Fault Location & Protection Methods Using Wavelet Energy Spectrum Analysis Of Traveling Waves For Transmission Lines

Power grids faults produce transient traveling wave signals, which transmit along the transmission line to each substation with the velocity of light. With the accurately arriving time of the fault traveling wave and the waveform characteristics recorded at each substation, traveling wave based fault location and protection can be implemented. Because the fault location has high precision, the protection has fast faults detection, and they cannot be influenced by current transformer saturation, low frequency oscillation and fault resistance, traveling wave based fault location and protection have become hot topical in power system research throughout the world. Whereas, the traveling wave signals vary fast, and the signal characteristics are difficult to extract. In order to solve the problems, wavelet energy spectrum is applied to analyze fault traveling wave, and some novel traveling wave based protection and location methods are proposed in the paper.The transmission characteristics of traveling wave are analyzed in the paper firstly. It is found that the faults generated traveling waves contain wide-area frequency bands signals, and the dispersion characteristics of traveling wave affect the traveling wave head detection and wave velocity calculation. Wavelet energy spectrum analysis is presented and applied to process traveling wave signals, and the frequency band signal with energy concentrated is extracted for fault location. The transmission velocity of the frequency band signal is calculated by the transmission line two ends measured traveling wave data of an external disturbance, and the arrival time of the frequency band signal is calculated by its characteristic points which are extracted by wavelet energy spectrum analysis in time domain. Fault location in a power grid is simulated in the paper, and the traveling wave head is extracted by the wavelet energy spectrum algorithm, the wavelet modulus maxima algorithm, and the wavelet Lipischitzαalgorithm respectively. Results show that the wavelet energy spectrum algorithm is the best.The influences on the transmission characteristics of traveling wave are analyzed for substation bus, grounding distributed capacitance of substation equipment, and transmission line trapper in the paper. And the frequency spectrum of traveling wave caused by internal faults and external faults are compared and analyzed. A novel transmission line protection method which uses the signal energy ratio between in-band of trapper and out-of-band of trapper is proposed. When the ratio is larger than its threshold, faults will be detected. EMTP simulation results show that the protection method can protect the whole transmission line with high speed without communication between the two ends of transmission line, and it has high precision, selectivity and the reliability.