To promote the integration of renewable energy resources into modern energy systems, high-voltage dc (HVdc) and circuit breaker (CB) technologies have become critical to achieving secure and efficient energy transmission. This article reviews the technical development of the related areas, compares diverse breaker concepts and topologies, investigates possible coordination and testing solutions, and points out the remaining challenges as well as future needs. The time-domain simulation and comparative analysis are adopted in this article to analyze and compare the performances of different HVdc CBs. By making use of different selectivity levels of multiterminal HVdc (MTdc) grids, the suitable planning and placement of HVdc CBs can be conducted. Furthermore, by providing insights into the performance of HVdc CBs, the work presented in this article can serve as a useful asset for the upcoming standardization and industrial application process of HVdc grid and CB design and testing.

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This paper presents a non‐unit protection method for long transmission lines of multi‐terminal HVDC (MTDC) grids based on the magnitude and direction of modal voltage and current travelling waves. The method overcomes the difficulty resulting from high attenuation and distortion as reported in previous methods using fault‐generated transients for protection of long HVDC lines. The proposed method determines the faulted pole using multi‐resolution morphological gradient of the pole voltage. Then, the multiplication of multi‐resolution morphological gradient of the modal travelling waves is utilised as a criterion to discriminate between internal and external faults and non‐fault events. The criterion is a negative high value for internal faults, a negative low value for forward external faults and events, and a positive value for backward external faults and events. A four‐terminal HVDC grid with modular multilevel converters including long HVDC lines is modelled using the PSCAD/EMTDC software. The simulation study validates effectiveness of the method for detection and discrimination of high resistance faults on long lines, as well as stability against external DC and AC faults, and DC circuit breaker opening and reclosing transients. The proposed method uses a relatively low sampling frequency and local data, i.e. no requirement for a communication link.@en

In order to test protection performance of future multi-terminal HVDC grids where DC circuit breakers (DC CBs) play an important role, a DC CB model in real time test environment should be developed. It is well known that a DC CB needs to interrupt DC faults very quickly in order to avoid converter damages and to ensure security of supply. The total current interruption time consists of a fault detection time, which is needed for the DC protection to provide a trip command to the DC CB, and a DC CB interruption time. Thus, it is necessary to demonstrate the performance of associated protective devices through real time simulations, before these devices can be implemented and commissioned in practice. This paper presents a detailed modeling of the voltage source converter assisted resonant current DC circuit breaker (VARC DC CB) in real time simulation environment based on RTDS. The proposed model provides sufficient representation of the circuit breaker for system level studies. External current-voltage characteristics of the proposed VARC DC CB models replicate the ones of the device in the real world. The proposed model of the breaker is tested in a simple test circuit including a DC voltage source and a T-scheme HVDC cable. Additionally, a case study has been presented by making use of a protection algorithm in a multi-terminal HVDC grid with frequency dependent parameters of the HVDC cables to show both protection performance and current interruption.

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This paper deals with the modeling, hardware results and model validation by measurements of a VSC assisted resonant current (VARC) dc circuit breaker (CB) and the application within a future network by simulation. The newly emerging VARC dc CB can be used as a solution for the protection of offshore multi-terminal HVDC (MTDC) grids. In this paper, the proposed VARC dc CB is modeled in detail in a PSCAD environment, by taking into account dielectric strength of the vacuum gap, high-frequency current quenching ability and parasitic components. The PSCAD-model is then verified by data from the testing of a 27 kV VARC dc CB prototype with maximum current interruption capability of 10 kA. Additionally, the initial transient interruption voltage and current slope at zero-crossing during the interruption are analyzed. With respect to scaling to a higher voltage level, three types of series connected modules are presented and the performances are compared. The performance of the series connected modules is simulated in a model of a 4-terminal HVDC grid. The obtained results validate the VARC dc CB as a promising solution for the dc fault isolation in MTDC grids.

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eAssessment The application of multiterminal (MT), high-voltage dc (HVdc) (MTdc) grid technology requires test procedures for the operation and implementation of the protection solutions. The test procedures are usually derived from experience and from extensive measurement data, which, at present, are still not widely available. Based on a hardware-inthe- loop (HIL) method, advanced dc protection testing strategies, utilizing existing experience for ac grids and requirements for MTdc grids, may overcome this gap.@en