A novel S-Transform-based pilot protection algorithm for transmission lines

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Traveling wave (TW) directional protection has attracted significant attention due to its ultra-high-speed action and susceptible performance. However, its low reliability under weak fault conditions makes it difficult to apply in practice. Based on the difference between the forward TW and the reverse TW after faults, this paper proposes a novel transient directional pilot protection algorithm for extra-high-voltage (EHV) transmission lines. The algorithm employs the S-transformed transient energy within a short time window to characterize the directional TW and determines the fault direction based on the polarity of the difference between the reverse TW energy and the forward TW energy. In a forward fault, the polarity of the difference between the reverse TW energy and the forward TW energy is positive. In a reverse fault, the polarity changes to negative. If the directional relays mounted at both terminals indicate a forward fault, an internal fault can be identified. Extensive EMTP-RV test results indicate that the proposed algorithm can accurately recognize the fault orientation at diverse strat fault angles, fault resistances, fault categories, and fault positions. Furthermore, even under adverse scenarios such as a 1000 Ω resistance fault, the algorithm exhibits high reliability.