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.

I. Introduction

Transmission lines in modern power network demand high-speed protection [1]. Power network’s stability increases with a decrease in the fault clearing time [2]. High-speed protection also reduces the stress on transformers, decreases the duration of voltage-sag, and minimizes damage due to faults [3]. However, too slow or fast relay operation may negatively affect the network’s stability [4].