典型变电站阻燃低压电缆外护套材料火灾条件下热解固气产物特性及反应机理

Solid-gas products and reaction mechanism of pyrolysis of the sheath material of a typical flame-retardant low-voltage cable in substations during a fire

变电站作为电力系统的核心部分,一旦发生火灾将可能造成严重的后果,研究变电站电缆的热解反应机理具有重要的现实意义。目前,针对变电站电缆热解机理,特别是元素变化规律和气体产物定量的研究较少。该文针对典型变电站阻燃低压电力电缆(ZRB-VV22-0.6/1.0 kV型)的外护套材料开展无氧条件下的热解动力学、固气产物特性及反应机理研究。利用热重实验(thermogravimetric,TG)研究外护套在氮气气氛下的热解行为,发现其热解主要分为2个阶段,应用Friedman、FWO和KAS方法,计算得到活化能分别为145.17和241.71 kJ/mol。采用场扫描电镜和X射线能谱仪联用技术(EDS)对原料和热解残碳进行元素分析,发现热解导致C元素挥发,其质量占比在热解后明显降低;Ca、Mg、Si元素无法挥发,以氧化物或其他化合物的形式保留在残碳中,质量占比明显升高;Cl和O元素部分挥发,质量占比有所升高,其中Cl元素的挥发可推断产物中存在HCl。进而,利用热裂解-气相色谱质谱联用(Py-GC/MS)对该电缆外护套的挥发性产物进行定性定量分析,发现其热解第一阶段(<623 K)产物以HCl和苯为主,当热裂解温度上升到773 K时产物中出现多环芳烃及苯系物,其热解过程以内部聚氯乙烯(PVC)材料受热分解为主,主体产物与PVC热解类似,用内标法对HCl、苯及苯系物进行定量,得到HCl和苯的产率分别为0.077和0.266 g/g,其余苯系物的产率较低。

Substations are key power system components,so substation fires can have serious consequences on system operations.In particular,more research is needed on the pyrolysis mechanism of cables in substations.There is little research on the chemical reactions and the gas products produced during pyrolysis of substation cables.The current study analyzed the pyrolysis kinetics,solid-gas product characteristics and reaction mechanism of the sheath material of a typical flame-retardant low-voltage power cable(type ZRB-VV22-0.6/1.0 kV)in a substation in the absence of oxygen.Thermogravimetric(TG)experiments were used to investigate the pyrolysis of the sheath material in a nitrogen atmosphere.The experiments showed that the pyrolysis can be divided into two major stages with activation energies of 145.17 and 241.71 kJ/mol for the two stages based on the Friedman,FWO and KAS methods.A field scanning electron microscope and an X-ray energy spectrometer(EDS)were used to analyze the elemental mass fractions of the raw material before pyrolysis and the residue after pyrolysis.The carbon mass fraction decreased due to volatilization of the carbon in the sheath.Ca,Mg and Si were not volatilized but remained in the residue with significantly greater mass fractions.Cl and O were partially volatilized with somewhat higher mass fractions in the residue.The volatilization of Cl infers the existence of HCl in the gas products.The use of Py-GC/MS to quantify the volatile products showed that the products of the first pyrolysis stage(<623 K)are mainly HCl and benzene.When the pyrolysis temperature rises up to 773 K,the products contain polycyclic aromatic hydrocarbons and benzene series.The main pyrolysis process is attributed to the pyrolysis of the PVC in the sheath material.Therefore,the main products are similar to PVC pyrolysis.The HCl yield was 0.077 g/g and the benzene yield was 0.266 g/g while the benzene series yields were relatively low.