DC Fault Identification in Multiterminal HVDC Systems Based on Reactor Voltage Gradient

Abstract

With the increasing number of renewable generations, the prospects of long-distance bulk power transmission impels the expansion of point-to-point High Voltage Direct Current (HVDC) grid to an emerging Multi-terminal high-voltage Direct Current (MTDC) grid. The DC grid protection with faster selectivity enhances the operational continuity of the MTDC grid. Based on the reactor voltage gradient (RVG), this paper proposes a fast and reliable fault identification technique with precise discrimination of internal and external DC faults. Considering the voltage developed across the modular multilevel converter (MMC) reactor and DC terminal reactor, the RVG is formulated to characterise an internal and external DC fault. With a window of four RVG samples, the fault is detected and discriminated by the proposed main protection scheme amidst a period of five sampling intervals. Depending on the reactor current increment, a backup protection scheme is also proposed to enhance the protection reliability. The performance of the proposed scheme is validated in a four-terminal MTDC grid. The results under meaningful fault events show that the proposed scheme is capable to identify the DC fault within millisecond. Moreover, the evaluation of the protection sensitivity and robustness reveals that the proposed scheme is highly selective for a wide range of fault resistances and locations, higher sampling frequencies, and irrelevant transient events. Furthermore, the comparison results exhibit that the proposed RVG method improves the discrimination performance of the protection scheme and thereby, proves to be a better choice for future DC fault identification.

An Efficient Bidirectional DC Circuit Breaker Capable of Regenerative Current Breaking for DC Microgrid Application

“…The inherent characteristics of renewable energy sources (RES)-based power systems in DC systems, such as low system impedance and higher charged capacitances, result in a significant surge in fault current during sudden fault inception, reaching magnitudes several hundred times higher than the nominal value. However, this drawback of DC microgrids can be mitigated through the utilization of various advanced fault detection and load isolation methods [10][11][12]. Throughout the years, DC circuit breakers have proven to be a reliable solution for interrupting the flow of current in DC systems, serving the crucial purposes of fault isolation and load switching.…”