Insight into gaseous product distribution of cross-linked polyethylene pyrolysis using ReaxFF MD simulation and TG-MS

Abstract

Cross-linked polyethylene (XLPE) has been widely used as the insulation material of power cables due to the great electrical and thermal properties. However, the material deteriorated when subjected to excessive thermal stress, leading to performance reduction and even failure of the cables. In this paper, we proposed a novel thermal fault detection method in power cables by exploring the gaseous product distribution of XLPE pyrolysis. Firstly, the gas generation characteristics of the XLPE pyrolysis was investigated using large scale ReaxFF molecular dynamics simulation. The simulation results showed that the major gaseous products included H2, CH4, C2H6, C2H4, C2H2, CO. The pyrolysis kinetics as well as the formation mechanism of the gases was illustrated using the real-time trajectory obtained by molecular dynamic calculation. Furthermore, the influence of temperature on the gas product distribution was characterized. Higher temperature increased the yield of H2, C2H4, C2H2, but decreased that of CH4. The yield of C2H6 and CO almost kept constant as temperature changing. The influencing mechanism of temperature was reasonably explained by the proposed gas formation mechanism. On the basis of investigation on XLPE pyrolysis, a three ratios technique was proposed for the detection of thermal faults in power cables. Finally, the chemical composition of the gas product was validated by thermogravimetric and mass spectrometric simultaneous experiment. The experimental results exhibited good agreement with the numeric simulation.