The three separate JEC standards have been applied to switchgear: JEC-2300 (for AC circuit breakers), JEC-2310 (for AC disconnectors) and JEC-2350 (for gas-insulated switchgear). There are differences in the details of these standards, and these differences have caused problems in areas such as uniformity among electric power station systems, and consistency with IEC standards. This overview describes the background and main points of discussion leading to the enactment of JEC-2390. JEC-2390 includes the common requirements for high-voltage switchgear and cotrolgear based on IEC 62271-1. In future, there will be a need for ongoing study of IEC provisions that were passed over for inclusion in JEC-2390.

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This paper describes a method for predicts future behavior of generating power of photovoltaic power generation apparatus, PV for short, using time-series datamining technique. Introducing the renewable energy apparatus, such as PV, and then operating pieces of apparatus by renewable power are essential for reducing the total emission of carbon dioxide. The point here is harmonization among the whole pieces of apparatus, we thus are necessary making a plan to share the limited PV power. The generating power of PV varies depending on meteorological factors, which means the optimized harmonization plan must be dynamically changed in accordance with the generated power. For this reason, we need a method to predict the future generation power of PV in making a plan. In this paper, we develop a prediction method based on a combination of clustering, decision tree learning and dynamic time warping. The utilization data is time series from five sensors that are the temperature, the atmospheric pressure, humidity, the velocity of the wind, and the solar radiation. The output of the system as prediction is a sequence of daily generating power of PV at intervals of five minutes. We carry out to install and experiment with a PV of 25 [m²] and several sensors on a detached house. As a result of comparing measurements to prediction values, the mean absolute error per day is 0.34 [kW].

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Power output fluctuation of high penetration renewable energy such as photovoltaic power generation (PV) may cause negative impact on electric power systems. Accordingly, quantitative analysis of the fluctuation characteristics in consideration of smoothing effect of solar radiation intensity is necessary to accurately evaluate the negative impact. Based on this background, first, we propose a method for a systematic analysis of the power output fluctuation characteristics over various weather conditions by using long-term measurement data. We classify the daily weather into three categories based on the proposed method by using solar radiation intensity data obtained from pyranometers installed in Sakai Solar Power Plant for one year from January to December 2012. Secondly, we propose a method to quantitatively analyze the impact of PV distribution on the smoothing effect, and we quantitatively analyze the smoothing effect in each category of the daily weather by using power output data sampled from power conditioning subsystems (PCS) concurrently observed with the pyranometer data. Our results demonstrate strong dependency of the smoothing effect to the weather conditions and the PV distribution.

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Recently, in the distribution network, the rated capacities of the special loads that have the large starting currents are becoming bigger. So, the technical pre-studies for power quality are very important to suppress voltage troubles. In this study, as a special load, we consider the case that a large low-frequency induction furnace is connected to near the end of distribution network. The rated output is 800kW, and the rated capacity of the electric furnace transformer is 1000kVA. The inrush current generates during startup of the low-frequency induction furnace. By measurement of power quality, it is revealed that the inrush currents consist of the “magnetizing inrush current due to magnetic saturation of the electric furnace transformer” and the “inrush current due to the power factor correction capacitors”. We clarify the influence of the inrush currents on the voltage dip. And the effective measure (resistor insertion method) to reduce the inrush currents is proposed. We performed the EMTP simulation for the optimization of proposed method. As a result, it was verified that the analysis value and the measured value are in good agreement.

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This paper proposes a coordinated control method for battery energy storage systems (BESSs) and load-ratio control transformer (LRT) to control the voltage of a middle-voltage 6.6-kV photovoltaic (PV)-supplied microgrid (MG). Each local BESS minimizes the active power flow through the feeder bus where it is installed. A central BESS minimizes the power flow from the utility to the MG through the interconnection point where it is installed, which in turn limits the load bus voltages in the MG, such as those supplied by PV systems and the utility. This paper proposes a central BESS structure which can act as a distribution static compensator when its batteries are fully charged or fully discharged. MGs with loop and radial structures are studied to evaluate the effectiveness of the proposed method. MATLAB/Simulink is used to simulate an MG model using actual PV data and residential loads from Ota City, Japan. Experiments are carried out on ANSWER (Active Network System with Energy Resources) to demonstrate the proposed control method.

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Massive variable renewable integration will serve as an important measure to address energy and environmental issues, while its extensive installation would place a technical challenge in power grid management for controlling its intermittency. Among various treatment measures for the variable renewables, hydrogen storage system is one of technical candidates besides rechargeable battery, suppression control and back-up generator. For practically positioning it in power system, the development of an energy model is a key procedure to quantify and qualitatively understand the potential benefits of hydrogen storage system for variable renewables. The authors assess the potential for hydrogen storage of variable renewables in Hokkaido region of Japan with abundant wind resources by employing a high time-resolution optimal power generation mix model. The main feature of the developed model is that considered time-resolution is 10-min through a year, allowing us to investigate the impact of various short-cycle renewable variation on the deployment of hydrogen storage system in a detailed manner. Simulation results potentially suggest that CO₂ regulation encourages the installation of hydrogen storage for variable renewable if its cost reduction is fully realized, and the results reveal as well that hydrogen is suitable energy carrier for long-term storage of wind power output.

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[in Japanese]

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