A pilot protection scheme based on similarity comparison of voltage waveforms for active distribution networks

In active distribution networks with a high penetration of distributed generation, the electrical characteristics of phase-to-phase short-circuit faults are significantly affected by factors such as distributed generation capacity and control strategy, making it difficult for conventional overcurrent protection to achieve both fast operation and high reliability. Therefore, it is of great importance to develop a fast protection method that is insensitive to control strategies. Although pilot protection can provide instantaneous protection over the entire line, existing pilot protection schemes mostly rely on synchronized data sampling and thus impose high communication requirements. To address this issue, this paper proposes a pilot protection method based on the transmission of logical quantities. First, the reference-point voltage is calculated from the electrical quantities at the measurement point, and faults are identified by comparing the waveform similarity between the measured voltage and the reference voltage, using cosine similarity to quantify the degree of waveform similarity. Second, an auxiliary criterion is constructed using the phase difference between the positive-sequence voltage and current fault components to improve tolerance to fault resistance. Finally, the decision results of the protections at both ends of the line are compared to reliably distinguish internal faults from external faults. Simulation results from PSCAD/EMTDC and RTDS demonstrate that the proposed method can rapidly and reliably identify phase-to-phase short-circuit faults, is well-adapted to different control strategies for distributed generation, exhibits strong tolerance to fault resistance, and is only slightly affected by outliers and noise.