Study On Space Charge Characteristics Of Zno Varistor At Single Grain Boundary

With the development of UHV transmission lines,the demand for lightning arresters in the power system is getting higher and higher.As the core element of the lightning arresters,the electrical performance of ZnO varistor determines the over-voltage protection level of the arresters.ZnO varistors is possessed of excellent nonlinear characteristics.It is found that the double Schottky barrier formed at the grain boundary is the main reason for the nonlinear characteristics of ZnO varistors.The nonlinear characteristics of ZnO varistor was studied from the angle of the grain boundary deeply in this paper.Firstly,an interlayer film containing multiple metal oxides was prepared by solution casting,and the sintering temperature,holding time,temperature rise rate,cooling rate was analyzed to determine the sintering plan of the sample.A ZnO varistor sample with only one grain boundary structure was prepared,the test results show that the prepared sample exhibits a "sandwich structure" of two grains and one grain boundary,and the sample has certain nonlinear characteristics.Secondly,a single-grain boundary space charge simulation model was established based on the bipolar carrier transport model.In the process of simulation,ZnO grain boundary structure was partitioned by the plate electrode model.The electric field distribution of ZnO grain boundary was calculated by poisson equation,and the migration velocity was calculated according to the carrier migration law.The conduction equation is used to describe the ion migration process under the action of electric field.Then the relation curve of the space charge distribution in ZnO grain boundary changing with time is obtained by simulation.Finally,the simulation of the carrier migration law inside the ZnO grain boundary was carried out based on the bipolar carrier transport model.and the space charge,schottky barrier height,and grain boundary leakage current were studied from three aspects:pressurization time,ambient temperature,and depletion layer density.It provides significant theoretical support for further research on the conduction mechanism,aging mechanism and performance improvement of ZnO varistors.