| China’s energy distribution and electricity demand are unbalanced, which in the objective determines that the remote and high-power electricity transmission and network connection are imperative. HVDC(High-voltage direct current) has obvious advantages in high-capacity and long-distance Electricity transmission, submarine power transmission with cable and power system interconnection. HVDC can obtain asynchronous interconnection of the grid with great benefits, which not only avoids the problems caused by large power grids, but also improves the operating performance of the original AC grid. With the rapid development of HVDC in our country, it has become an urgent problem to improve the operational safety and the operational reliability of HVDC line. HVDC line protection bears the task of fast detecting and handling line fault, and whether it can act fast and reliably when the line failure occurs relates to the safe and stable operation of the entire power system. However the existing traveling wave protection has general problems of poor reliability, easy malfunction and other issues, therefore it is necessary to do further analysis and research about the HVDC line protection.In this paper, on the basis of evaluating the DC line protection scheme in the project, the current research status of the line protection at home and abroad is summarized in categories and the existing problems are pointed out.This paper analyzes the characteristics of the mutant voltage and the mutant current at both ends of the HVDC transmission line with faults inside and outside the line. Through extracting the DC component of the mutant voltage and the mutant current by kaiser window, the line protection principle is proposed based on polarities of the mutant power at the two ends of the same line. By comparing the mutant power magnitude with the threshold value, the start criterion for the line protection is presented. The identification criterion of the fault pole is proposed based on the mutant voltage. Finally, a complete line protection scheme is designed. The simulation results show that the protection scheme proposed by this paper can correctly distinguish between internal faults and external faults with strong transition-resistance-tolerated ability, and be able to accurately identify the fault line as well.Moreover, this paper also studies the propagation rule of traveling wave under the HVDC line fault and analyzes the transmission characteristics of the line border composed of the reactor and the DC filter. On this basis, the traveling wave sequence protection principle and transient energy protection principle using wavelet transform have been proposed. The traveling wave sequence protection has high reliability by detecting the wavelet transform modulus maxima sequence with specific time and polarity relations to identify the internal line-ground faults; and the transient energy protection, as a reserve of the traveling wave sequence protection, has a high degree of differentiation. At last, a complete protection scheme is designed. Multiple simulation results show that the proposed scheme is correct and effective.Finally, several research directions of the HVDC line protection are proposed for related research scholars’ reference only. |
