Boundary Protection Algorithm Based on Phase Information of Improved Recursive Wavelet Transform for EHV Transmission Lines

According to the frequency characteristics of transmission line boundary, this paper proposes a new algorithm of boundary protection for extra-high-voltage (EHV) transmission lines based on improved recursive wavelet transform (IRWT). IRWT is used to directly extract desirable frequency components of fault-induced transient current signals. By comparing the average frequency of the extracted signals, which measured by the phase information of wavelet transformation, an internal or external fault can be distinguished definitely. Due to the IRWT update only using previous values and regardless of the sampling rate, the proposed algorithm reduces computational complexity, improves the real-time capability and is very desirable for ultra-high-speed protection. The EMTDC simulation results show that the new boundary protection algorithm is insensitive to fault location, fault resistance, fault type, and fault initial angle, and that the algorithm is feasible.