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An adaptive fault line detecting method with correlation analysis using energy ratio is proposed based on the features of big capacitance current and high attenuation speed of hybrid transmission lines following single phase earthed fault. Applying wavelet packet decomposition, characteristic waveband of each zero sequence current can be determined by the theory of maximum energy, which can exclude static-component and the other wave band and enhance margin of fault line detection. According to the attenuation speed characteristic wave band of fault line's transient capacitance current is highest, fault line can be detected by comparing relative energy of first 1/4 cycle and last 1/4 cycle during the first cycle after fault. The theoretic analysis and simulations show that, transient characteristic can be enlarged and effect of CT's intermittent angle can be avoided by using relative energy of first 1/4 cycle and last 1/4 cycle in the fist cycle after fault to realize fault line detection, the fault line detecting method is correct and reliable within the distribution network with hybrid transmission lines.