Novel transient current-based protection scheme for DC line faults in UHVDC system

DC line faults are a major threat for Ultra High-Voltage Direct-Current (UHVDC) transmission systems. This paper proposes a non-unit protection scheme based on transient current. The difference in transient current magnitudes can be used to differentiate the faults on the protected DC line from the inverter-side-external faults. The magnitudes of transient currents on both sides of the boundary unit are used to distinguish DC line faults from the rectifier-side-external faults. Using these characteristics, the proposed protection is constructed. Since the measured transient currents are local, there is no need for fast telecommunication link and the relay can detect DC line faults within a few milliseconds. Theory analysis and simulation results have demonstrated the correctness and validity of the proposed method.

I. Introduction

The power industry in China is currently developing 1000-kV UHV AC transmission systems and ±800-kV UHVDC transmission systems, which will form the backbone of the future Chinese grid [1]. While the voltage-source converter (VSC) technology is considered as a preferred way to operate in weak ac systems and interconnect offshore wind resources, the line-commutated converter (LCC) technology dominates the point-to-point HVDC schemes over longer distances [2]. The DC lines inevitably go through the valley and mountain and operate under harsh weather conditions. Compared with the conventional HVDC systems, the UHVDC systems have larger capacity and longer transmission lines. Thus, UHVDC lines may suffer from faults more easily. A fast and reliable DC line protection is very important to detect and clear dc line faults [3].