Effect of SiO_(2) nano film deposited on copper and aluminium electrodes on the power frequency breakdown voltage of SF_(6) gas

In order to reveal the effect of insulating nano film on the insulation strength of SF_(6) gas gap,SiO_(2) nano film was deposited on the electrode surface by the plasma-enhanced chemical vapour deposition technique.The power frequency breakdown characteristics of SF_(6) gas under Cu and Al electrodes were obtained before and after coating.The results showed that when the Cu electrode was coated,the breakdown voltage was up to at most 11.5% higher than that of an uncoated Cu electrode in the pressure range of 0.2-0.5 MPa.When the Al electrode was coated,the breakdown voltage of SF_(6) gas was lower than that of an uncoated one in the pressure range of 0.2-0.5 MPa.The breakdown voltage of SF_(6) gas under the Cu electrode was slightly lower than that under the Al electrode,but the breakdown voltages under the coated Cu electrode were significantly higher than that under the coated Al electrode.Through SEM tests,it was found that the surface roughness of the electrode decreases after coating,but particles were formed on the surface of the Al electrode.The content of metal fluoride formed on the coated Al electrode under multiple breakdowns was significantly higher than that on the coated Cu electrode.The research results could provide references for improving insulation performance of GIS equipment.

Multiple discharges before leader inception in long air gaps under positive switching impulses

There are multiple corona bursts before leader inception when the rising rate of the applied voltage or electric field is not sufficiently high enough in long positive sparks.In existing studies,no attention has been paid to whether these corona bursts occur in the same location,and they are mostly considered directly as belonging to the same discharge.However,this paper presents that in a typical rod-plate long air gap,the multiple corona bursts before leader inception are distributed in at least two different locations,and the highest probability of three discharges occurs.Also,the discharge occurs with the highest probability in the time sequence‘tip-tip-side-tip-other side’of the electrode in the first five corona bursts.For each discharge,the first corona current is a single,double exponential pulse,while the following corona currents are mostly a superposition of multiple pulses.The above findings are mainly based on experiments in a 1.4 m air gap under positive switching impulses,in which the voltage,current,and high-speed images were recorded simultaneously.Finally,based on the experimental results,this paper discusses the effects brought by ignoring the multiple discharges on key parameters of leader inception and makes some suggestions to optimise long spark experiments.