Phase Angle-Based Sub-Cycle Algorithm for High-Speed Digital Relaying of Transmission Lines

Sub-cycle algorithms aid in quick fault detection and isolation by digital relays. A new sub-cycle phase angle-based algorithm, to achieve 3 cycle Circuit Breaker (CB) operation, is proposed in this letter. Half-cycle DFT (HCDFT) is used to estimate the Instantaneous Phase Angles (IPAs) of the fundamental current and voltage. Modified IPAs (MIPAs) are derived from the IPAs. A Sub-Cycle Similarity Index (SCSI), obtained from the MIPAs, is used for Fault Detection (FD) and Fault Classification (FC). A Directional Index (DI) based process, which runs in parallel to FD and FC, is also proposed to distinguish internal and external faults. Simulation results and comparison with previous methods reveal the efficacy of the proposed algorithm in achieving high-speed protection of transmission lines.