Analysis Of Surface Flashover Characteristics And Surface Topography Of Insulators In SF₆/CF₄ Mixed Gas

With the annual increase of electricity consumption,the scale of power grid increases year by year.With the rapid development of HVDC transmission,the insulation problem of high.voltage power equipment also emerges.Although,epoxy resin as a solid insulating medium has good insulating properties,but as a non-self-restoring medium once flashover occurs in engineering,it may cause the insulation failure and lead to large-scale power failure or power equipment damage and other malignant events.The flashover characteristics of epoxy resin are different under the action of gas type,pressure and other factors.Therefore,it is of great theoretical and practical significance to study the surface flashover characteristics of epoxy resin in SF₆/CF₄ mixture and the damage characteristics of the surface of epoxy resin under different environmental factors.In this paper,an experimental study was conducted on the surface flashover of epoxy resin dc under non-uniform electric field.The specific work is as follows:（1）Set up a surface flashover test platform of epoxy resin dc in a mixed gas environment,including HVDC generating system,protection resistance,resistance and capacity divider,gas compression and recovery device,and sealed experimental chamber.The electrode system and epoxy resin insulator used in the experiment were placed in the experimental chamber,and SF₆and its mixed gas with a certain pressure were filled inside.And the preliminary determination of the test program.（2）The surface flashover experiment of epoxy resin in SF₆/CF₄ mixture was conducted.The relationship between epoxy resin dc flashover voltage and SF₆ mixing ratio,voltage polarity and gas pressure at different electrodes was compared.The experimental results show that when the mixing ratio of SF₆ in the mixed gas is 40%,the insulator flashover voltage can reach more than60%of the flashover voltage in SF₆ at the same pressure.The synergistic effect of flashover voltage of finger electrode is better than that of needle plate electrode.The flashover voltage of the two electrodes has obvious polarity effect,and the polarity reversal of the pin-plate electrode occurs with the increase of air pressure.（3）The surface flashover test on the damage degree of insulator surface was conducted.The influences of different electrodes,different SF₆ mixing ratio,voltage polarity,and the number of repeated flashover times under gas pressure on flashover voltage were compared.With the help of scanning electron microscope,the morphological characteristics and element content of different areas on the surface of epoxy resin were measured after the flashover of finger electrode for different times.It was found that a large number of particles and micropores appeared on the surface after the dielectric property of epoxy resin was decreased,and the damage was most serious at the junction of electrode,material and gas.By comparing the surface morphology of the insulator after flashover under the pin-plate electrode and the finger electrode,it is found that the particles in the discharge channel of the pin-plate electrode are larger and more numerous than those in the concentrated channel,and the damage to the insulator is greater than the flashover of the finger electrode.