On-line monitoring of the insulating state of metal oxide surge arresters (MOA) is monitoring its resistive leakage current. This paper analyses the common detection methods of resistive current, pointed out the problems. According to the relationship among the grid voltage and the flow through the leakage current of MOA, the resistive and capacitive current, put forward a new resistive leakage current detection method, and established a mathematical model. Using this mathematical model, new detection method can be verified by simulation. Confirmed that the new method can effectively reduce the impact of the power grid of the third harmonic voltage and phase coupling capacitor, this create a precise measurement for MOA resistance current online testing.
