Detection and selection of singlephasetoground fault in distribution system with nonsolidgrounded neural are difficult. A new principle based on transient current traveling waves is presented to solve the problem. Through comparing the first current travelling waves of different lines at the bus bar

the fault line

whose first current travelling wave is of the reverse polarity and higher amplitude

is selected. In order to clearly recognize the traveling wave signal generated by fault

a new analysis tool

the wavelet transform is adopted. The new principle is also suitable for application to distribution and transmission system with solid grounded neutral. Extensive theoretical studies and simulations using EMTP have proven the feasibility of the proposed fault line selection method.