A combined algorithm for high speed transmission-line protection based on traveling-wave

This paper investigates a high-speed and reliable transmission-line protection algorithm utilizing the fault induced traveling-waves in addition to the impedance measurements from the signals fundamental phasor. The wavelet transform is used to decompose the fault signals into different frequency bands, and the signal energy spectrum is calculated using obtained detail coefficients. Since the bus equipments influence the propagated traveling-waves in the power system, the signal spectral energy in different frequency bands would be different for the internal and external faults. This is used to accelerate the impedance relay operation when the measured impedance enters the second protective zone. A lot of simulation studies are carried out by using PSCAD/EMTDC software to evaluate the proposed algorithm and some of the obtained results are presented.