Review of Protection Coordination Technologies in DC Distribution Systems

With the evolution of power electronics technologies, DC networks have been considered as promising distribution systems for future grids. This new concept of power systems comes with technical challenges in protection coordination, a result of the no natural current zero- crossing point and very low thermal capacity of semiconductors in power converters. In order to overcome this technological barrier, many researches have been conducted. This paper presents a summary of the state-of-the-art on protection coordination technologies in DC distribution systems considering whole DC protection procedure: fault detection, fault localization, fault isolation and backup protection. In addition, two different protection schemes for low-voltage DC (LVDC) shipboard power systems (SPS) which are commercially viable measures are described

Deexcitation Characterization for Power Supply Protection in DC Shipboard Power Systems

The deexcitation of a synchronous machine has been used for the protection of the power supply based on a diode rectifier in marine dc power distribution networks. The fault current from the generator can be eliminated with the protection method utilizing the deexcitation. This allows for removing generator circuit breakers. In this method, the rectifier should be designed to manage the peak fault current and energy limited by the deexcitation. Hence, this paper presents the fault current characteristics with the generator deexcitation by analytical and experimental approaches. The fault behaviours under the deexcitation are theoretically described and the rectifier sizing is discussed for the peak fault current and the overloading capability of the diodes. The deexcitation characteristics are calculated by the analytical expression and investigated in a test setup for different subtransient reactance, fault resistance, exciter response, and time delay

Hard X-ray free-electron laser with femtosecond-scale timing jitter

The hard X-ray free-electron laser at the Pohang Accelerator Laboratory (PAL-XFEL) in the Republic of Korea achieved saturation of a 0.144 nm free-electron laser beam on 27 November 2016, making it the third hard X-ray free-electron laser in the world, following the demonstrations of the Linac Coherent Light Source (LCLS) and the SPring-8 Angstrom Compact Free Electron Laser (SACLA). The use of electron-beam-based alignment incorporating undulator radiation spectrum analysis has allowed reliable operation of PAL-XFEL with unprecedented temporal stability and dispersion-free orbits. In particular, a timing jitter of just 20 fs for the free-electron laser photon beam is consistently achieved due to the use of a state-of-the-art design of the electron linear accelerator and electron-beam-based alignment. The low timing jitter of the electron beam makes it possible to observe Bi(111) phonon dynamics without the need for timing-jitter correction, indicating that PAL-XFEL will be an extremely useful tool for hard X-ray time-resolved experiments.1143Nsciescopu