Molecular dynamics simulation of pyrolysis in polyethylene cable sheaths under electric field
Shuangshuang Tian, Dunpeng Yang, Yingyu Wu, Chenying Li, Benli Liu, Nnditshedzeni Eric Maluta, Zhou Huang
Abstract
Power cable pyrolysis is typically a precursor to combustion. The pyrolytic reaction of the cable during operation is influenced by the electric field. Investigating the mechanisms underlying cable pyrolysis in the presence of an electric field is crucial for preventing cable fires. This paper examines the pyrolysis process and key reaction processes of the polyethylene (PE) sheath of a typical power cable, utilizing the ReaxFF-MD method as a theoretical framework. The effect of temperature on pyrolysis products is studied. The influence of the electric field on pyrolysis products, pathways, and major radical reactions is investigated. The combined effect of the electric field and temperature on PE pyrolysis is also investigated. The results show that the main pyrolysis products of PE are C<sub>2</sub>H<sub>4</sub>, H<sub>2</sub>, C<sub>2</sub>H<sub>2</sub>, and CH<sub>4</sub>, consistent with the conclusions of the pyrolysis product experiments. The total number of pyrolysis products increased in a significant manner with increasing temperature. Under the action of the electric field, the type and number of final products are almost constant. However, the electric field reduces the activation energy of PE pyrolysis. The electric field affects the pyrolysis process by affecting the key reactions of PE pyrolysis. In the initial stages of pyrolysis, PE generates the primary intermediate product C<sub>2</sub>H<sub>4</sub>, in addition to a minor quantity of H and CH<sub>3</sub> radicals through chain reactions. C<sub>2</sub>H<sub>4</sub> is decomposed to form C<sub>2</sub>H<sub>2</sub> and dehydrogenates with H to produce H<sub>2</sub>. The CH<sub>3</sub> radical combines with the H radical to generate CH<sub>4</sub>. The applied electric field made the pyrolysis particles more susceptible to cracking, leading to an increase in the number of CH<sub>4</sub>. The electric field has a significant effect on the PE pyrolysis process by regulating the collision frequency of partially reactive molecules. This study reveals the mechanism of the electric field effect on cable pyrolysis and provides an important reference for preventing similar cable fires. It provides an important reference for preventing similar cable fires.