The UHVDC Transmission Line Transient Protection And Fault Location Based On ESMD

The transmission line of UHVDC transmission system, high voltage, long after the terrain and complex natural environment, increase the probability of occurrence of the fault line, causing a serious threat to the safe and stable operation of U-HVDC system. Study on protection scheme of UHVDC transmission lines has become an important job. In the transmission line when a fault occurs, the transient signal contains abundant fault information generated by faults, can identify the fault location and fault type by using a variety of detection methods, to study the fault protection method of UHVDC transmission lines. According to Yun Guang UHVDC system actual parameters simulation model is established to analyze the frequency characteristics of UHVDC transmission line and the line boundary, the principle of transmission line transient protection is proposed; analysis of the maximum of wavelet transform modulus line fault voltage signal, the proposed fault location method. The main research work includes:(1) Study on frequency characteristics of UHVDC transmission line. Analysis of line boundary exist the phenomenon of refraction and reflection, refraction coefficient of line boundary with low-pass filter characteristics and external fault occurs, due to the role of the line boundary, boundary frequency and frequency amplitude has attenuated, in the high frequency band, faster decay.(2)Analysis of the principle of single ended transient current protection of UHVDC transmission lines, different fault current corresponding to fault section mutation in different directions. Can be used to distinguish between the failure in the side area or on the opposite side of the fault; lateral area to high frequency transient fault signal by line and the boundary of the double damping effect, measured fault signal instantaneous frequency amplitude is smaller; in high frequency transient fault signal only after the line attenuation, measured fault signal instantaneous frequency large amplitude. Based on the maximum difference of instantaneous frequency, a criterion for distinguishing the fault from the inner and outer regions is proposed. The simulation results show that this method is effective.(3) Are proposed based on ESMD and support vector machine of UHVDC transmission line fault location method and ratio of UHVDC transmission line fault location method based on line voltage mode and transient zero mode first wave head of wavelet modulus maxima. A lot of simulation results show that the accuracy of the two fault location method is higher, and the transition resistance is strong. And two methods do not need to calculation of traveling between the fault point and measurement point in the transmission time and transmission speed, so as to avoid the traditional double terminal traveling wave fault location method of wave velocity is difficult to be defined and on both ends of the clock synchronization device accuracy requirements are too high.