Study On Space Charge Characteristics Of Grafted Polypropylene DC Cable

In recent years,with the proposal of the two-carbon strategy,the demand of new environment-friendly DC cable is more and more urgent.Compared with the traditional crosslinked polyethylene(XLPE)cable,thermoplastic polypropylene(PP)has the advantages of no crosslinking,recyclable,high heat resistance,and so on.It is the future development direction of large capacity and environmental protection DC cable insulation.But PP needs to face the problem of poor mechanical properties and space charge injection.The grafting of functional groups with benzene ring structure to improve the properties of materials has attracted the attention of many scholars.Therefore,this paper conducted space charge test and DC breakdown test on styrene(St)grafted modified polypropylene to test its corresponding properties,and explored its improvement mechanism.Finally,it prepared polypropylene cable material meeting the actual use and compared its electrical properties with XLPE cable material.In this paper,with using styrene as the grafted monomer,samples with grafted PP-g-St with mass fraction of 2.5%,5%and 10%were prepared by aqueous suspension grafting technology.Calculation of grafting rate and grafting efficiency and utilization of infrared characterization showed that styrene had been successfully grafted to polypropylene.Through scanning electron microscopy observation,it was found that St formed a microscopic interface with PP.It was found by differential scanning calorimetry and X-ray scattering techniques that grafting St reduced the perfection of crystal zone.At 30℃,60℃ and 90℃,the space charge characteristics under DC electric field and polarity reversal electric field were tested by pulsed electroacoustic,and its conductivity characteristics and DC breakdown strength was tested.The microscopic morphology was observed by polarizing microscope,and the trap characteristics were tested by thermal stimulation current method to explore how grafted styrene affects the space charge characteristics,conductivity characteristics,and DC breakdown strength of polypropylene.The research results show that polypropylene is mainly the accumulation of charges of the same polarity.Grafting styrene can effectively improve the space charge suppression ability of polypropylene,and it increases with the increase of grafting amount.PP-g-10St performs best;The conductivity test shows that the grafted styrene makes the threshold field strength increase with the increase of the grafting amount;DC The breakdown strength first increased and then decreased with the increase of grafting amount,and the breakdown field strength of PP-g-5St was the highest.the observation of the polarized light microscope shows that the grafted styrene makes the polypropylene spherulites smaller and the boundary is blurred,which makes the charge injection difficult and inhibits the initiation of the low-density region.The thermally stimulated current method showed that the grafted styrene made the trap density and energy level of polypropylene increased with the increase of the grafted amount,indicating that a large number of deep traps were introduced.Finally,this paper uses molecular chain regulation to improve the mechanical properties of polypropylene and then grafts styrene to prepare polypropylene cable materials that meet the actual mechanical performance requirements.Compared with 35kV voltage grade XLPE cable materials,the space charge characteristics,electrical conductivity and DC breakdown field strength.It is found that although the electrical properties of polypropylene cable materials are slightly weaker than those of styrene grafted polypropylene,they are stronger than 35kV grade XLPE cable materials.