Performance Test And Analysis Of High Voltage AC Crosslinked Polyethylene Cable Insulation

Due to the excellent mechanical and electrical properties,Crosslinking Polyethylene(XLPE)insulated cable has become the main cable produced and used in our country.The physical and chemical properties such as crystal structure and cross-linking degree will directly affect the macro-mechanical and dielectric properties of material.It is proven that material with better comprehensive performance will have a smaller probability of failure in the actual operating condition of the cable.Therefore,XLPE insulation material with good comprehensive performance,low cost and stable supply can not only reduce the production cost of enterprises,but also be conducive to the stable operation of transmission lines.The research object of this paper is four cables of high voltage AC XLPE insulated which are manufactured from the same production line and the same extrusion process in domestic factories.The XLPE insulation materials are provided by different material manufacturers,and noted as cable A,cable B,cable C and cable D.The insulating materials of the four cables are sliced and their physical and chemical properties are tested.By means of differential scanning calorimeter,scanning electron microscope,X-ray diffractometer and other instruments,the crystal and crosslinking properties of insulating materials of the four cables are analyzed.Then,by using tension machine and dynamic thermomechanical analyzer,the mechanical properties of layer of four cables insulation were tested,including tensile strength,elongation at break and dynamic thermomechanical properties.Finally,by using broadband dielectric spectroscopy system and AC breakdown system the dielectric performance at different temperatures(30 ° C,50 ° C and 70 ° C and 90 ° C)were analyzed,including permittivity and dielectric loss tangent and power frequency withstand voltage.Combining with the results of physical and chemical properties,the factors affecting the macroscopic mechanical properties and dielectric properties of XLPE materials were analyzed.Through the above analysis,it can be concluded that: in terms of physical and chemical testing,the crystal state of cable B and D insulation is more perfect than that of cable A and C insulation,with high crystallinity,uniform crystal cell distribution and small crystal plane spacing,and there is no significant difference in the crosslinking degree of the four cables.In terms of mechanical properties,the breaking elongation of cable C insulation is slightly lower than that of the other three types of cable insulation.The energy storage modulus of cable B insulation is the highest,and that of cable A insulation is the lowest.In the aspect of dielectric spectrum test,the permittivity of cable A insulation were higher than other cables under the condition of different temperature,and the dielectric loss at low-frequency of cable A insulation is significantly higher than the other three kinds of cable insulation under 30 ° C.In terms of power-frequency breakdown performance,the power-frequency breakdown field strength of cable A insulation is the largest,and that of cable C insulation is the lowest.The power-frequency breakdown field strength of the four kinds of cable insulation chip samples increases slightly first and then decreases with the increase of temperature,but the change range is small.After the comparison of several parameters,it is concluded that the XLPE insulation comprehensive performance of cable B and D is more excellent.