Railway signalling systems have made remarkable progress in recent years. For example, their components have increasingly become compact and multi-functional due to the adoption of microcomputers and other electronic devices. However, circuit burnout, system failure and other types of lightning damage frequently occur in signalling systems because the electronic devices are easily damaged by lightning surges. Effective and economical lightning protection measures are therefore necessary for railway signalling systems because suspended operation or train delays due to lightning damage may cause social disruption. This article overviews countermeasure against lightning damages at the present condition, its characteristics, and approach to study on lightning protection measures for railway signalling systems.
This paper proposes a new method to estimate accurately modal damping of a weakly damped electromechanical oscillation in power systems. The proposed method is based on a whitening filter (FIR filter) to estimate modal damping from system response and a regression model to express the relation between the modal damping and system state variables such as active and reactive power outputs of generators. The feature of the method is that an optimal order of the whitening filter is determined so as to minimize the error of the linear regression model. The simulation study by using the IEEJ EAST 10 machine model shows that the proposed method is effective for accurate estimation of weakly damped oscillation mode.
This paper presents applying multi-objective optimization methods to network expansion planning. The distribution network expansion planning minimizes system cost and distribution loss while satisfying the constraints. Problem formulation results in combinatorial optimization problems that are difficult to solve due to complexity. This research applies a genetic algorithm, which is a meta-heuristics method. The present study proposes a new method of multi-objective optimization methods; NSGA-II and SPEA2 are assumed to be the best method now. The proposed method introduces the concept of a linkage identification genetic algorithm, enabling more efficient searching than methods hitherto known. In the past, most research that's network expansion planning didn't include load curve. This research demonstrated that the research has to include load curve. Also it proposed new method that's how to search including load curve for the research.
Photovoltaic power plants and wind turbines are eco-friendly power generators that utilize solar energy and wind energy, respectively. Many large-scale photovoltaic power plants have been constructed using government subsidies. Large-scale photovoltaic power plants are usually constructed in large open spaces that contain some tall structures. Therefore, such large-scale photovoltaic power plants are likely to attract lightning, which may result in the malfunction or breakdown of the electrical and electronic equipment. In this study, overvoltages generated when a lightning strikes a structure anchoring photovoltaic panels are measured using a 1 : 10 scale model. Additionally, the measurements have been verified using the FDTD (finite-difference time-domain) method. The mechanisms of the overvoltage generations on an actual-scale photovoltaic power plant have also been clarified.
Operators of navigation beacons have been searching for self-contained energy sources, as it is difficult to supply buoys in the ocean from the commercial power net. Solar, wind and wave-powered renewable energy mechanisms have been developed for navigation buoys. The advantage of tidal currents over other renewable energy sources is they are independent of the weather, so the available power can be calculated. In this paper, a Darrieus-type water turbine using the energy in the local tidal current was developed as energy conversion device for powering a navigation buoy, and the characteristics of the water turbine were observed in a water channel experiment. The energy converter of the electric power generation system was installed in a buoy in a pilot project in the Akashi Strait in Japan. As the result, the changes in generated electric power with current speed were observed. Sufficient energy was obtained from the tidal currents to operate this navigation buoy.
The authors evaluate the sparkover rate of a medium-voltage line associated with direct strokes to the line by using peak currents obtained at southern Kyusyu by the JLDN (Japan Lightning Detection Network). In the evaluation, the correlation between the front duration and the peak currents is taken into account as well as the low-voltage line often installed below. As the result, the estimated sparkover rate for a flash is in reasonable agreement with the reported rate.
In this paper, the authors propose a new identification method of the magnetizing inrush current phenomena. In general, the saturations of cores are overlapping. Then, the inrush current waveforms become two equivalent single transformer inrush currents. Moreover, the two inrush currents have the same polarity and the phase of first current is lead to the second current about (2π/3). Therefore, the authors introduce the identification method using with saturation overlap pattern. In this method, since the exact saturation on/off time is unused, the voltage measurements are not needed.