In a deregulated power system, many distributed generations and power storages will be introduced. This article shows technical trends around power system analysis and summarizes roles of this technique in manufacturers. Then, some topics on today’s power system analysis are represented, including synchronous /induction generator modeling, Microgrid’s application and surge analysis of distributed generators.
Mesospheric optical phenomena(including sprites) are becoming an interesting subject from the standpoint of atmosphere-ionosphere coupling. This paper deals with our observation of sprites associated with winter thunderstorms in the Hokuriku area and we show the characteristics of those sprites and their parent lightning discharges. Although the scale of Japanese lightning in winter is very small as compared with the MCS (Mesoscale Convective System) for the summer continental lightning, the essential quantities (polarity, charge transfer etc.) are found to be nearly the same as those for those MCS. However, there might be required an additional factor, such as the self-organization of the lightning.
An open-cycle ocean thermal energy conversion (OC-OTEC) system is one of energy conversion methods to generate electricity from ocean thermal energy. For OC-OTEC system, steam evaporated from the surface seawater due to flash evaporation drives the turbine. At that time, dissolved gas such as air is introduced into the low-pressure system (OC-OTEC system) as the non-condensable gas, which degrades the performance of condensation heat transfer. In this paper, a small scale OC-OTEC experimental unit experimentally investigates the effect of non-condensable gas on the heat transfer performance in a condenser. The experimental results are discussed in comparison with theoretical estimation by Sparrow-Lin method. It is shown that the condensation is occupied by heat and mass transfer near a condensation surface and that the condensation efficiency is affected by exhaust quantity of non-condensable gas at relative high concentration ratio of condensable gas.
A fault current limiter (FCL) is extensively needed to suppress fault current, particularly required for trunk power systems connecting high-voltage transmission lines, such as 500kV class power system which constitutes the nucleus of the electric power system. We proposed a new type FCL system (rectifier type FCL), consisting of solid-state diodes, DC reactor and bypass AC reactor, and demonstrated the excellent performances of this FCL by developing the small 6.6kV and 66kV model. It is important to detect the failure of power devices used in the rectifier under the normal operating condition, for keeping the excellent reliability of the power system. In this paper, we have proposed a new failure detecting method of power devices most suitable for the rectifier type FCL. This failure detecting system is simple and compact. We have adapted the proposed system to the 66kV prototype single-phase model and successfully demonstrated to detect the failure of power devices.
Because of the lower insulation level than is for transmission line, in this study on lightning protection design of distribution line, not only direct lightning strokes but also induced voltages caused by nearby strokes must be taken into account. So it is necessary to grasp the frequency of occurrence on lightning phenomena around distribution lines. For this aim, lightning phenomena on TEPCO’s distribution lines in use had been continuously observed for 6 years (1996-2001). Through this observation, new interesting statistical data, that can be useful basis for rationalization of lightning protection design of distribution lines was obtained. 204 lightning was observed through six years observation in all. Probability of occurrence of direct stroke was 22% (45 data of direct stroke was obtained). The fact that in 47% case of direct stroke the electric outage didn’t occur is very interesting. Moreover, the value of surge discharge current of arrester in case of nearby stroke is basis for conventional theory of grounding system. Therefore statistical analysis of ZnO discharging current in case of nearby strokes was carried out. As a result, in case of nearby strokes, 5% value of cumulative frequency of discharging current is 0.5kA. This value is half of conventional data.
To develop large-sized lithium-ion secondary batteries for electric vehicles etc., it is necessary to take temperature and current distributions in the batteries into consideration. To make clear these distributions, the authors develop a two-dimensional time-dependent simulation code of temperature and current distributions during discharge cycles in cylindrical lithium-ion secondary batteries. The code is handy but sufficiently accurate because it uses the simple heat generation model recently established by the authors. Numerical simulations are, at first, performed for a commercially available small-sized battery, and accuracy of the code is confirmed through the comparison between the calculation results and the corresponding experimental results. Calculations are also performed for a large-sized battery and it is made clear that the temperature and current distributions become fairly inhomogeneous, indicating the necessity of the developed code.
Optimization of urban energy systems in a small urban area can reduce CO2 emission from the specific area. However, large-scale introduction of these locally optimized energy systems in a wider region may not necessarily reduce CO2 emission from the whole region. This is because optimization in a small area depends on CO2 emission per unit of commercial electricity that is determined by an assumed generation mix of commercial power. If these locally optimized energy systems are introduced on large scale, the optimal generation mix would be modified. This paper investigates the relation between the scale of locally optimized energy systems in a region and the CO2 emission from the region. The analysis is performed by developing an integrated model that consists of two separate optimization models, i.e., one is for energy systems in a small area and the other is for determining an optimal generation mix. The developed model is applied to Kansai region of Japan. The results show that large-scale introduction of locally optimized energy systems can generally reduce CO2 emission from the whole region.
The increased renewable energy utilization, especially photovoltaic panels using solar energy or wind turbine generators (WTGs) using wind energy, has been expected in recent years from view point of CO2 gas emission reduction and environmental conservation. However, the generated power is always fluctuating because the WTGs are driven by fluctuating wind. Therefore, an energy storage system should be installed to compensate these fluctuating elements. The energy capacitor system (ECS) which combined the electric double-layer capacitor (EDLC) and the electronic circuits are now under development. In this paper, control system configuration for active and reactive output power simultaneous control and the bi-directional inverter using current source EDLC are proposed. Moreover, we discusse control methods required in generating-power leveling for WTGs, and show the effectiveness of the proposed system through simulations.
The magnetohydrodynamic flow in a liquid metal MHD generator is investigated with two-dimensional numerical simulation, where the induced magnetic field is considered. Numerical results indicate that the power output becomes the highest at the loading parameter of 0.64, which is higher than the loading parameter of 0.5 giving the highest power output in the theoretical analysis without the induced magnetic field. This results from the strong negative induced magnetic field with the low loading parameter. It is shown that the eddy current exists in the upstream and downstream region of the generator channel. And the induced magnetic flux density is the strongest at the center of the eddy current. This is because x-direction electric field is generated near the upstream and downstream edge of the electrodes. It is observed that the distributions of the x-direction velocity become M-shaped in the generator channel. In the downstream region, the M-shaped Hartmann velocity profile is developed with the high loading parameter. With the low loading parameter, on the contrary, the velocity in the main flow is higher than that near the wall.
This paper proposes the high-speed reclosing operating method to improve for the stability in the power system. The reclosing time by proposed method is computed from the energy function (the kinetic energy) on the basis of the case where reclosing is not carried out. The effectiveness of the proposed method was confirmed using Power System Analyzer (PSA).