Wavelet-based Relaying Scheme for Tapped Transmission Line

A wavelet-based digital protection scheme for a tapped transmission line is presented in this article. As the wavelet packet transform provides more detailed and accurate signal decomposition than the discrete wavelet transform, proper discrimination can be achieved between the forward and reverse faults on extra-high voltage tapped lines. The idea of the proposed scheme depends on deriving an ADD signal using wavelet packet transform coefficients that are proportional to the fault current at each terminal. Due to the finer characterization of current signal, the proposed wavelet-based digital relaying scheme has successfully distinguished high resistance fault. Verification of the proposed technique has been done in the field as well as on simulated data of an existing part of an Indian system (UKAI-KAKRAPAR 400-kV tapped transmission line) using a PSCAD/EMTDC software package. The relay has shown satisfactory performance under various fault conditions, especially for high-resistance faults and also for reverse faults in the case of weak sources. This article concludes with a comparative study in the form of simulation between the existing scheme and the proposed scheme by analyzing different fault and system conditions.