Online differential protection methodology based on DWT for power transmission system

Abstract

This paper presents an online methodology for transmission line relaying based on discrete wavelet transform (DWT) and differential energy estimation. Irrespective of traditional current differential relaying, the energy level of wavelet coefficients of differential and average currents are used as the discriminating factor in the proposed scheme. First, the wavelet coefficients of differential current (IΔ) and average current (Iavg) are acquired by applying DWT. Thereafter, the energy of the wavelet coefficients (both IΔ and Iavg) are computed, as operating and restraining factors. Finally, the decision regarding issuing of tripping signal is taken by comparing the operating and restraining factors. In order to effectuate the competency of the proposed methodology, it has been tested on simulated transmission system designed in MATLAB. The results of various test cases indicate that the present approach is capable of providing fast and efficient online protection to power transmission system. It has also been observed that developed methodology remains unaffected for external faults and power swings condition, which arises due to emergent load changes in the system.