A Fault Line-Selection Method of Hybrid Cable-Overhead Line in Distribution Network Based on Morphology Filter and Hilbert-Huang Transform

While the hybrid transmission lines of distribution network occur the single line to ground faults, a fault line detecting method with HHT detective then compare the phase relation based on the phase relation of zero sequence current between fault line and unfault line is reverse. A morphological filter is first developed to filter noise in transient zero sequence currents. Applying HHT detective to define the fault time, then using the EMD to decompose the zero sequence current of 1/4 cycle after the fault happens and compare the mutate direction of highest frequency of IMF to identify the fault line. According to analyze the transient signals of distribution network occur the single line to ground faults, in the first 1/4 cycle after fault, the phase inversion is not happened and also can avoid the influence of CT saturation. The theoretic analysis and simulations indicate that the fault line detecting method is correct and reliable within the distribution network with overhead-cable mixed lines. In addition, HHT detective require the low hardware and easy to implement, so the method also has economical efficiency.