| With the development of electrical networks and continuous construction of HV & EHV transmission, HV & EHV transmission lines become main network in our country. In order to improve power system stability and to increase the transmission lines capacity, fault clearing time must be shorter and operating speed of relay protection must be faster. For fast action reaction, not influenced by current transformer saturation, low frequency oscillation and fault resistance, traveling wave protection have become the hot area around the world. Hilbert-Huang Transform (HHT) is used in traveling wave analysis, and HHT based traveling wave protection methods are proposed in the paper.HHT theory is introduced, its characteristics are summarized in the paper, and an example is taken to show the detection of traveling wave using HHT. In order to simulate transient process correctly, transient model is analyzed in detail, J. Marti model is established, and influence of substation equipment such as bus stray capacitance and line trap is discussed, the difference of traveling wave detected by protection system when faults occur in internal and external is also discussed. According to the difference, traveling wave protection based on instantaneous frequency crest of traveling wave and protection based on Hilbert energy spectrum are proposed respectively. Extract Intrinsic Mode Function (IMF) of Fault traveling wave signals by Empirical Mode Decomposition (EMD), and then obtain time-frequency map and Hilbert energy spectrum by Hilbert transform form the first IMF component. Using instantaneous frequency of traveling wave crest and the energy characteristics of high and low frequency component, traveling wave protection is realized.Theoretical Analysis and simulation results show high speed, independence from type and angle of fault and fault resistance, what's more it can distinguish switching operation. It is simple and useful for HV & EHV transmission line protection.
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