In order to study the effect of partial arc on the relationship between the leakage current and the surface conductivity under the saturated humidity condition

experiments were carried out in a small fog chamber.Moreover

the surface leakage current of U70 B/146

U70 BP/146 D and triangular glass plates under different equivalent salt deposit density（ESDD） values were monitored by applying electricity and moisture

and the maximum value of leakage current was used to calculate the surface conductivity under different ESDD values. The test results show that when the partial arc appears on the surface of the sample

the calculated equivalent values of the surface conductivity of different types of insulators are different

and there is a great deviation from the actual value of the surface conductivity. The calculated equivalent value of surface conductivity of the triangular glass plate is almost the same as the actual value. The test results show that the appearance of partial arc changes the development path of current on the pollution layer

and then causes the change of shape coefficient

so that the calculated equivalent value of the surface conductivity of insulator is smaller than the actual value. When the leakage current is used to calculate the surface conductivity

the correction factor of U70 B/146 is 1.82～2.86

and the correction factor of U70 BP/146 D is 1.18～1.33.