Porcelain post insulators have been widely used in DC converter stations. Recent studies have shown that the pollution of the top surface is heavier than that of the bottom surface. The ZSW56-126/8 insulator was artificially contaminated to study the DC flashover characteristics under the non-uniform pollution

and the flashover voltage under each non-uniformity was obtained. The relationship between the flashover voltage and the salt density was fitted by the least squares method

and the DC flashover characteristics of the non-uniform pollution were obtained. Furthermore

the influence of non-uniform pollution on the surface conductivity of the insulator was analyzed

and the equivalent conductivity was obtained as a function of the non-uniformity. Based on the equivalent conductivity function

the theoretical expression of the non-uniform pollution flashover voltage correction coefficient was derived and verified

providing a theoretical basis for the non-uniform pollution flashover voltage variation. Meanwhile

the empirical formula of the correction coefficient was analyzed

and the expression of the flashover voltage with the correction coefficient was obtained and verified by error calculation. It can concluded that the empirical formula of DC flashover voltage Uf and salt density ρ

SDD

can be obtained as: U

f

=aρ

SDD

-b

positively correlated with the inhomogeneity

the a increases with the increase of the inhomogeneity

and the index b value is not affected by the inhomogeneity. Non-uniform pollution on the upper and lower surfaces of the pillar insulators will affect the conductivity of the surface fouling layer and then the flashover voltage.