Fast discrete S-transform based differential relaying scheme for UPFC compensated parallel line

This paper presents a new differential relaying scheme for a parallel transmission line in presence of Unified Power Flow Controller (UPFC). In this work, a new algorithm is proposed to detect and classify the fault along with to identify the faulty section with respect to UPFC location. The UPFC is placed at midpoint of the one of the transmission line. The scheme starts by retrieving the three phase currents signals at both ends of the transmission line synchronously and processing it though Fast Discrete S- transform to derive the spectral energy of the current signals. The differential spectral energy of current signals (i.e spectral energy of current measured at sending end minus spectral energy of current measured at receiving end) of respective phases of transmission lines is used to register the fault pattern. The proposed algorithm is very simple and accurate for fault detection and classification in double-circuit transmission lines including UPFC in one of the line. The scheme has been extensively tested on different faulted conditions with wide variations in operating parameters of the UPFC as well as transmission line and the test results indicate the effectiveness of this scheme.