Contamination wetting is one of key factors affecting the external insulation safety of transmission lines. To obtain the surface wetting characteristics of the pollution insulator

we proposed a new detecting method based on phase angle difference（PAD） characteristic quantity and developed a corresponding detection system. Then the wetting experiments were carried out on the typical LXAY-70 insulators in artificial climate laboratory. The test results show that the PAD parameter can accurately reflects the entire wetting process of the pollution layer from the initial stage

through the saturated stage to the oversaturated and washing-away stages. During the wetting process

the PAD gradually decreases from the initial val

ue

and the minimum value is obtained when the contamination is saturated and wetted. The steam fog input rates mainly affect the saturation time of surface contamination. The larger the input rate is

the less time the saturation of surface pollution takes. The saturated wetting PADs have obvious difference under different equivalent siut deposit densities（ESDDs）. The different pollution salts for NaCl and CaSO

4

have a closer saturated wetting times but the saturated wetting PADs are obviously different. The different insoluble substances for kaolin

diatomite and Al

2

O

3

have certain difference both in saturated wetting times and saturated wetting PADs. Test results can provide quantitative references for artificial pollution tests.