Research On Program Of High-voltage Direct Current Transmission Line Protection Based On The HHT

With the continuous development of power electronics technology, computer technology, and other related technology, High-Voltage Direct Current(HVDC) has the highlighted advantages in the long-distance, large-capacity transmission. And in order to respond to the call of the national network policy, More and more HVDC projects put into operation, and it is usually used as contact lines among large power grids, making their relationship more closely. The operation stability of HVDC transmission line is directly related to the safe operation of the connected AC grid systems. However, since HVDC transmission line is usually long and complex cross-regional geographical environment and climate, it has a high fault rate with many unfavorable factors. So in order to ensure the security and stability of the DC system and interconnected other power grids, it is very significant to make great effort in research of HVDC transmission line, which effectively improve the protective properties of the secondary protection device, reducing the incidence of failure.Firstly, the paper studies depth the principle of Hilbert-Huang Transform(HHT), and discusses processes of analysis signal. It researchs the characteristics of the Hilbert spectrum and Hilbert marginal spectrum. At the same time, it also studies the applications of power traveling wave detection and harmonics analysis.Secondly, the paper studies the physical structure and amplitude-frequency characteristics of HVDC transmission line’s boundary elements. and also studies characteristics of transient voltage signals when the ransmission line occurs faults and introduces the concept of Hilbert energy. Because there’s a big difference in high-frequency signal components’ Hilbert energy of internal faults and internal faults, the paper proposes an identification criterion based on Hilbert energy.Thirdly, based on the structure and parameters of the CIGRE standard model, the paper uses the electromagnetic transient simulation software PSCAD/EMTDC to build a unipolar 12 pulse HVDC system model. it simulate operating conditions of the system during the normal operation and variety of typical line failures, and it also analysis the characteristics of various faults with using the programming software MATLAB to process the experimental datas. it studies comparatively the differences of Hilbert energy of internal faults and internal faults and sets a threshold value of Hilbert energy with fully ensuring selectivity and sensitivity of protection device. At the same time, the protection criterion can accurately determine ground faults without the influence of different transition resistances.Finally, According to characteristics of transient current signals, the paper introduces the empirical mode decomposition method of HHT, and useing its good mutation point detection capability to detect the arrival time of faults travel wave with modern traveling wave principle, an new faults location algorithm of HVDC transmission line based on EMD is proposed. Comparativiy analysising the difference between the calculation distance and the actual distance with different fault locations and different transition resistances, the ranging method is feasible.