CIGRE B4 DC Grid Test System: Performance of a DC Hybrid Breaker during a pole-to-ground DC Bus Fault

The continuous increasing demand for electric power for renewable sources, such as off-shore wind power or solar generation, along with the economic access to remote sources of these type have revived the interest in high-voltage direct current multi-terminal systems (MTDC). In this context, the Modular Multilevel Converter (MMC) configuration is considered to be most promising VSC topology, but it lacks DC fault clearance capability. There are several ways to solve the earlier drawback, but they are costly, slow in response to faults or with large power losses. In this paper a hybrid HVDC breaker and the corresponding fault isolation strategy are proposed to overcome these drawbacks. The assemble of the hybrid HVDC consist of an active short-circuit breaker (ASCB), a main mechanical disconnector, a main breaker (MB), and an accessory discharging switch (ADS). A dc-side bus short-circuit fault is used to test the performance of the breaker in this particular situation. The MB open isolating the faulted line and then the mechanical disconnector opens. The proposed breaker can handle the dc-side fault with competitively low cost, and the operating speed is fast enough. The time that it takes to isolate the fault is about 5ms, and the full restore of voltage at converters is about 0.2 s. A model of an eleven-terminal monopolar and bipolar MTDC grid, based on the CIGRE model, is developed in EMTDC/PSCAD simulation tool to proves the validity and the feasibility of the proposed solution.