As power semiconductor devices are the key components of hybrid DC circuit breakers (HCBs), how to select suitable devices is critical for the whole HCB design. First, this paper compared the general characteristics of press pack insulated gate bipolar transistor (IGBT), injection-enhanced gate transistor (IEGT), and integrated gate commutated thyristor (IGCT). Then working conditions of devices were analyzed from the perspective of HCBs. According to these, vital features of devices including maximum turn-off current, on-state voltage, conduction ability, and robustness of power semiconductor devices were carefully analyzed and compared. Related experiments were implemented to compare maximum turn-off capability, and the 4.5 kV/3 kA IGBT/IEGT was able to turn off 19 and 22 kA respectively after 5-ms current conduction. Analysis and experiments indicated that IGCT was suitable for natural commutation low-voltage and low-current hybrid circuit breakers, due to its low on-state voltage and huge surge current conduction ability. Comparatively, IGBT and IEGT were more suitable for very high current interruption, and IEGT was the superior selection among available commercial devices. However, the interference should be considered in applications.

High-voltage dc (HVdc) circuit breakers (CBs) are a key technology of multiterminal dc (MTdc) systems and grids. In this article, a state-of-the-art 500-kV hybrid CB (HCB) topology is proposed and compared with other existing HCB solutions. Implementing the topology includes three important components: a modular designed high-current bidirectional solid-state switch (SS), an ultrafast mechanical switch (MS) based on a Thomson (CCDC) equipment with no conduction loss, whose corresponding functional verification test results have been presented in detail. On this basis, the overall 500-kV HCB and a comprehensive experimental platform are developed. Detailed experiments, including 25-kA turn-off and reclosing experiments, are conducted. The HCB was found to be capable of breaking a 25-kA current in 2.7 ms with 800-kV overvoltage, which is on par with the level of leading CBs worldwide.

The oxygen redox (OR) activity is conventionally considered detrimental to the stability and kinetics of batteries. However, OR reactions are often confused by irreversible oxygen oxidation. Here, based on high-efficiency mapping of resonant inelastic x-ray scattering of both the transition metal and oxygen, we distinguish the lattice OR in Na_0.6[Li_0.2Mn_0.8]O₂ and compare it with Na_2/3[Mg_1/3Mn_2/3]O₂. Both systems display strong lattice OR activities but with distinct electrochemical stability. The comparison shows that the substantial capacity drop in Na_0.6[Li_0.2Mn_0.8]O₂ stems from non-lattice oxygen oxidations, and its voltage decay from an increasing Mn redox contribution upon cycling, contrasting those in Na_2/3[Mg_1/3Mn_2/3]O₂. We conclude that lattice OR is not the ringleader of the stability issue. Instead, irreversible oxygen oxidation and the changing cationic reactions lead to the capacity and voltage fade. We argue that lattice OR and other oxygen activities should/could be studied and treated separately to achieve viable OR-based electrodes.

Different from the continuous-switching behavior of series power electronic devices in converters, the single-switching attribute of DC breakers (DCBs) provide opportunities to integrate metal oxide varistors (MOVs), balancing circuits and series power power devices. This paper proposes a modular design methodology based on discrete MOVs of DC breaker (DCB) with series power electronic devices. The modular DCB (MDCB) topology and voltage balance issues, the steep front effect and solution, and the design method are proposed and analyzed in this study. Compared with the traditional DCB, the MDCB has self-balancing ability, thereby removing the voltage-balancing circuit and reducing the series module amount. The standard designed cell can be operated as an independent DCB or compose a high-voltage DCB in series flexibly, which decreases the difficulty of design and commission. Finally, a series experimental platform based on IGCT, IGBT, and IEGT is built to verify the correctness and effectiveness of the proposed design methodology.

Lightning and lightning induced effects have significant influence on many aspects affecting the public, which makes the research of lightning and lightning protection very important. However, due to the strong randomness and complex discharge mechanisms of lightning, the understanding of lightning is still far from satisfactory. On the basis of the International Conference on Lightning Protection 2014, this study gives a review of recent progress on lightning and lightning protection research covering the following aspects: lightning locating and observation, lightning physics, lightning electromagnetic transients, and lightning protection for various systems. The goals of this study are to give readers an overall introduction to the recent progress in lightning and lightning protection research, and to motivate them to conduct further studies to address the unsolved problems in lightning‐related research.