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Abstract An arc is the high‐temperature discharge plasma produced in the opening process of mechanical switches, which directly affects the breaking capability of a hybrid DC circuit breaker. According to the physical mechanism of an electric arc, the construction of an arc model for simulation analysis is an important technical means in the electrical field. In this study, based on the theory of magneto hydrodynamics (MHD), a gas mechanical switch model of a natural commutation DC circuit breaker with a compound gap is established. The arc motion process under different conditions is simulated and calculated. The influence of different initial pressures, different opening speeds, and different striking currents on the arc voltage characteristics is analysed. The results show that the larger the gas pressure, the smaller the arc volume and the higher the arc voltage. The faster the opening speed, the longer the arc and the higher the arc voltage; with the increase of the current, the arc voltage increases rapidly at a low current, while the arc voltage increases slowly at a high current.

Abstract 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 Electro‐optic electric field sensors based on LiNbO3 are widely used for the measurement of electric fields or transient voltages. However, the working bias of the sensor is influenced by the temperature due to the thermo‐optic effect of LiNbO3. An athermal electro‐optic electric field sensor was demonstrated by coating a thin layer of TiO2 film which has a negative thermo‐optic coefficient, on the common‐path interferometer based sensor to compensate LiNbO3's positive thermo‐optic coefficient. Both calculation and experimental studies were conducted. The experimental results reasonably agree well with the calculated values, and the results show the sensor coated with a 640 nm thick TiO2 film has a much smaller temperature dependence of 0.011°/°C compared to the initial value of 0.1°/°C.

Abstract The exploitation of offshore wind power has increased rapidly in recent years. To gain more wind power energy, offshore wind farms move farther from onshore. A comparison between HVAC and HVDC in terms of reliability, cost and transmission capability shows that HVDC is more suitable for long‐distance, high‐capacity bulk power transmission. However, the HVDC transmission for offshore wind power also faces great challenges because the offshore applications bring critical demands for low volume and low weight for the converters at the offshore side. On the other hand, the new topologies and conversion techniques of power electronic converters expedite many new DC transmission architectures for offshore wind power. Different HVDC architectures by using centralised voltage source converter (VSC), diode rectifier (DR), series‐connected wind turbine converters and all‐DC wind farm based on DC transformers are reviewed and compared. The advantages, challenges and development and application prospects for various DC transmission solutions are discussed.

Abstract The direct‐current circuit breaker (DCCB) is the most ideal choice for DC fault isolation in DC grids. Despite a late start, China's research and development on the DCCB have made outstanding achievements. This article provides a brief glance of current China's DCCB development status. It begins by sorting out the technical route according to the topology of DCCB. Then it systematically summarises both mechanical and hybrid DCCBs with focussing on the aspects of topology structure and principle, key technology and characteristics, prototype development and application. It is apparent that Chinese scientists and engineers confronted the worldwide problem of large capacity DC breaking, and put forward a comprehensive solution which consists of an innovative topology structure based on coupled negative voltage circuit, breaking throughs on the key technologies such as highly controllable and reliable fault current commutation, millisecond‐level ultra‐fast and efficient electromagnetic repulsion mechanism, high tolerance and high stability power electronic switch, low residual voltage and fast response energy consumption device, etc. The article states that the world's first set of hybrid high‐voltage (HV) DCCB, and the first set of mechanical HV DCCB have been developed. These DCCBs will soon be deployed to the DC grids which have the highest voltage levels therefore require the strongest breaking capacity. These achievements are leading the world in the development and application of DCCB. The article also discusses the overall development trends of DCCB in the areas of new topologies, key technological breakthroughs and application scenarios, etc. These discussions serve as references for DCCB's future technological advancement and its ever‐expanding applications.

Copper (Cu) is one of the essential microelements for all living systems. Studies have illustrated the biological significance of Cu homeostasis in human cancers, including breast cancer (BRCA). Nevertheless, the detailed roles of Cu homeostasis in BRCA need to be further explored. Here, we identified a downregulated Cu homeostasis-related gene FOXO1 and investigated the potential functions of FOXO1 in BRCA through several bioinformation databases. The BRCA patients with high level of FOXO1 displayed favorable prognostic values. Subsequently, enrichment analysis of FOXO1 coexpressed genes revealed that the top three enriched KEGG pathways were spliceosome, oxidative phosphorylation, and ribosome. Immunoinfiltration analysis indicated that aberrantly expressed FOXO1 showed positive correlations with the subcellular infiltration of macrophages and neutrophils in BRCA. Moreover, FOXO1 expression was positively associated with multiple immune checkpoints, such as sialic acid-binding immunoglobulin-like lectin 15 (SIGLEC15), indoleamine 2,3-dioxygenase 1 (IDO1), programmed cell death 1 ligand 1 (PD-L1/CD274), hepatitis A virus cellular receptor 2 (HAVCR2), programmed cell death 1 (PDCD1), cytotoxic T lymphocyte antigen 4 (CTLA4), and programmed cell death 1 ligand 2 (PDCD1LG2). Overall, these findings would deepen our understanding of FOXO1 in BRCA prognosis and immunotherapy response, representing a promising therapeutic strategy for BRCA patients.

Knee arthroplasty, including total knee arthroplasty (TKA) and unicondylar knee arthroplasty (UKA), is an effective procedure for patients with severe knee joint diseases. Arterial occlusion after knee arthroplasty is a rare but severe complication. However, there are few comprehensive reviews or analyses focusing on it. In this study, we presented a case of successful treatment of acute arterial occlusion of the popliteal artery after TKA by emergent balloon angioplasty, and conducted a review and analysis of published cases with this complication. After search and screening, 36 studies with 47 cases of arterial occlusion after knee arthroplasty in the past 35 years (1984–2018) were included. Among the 47 patients, there were 22 men and 25 women. The mean age was 68 years old. A total of 43 patients had primary TKA while 2 had revision surgery for TKA and 2 for UKA. For arterial occlusions, 66% presented symptoms in less than 1 day after knee surgery and 95% of the occlusion sites were around the popliteal artery. For treatment, 89% chose surgical treatment. Compared with conservative treatment, surgical treatment was more effective (P

High-voltage direct current circuit breakers (HVDC CB) are one of the key technologies of multi-terminal DC systems and DC grids. Different from other equipment that use a large number of power electronic devices, the HVDC CB cannot obtain its power from the primary system at high potential, making the power supply of the complex multiple electrical potential equipment in HVDC CB a challenge. In this study, the authors propose an HV isolated power supply system based on the multi-output high-frequency isolated power supply unit and the cascaded isolation transformer network. This power supply system can support the 500 kV CB to turn-off 25 kA current with 800 kV overvoltage.

This study proposes a novel multiple modular dc transformer (MMDCT) scheme for flexible high-voltage dc (HVDC) application. The MMDCT is composed of n consistent modular dual-active-bridge converters (MDABs), and every MDAB can work independently. The MDABs are series connected and also connects to the HVDC bus. The multiple distributed design decreases the manufacturing difficulty in high-frequency transformer and its installation. Besides, modular discrete design decreases commissioning difficulty of system in practice and also increases reliability and fault-treatment ability. Moreover, the MMDCT still has good soft-switching performance and low operation current for switches. The MMDCT is a practical scheme for HVDC application, and it will be welcomed by engineers.

Electromagnetic environment (EME) is one of the key issues during the ultra-high voltage direct current power transmission projects. There are many factors affecting the parameters of the EME, which are mainly divided into line structure parameters and meteorological parameters. In this study, the concept of variable selection is used to analyse the influence of different factors on the EME parameters and to determine the factors which have greater influence. By comparing the advantages and disadvantages of the subset selection method and the compression estimation method, the more reliable results are determined. Then physical model and linear fitting method are used to analyse the influential factors of corona loss, audible noise, and radio interference.

With the increase of the load of the switchgear, the overheating of the switchgear is more and more serious. In this article, the authors give the primary heat sources in the electrical equipment. According to these sources, they explore the reason of why the switchgear can be overheated during operation. Then, they build a 3D model in the Comsol & Multiphysics® and analyse the temperature state of the switchgear from the simulation. They also carry out temperature test on KYN28 switchgear to summarise the laws of the temperature change of the switchgear. Finally, they propose a brief method to monitor the temperature and realise the function of temperature warning to avoid accidents caused by overheating.

Corona loss is one of the electromagnetic environment parameters of high-voltage direct current (HVDC) transmission lines. So far many countries have carried out researches and measurements on it. In 2008, UHVDC test lines were established in the National Engineering Laboratory for UHV Technology (Kunming) at the altitude about 2100 m. The results in this study are based on the measurement data at the Kunming Experimental Base. The study mainly introduces the influence of the minimum conductor-to-ground height, bundle distance and pole spacing on the corona loss.

Fault current limiter (FCL) is an effective technique for the fault isolation and protection in the direct current (DC) grid. In this study, a magnetic saturation-type FCL is designed and tested. Firstly, its basic principle is introduced. Compared with the traditional saturable reactor-type FCL, it has advantages of simple structure, small size, and better economy. Then design procedure of the magnetic saturation-type FCL is described, which includes selection of the ferromagnetic materials and determination of parameters of the iron core. After that, a set of principle prototype is designed, and the experiment and simulation are carried out to verify the current limiting ability of the magnetic saturation-type FCL. Results show that the magnetic saturation-type FCL can effectively limit the fault current from 110 to 40 A. What is more, the new magnetic saturation-type FCL can be extended from changing the size of a single core and the distributed arrangement for large-capacity applications.

With the development of high-voltage direct-current (HVDC) transmission projects, the issue of electromagnetic compatibility has become more and more severe, especially the synthetic ion flow electric field. The DC electric field is inseparable from the equipment insulation, the safety of the system operation, and effects on organisms nearby. The measurement of the synthetic electric field of ion flow has been a major difficulty due to the influence of ion currents and distorted field. A differential electric field sensor for measuring the synthetic electric field is proposed. The calibration method and the experimental device for the measurement of the air synthetic electric field of ion flow are presented. Calibration experiments show that the calibration method is practical and effective, and the test result from the sensor is in good agreement with the theoretical value. The experiments in the library show the validity of the calibration method and the excellent performance of the sensor.

Transient processes at neutral bus of ultra-high value direct current (UHVDC) converter station received insufficient attention, because of the lower amplitude compare to poles. However due to the lower insulation level, electromagnetic transient processes at neutral bus may cause serious fault, and become an important issue that should be studied carefully in the design stage. A method to analyse the electromagnetic transient based on time-domain wide-band circuit simulation is proposed in this study. Models of major equipment are described. The electromagnetic transient of a ±800 kV converter station is calculated. The transient under different operation statuses is compared. Effects of suppression method such as arresters and capacitors are analysed.

The extracellular microvesicles (MVs) are attracting much attention because they are found to be the key paracrine mediator participating in tissue regeneration. Dexamethasone (DXM) is widely accepted as an important regulator in tailoring the differentiation potential of mesenchymal stem cells (MSCs). However, the effect of DXM on the paracrine signaling of MSCs remains unknown. To this point, we aimed to explore the role of DXM in regulating the paracrine activity of MSCs through evaluating the release and function of MSC-MVs, based on their physicochemical characteristics and support on osteogenic response. Results showed that DXM had no evident impact on the release of MSC-MVs but played a pivotal role in regulating the function of MSC-MVs. MVs obtained from the DXM-stimulated MSCs (DXM-MVs) increased MC3T3 cell proliferation and migration and upregulated Runt-related transcription factor 2 (Runx2), alkaline phosphatase (ALP), and osteopontin (OPN) expression. The repair efficiency of DXM-MVs for femur defects was further investigated in an established rat model. It was found that DXM-MVs accelerated the healing process of bone formation in the defect area. Thus, we conclude that using DXM as stimuli to obtain functional MSCs-MVs could become a valuable tool for promoting bone regeneration.

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.