Travelling Wave Protection of UHV Half-wavelength AC Transmission Lines

The energy bases and the power load centers in China have reverse distribution, and the load demand is constantly increasing. Energy transmission becomes a key problem related to national economy and people's livelihood. Ultra-high-voltage (UHV) transmission is an effective solution to the problem of energy transmission in China, so the research of UHV half-wavelength alternating current transmission (HWACT) is of great significance. Traveling wave protection has its unique advantages for long-line and long-distance transmission. According to the up-wave propagation characteristics of half-wavelength lines, the traveling wave protection criterion suitable for half-wavelength lines is proposed. Aiming at the protection of the whole line of HWACT lines, and based on the theory of wavelet transform, the third-order B-spline function is chosen as the wavelet function in dyadic wavelet transform which is the main wavelet method for this protection, and the main body of the protection is constructed by using Mallat algorithm. The sample frequency, the wavelet transform scale and the target frequency band are determined based on the analysis of the frequency space characteristics of the half-wavelength circuit modulus and the amplitude frequency characteristics of the wavelet function coefficient sequence. Then a traveling wave pilot protection strategy suitable for the HWACT line is proposed, and the PSCAD/EMTDC and the MATLAB are used to conduct simulation and programming. The simulation results prove that the protection strategy can protect the full length of the HWACT line under various fault types as well as fault conditions and has a good ability to resist the transition resistance. © 2020 Automation of Electric Power Systems Press.