Study On Internal Defects And Surface Discharge Characteristics Of Basin Insulator In UHV GIS

Gas-insulated metal-enclosed switchgear(GIS)is widely used in extra-high voltage and ultra-high voltage substations with the advantages of its superior insulation and reliability.Basin insulators,as the key devices of GIS,are crucial to the safe operation of GIS.Studies have shown that bubble defects and metal particles attached to the surface make the electric field distribution deteriorating.Especially,the insulation strength of the insulated equipment will greatly drop under the impulse voltage.The internal defects and surface discharge characteristics of basin insulator in 800 k V GIS are studied in this thesis.Firstly,a three-dimensional simulation model of the basin insulator is established based on the actual structure of the basin insulator.The basic equations of the three-dimensional electric field calculation of the basin insulator are derived and the boundary conditions are imposed.The electric field distribution of the basin insulator without defection under the power frequency voltage is analyzed using finite elements analysis.The cloud diagram of the electric field distribution of the insulator and the electric field distribution curve are given.The maximum value of the field strength is calculated and the characteristics of the electric field distribution are found.Secondly,three typical locations are selected according to the electric field distribution characteristics of the basin insulator under the power frequency voltage.On this basis,the metal particles attached to the surface of the basin insulator during the assembly process and the internal air bubble defects generated during the casting process or under prolonged operation are simulated.The electric fields of insulators under lightning impulse voltage and VFTO are simulated and analyzed respectively.Nextly,the transient electric field time domain model is established under the lightning impulse voltage and the transient electric field calculation analysis is carried out.In order to compare the analysis with the following simulation results,the same three typical locations are selected,and the surface metal particles and bubble defects are set up for the numerical simulation of the electric field.In the meanwhile,the frequency domain model of transient electric field is established under VFTO in this thesis.Considering the high frequency parameters of the dielectric,the electric field of the basin insulator attached to metal particles at different positions is simulated.Further,the electric field characteristics of the insulator with bubble defects at different locations inside the insulator are analyzed and the electric field distribution characteristic is identified.Finally,the comparison is carried for the electric field distribution characteristics among excited by the power frequency voltage,lightning impulse voltage and VFTO.The simulation results have shown that the electric field distribution is in approximately the same way when metal particles are present.The electric field of the basin insulator increases with the electric field strength in which the metal particles are located.The electric field distortion caused by the closer to the central conductor end becomes more severe.And when there are bubble defects,the electric field strength grows to double to three times the power frequency voltage without defects.It may cause gas ionization to cause breakdown of the basin insulator.