A fast discrete time-frequency filtering based current differential protection for shunt compensated wide area power system networks

This paper presents a time-frequency filtering approach suitable for current differential protection of transmission lines in a wide area power network. The current differential protection scheme efficiently discriminates between the internal and external faults in the protected zone of a transmission network and exhibits stability and robustness. For detecting the occurrence of a fault on the transmission line a cumulative sum average (CUSUM) technique is used and the fault classification and location are determined using the spectral energy of the average and differential currents based on a recent matrix version of the fast discrete S-transform. This new formulation uses intelligent frequency scaling, band pass filtering, and suitable interpolation techniques to reduce the computational overhead of the algorithm by almost 30 times in comparison to the earlier conventional S-transform. Further the new protection scheme will be a viable and competing one with the advent synchrophasors technology and wide area high speed communication and GPS systems. Also its viability is tested for the wide area network with a STATCOM placed at the middle of one of the transmission lines injecting reactive currents which requires the detection of the occurrence of the fault before or after the compensating device.