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High-voltage direct current (HVDC) circuit breaker development and deployment strongly depend on the testing process, which ensures that the HVDC circuit breakers will satisfy design requirements. This article presents an HVDC circuit breaker test bench circuit configuration that can provide controllable large output currents to simulate different fault conditions for the current breaking test and high output voltage for the dielectric withstand test. The current breaking test circuit is based on multiple cascaded power converters connected in parallel to provide the necessary output current capability. Each cascaded power converter is composed of multiple cells that are operated by a phase-shifted pulsewidth-modulated signal for greater controllability and higher quality of the output waveform. The dielectric withstand test circuit is a simple high-voltage source with a low power rating that can also be used to charge the test bench and the internal circuitry of the circuit breaker that is to be tested. The proposed test bench ensures that fault conditions can be replicated accurately and offers greater flexibility by being able to test mechanical, semiconductor-based, or hybrid HVDC circuit breakers with different current and voltage ratings on the same hardware without any changes. The idea and the operating principle of the proposed test bench are verified experimentally on a downscaled system that consists of three cascaded power converters connected in parallel with three cells per cascaded power converter and with a total equivalent switching frequency of 92.5 kHz. [ABSTRACT FROM AUTHOR]

To improve the reliability of power supply, reclosing schemes are required after transient faults, which commonly occur in overhead line based high voltage DC (HVDC) systems. However, in the event of permanent faults, the auto-reclosing scheme may cause a severe strike. To avoid the severe impacts caused by permanent faults, the fault type should be discriminated before activating the reclosing scheme. Therefore, an adaptive reclosing scheme based on phase characteristics is proposed in this paper. Firstly, the modulation of a periodic voltage by actively controlling the hybrid DC circuit breaker (DCCB) is introduced. Then, a cascaded π equivalent model and its decoupling algorithm are presented to analyze the frequency-domain characteristics of the measured impedance of the coupled overhead lines. From the frequency-domain characteristics, the frequency of the periodic detecting voltage is determined to analyze the phase features of the measured impedance at primary frequency. The permanent or transient faults can thus be accurately identified by using these different phase characteristics, with negligible influence on the healthy lines. In addition, the proposed scheme is robust to various fault resistances, leading to improved reliability. The effectiveness of the proposed scheme is verified in PSCAD/EMTDC. [ABSTRACT FROM AUTHOR]

Given the current evolution of Voltage Source Converters (VSC), Multi-Terminal High Voltage Direct Current (MTDC) grids are now becoming a real possibility. Still, some technical issues have to be addressed. The protection of High Voltage Direct Current (HVDC) grids is the main technical challenge that is slowing down the development of MTDC grids. Hence, this paper focuses on protection systems. Thus, protection devices, fault-clearing strategies and protection system requirements are considered. The main topic of this paper is the review of different types of protection methods for MTDC systems that are shown in the literature. They can be classified depending on the use of local measurements or a communication channel in their operation. The protection systems reviewed in this paper include protection systems based on current measurements, voltage measurement, traveling wave analysis and artificial intelligence. A protection system can employ only one of these methods or a combination of them. Finally, the main characteristics of the reviewed protection algorithms are compared, highlighting the system configuration, the converter technology, the adopted fault-clearing strategy, the implemented circuit breakers and the size of the limiting inductors. From the work presented in this paper, it is concluded that the actual tendency in MTDC protection systems is predominantly full-selective fault-clearing strategies combined with hybrid HVDC circuit breakers in series with limiting inductors. In addition, most protection methods are based on current measurement algorithms and a considerably high number of the reviewed protection systems employ a combination of several methods benefiting from their combined characteristics. • Review of protection systems for multi-terminal HVDC grids. • Classification into local-measurement-based and communication-based methods. • Current-based methods are more usually employed than voltage-based methods. • Combination of half-bridge MMCs and hybrid circuit breakers is predominant. • The preferred system configuration varies between symmetric-monopole and bipole. [ABSTRACT FROM AUTHOR]