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Multi‐terminal flexible DC power grid plays an important role in large‐scale new energy integration, which usually requires the installation of multi‐terminal DC circuit breaker (MTCB) at the intersection of multiple DC lines. At present, the research on multi‐terminal DC circuit breaker is mostly limited to theoretical simulation calculation, and there are few experimental studies and engineering applications. In this paper, a four‐terminal DC circuit breaker based on commutating path multiplexing is proposed, which combines with the compact natural commutation scheme of hybrid gap, greatly reducing the cost and volume of the circuit breaker. The commutation characteristics of the four‐terminal hybrid DC circuit breaker equivalent prototype at 10‐kV voltage level were tested. On this basis, the equivalent prototype of the circuit breaker test results shows that under 10‐kV voltage level, the four‐terminal circuit breaker topology can achieve breaking of 11 kA in 2.8 ms by the natural commutation method. [ABSTRACT FROM AUTHOR]

The high‐voltage direct current (HVDC) power transmission short‐circuit fault protection is a big challenge, and it is the main obstacle to promote the HVDC multi‐terminal networks. A natural commutation current topology (NCCT) of hybrid HVDC circuit breaker (DCCB) integrated with limiting fault current is proposed in this paper, which shares several obvious merits, such as lower peak fault current, shorter fault isolation time and low turn‐off loss. The main contributions in this paper are made as follows. (1). A second‐order RLC circuit in novel NCCT circuit breaker is utilized as the current limiting circuit to dramatically reduce the fault current rising slope and its peak value. (2) A asynchronous NCCT circuit breaker has been investigated to broaden the proposed NCCT circuit breaker's optimal working area. (3) By taking China Zhangbei 500 kV four‐terminal DC grid as an example, an optimization design technique of the asynchronous NCCT‐DCCB is developed to demonstrate the process of the theoretical analysis and parameter design. The correctness of the proposed NCCT‐DCCB and the feasibility of the optimization design technique are confirmed by EMT simulation on PSCAD/EMTDC and hardware‐in‐loop experiment on PLECS‐RtBox. [ABSTRACT FROM AUTHOR]

The fast raising nature of DC fault currents and sensitivity of high-voltage DC (HVDC) power converters to DC faults is critical protection issues. On the other hand, DC fault current does not meet zero; which causes DC to fault current breaking process become more challenging. Specifically, to protect HVDC grids against DC fault currents, the development of very fast breakers is crucial. This study proposes a DC fault current limiter and breaker, which is able to protect the HVDC system/grid in a very fast and safe manner. The main goal of this study is to enhance the performance of already in the market hybrid DC circuit breakersincluding the magnitude of fault current and breaker operation speed. In the proposed HVDC fault current limiter and breaker, the fault current is limited in two stages by an inductive and resistive current limiter, which drastically decreases the main breaker dissipated energy. The functionality of the proposed HVDC fault current limiter and breaker is mathematically analysed, and then verified by PSCAD and Matlab/Simulink. Finally, simulation results are validated by scaled-down laboratory examinations. [ABSTRACT FROM AUTHOR]

To achieve current balance between parallel‐connected insulated gate bipolar transistors (IGBTs) of a DC microgrid hybrid circuit breaker (DC MHCB), it is a simple and effective method to add impedance in parallel‐connected IGBTs, but this will also affect the vacuum arc commutation of the DC MHCB. The focus of this paper is the effects of adding impedance on vacuum arc commutation characteristics. By constructing a simplified model of vacuum arc commutation in the case of adding impedance, the effect of adding impedance on vacuum arc commutation is theoretically derived. The test circuit of vacuum arc commutation is established, and the effect of adding impedance on vacuum arc commutation in the presence or absence of the externally applied transverse magnetic field (TMF) is investigated using the electrical measure. The theoretical formula and related formulas of the effect of adding impedance on the duration of vacuum arc commutation are obtained. A method combining adding impedance and an externally applied TMF is proposed. The constraint formula for adding impedance during vacuum arc commutation is obtained. The main factors that limit the value of adding impedance are obtained. Research on the effect of adding impedance on vacuum arc commutation characteristics can provide theoretical guidance for the application of the method of adding impedance in a DC MHCB. © 2020 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]