다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

HVDC systems are playing an increasingly significant role in energy transmission due to their technical and economic superiority over HVAC systems for long distance transmission. HVDC is preferable beyond 300–800 km for overhead point-to-point transmission projects and for the cable based interconnection or the grid integration of remote offshore wind farms beyond 50–100 km. Several HVDC review papers exist in literature but often focus on specific geographic locations or system components. In contrast, this paper presents a detailed, up-to-date, analysis and assessment of HVDC transmission systems on a global scale, targeting expert and general audience alike. The paper covers the following aspects: technical and economic comparison of HVAC and HVDC systems; investigation of international HVDC market size, conditions, geographic sparsity of the technology adoption, as well as the main suppliers landscape; and high-level comparisons and analysis of HVDC system components such as Voltage Source Converters (VSCs) and Line Commutated Converters (LCCs), etc. The presented analysis are supported by practical case studies from existing projects in an effort to reveal the complex technical and economic considerations, factors and rationale involved in the evaluation and selection of transmission system technology for a given project. The contemporary operational challenges such as the ownership of Multi-Terminal DC (MTDC) networks are also discussed. Subsequently, the required development factors, both technically and regulatory, for proper MTDC networks operation are highlighted, including a future outlook of different HVDC system components. Collectively, the role of HVDC transmission in achieving national renewable energy targets in light of the Paris agreement commitments is highlighted with relevant examples of potential HVDC corridors.

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HVDC Transmission: Technology Review, Market Trends and Future Outlook

The use of direct current (dc) power networks, either at high voltage or at medium voltage, is being increasingly seen in modern smart grids. This is due to the flexible control possible with dc and its ability to transmit and distribute power under circumstances where alternating current (ac) networks are either unable to, or less economic. This paper provides an overview of the evolution of high-voltage dc (HVDC) transmission from early Thury systems, to modern ultrahigh-voltage dc and multiterminal voltage–source converter systems. The operation of both current–source and voltage–source systems is discussed, along with modeling requirements. The paper provides a snapshot of the state of the art of HVDC with copious references to enable in-depth reading. Key developments over the last 20 years are highlighted. Issues surrounding multiterminal operation and dc protection are explained, along with drivers in economics and policy. This will inform HVDC integration into smart grids.

HVDC Systems in Smart Grids

Aircraft electrification is currently the best alternative to address the rising demand for more air transportation and deal with anticipated economic and environmental impacts. Although the all-electric-aircraft (AEA) concept is not yet a feasible solution, the more-electric aircraft (MEA) is gaining significant attention. Electrical systems either partially or entirely replace the large and inefficient hydraulic, pneumatic, and mechanical conventional aircraft actuating systems. The upgrade could also encompass the propulsion system, as in hybrid- and turbo-electric aircraft. This upgrade reduces the aircraft weight, reduces the usage of pollutant fluids, increases fuel efficiency, reduces carbon emissions, and increases aircraft controllability and reliability. This article reviews various application areas of electric machines in electrified aircraft, such as actuation, taxiing, propulsion, and generation. Moreover, it reviews the main types of currently/to be utilized electric machines and the critically required specifications. Finally, a comparison between the different considered machines and potential future research is discussed.

Review of Electric Machines in More-/Hybrid-/Turbo-Electric Aircraft

Medium voltage direct current (MVDC) distribution networks have been considered for various applications, such as offshore wind farm collector systems, all-electric naval vessels, and aircraft. MVDC circuit breakers are a critical technology to directly manage faults in multi-terminal DC (MTDC) networks. However, DC current breaking is much more challenging than in AC systems because there is no natural zero-crossing of the current waveform to aid fault isolation. This paper reviews existing MVDC circuit breaker technologies and also discusses their advantages and disadvantages. This paper also introduces new topologies that can be applied in MVDC applications. The operation of several hybrid DC circuit breaker topologies with aided commutation is included. The paper illustrates that a hybrid DC circuit breaker with aided commutation can clear a fault within 2–5 msecs with low losses, this shows great potential for future MVDC applications. The implications for the practical design of commercial MVDC circuit breakers are also discussed.

A review of technologies for MVDC circuit breakers

HVDC circuit breakers are of increasing importance, as multi-terminal high voltage DC (HVDC) transmission becomes a commercial reality. Multiple HVDC breaker technologies have been developed, and are starting to appear as proof-of-concept installations on real networks. Information about them is however distributed widely in the literature. This article describes the underlying challenges, the leading candidate solutions, and discusses the requirements and construction of the component sub-assemblies. Its goal is to provide a comprehensive overview of the field.

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HVDC Circuit Breakers–A Review

Superconducting fault current limiters for HVDC systems

Direct current (DC) circuit breakers are a key enabling technology for fault management in multiterminal high-voltage DC (HVDC) systems DC fault isolation is challenging due to the high rate of rise of the fault current and the lack of natural current zero-crossings found in ac systems In this paper, we present a novel superconducting hybrid dc circuit breaker that utilizes the intrinsic characteristics of the superconductor material The automatic quench of the superconductor coil as a result of a high fault current transfers the current from the mechanical switch to the semiconductor switch The isolating mechanical switch is able therefore to open at low current and recover its dielectric capability rapidly A low voltage DC circuit breaker prototype has been built using a multistrand magnesium diboride (MgB2) coil, a vacuum interrupter, and an insulated-gate bipolar transistor module This prototype successfully demonstrated interruption of 500 A DC within 44 ms This paper presents the design of the superconducting hybrid breaker prototype and a detailed analysis of the experimental results This superconducting hybrid dc circuit breaker has significant potential for scaling up the high-voltage and high-current applications

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Xiaoze Pei

Papers

A review of technologies for MVDC circuit breakers

HVDC Circuit Breakers–A Review

Superconducting fault current limiters for HVDC systems

Design and Experimental Tests of a Superconducting Hybrid DC Circuit Breaker

Design and test of a new two-stage control scheme for SMES-battery hybrid energy storage systems for microgrid applications