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Flexible direct current (DC) grids face a serious challenge in terms of rapidly isolating DC faults. A DC circuit breaker is an effective solution for DC fault isolation. To improve the fault-isolation and reclosing capability of flexible DC systems, a new high voltage direct current (HVDC) circuit breaker topology with adaptive reclosing capability is proposed in this paper. The topology of the circuit breaker is a T-shaped structure, which has the ability to break the current in both directions and effectively reduce the cost of components. Meanwhile, after the fault is cleared, the circuit breaker is controlled to inject a voltage signal into the line. Based on this, to prevent the circuit breaker reclosing in the event of a permanent fault from having an impact on the system, a method for fault identification based on Euclidean distance that uses the voltage signal to identify the fault properties is proposed. Finally, the performance of the circuit breaker is simulated and verified by PSCAD/EMTDC simulation software, and compared with the typical existing circuit breakers to verify the effectiveness of the circuit breaker and reclosing scheme. [ABSTRACT FROM AUTHOR]

Nowadays, traditional DC circuit breakers (DCCBs) are always expensive and lack current-limiting capabilities. Hence, this paper proposes a current limiting and low-cost hybrid DC circuit breaker (HCB). When a fault occurs, the paralleled inductors in the proposed HCB are converted to a series connection due to the cutoff of the converter module, effectively limiting the increase of fault current. Then the cascaded IGBTs undertake the transient interruption voltage. Energy dissipation circuits (EDCs) reduce the fault isolation time (FIT) by bypassing the current-limiting inductor during energy dissipation based on the metal oxide varistors (MOVs). Therefore, the proposed HCB can limit the rate of the fault current increase, reducing the FIT and cost. Finally, the feasibility of the proposed HCB is verified by a single-ended equivalent system and DC grid test systems built in PSCAD/EMTDC. In addition, the proposed HCB FIT is 33.7% quicker, its energy consumption is 87%, and its cost is lower than that of the traditional ABB HCB. [ABSTRACT FROM AUTHOR]

This paper proposes a thyristor-based hybrid DC circuit breaker (HDCCB), which is composed of a fast mechanical circuit breaker and an LC resonant circuit with thyristor switches. The proposed HDCCB provides a zero-crossing point for fault current by injecting a resonant current in the reverse direction of the fault current. The proposed HDCCB has a low conduction loss in normal operation using a mechanical circuit breaker, and it offers the advantages of low cost, high reliability, and large capacity using thyristor switches instead of IGBT switches. It also has the design flexibility to adjust the magnitude of the injection current depending on the fault current level. A bidirectional HDCCB is also proposed by adding several components to the developed unidirectional HDCCB, which can offer compact system size and low system cost. Design considerations of the proposed structure are discussed. The validity of the proposed HDCCB is verified by simulation and experimental results. [ABSTRACT FROM AUTHOR]

Due to the rapid development of DC transmission, research on DC side fault protection has also made significant progress. The bipolar short-circuit fault is one of the most severe types of DC side faults. It can cause a current surge, which affects the safe operation of a system. Therefore, this paper proposes a new type of hybrid DC circuit breaker (DCCB) to realize the rapid suppression of bipolar short-circuit current. The new DCCB consists of three parts: a nominal current branch (NCB), an energy absorption branch (EAB), and a freewheeling branch (FB). Different control strategies can be adopted to achieve line protection functions for different types of faults. For transient faults, the absorption and suppression of the fault current are achieved mainly through the EAB and FB. The DCCB ensures that the amplitude of the current delivered by the DC line is maintained in a safe operating area of the transmission line. The EAB is disconnected after a short-term of operation for permanent faults to achieve complete isolation between the converter side and the fault side. The parameter design of the DCCB is carried out to provide a reference for the practical application of this research. Finally, the effectiveness of the proposed DCCB protection strategy is verified by simulations, and the function of the DCCB is further verified by experiments. [ABSTRACT FROM AUTHOR]