Study on the Pulsed Flashover Characteristics of Solid-Solid Interface in Electrical Devices Poured by Epoxy Resin

In electrical devices poured by epoxy resin, there are a lot of interfaces between epoxy resin and other solid dielectrics, i.e. solid-solid interfaces. Experiments were carried out to study the flashover characteristics of two typical solid-solid interfaces （epoxy-ceramic and epoxy~ PMMA） under steep high-voltage impulse for different electrode systems （coaxial electrodes and finger electrodes） and different types of epoxy resin （neat epoxy resin, polyether modified epoxy resin and polyurethane modified epoxy resin）. Results showed that, the flashover of solid-solid interface is similar to the breakdown of solid dielectric, and there are unrecoverable carbonated tracks after flashover. Under the same distance of electrodes, the electric stress of coaxial electrodes is lower than that of finger electrodes; and after the flashover, there are more severe breakdown and larger enhanced surface conductivity at interface for coaxial electrodes, as compared with the case of finger electrode. The dielectric properties are also discussed.

Flashover Characteristics of Dry Band-water band on Hydrophobic Surfaces

Due to their outstanding anti-flashover characteristics,composite insulators have been extensively applied in power systems.A lot of research has investigated flashover characteristics of hydrophobic specimens with artificial water droplets.However,the phenomenon is not consistent with that of the contaminated composite insulators.On the test specimens covered with water droplets,there is no obvious leakage current before the flashover and no obvious relationship between flashover voltage and the conductivity of water droplets.On the contaminated composite insulator surface,there are short continuous arcs on the insulators before critical flashover,making insulators look like a luminous lantern.Considering that under these two conditions,the proportion of water along the insulation distance is different,the flashover characteristic of“dry band-water band”on a hydrophobicity surface is analyzed in the present study.The influence of the water band parameter(including length,width,and conductivity)as well as the length of dry band is studied.On this basis,the arc generation and development process of the surface covered with“dry band-water band”is analyzed.The research results improve the understanding of the flashover process on contaminated composite insulators.

Effect of Salty Fog on Flashover Characteristics of OCS Composite Insulators

To study the flashover characteristics of the fog water in saline-alkali areas for high-speed railway OSC insulators,the spatial distributions of both the potential and electric field of soiled insulators in the presence of salty fog are analyzed using COMSOL Multiphysics,a multi-physics coupling software.Furthermore,to analyze the effect of the contamination of insulators due to salty fog water,a saline solution is used for staining an insulator sample by using the solid coating method.In an artificial climate chamber,the salty fog environment is simulated,and the flashover voltage for different salty fog water conductivities and surface staining are obtained.The salt-density correction coefficient K is also proposed.It provides a strong basis for the selection of railway insulators in saline-alkali areas.The results show that the salty fog water changes the original surface equivalent salt density,ρESDD,by wetting the existing fouling layer on the surface of the insulator,so that the original surface contamination layer becomes equivalent to KρESDD;the smaller is the value ofρESDD of the insulator surface,the larger is the value of K;the surface of the same insulator is dirty,and as the concentration of salty fog-water increases,K also increases.