show that the cable core is too thin and the thickness of the sheath material is thickened,which will all lead to a significant increase in the temperature inside and outside the cable,thus increasing the possibility of thermal disasters,its core temperature is easier to exceed 90?;Cables under buried laying conditions,the surrounding ventilation and heat dissipation conditions are often relatively poor,and will further promote the overall temperature rise of the live power cable,easily forming overheating and causing accidents.The thermal behavior of the outer sheath of the cable sprayed fire retardant coating was studied under different external heating flow conditions.The results showed that under the condition of lower heating power,the outer sheath of the cable with different thickness coatings will melt,fall off,and ignited,as the thickness of the coating increases,the PE outer sheath melts and falls off longer.Under medium heating power,the cable samples coated with different thickness coatings,the outer sheath is ignited before melting and falling off.This indicated that the cable under this radiation condition in the actual fire scene is more prone to fire propagation along the axial direction of the cable after a fire.For the power cables coated with different types and different thicknesses of fire-retardant coatings,the heating ignition test based on the medium heating power of the furnace was carried out.The results showed that the cables were coated with 0.5mm,1.0mm and 1.5mm,when the thickness of the coating is increased,the ignition time of the cable increases with the increase of the thickness of the coating.After the oil-based fire retardant coating is applied,the average ignition time of the cable is longer than that of the water-based fire retardant coating.The cable coated with s-1,s-2,s-3 and y-4 fire-retardant coatings,before the cable is ignited,analyze the surface morphology change of the coating,which can be divided into three stages:inert stage,swelling stage and stable stage.The change of the overall quality and mass loss rate during the heating process by the oil-based coating shows that the protection of the cable shows a significant stage,namely:dehydration into carbon,formation of foamy,pyrolysis,ignition.The protection of the coating on the cable mainly acts on the stage of forming the foamy carbonaceous layer;the cable coated with the oil-based fire retardant coating is heated and then swelled,the coating volume is obviously increased.After forming the "foamy" carbonaceous layer,the heat insulation effect is better.Before the cable is ignited,the temperature rise of the cable surface is slowed down;and after the cable coated with water-based fire retardant coating is heated,the surface of the coating forms a "bubble bump",delaying the ignition time of the cable.After the cable is painted with fire-retardant coating,the fire spreads slowly,and the oil-based fire-retardant coating has better suppression effect on the cable fire spread than the water-based fire-retardant coating.