A Whole-Line Fast Protection Scheme for HVDC Transmission Line Based on Single-Ended Boundary Energy

Compared with high voltage alternating current (HVAC) power transmission systems, high-voltage direct current (HVDC) power transmission systems have lower power losses and more flexible power control capabilities. The HVDC transmission system plays an important role in modern new type power systems. Presently, the line protection methods operated in practical HVDC project include main protections and backup protections. The travelling-wave protection is widely used as the main protection. However, the transient travelling-wave signals would be weakened during high fault resistance grounded faults, which make it difficult to catch the wave-head. For backup protection methods, the voltage derivative protection and current differential protection operate with low reliability. As for the former, the rate of the voltage change may not reach the threshold, because high fault resistances could the attenuation of transient voltage caused by fault resistance. And the action speed of current differential protection is too slow to realize the protection function. Thus, the line protection methods in engineering applications can not completely meet the requirements of the practical HVDC project. To overcome these problems, some novel protection schemes have been proposed in recent years. However, the existing single-ended boundary energy protection schemes are not able to distinguish the remote end DC line faults from the rectifier-side-external faults. Single-ended hybrid protection methods overcome this problem, while these methods are complicated. In addition, the single-ended boundary energy protection schemes use the attenuation characteristic of line boundary on high frequency components to achieve fault identification. At the same time, these protection algorithms need a high sampling frequency. In view of the above problems, a novel single-end boundary energy based whole-line fast protection is proposed. During rectifier-side-external faults, the rectifier-line-side boundary energy is lower than the rectifier-valve-side boundary energy. During inverter-side-external faults, the rectifier-line-side boundary energy is lower than that for internal faults. During internal faults, the rectifier-line-side boundary energy is greater than the rectifier-valve-side boundary energy, and is greater than that for inverter-side-external faults. According to these characteristics, the boundary energy give a promising solution to determine whether a DC line fault occurs. Two-ended faulty pole selection criterion requires information coming from both ends of the DC lines. For speed, a single-ended faulty pole selection criterion is also proposed in this paper. A HVDC transmission test system established in PSCAD/EMTDC is applied to verify the proposed protection scheme. The following conclusions can be drawn from extensive simulation results in this paper: (1) Compared with existing travelling-wave protection, the proposed method has better reliability. (2) The proposed method is able to detect DC line faults with good speed. (3) The proposed method has good robustness with respect to fault location, fault resistance and sampling frequency. (4) The faulty pole selection criterion can differentiate the faulty pole from the healthy pole reliably. The contributions of this novel single-end boundary energy based whole-line fast protection are: (1) The proposed protection is able to distinguish the remote end DC line faults from the rectifier-side-external faults. Compared with single-ended hybrid protection methods, the proposed method is simple and is easy for practical applications. (2) The protection has low requirement for sampling device. (3) Even during a remote end fault with a high resistance as large as 300 Ω, the fault discrimination criterion is able to identify the DC line fault correctly. © 2023 Chinese Machine Press. All rights reserved.