In a resonant grounding system

the free-oscillation frequency of the cable-overhead line is typically between 3 00 and 3 000 Hz. In the initial stage of the fault

the transient information of the distribution network is rich

and the sequential overlapping derivative(SOD)transform can reflect the transient characteristic of the zero-sequence current. Therefore

the single-phase-to-ground fault line selection method based on SOD transform correlation analysis is proposed. And combined with the zero sequence voltage gradient summation as the starting criterion

the sensitivity and rapidity of the fault line selection are improved. The information of the transient zero-sequence current in the 0~2. 5 kHz band is extracted by wavelet transform and SOD transform is conducted. After the SOD transform

the similarity between the healthy lines is improved and the difference between the fault line and healthy lines is increased. Therefore

the correlation analysis of the results of the SOD transform is performed to form a fault line discrimination matrix. If the fault line discriminant matrix is all “1”

it is judged that the bus is faulty; otherwise

the line corresponding to“-1” is the fault line. The simulation shows that the method is almost independent of the initial phase angle

transition resistance and fault location

and the line selection result is accurate and reliable.