The AC-DC method (the AC method combined with the DC method) has integrated the superiority of the AC method's easy measurement and the DC method's reliability, so it has achieved some degree of use. The method before only took the ground resistor as the condition of combination, so it is not perfect. Based on deep analysis on the AC method's reflect factors, this paper drew a conclusion that the reliability of the AC method is affected by the fault resistor and the line's distributed capacitance. The paper took the impedance phase as the integration condition, using the AC method while impedance phase meets certain conditions, using the DC method on the other situation. This strategy combined the affluence of ground resistor and distributed capacitance effectively, so it can promote the application on spot of the AC-DC method.
