Faulty line detection by relative energy method for hybrid transmission lines

As the transient energy and abundant fault information are concentrated in the first half wave of zero sequence current when single phase grounding fault occurs,an adaptive faulty line detection method based on the relative energy of characteristic frequency band. The morphological filter is developed to filter the noises in transient zero sequence current of every line and the wavelet packet decomposition is then used to determine its characteristic frequency band according to the maximum energy theory and to exclude the steady-state components and the information outside the band for enhancing the margin of faulty line detection. Faulty line is detected by comparing the relative energy between the first and the last quarters of the fist cycle after fault. Theoretic analysis and simulations show that,the method enlarges the transient characteristics and avoids the effect of CT saturation on disconnection angle,being correct and reliable for the faulty line detection of distribution network with hybrid transmission lines.