Electrical Tree Degradation Characteristics And Space Charge Distribution In HVDC Cables

Due to the special form of energy and economic distribution in China,HVDC cable plays an important role in energy transmission,such as "power transmission from west to East".Cross linked polyethylene(XLPE)insulated cables are widely used in HVDC transmission because of their wear resistance,high temperature resistance,good insulation performance,easy installation and manufacturing,light weight and other characteristics.However,under the long-term effect of voltage,HVDC cable is easy to accumulate space charge,which leads to the generation of electrical trees,and eventually leads to the complete failure of cable insulation.Although a lot of researches have been done on the phenomenon of cable electrical tree by domestic and foreign scholars,the research on the influence mechanism of space charge and electrical tree under DC voltage is not deep enough.Therefore,this paper studies the space charge distribution characteristics under DC voltage;the correlation between space charge distribution and electrical tree initiation;the influence of temperature on DC grounded electrical tree and space charge distribution characteristics;the electrical tree initiation characteristics of DC superimposed impulse voltage;the related research results are as follows:In this paper,through the method of simulation and experiment,the change law of space charge distribution with DC voltage and DC pre-stress time under DC voltage is explored.The results show that the numerical simulation of space charge using bipolar charge transport model is consistent with the measurement result of space charge using PEA.When the DC pre-stress time is short,the space charge density increases rapidly with the increasing DC pre-stress time.With the further increase of DC pre-stress time,the increasing space charge density gradually decreases and finally reaches saturation.The influence of temperature and DC voltage on the initiation length of DC grounded electrical tree was studied by DC grounded electrical tree test.The influence of temperature on the space charge distribution is investigated by simulation.The injection depth of space charge and the initiation length of electrical tree are compared and analyzed,and the relationship between space charge and electrical tree at different temperatures is explored.The results show that the depth of space charge injection is highly consistent with the initiation length of electrical tree,and the large difference between them is 21.182 μm.The distribution range of space charge is consistent with that of electrical tree,which indicates that space charge is one of the main factors affecting the initiation length of electrical tree.The influence of DC pre-stress time and amplitude on the initiation length of electrical tree under DC superimposed impulse voltage was investigated.The influence of DC pre-stress time and amplitude on space charge and electric field strength is explored through simulation analysis.The effects of DC pre-stress time,amplitude and polarity on the space charge and electrical tree initiation characteristics are analyzed.The results show that the effects of DC pre-stress time on the initiation characteristics of space charge and electrical tree under composite voltage are highly similar,and space charge,electric field strength and streamer development direction are the main reasons for the initiation of electrical tree.