Protection of Transmission Line Paralleled along the Same Right-of-way

Abstract

This article presents a novel scheme for the protection of parallel transmission line paralleled along the same right-of-way using wavelet packet transform (WPT). The proposed scheme is based on the difference between the absolute of the additions of wavelet coefficients computed using WPT at the third level with the help of db4 wavelet function. This concept has been applied to the corresponding phases of both the lines in parallel. The WPT is used to capture important features of the decomposed signal that are sensitive to infeed current and mutual coupling and provides stability against in-zone faults. The wavelet packets are highly sensitive toward high-resistance faults and a computationally more flexible way to conduct signal discrimination than wavelet transforms-based methods. The proposed method completely avoids voltage signal used in conventional relays and also ignores the requirement of communication channel. The relay provides reliability and selectivity for discriminating cross-country faults and internal faults and remains stable against external faults. The proposed scheme has been tested under different fault and system conditions with varying fault resistance between 0–200 Ω. A series of tests using test signals generated by Power System Computer Aided Design/Electro-magnetic Transients in DC Systems (PSCAD/EMTDC) for a 400-kV parallel transmission line have proven the accuracy and effectiveness of the proposed scheme.