Research On The Water Tree Resistance Of Crosslinked Polyethylene Grafted With Antioxidant MAE

Cross-linked polyethylene(XLPE)power cables are prone to water tree aging in humid environments,which lead to the degradation of the mechanical and dielectric properties of the cable.With the growth of water trees,the electric field at the insulation defect becomes more concentrated,and the local high electric field will eventually lead to the transformation of water trees into electric trees,resulting in insulation breakdown and damage to the insulation layer structure.The initiation and growth of water trees seriously threaten the safety and reliability of XLPE cables in long-term operation,especially medium-voltage power cables without external metal sheaths.Therefore,the development of XLPE insulation materials with excellent water resistance is of great significance to the stable operation of the power systemIn order to study the effect of antioxidant MAE grafting on the growth of water trees in XLPE,XLPE and antioxidant MAE grafted XLPE(XLPE-g-MAE)insulation materials were obtained.A water blade electrode method was used to accelerate water tree aging,and it was found that antioxidant MAE grafting can significantly improve the water tree resistance of XLPE,and its water-resistant tree performance gradually increased with the increase of grafting.XLPE-g-2.0phr MAE had the shortest water tree length,and when it was aged for 7 days,its water tree length was reduced by 25.7% compared with XLPE,and its water-resistant tree performance was the best.The effects of antioxidant MAE grafting on the microstructure of XLPE were studied by infrared spectroscopy,gel content,thermal extension,crystallization characteristics,static contact angle,and simulation calculation of grafted molecular/water compatibility,and the mechanism of improving the water tree resistance of the XLPE was discussed.The antioxidant MAE was successfully grafted onto the XLPE molecular chain,which reduce the crosslinking degree of XLPE,increase the crystallinity and enhance the hydrophilic property.It can reduce the area of amorphous region,and make the convergence of materials more compact,reducing the structural defects as well as the water penetration and water droplet formation.And the polar groups of the antioxidant MAE can effectively disperse micro-water droplets that penetrate into the inside of the material.So,the water was not easy to aggregate into water droplets,together with the antioxidant effect,improving the water tree resistance.The effects of antioxidant MAE on the dielectric properties and mechanical properties of XLPE were studied by broadband dielectric spectrum,AC breakdown strength,DC conductivity current and tensile test,and it was found that the grafted antioxidant MAE would make XLPE relative permittivity and dielectric loss factor larger,the relative permittivity of XLPE and XLPE-g-MAE insulation materials were between 2.2-2.35,and the dielectric loss factor were all less than 0.0015.The AC breakdown field strength and conductivity current of XLPE-g-MAE were lower than those of XLPE at different test temperatures,XLPE-g-2.0phr MAE reduced the breakdown strength of XLPE by 2.8 %,13.3 %,10.2 % and 10.6 % at 30 ℃,50 ℃,70 ℃ and 90 ℃ compared with the same temperature,the conductivity current density decreases by more than an order of magnitude compared to XLPE at the same temperature.Compared with XLPE,XLPE-g-2.0phr MAE increases the tensile strength by 0.1MPa and the elongation at break by 123.6 %.