Cosine Similarity Based Directional Comparison Scheme for Subcycle Transmission Line Protection

Subcycle protection is of importance in the context of system operation near stability margins. A cosine similarity based directional comparison scheme using time-domain sampled data is proposed in this work for subcycle overhead line protection. Sign of cosine similarity computed between instantaneous incremental current of a phase and pre-fault voltage across other two phases is utilized for determining fault direction. Inherent faulted phase selection with the proposed scheme can facilitate single-pole-tripping, if required for high voltage line protection. Proposed method is tested using PSCAD/EMTDC simulated data for various fault parameters like type, location, fault inception angle, and fault resistance. Results confirm the effectiveness of proposed scheme and its ability to protect the line within 6 ms after fault inception for 50 Hz system including communication latency for directional comparison.