The contamination conductivity on the surface of an insulator plays an important role in the warning of pollution flashover. However

as the contamination is usually inhomogeneous

the resulting micro-capacitance exerts great influence on the detection of the insulator surface conductivity. To tackle this problem

the authors developed a method for detecting the contamination conductivity on the surface of an insulator based on phase angle difference. In this study

the detection theory of the system was analyzed

and the key parts of the system were designed and simulated. Then

contamination wetting tests were conducted in laboratory to obtain the changing rule of the surface conductivity of an insulator. The results show that: 1)the surface conductivity is small when the contamination is dry; 2)the surface conductivity increases as the contamination gets wet; 3)the surface conductivity reaches its maximum when the contamination wetting is saturated; and 4)the surface conductivity decreases when the damp in contamination is over-saturated and the contamination drains. Therefore

the wetting process can be divided into three stages

i.e. wetting

saturation

and draining stages. More attention should be paid to the wetting stage in the prevention of pollution flashover. This research shows that the present system can effectively detect contamination conductivity on insulator surface and may provide guidance for the prevention of flashover.