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 Kρ ESDD ; the smaller is the value of ρ ESDD 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.

Calcium sulfate and other slightly soluble salts in the natural pollution of catenary insulators could result in differences in flashover voltages between artificially and naturally polluted insulators at the same salt deposition density. Based on the insulator pollution characteristics in saline‐alkali areas and the saturated water absorption of polluted insulators, the equivalent salt deposit density and nonsoluble deposit density of insulators are corrected according to the influence of other coexisting soluble salts on the solubility of calcium sulfate. The correction formula of the insulator flashover voltage is proposed, which considers the equivalent salt deposit density, nonsoluble deposit density and pollution components. The results from the correction formula are compared with the experimental data from the artificial pollution test of the ceramic cap and pin insulator. The results show that salt‐alkali areas are more easy to flashover than other areas. The remaining pollutants can change the conductivity of the pollutant layer by inhibiting or promoting the dissolution of calcium sulfate. Moreover, its effect on the flashover voltage cannot be ignored. The error between the calculated value based on the correction formula and the experimental data is below 6%. A pollution flashover warning mechanism based on relevant meteorological data is proposed. The results can be used as an important reference for the operation and maintenance of catenary insulators in saline‐alkali areas. © 2020 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.