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Because of global warming, the attention to the photovoltaic generation has increased, and a lot of photovoltaic generations will be installed to the power system in future. In Japan, most photovoltaic generations will be connected to the distribution system. This will make the power flow in the power system changed. That is to say that the forward power flow (flow from higher voltage system to lower voltage system) reduces, or, moreover, that the reverse power flow occurs. Because of the change in power flow, the voltage characteristics will be also changed. Consequently, it is expected that the penetration of photovoltaic generation has some impacts on voltage stability. In this paper, simple power system model which consists of one infinite bus, one load, and one photovoltaic generation is considered, and the fundamental voltage characteristics are discussed by PV curves and phasor diagram. The voltage characteristics considering the current limit by PCS (Power Conditioning System) in the photovoltaic generation are also discussed.

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This paper presents a result of study for a next day electric load curve forecasting method and its accuracy improvement. Electric load curve forecasting is one of the most important tasks for insuring reliability and economic electric power supply. Because start-stop time of generators is decided using the load curve forecasting. This paper proposes three methods. First one is a new structure of forecasting models. It consists of single-output neural networks and a multi-output neural network. Second one corrects load curve using the operation information of commercial-scale utility customers. Last one selects the accuracy forecasting models adaptively using recent forecasting error. Input data of each forecasting model is different type of weather information. The simulation results reveal the effectiveness of the proposed methods for a next day electric load curve forecasting.

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The several approaches have been proposed for evaluating the capacity value of intermittent generation by now. In this paper, we assume the uncertainty included in the demand, the existing generation and the intermittent generation, can be treated through the normal distribution model. By using the newly developed approximating method similar to the Garver approximation, and the Z-stochastic approach, the ELCC (effective load carrying capability) method is comprehensively surveyed. The percentile method adopting in the higher demand level is also discussed concerning the probabilistic property of the intermittent generation. Numerical examples and the simulation for illustrating the probabilistic approach are included.

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This paper presents a demand response forecasting model by Just-in-Time modeling. It is planned to introduce the renewable energy on a large scale into the power system in order to achieve the low carbon society. However, the renewable energy has a negative effect on the power system. In recent years, demand response is expected to control the load as the reserve power. Thus, it is necessary to forecast load with demand response for unit commitment. The proposed JIT modeling uses the decision tree to analyze demand factors and the load correcting method of similar day. The former has functions to extract if-then rules and evaluate the variable importance. The latter corrects the load of similar day with demand rate and weather condition. The effectiveness of the proposed method is demonstrated using actual data of demand response about the adjustable Critical Peak Pricing field test at Kitakyushu Smart Community Project. The proposed method with the decision tree can extract similar day more accurately than a conventional method based on meteorological condition and day type. Moreover, the proposed load correcting method can correct the extracted load accurately.

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Voltage distortion of high-order harmonic has occurred at a 22kV customer. There are only two customers who are supplied by this 22kV distribution feeder. Therefore, it is likely that induction heater of another customer have become the harmonic source. In 22kV customer, so far, there are no cases where such voltage distortion has occurred. It is necessary to understand the actual condition for this case and to clarify the effective countermeasure.
As a result of analyzing the measured data, even though the high-order harmonic current generated from the induction heater is small, the voltage distortion of the high-order harmonic was increased. This is suggests that the current generated by the induction heater and the impedance conditions of the distribution system generate voltage distortion. We have constructed an analysis model, and have considered a countermeasure utilizing shunt capacitor by simulation. Based on the results of the simulation, we have demonstrated the effect of the shunt capacitor.

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This paper describes a newly developed demand and supply control system for micro grid. Renewable energy is expected to reduce green house gases and becomes widely used in the world. By contrast, fluctuated power output from renewable energy may affect the power systems, especially frequency. The demand and supply control system for micro grid is expected to reduce it. The developed system consists of 4 control layers. The first layer is a planning of demand and supply every 30 minutes until next day. The second layer is an economic dispatch control (EDC) every 1 minute. The third layer is a load frequency control (LFC) every 1 second. The last layer is battery local control every 0.1 second. The developed system can control frequency stably against fast change of renewable energy output, and can operate generators economically by cooperating EDC and LFC, and using battery local control. Moreover, the battery can be operated systematically by managing battery states of charge (SOC). The developed system is verified using a real time digital simulator with promising results.

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High-speed spring-operated mechanism that enables 2-cycle interruption was developed by improving the trip control unit and the link mechanism that connects the interrupter. This mechanism had almost the same composition as a conventional 3-cycle interruption GCB, and we optimized the mechanism to achieve 2-cycle interruption. The solenoid was optimally designed by using a coupled analysis of a nonlinear magnetic field analysis with finite elements model and a dynamic analysis with a kinematic model. We used these analyses to investigate the core material, the number of coil turns, and the stroke of the solenoid. We also calculated the dynamic characteristics of the GCB with the spring operated mechanism in order to satisfy the objective time of opening contact, and the lever of the trip control unit and the lever of the link mechanism were improved. A prototype GCB, which was built based on the above analyses, demonstrated sufficient performance.

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Since output of photovoltaic generation (PV) includes power fluctuation caused by natural conditions, installation of PV on a large scale is supposed to affect Load Frequency Control (LFC) of the power grid. One method to compensate power fluctuation is the use of energy storage (ES), such as batteries and capacitors. A power fluctuation compensation system composed of an electrical double layer capacitor energy storage system (EDLC ESS) and a Li-ion battery energy storage system (Li-ion BESS) is considered. Power loss characteristics of both ESSs during power fluctuation compensation are modeled by equivalent circuits based on ES impedance spectra. The models are validated through experiments simulating power fluctuation compensation. Using these ES models, simulations were carried out to determine power fluctuation dispatch method between both ESSs and ESSs' capacity in consideration of power loss minimization.

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Long term DC properties of DC-XLPE insulation material, which have been developed for DC use, were investigated. It was found that the life time of DC-XLPE under DC voltage application becomes longer by addition of nano-sized filler. The time dependence of space charge distribution at 50kV/mm was observed for 7 days. As a result, there is almost no accumulation of space charge in DC-XLPE. The 250kV DC-XLPE cables and accessories were manufactured and subjected to a type test and PQ test for the use in the Hokkaido-Honshu DC link facility owned by the Electric Power Development Co., Ltd. These tests were done under the conditions that include a polarity reversal test for line commutated converter (LCC) systems as recommended in CIGRE TB 219. The test temperature was set at 90°C. The type test and PQ test were successfully completed. The DC-XLPE cable and accessories were installed in summer 2012 for the Hokkaido-Honshu DC link. After the installation of the DC extruded cable system, a DC high voltage test at 362.5kV (=1.45PU) for 15 minutes was successfully completed in accordance with CIGRE TB 219. This DC extruded cable system was put into operation in December 2012 as the world's highest voltage extruded DC cable in service and the world's first DC extruded cable for a LCC system including polarity reversal operation.

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Energy storage will be critically important for stabilizing grids with renewable energy power sources; therefore various kinds of high performance devices such as batteries and capacitors are being developed at present. In particular, Li-ion batteries exhibit high energy density, and Li-ion capacitors have high input/output power ability with almost zero self-discharge. The authors have proposed a BAttery/Capacitor Hybrid Energy Storage system (BACHES) which delivers wide-range charge/discharge power with a large capacity by Li-ion capacitors and batteries. In this paper, the authors show the conceptual details and the features of this system. Also, experimental equipment was manufactured as specifications of maximum power of 6kW for connection to a 380V bus. The fundamental performances of the system components of Li-ion capacitors, Li-ion batteries, and converters were evaluated in test runs. This study concluded that the system operates itself by sharing roles between the Li-ion capacitors and the Li-ion batteries according to the characteristics of each, and then can control the bus voltage within 1.2% and 4.4% drops under sudden 0.47kW and 1.8kW power losses, respectively.

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Lightning hits to Tokyo Skytree have been under observation by a high-speed camera since August 2012. First data were obtained when negative downward lightning flashes hit the tower on July 08, 2013. This letter reports on observation of a negative single-stroke flash with a positive upward leader initiated from Tokyo Skytree extended about 400m before connection with a downward leader. Simultaneously observed electric field observed by a fast antenna showed much weaker stepped-leader pulses compared to ordinary negative downward flashes hitting ground.

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The 24th Power and Energy Society Annual Conference was held on August 27 - 29, 2013 at Toki Messe in Niigata. The total number of technical papers was 401, and technical sessions were 58 (57 oral sessions and 1 poster session). A invited lecture, a panel discussion and a special lecture were organized. All events were very well attended and the final enrollment attained to 831 registrations. The conference was successfully closed by the great contribution of all participants. The outline of the conference is reported in this article.

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