| With the rapid development of economy,cross-linked polyethylene(XLPE)insulated cable has been more widely used.However,under the combined effect of electric filed and moisture,water tree is easy to form in XLPE insulation.Once formed,water tree will gradually transform to electrical tree with the increase of electric field at the tip of the tree.Electrical tree may lead to breakdown of the insulation layer in a short period and cause power outage.Water treeing is one of the main aging types of XLPE insulation.Therefore,to develop and apply water tree retardant XLPE cable insulation material is of great meaning to improve the reliability of power supply.In order to accelerate the initiation and propagation of water tree in XLPE insulation material,a water-blade electrode method is proposed in this paper,and the efficiency of this method is verified.The water-blade electrode method is employed to accelerate the initiation and propagation of water tree in XLPE,nano SiO2/XLPE composites and imported water tree retardant XLPE.Optical microscope is applied to observe water tree and measure the relationship between the length of water tree and time.The experimental results are compared with the traditional water needle electrode method.Meanwhile,the effect of the supply frequency on the water tree initiation is also studied.Besides,XLPE is melt blended with different types and different mass fractions of metallocene polyethylene(MPE)to improve the water tree retardant property of XLPE.It is indicated by the results that:The water blade electrode method can effectively accelerate the water tree aging and it is more convenient for slicing the specimens used for observation.For the two selected supply frequencies,the higher the frequency is the faster the water tree initiates and propagates.This suggests that apply the water blade electrode method and choose an appropriate supply frequency is beneficial to improve the water tree initiation rate and shorten the test time.Compared with the original XLPE,the colors of the water trees in MPE/XLPE composites prepared by melt blending with three types of MPE are much lighter.This indicates that the water tree is sparser and blending polymer provides better suppression of water tree propagation.Among the selected three types of MPE,the water tree retardant effect of MPE3 is the best,and especially when the mass fraction of MPE3 in MPE3/XLPE composite is 10 phr,the water tree retardant effect is the most remarkable. |
