Insulator surface pollution contains various kinds of materials

in which CaSO

4

and Na Cl are the two major soluble contaminants. The current method of predicting flashover voltage is still based on the exponent function of equivalent salt deposit density（ESDD）

while the contributions of other conductive pollution materials on ESDD are always ignored. As a weak electrolyte with lower solubility

CaSO

4

affects flashover voltage dramatically. In this paper

the standard porcelain insulator XP-160 was chosen as an object

and the conductive pollution was simulated by CaSO

4

and NaCl. Through artificial pollution tests

the ac flashover voltages of insulator were firstly obtained. T

hen

conductivity curves of NaCl and CaSO

4

solution were measured by a conductivity meter

by which the contribution of CaSO

4

on ESDD could be calculated. Finally

two different methods of flashover correction were compared

and in the second method the factor of insulator saturate moisture was considered. Research results indicate that

it is deficient to calculate the flashover voltage by equivalent conversion using the contribution of mixed pollution materials on ESDD. But the relative errors can be limited under 10% if the saturate moisture is considered when converting the ESDD and calculating the flashover voltage

and this method also lacks some accuracy. It is not sufficient to just consider the change of conductivity when the flashover voltage under mixed materials is corrected. This research can help explain the influences of different pollution materials on insulator ac flashover voltage

and also can provide references for the method of flashover voltage correction under mixed pollution materials.