Based on the theoretical analysis of insulator strings’ equivalent circuit

this paper establishes a leakage current test circuit of insulator strings.The leakage currents of insulator strings in clean and pollution conditions are measured.The leakage current spectrum is analyzed by using FFT

and the leakage current fundamental resistive component is extracted.The relations among the leakage current fundamental resistive component

pollution degree and relative humidity are obtained.The results show that the leakage current is small and mainly contains capacitive current in dry pollution.Compared with the clean condition

the changes of leakage current and leakage current fundamental component of the polluted insulator are not obvious

however the leakage current fundamental resistive component has non-linear relations with the pollution’s ESDD and the relative humidity.The change of leakage current fundamental resistive component is more obvious in low humidity condition

therefore the pollution degree of insulator can be more effectively represented by measuring the leakage current fundamental resistive component instead of the leakage current.However

this method is not suitable for estimating the pollution degree in high humidity condition.Furthermore

the collector ring need not be fixed on the insulator strings

which ensures the system security.