Comparison of time-dependent variation of surface charge accumulation in SF6/N2and pure SF6

摘要

SF_6/N_2 Mixture has good insulation properties and reduces the use of SF_6 , thus it has drawn more and more attention. In addition, Surface charge accumulation on insulating materials is a major factor that greatly distorts the electrical field and reduces the insulation level. Therefore, it is necessary to research the characteristics of surface charge accumulation in SF_6/N_2 mixture. In this paper, the difference between the time-dependent variation of surface accumulated charge of spacer in 5atm pure SF_6 and that in 5atm 20% SF_6/N_2 is researched. The downsized truncated cone-type spacer made of 70% Al_2O_3 filled epoxy resin and coaxial cylinder electrodes are used to model a GIL. In the experiment, ±30kV and ±40kV DC voltage are applied to the central electrode for 30-1080 min, then the surface potential of spacer is measured by a Kelvin vibrating electrostatic probe, and the corresponding surface charge density is further calculated by a calibration method. The results reveal that in both gases, the surface accumulated charge exhibits a time-dependent variation characteristic that the local fluctuates and the whole tends to saturate. Under the DC voltage of same amplitude and same applied time, the total amount of surface charge in 20% SF_6/N_2 is far more than that in pure SF_6. However, the maximum of surface charge density in 20% SF_6/N_2 is not much different from that in pure SF_6 under the same condition of DC voltage. Moreover, in pure SF_6, the total amount of surface charge under negative DC voltage is far more than that under positive DC voltage, which means there is polar effect in pure SF_6. However, in 20% SF_6/N_2 the polar effect does not exist.