Fast S-transform based distance relaying in transmission line

The paper presents distance relaying of transmission line using Fast S-transform (FST). Basically distance relaying needs a faster and accurate phasor estimation of the fault current and voltage signals, which are used to compute apparent impedance for issuing the tripping signal in case of faulty situations. Originally developed conventional S-transform is an invertible time–frequency spectral localization technique that combines elements of wavelet and short-time Fourier transforms. However, the computational burden (processing time) of conventional S-transform is high and thus, not suitable for on-line applications such as digital protection of transmission lines. However, recent development of FST reduces the computational burden by utilizing downsampling. The FST is found to be accurate and faster compared to conventional S-transform while estimating the phasor and computing impedance trajectory. The accuracy in estimation with high DC off-set and performance in noisy environment ensures the robustness of the FST for relaying applications. The results from extensive study indicate that the FST can suitably replace the existing DFT based algorithm for on-line digital distance relaying task in large power transmission network.

► A fast and accurate relaying scheme based on Fast S-transform is proposed.
► The developed algorithm is more accurate in presence of DC-offsets and noisy situations.
► The relaying scheme is faster (one cycle response time) compared to conventional S-transform.
► The proposed algorithm can replace DFT based algorithm for relaying applications.