The Great East Japan Earthquake drastically changed Japanese energy management scheme in Japanese electrical grid. Stopped nuclear power plants caused a rise of the electricity costs. Demand side energy management scheme such as demand response is newly needed to reduce the peak of electric power demand by using HEMS (Home Energy Management System) and BEMS (Building Energy Management System). This paper describes Japanese trend of energy management based on demand response and international standardization of communications protocol and indicate the future issues and vision.

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The widespread installation of distributed generations (DGs) is crucial for making optimal utilization of renewable energy. However, distribution networks face voltage variation problems if numerous DGs are connected. The roof-top photovoltaic systems among distributed generators are connected to low-voltage distribution networks via service drop wires. Consequently, voltage-rise at low-voltage wires and service drop wires are significant because those wires have higher impedances than medium voltage wires. This paper proposes a methodology to analyse the maximum installable capacity of DGs for medium and low voltage distribution networks. In particular, customer-side voltage constraints in the Electricity Business Act can be applied to an evaluation of maximum DG installable capacity by considering low-voltage wires and service drop wires. In numerical simulations, maximum DG installable capacity is analysed on a basis of some spatial installation scenarios of DGs in distribution networks.

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This paper presents a novel system reduction method which enables to consider the impact of PV penetration on the transient stability precisely. The object system for system reduction can be aggregated into the simple equivalent circuit by using the proposed method. The equivalent circuit consists of a lumped load model, a lumped PV model, and three equivalent impedances. Using the equivalent circuit, power flow into the object system when system voltage changes can be analyzed without repeated power flow calculation of the original system. In order to verify the proposed method, this paper presents the numerical example of transient stability analysis with one-generator-to-infinite-bus system model. The results of analysis indicate that the transient stability considering PV penetration can be analyzed with high accuracy with the proposed method.

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This paper proposes a multi-agent approach to decentralized power system restoration for distribution system networks and discusses a comparison with centralized and decentralized systems for power system restoration. So far, numerous studies have been conducted on power system restoration problems. From the view point of system structures, this research can be divided into two categories: centralized system and decentralized system. In this study, we have solved a power system restoration problem for the power distribution network with two kinds of methods: mathematical programming method (MIP) and the proposed multi-agent based method (MAS). The proposed multi-agent system consists of several Distributing Substation Agents (DSAGs) and Load Agents (LAGs). LAG corresponds to the customer load, while a DSAG supply electricity to LAG.
From the simulation results, it can be seen the proposed system could reach the right solution by making use of only local information and the solution quality is better than that of the centralized system (MIP). This means that the proposed multi-agent restoration system is a promising approach to more large-scale distribution networks.

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It is well known that total fluctuation of geographically diversified renewable energy (RE) such as photovoltaic generation (PV) is less than the sum of individual fluctuation. The phenomenon is called mutual smoothing effect. It is very important to evaluate the effect because cost of countermeasures to mitigate the voltage rise on distribution network caused by highly penetrated PVs' active power injection will depend in the effect. By analyzing irradiance data measured in an existing distribution line area, it turned out that fluctuation tendency is coherent at slower swing period and random at faster. This paper shows the fluctuation tendency is represented by the method called “Transfer Hypothesis”. The hypothesis is verified using measured irradiance data. Finally the paper shows a presumption example of total output of highly penetrated PVs, which will be necessary for voltage rise study on a distribution line.

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This paper evaluates optimal power generation mix considering massive deployment of variable renewable energy and regional power interchange. Japan has initiated feed-in-tariff (FIT) and expected significant introduction of PV and wind power for energy self-sufficiency and climate change. Wind power resource in Japan, however, concentrates mainly on Hokkaido and Tohoku region which is remote from electricity-consuming area such as Tokyo, and facilitating the considerable deployment of wind power requires the establishment of inter-regional power transmission line. On these backgrounds, we develop optimal power generation mix model including regional electricity exchange as large-scale linear programming model with 10 million variables and 30 million constraints. Calculated results show that regional grid expansion encourages wind power installation in Hokkaido and Tohoku region for supplying it to Tokyo area where PV power and stationary battery are alternatively replaced. The grid expansion, as well, promotes the shift of PV installation to Kyushu and Shikoku region which have longer sunshine duration, and interchangeably mitigates PV deployment in other regions through the transport of PV power from those two regions.

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We develop a novel simplified time periodic-explicit error correction (TP-EEC) method with the half cycle periodicity and with the ordinary cycle periodicity of eddy current to rapidly obtain the steady-state of the time-periodic magnetic field including the DC component. The usefulness of our novel method is verified through the magnetic field analysis of the electromagnetic equipments including the DC magnetic field.

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We report the results obtained on the developing characteristics of creeping discharges along the insulated wire surface under inductive lightning surge voltages with various durations of wave front. The aerial insulated wires usually are supported by the post insulator and the binding wire at the reinforced concrete pole. When a lightning strikes near by the aerial insulated wires, the overvoltage due to the inductive lightning surge invades to the central line of the wire. The creeping discharge can develop along the wire surface from the free end of the binding wire just after a flashover of the post insulator at the wire supporting point. This creeping discharge may give rise to the accidents such as a melting or snapping of the wire. An important subject to prevent these accidents is to clarify the characteristics of creeping discharge along the wire surface and the developing mechanism of discharges. In this study, the impulse voltages with various durations of wave front are applied to the central line of the wire as the inductive lightning surge. The length and aspect of positive and negative creeping discharges developing along the wire surface are measured using a still camera with an image intensifier, and the developing mechanisms of creeping discharges are discussed on the basis of the models which are proposed taking into account obtained results.

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Recently, a more highly accurate transmission capacity calculation program is needed in considering the increase of current value and avoidance of a heavy load in summer to operate the existing power equipment efficiently. Therefore, Tokyo Electric Power Company and JSOL Corporation jointly developed the highly accurate transmission capacity calculation program that a transient analysis by two-dimension finite element method is possible. In general, the air around the underground transmission cable influences the conductor temperature of the cable by the thermal resistance of the air. If this thermal resistance is greatly estimated, the temperature of the cable is calculated highly, and might become the result of far apart from actual temperature distribution.
In this report, we newly evaluated the influence of convection and heat radiation upon the thermal resistance of the air in a duct and trough by the thermal fluid analysis in detail, and applied the examination result to the highly accurate transmission capacity calculation program. In addition, we also report that the tunnel model which can take into consideration compulsory cooling equipment such as cooling pipes and ventilators in a tunnel was established.

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It is necessary to calculate the tilted angle irradiation from horizontal global irradiation using solar energy. A separation of global irradiation into direct and diffuse components must be required. There are various models in the separation, IEA model have been widely used because of its simplicity. However, the accuracy of IEA model is not sufficient. Examining the correlativity of several parameters for the measured direct irradiation, the correlation coefficient of the 2^nd and 3^rd power of clearness index became much higher. So, we propose improved IEA model which is more accurate using power section of clearness index.

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