For polypropylene (PP) film capacitor

which is used widely in high-voltage direct current (HVDC) engineering

its internal high temperature and high field strength are the main causes of PP aging. Based on simulation method of dynamics

the aging process of PP under electrothermal stress is analyzed at molecular level. Firstly

molecular models of PP and PP containing carbonyl groups are set up. Based on the reaction force field

the pyrolysis reaction of PP under thermal and electrical stress is simulated and the main product formation process is analyzed; Then

based on the COMPASS force field

the variation of mechanical and insulation performance of PP under thermal stress is analyzed. The results show that the C—H bond firstly breaks during the PP cracking reaction

followed by the C—C bond breaking and the formation of carbonyl groups. During this process

thermal stress has a more significant effect on the electrothermal aging of PP; When the temperature is below 450 K

the mechanical parameters of PP remain basically unchanged. While

when the temperature reaches 600 K

the mechanical parameters of PP change significantly and the stability decreases; Carbonyl groups affect variation of mechanical and insulation properties of PP during aging. The energy gap of PP containing carbonyl groups decreases by 28.21%

and the elastic modulus increases by 15.3%

32.85%

and 27.08% at 300 K

450 K

and 600 K

respectively.