Theory And Techiniques Of Wavelet Transformer Applied In Identification Of Fualt Character Of Protection Of HVDC

With the development of power system and our country 's economy, our country will implement the developing strategy of "the west power transmitted to the east area", "the south power transmitted to north" and "uniting the whole power system into a integrity". As the HVDC has the properties of long distance of power transmission, good regulation, lower overvoltage and lower losses, it suits to transmission of large power of long distance, peak modulation and link by water cables. Our country put HVDC as a part of the whole programming. HVDC will get more usage in power system, while the mature of technology of HVDC, decent of price of power transmission equipment, and enhancement of utilize ratio of converter station. It is inevitably to get fault and be malfunction during its operation as AC system. So we must find a new method for HVDC protection to avoid the influence of power transmission and to avoid damaging equipment when fault occurred, according with difference between AC and DC.Not only element of current and voltage of every component of system is required to be got rapidly in time in microprocessor based protection, but corresponding algorithm of protection must be given to do with data to analysis and to make decision, At last switch order or calculated result is given. But the prior algorithm has flaw during calculation process.The transient signal of high frequency has abundant fault signals when DC systems come to fault. Because the transient signals happen in a short time and its frequency is broad, Fourier transform and Windowed Fourier transform can't analyze it efficiently. Wavelet has property of localization in time domain andunchangeableness both in time domain and space domain in the condition that signals move parallel. So it can analysis transient signals of changing suddenly and faint signals by diverse characteristic of transient signals better through wavelet base zooming and moving parallel to adjust width of analytic window adaptively. In the dissertation, an integral HVDC model is built using simulation tool MATLAB. The simulation of analyzing by wavelet in time domain shows a good result.There have signals of high frequency of changing suddenly and noise when faults of HVDC taken place. De-noise theory based on wavelet with adaptive property is excellent to deal with transient signals. In this paper that analysis of wavelet is used to pretreatment signals proved this.First, protection of HVDC, how to get its values, how to classify faults and what kind of method should be taken are summarized, as well as the development of HVDC in our country. Second, the theory of wavelet and analysis method of wavelet is introduced. Fault signals are analyzed by wavelet. The simulation proved the superiority of this method...