Study On Influencing Factors Of High Voltage Dc Crosslinked Polyethylene Performance

In this paper,the crosslinked polyethylene?XLPE?was prepared by means of mechanical blending and hot-pressed crosslinking,which was used as the master batch of the insulation material of HVDC cable.Firstly,different crosslinking agents were used to prepare crosslinked polyethylene,and the effects of different crosslinking agents and different crosslinking degrees on the electrical properties of crosslinked polyethylene were tested,so as to obtain the crosslinking degree and the types of crosslinking agents when the electrical properties of crosslinked polyethylene were the best.Then,?-Al2O3 nanosheets were synthesized by molten salt method and surface-modified,and the XLPE/?-Al2O3 nanocomposites were prepared.The effect of addition of?-Al₂O₃ nanosheets on the electrical properties of nanocomposites was studied.Finally,another morphology of?-Al2O3 nanosheets were synthesized by hydrothermal method,and XLPE/?-Al2O3 nanocomposites were prepared,and the influence of?-Al2O3 nanosheet on the thermal properties of nanocomposite was studied.1.Crosslinked polyethylene samples with different crosslinking agents and different crosslinking degrees were prepared by using two kind of peroxide crosslinking agents:diisopropyl benzene peroxide?DCP?and ditert-butyl peroxide isopropyl benzene?BIPB?.The extraction method was used to measure the cross-linking degrees of the crosslinked polyethylene samples,and it was found that the cross-linking efficiency of BIPB was better than that of DCP.When the cross-linking degree of crosslinked polyethylene reached about 90%,the dosage of DCP was 2.5 wt%,while that of BIPB was only 1.5 wt%.After the crosslinking degrees were obtained,the DC voltage breakdown testings were carried out on the cross-linked polyethylene samples with different cross-linking degrees to study the effect of cross-linking degree on the dc breakdown field strength of cross-linked polyethylene materials.Finally,the space charge of crosslinked polyethylene samples with the same crosslinking degree and different crosslinking agents was measured.The influence of the type of crosslinking agent on the space charge density and distribution of crosslinked polyethylene insulation was studied.2.Crosslinked polyethylene samples with different crosslinking agents and different crosslinking degrees were prepared by using two kind of peroxide crosslinking agents:diisopropyl benzene peroxide?DCP?and ditert-butyl peroxide isopropyl benzene?BIPB?.The extraction method was used to measure the cross-linking degrees of the crosslinked polyethylene samples,and it was found that the cross-linking efficiency of BIPB was better than that of DCP.When the cross-linking degree of crosslinked polyethylene reached about 90%,the dosage of DCP was 2.5 wt%,while that of BIPB was only 1.5 wt%.After the crosslinking degrees were obtained,the DC voltage breakdown testings were carried out on the cross-linked polyethylene samples with different cross-linking degrees to study the effect of cross-linking degree on the dc breakdown field strength of cross-linked polyethylene materials.Finally,the space charge of crosslinked polyethylene samples with the same crosslinking degree and different crosslinking agents was measured.The influence of the type of crosslinking agent on the space charge density and distribution of crosslinked polyethylene insulation was studied.The DC breakdown strength of the cross-linked polyethylene samples cross-linked by BIPB were bigger than that cross-linked by the DCP.It can reach a maximum of 240 kV/mm.And the space charge content of the cross-linked polyethylene samples prepared by BIPB were also significantly lower than that of the samples cross-linked by DCP.3.The?-Al2O3 nanosheets with small size and slender shape were synthesized by hydrothermal method and and surface modified by silane coupling agents??-MPS?.Then?-Al2O3nanosheets synthesized by hydrothermal method were uniformly added to the linear low density polyethylene matrix by mechanical blending and hot-pressed crosslinking,and the XLPE/?-Al2O3 nanocomposites were prepared.Through the thermogravimetric analysis,differential scanning calorimetry analysis and thermal conductivity measurement of XLPE/?-Al2O3 nanocomposites,the effects of?-Al2O3nanosheetson thermal stability,thermal conductivity and other thermal properties of nanocomposites were studied.The results showed that the addition of?-Al₂O₃nanosheets reduced the thermogravimetric rate,improved thermal decomposition temperature,thermal stability and thermal conductivity of XLPE.When the content of?-Al2O3 nanosheetsreached 10 wt%,compared with pure XLPE,the thermal mass loss rate of XLPE/?-Al₂O₃ nanocomposites decreased by 2.27%/min,the thermal decomposition temperature increased by nearly 4?,and the thermal conductivity increased by about 1.5 times.