Study On The Influence Of High Frequency Characteristics Of Medium On Insulation Performance Of GIS Insulators

In addition to the SF6 gas with excellent insulation and arc extinguishing performance,there are a large number of insulators with epoxy resin as insulation medium.Because the permittivity of dielectric can change the electric field intensity,when the material with high permittivity is placed in the electric field,the electric field intensity will be decreased,and vice versa.The permittivity is not only related to the material,but also to the temperature and frequency.In this thesis,the insulator in 1100 kV GIS,analysis of the permittivity frequency changes,as the Lightning Overvoltage and Very Fast and Transient Over-voltage,under the action of high frequency electric performance of the insulator,improve the reliability of GIS operation.When the lightning impulse voltage acts on the GIS,it will produce a time varying field.In this thesis,the time domain calculation model of transient electric field is given,and the influence of the static permittivity,the permittivity and relaxation time on the electric field distribution is considered.The electric field distribution of insulator and the electric field distribution on the upper and lower surfaces of insulators are calculated under the impact of lightning,which provides the basis for improving the reliability and reducing the probability of surface discharge.In addition,the VFTO overvoltage caused by the separation of the isolated switch is characterized by high amplitude and fast rise,and the waveform contains a frequency component from several megahertz to tens of megahertz.The equivalent circuit of disconnecting switch in GIS is established and the numerical simulation is carried out.According to the characteristics of the VFTO voltage wave,considering the complex permittivity of the insulating material at high frequency,the discrete Fourier transform is used to obtain the different spectral components in the waveform.Analysis of different frequency components in the insulation medium,the changes of the relative permittivity of insulating medium;calculation of different frequency components under the action of insulator electric field,and obtains the internal electric field distribution of insulator in the presence of VFTO and several specific rules on the insulator of the electric field distribution along the surface,find the insulators relatively weak link.In order to further investigate the dielectric properties of insulators,the influence of the lightning impulse voltage on the electric field distribution of insulator is considered when the permittivity of the insulator is different or anisotropic.When the permittivity at the basin type insulator electric field distribution trend roughly the same,the maximum electric field intensity decreases with the increase of permittivity;Considering the anisotropy of the medium,the electric field distribution of the basin insulator is very different from that of the isotropic one,so the anisotropy of the medium should be one of the factors to consider the insulation performance.