Study On The Development Mechanism Of The Breakdown Of The Interface Between Modified Polypropylene And Silicone Rubber

Power cable especially extruded cable has been increasingly used in power transmission and distribution system in the cities.Polypropylene(PP)is a kind of thermoplastic materials which can be recycled,with good electrical properties will bring great economic and social benefits if used instead of polypropylene cross-linked polyethylene(XLPE)in the future.In the power cable system,the cable joint is the weakest link.There is a strong tangential electric field along the interface between cable main insulation and joint insulation,which is a main factor leading to joint failure.For the insulation safety of PP cable joint,research on initiation mechanism and development process and the method of improving the interface breakdown strength is necessary for the interface discharge.The purpose of this work is to obtain a theoretical model of solid-solid dielectric interface breakdown,and study the effects of addition of elastomer and fluorination on PP/SiR interface breakdown process,and study the effect of different modification methods on the breakdown process of PP/SiR interface.In this work,two kinds of elastomer,ethylene octene elastomer POE(DOW 8510)and propylene based elastomer PBE(Vistamaxx 6202)were employed to toughen isotactic PP.Mechanical properties and electrical properties of PP/elastomer blends with different elastomer content were investigated.The initiation and development of PP ? SiR interface breakdown between PP/elastomer blends with different elastomer content and SiR were studied.The results showed that the addition of POE and PBE can greatly prolong the breakdown time of the PP/SiR interface,but the time of breakdown is shortened after 35wt% or more elastomer was added.Because of the blends of PP/PBE and PP/POE with different microstructures has different compatibility with PP,the distribution of deep traps should be different.And PP/POE? SiR and PP/PBE ? SiR interface makes the time of initiation stage and thepropagation stage exhibit difference changes.In this work,PP was treated by surface fluorination,and the effects of direct fluorination of PP on interface discharge behavior was estimated as well.With the surface layer of C-F formed on the surface of PP,and the static contact angle decreased,and the roughness became larger.Comparing with the original PP/SiR,the initiation stage of the interface discharge for fluorinated PP/SiR was extended whereas the propagation stage was significantly accelerated.Thus,the time to breakdown was shortened.It is suggested that the trap depth,roughness and hydrophilicity of PP sample surface is varied by means of the fluorination,which in turn affects the characteristics of the interface discharge.