Abstract：The state of the DC system of substation is directly related to the normal operation of the substation.

A new method for ground fault detection in substation DC systems，which is a combination of double-tree complex

wavelet transform and singular value decomposition，was proposed to achieve fast and accurate location of ground

faults occurring in substation DC systems. Firstly，the method constructed a Hankel matrix to decompose the

branch current signal through a dual-tree complex wavelet transform（DT-CWT）. Secondly，the Hankel matrix was

decomposed by the singular value decomposition（SVD）method with the aim of obtaining a series of singular

eigenvalues. Thirdly，the singular value difference spectrum was constructed using the adjacent singular value

differences，and the number of singular values was retained by the maximum peak of the singular value difference

spectrum. Finally，the low-frequency signal was reconstructed by the retained singular values. The analysis results

of the algorithm show that the method can accurately extract the low-frequency AC signal from the branch current

signal and achieve the accurate location of the DC system ground fault in the substation，which can largely reduce

the influence of the ground capacitance on the detection accuracy.

      Key words：DC system；ground fault detection；double-tree complex wavelet transform（DT-CWT）；singular

value decomposition（SVD）