A high speed noncommunication protection scheme for power transmission lines based on wavelet transform

Abstract

This paper presents a high-speed protection scheme for power transmission lines based on wavelet transform (WT). It is a noncommunication protection scheme as it depends completely on locally measured currents. It utilizes WT, which acts as a multi-level bandpass filter, to extract two distinct bands of frequency from the fault induced high frequency (HF) transient currents; the first band is high while the second band is relatively lower. The spectral energies of the extracted signals are then calculated to form two discriminating signals of the relay (operative and restraint). Based on the ratio between these discriminating signals the relay can distinguish whether a fault is internal or external to the protected line.The performance of the introduced protection scheme was evaluated by simulating several faults on 400kV–50Hz transmission system using an electro magnetic transient program (EMTDC). The simulation results showed distinct performance of the scheme irrespective of the fault type, fault inception angle, fault position and fault resistance. Moreover, it is not affected by a system configuration and system source parameters.