Research Of High-voltage Transmission Line Relaying Based On The Fault Transient Components

EHV/UHV transmission line plays an important role in strong smart grid in China. The transient based protection of transmission lines has the unique advantage of fast operation and immunity to problems such as fault resistance, current transformer saturation, system oscillation and line distributed capacitance etc. So, the transient based protection has broad application prospects in high-voltage transmission line relaying.This paper studies the high-voltage transmission line relaying based on transient fault component and compression scheme of recording data which is suitable for the frequency spectrum’s characteristics of transmission line fault signals.First of all, this paper analyzes the cause and propagation delay of fault transient component and the size of the fault current. The fundamental principle of commonly used algorithms for detecting and extracting transient signals are expounded. Much emphasis has been placed on the introduction about the wavelet multi-resolution and wavelet of db wavelet series.Secondly, several criterions of current differential protection and the application of transient signal wavelet coefficients in transient based relaying are discussed, the advantage of wavelet detail coefficients which are applied to transmission line relaying is studied. Combining with the current differential principle, a novel relaying scheme based on the transient energy in the fault current signals is presented in this paper, which is adapted to the quick and reliability requirements of high-voltage transmission line relaying.The500kV transmission line model is established to emulate transmission line fault in Matlab, all kinds of fault transient current signal under various fault conditions are obtained. The db6wavelet is used to decompose signals by Discrete Wavelet Transform(DWT) multi-scale decomposition, d4detail coefficients are obtained to calculate the operating signal and restraining one. The operating situation under various fault conditions is analyzed. The simulation results show that the criterion that presented in this paper can be better adapted to the variation of fault conditions.Fault analysis is another important means to improve the level of operation and management in transmission line relaying. To improve the efficiency of transmission line fault recording data’s storage and transmission, a new utility method for fault recording data compression is proposed. In this method, Fast Fourier Transform(FFT) and wavelet transform are employed to respectively compress the fault channel recording data and non-fault channel recording data because of the difference of spectrum characteristics between the fault channel recording data and non-fault channel recording data. In the case of frequency offset in power system, a windowed Discrete Fourier Transform(DFT) algorithm is used to enhance the compression ratio of non-fault channel recording data. Matlab simulation results show that this sub-channel and sub-time compression algorithm can obtain excellent compression performance, significantly reduce the storage space and communication transmission time of recording files.