AC Flashover Voltage Model for Polluted Suspension Insulators and an Experimental Investigation in Salt Fog

In recent years, the electrical performance of polluted suspension insulators operating in coastal foggy regions has attracted wide attention because of the occurrence of flashover. Surface wetting by salt fog accretion increases the surface conductivity and degrades the flashover voltage of insulators. Normally, the effect of conductivity under fog condition and pre-contamination on the flashover of polluted insulators are analyzed separately. Therefore, this does not reveal the flashover characteristic in salt fog, which requires further research. This paper describes salt fog experiments with an AC test voltage conducted using suspension insulators in a 110-kV power system. The electrical strength performance of insulators with salt fog treatments is analyzed, and the effects of salt deposit density (SDD) and the fog water conductivity (FWC) on the flashover of three types of suspension insulators are studied. The concept of additional SDD is proposed to quantify analyze the effects of salt fog. The results show that there is less dependence on FWC at higher pollution levels than at lower pollution levels. That is, the effect of FWC on 50% AC flashover voltage ( $U_{50}$ ) can be neglected for SDD >0.15 mg/cm2, whereas FWC has a strong effect on $U_{50}$ for SDD $U_{50}$ of ceramic insulators than on that of silicone rubber insulator. A model for calculating the critical flashover voltage of insulators is proposed by considering the combined effect of FWC and pre-polluting SDD.