Surface modification of aluminum alloy electrodes via direct fluorination to enhance flashover voltage of epoxy insulators and related mechanisms

Electrical charges are prone to accumulate on the insulator surface which will distort the electric field and threaten the safe operation of high-voltage equipment. The electrodes are the source of electric charges , and to decrease the charge accumulation on insulators, aluminum alloy electrodes were fluorinated in a laboratory reactor. DC flashover tests on the combination of the aluminum alloy round electrode/truncated cone epoxy insulator reveal that the fluorination of electrodes enhanced the flashover voltage of epoxy insulators. SEM observations indicate that the aluminum alloy surface was roughened by the fluorination. EDS and XPS analyses manifest that fluorine atoms were introduced to the surface layer of the aluminum alloy during the fluorination, forming aluminum fluorides and magnesium fluorides . Further, XPS valence band analysis reveals that the fluorination changed the surface valence band structure of the electrode from conductive to insulating. This makes it difficult for electron emission from the electrode, and is the reason for the increase in flashover voltage of the epoxy insulator by the electrode fluorination. An enhancement of gap breakdown voltage of the aluminum alloy sphere/plate electrode combination by the fluorination further confirms the increase in the difficulty of electron emission from the electrode. In addition, a dielectric-coated electrode model can also explain the increase in the difficulty of the electron emission by a significant reduction of the interface field between the fluorinated layer and the unfluorinated inner layer and the blocking of the fluorinated layer to electron emission into the gas phase.