Keywords: digital protection, modified fast S–transform, spectral energy, transmission lines, current differential protection, fault location, time–frequency approach, impedance protection, smart grid, simulation, fault detection, fault classification
A new time–frequency approach for hybrid differential and impedance protection of transmission lines
A new current differential protection of transmission lines is presented in this paper using an S–transform variant having very fast computational speed suitable for real–time applications. The conventional S–transform used earlier for transmission line protection has large computational overhead and thus is not suitable for generating decisions regarding the occurrence of a fault and its type on a transmission line. The new S–transform variant is based on different types of frequency scaling, band pass filtering, and interpolation techniques to achieve a significant reduction of computation time in comparison to the original S–transform. For wide area protection as in the case of smart grid the current differential protection is realised by extracting the relevant features from the current signals at both the sending end and receiving end terminals from the new S–transform generated contours. This paper focuses on the fault detection, classification, and location aspects using a new S–transform variant applied to synchronised measurement of the differential and average energy of current signals. Digital simulation results using EMTP for a long distance transmission line show the computational speed and efficiency of this new algorithm.