Study On The Effect Of Electrical-thermal Aging On Space Charge Characteristics Of XLPE Cable At Stress Cone

Cable accessories are weak locations and fault-prone locations during cable operation.The accumulation of space charges is an important cause of cable accessories failures.The accumulated space charge is easy to cause local electric field distortion,damage the micro structure of the insulating material,and cause insulation breakdown.The accumulation of space charge is closely related to the aging degree of the dielectric.The stress cone is an important part of the cable accessories.Studies have found that compared to other locations,the stress cone is easier to accumulate space charges during long-term operation of the cable,and the stress cone itself,as the part of the cable accessory with stronger electric field strength,is more likely to accumulate space charges.It is easily affected by the accumulation of space charges,so studying the accumulation characteristics of space charges at the stress cone is of great significance to the design and maintenance of cables.The complex structure of the stress cone makes it impossible to directly test the space charge.In order to solve this problem,this paper adopts an indirect method to study the space charge characteristics at the stress cone,that is,by analyzing the structure and characteristics of the actual stress cone,a model is designed.The cable replaces the actual stress cone for research.In order to study the space charge accumulation characteristics at the stress cone,a combined electric and thermal aging experiment was designed for the model cable,and an electric and thermal combined aging platform was built.The space charge distribution of the model cable before and after aging was tested,The form and accumulation rule of space charge in the insulation of model cable after Electrical-thermal aging are analyzed,and the corresponding mechanism is proposed to explain the cause of space charge accumulation.The test results show that the space charge accumulated in the model cable has obvious axial and radial distribution.In the axial direction,the closer to the root of the stress cone,the higher the space charge density,and in the radial direction,the closer to the outside of the insulation.The higher the charge density,and the total amount of space charge increases with the aging time;the space charge accumulated in the model cable can be divided into insulation internal charge and interface charge according to the difference in polarity and distribution position.The non-alternating charge theory and the interface polarization theory explain the causes of the two types of space charges;according to the trap energy level theory,it points out the charge transfer law under the alternating electric field.After analyzing the electric field distribution of the model cable,it is concluded that the space charge migrates from the outside of the main insulation to the root of the stress cone.Finally,the space charge accumulation in the model cable is simulated,and the simulation results show that the space charge is easy to accumulate in the root of the stress cone.