Effect of UV Irradiation Time on Dielectric Performance of PP Film for HVDC Capacitor

The dielectric properties of polypropylene (PP) for metalized film capacitors deteriorate severely at high temperatures. This paper proposes a method to improve the dielectric strength of PP by introducing crosslinked structure. Compared with the original PP, the study shows that the crosslinking reaction creates chemical bonding linkages between the molecular chains and reduces the inter-chain distance, thereby inhibiting the mobility of the chain segments at high temperatures and weakening the free volume change at high temperatures. The traps introduced by the crosslinking points enhance the capture of carriers and reduce the electrical conductivity. At 115 °C, the breakdown strength of the modified films is enhanced by 20.2 %, and the conductivity is reduced by 97.5 %. In addition, the effect of irradiation time on the UV crosslinking reaction was investigated. The results show that the film properties can be improved at an irradiation time of the 90s. This method guides improving the PP high-temperature insulation from the molecular chain structure regulation perspective.