Fault Location And Protection Methods Using Hilbert-Huang Transform Of Traveling Waves For Transmission Lines

With the development of power systems, fast and accurate faults locations and protections become more and more important. Power grids produce transient travelling wave signals, which transmit along the transmission line to each substation with the speed approaching the velocity of light. Using the exact arrival time of the fault traveling wave and the waveform characteristics recorded at each substation, the traveling wave based fault location and protection can be realized. The fault location has high precision, and the protection has fast action speed. They cannot be influenced by current transformer saturation, low frequency oscillation and fault resistance. Traveling wave based fault location and protection thus become a hot research area in the world. Whereas, the traveling wave signals variation is quick, and the signal characteristics are difficult to extract. In order to improve them, Hilbert-Huang Transform is applied to analyze the fault traveling waves, and a new traveling wave based faults protection and location method is proposed in the thesis.The thesis first analyzes the theory of traveling waves on transmission lines. In view of the key problem of traveling wave fault location—the fault time accurate recording, a novel time-frequency analysis method for the traveling wave signals is proposed. Hilbert-Huang Transform (HHT) is applied to detect the signals. Intrinsic Mode Functions (IMF) of traveling waves are extracted by Empirical Mode Decomposition (EMD), and then Hilbert transform is applied to calculate the corresponding instantaneous frequency of each IMF component. The arrival time of traveling wave can be detected by the instantaneous frequency. Comparing with Wavelet Transform, HHT is not necessary to select parameters and has only one result. Power grid faults locations are simulated, and the faults generated traveling waves are extracted by wavelet transform and HHT respectively. Results show that traveling wave arrival time extracted by HHT algorithm is more accurate, and the fault location accuracy is higher.The influence of substation equipments ground distributed capacitance and transmission line trappers on the traveling wave propagation characteristics is simulated. The characteristics difference caused by internal faults and external faults of transmission line is analyzed. A new traveling wave based transient protection using the frequencies ratio of the two end voltage traveling waves of the transmission line is proposed. The frequency is obtained from HHT.. EMTP simulation results show that the protection is with high precision, good selectivity and reliability.