[in Japanese]

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Although the number of pieces of equipment that emit harmonic currents has increased, the harmonic voltages in Japan have gradually decreased since about 1999. In addition, the harmonic voltages are generally lower during the daytime when there is greater usage of different types of equipment that emit harmonic currents. In a previous study, the authors showed that the reason for this phenomenon is that the phase angles of the harmonic currents emitted by three-phase equipment of consumers using 6.6kV or higher voltage power supply and the phase angles of harmonic currents emitted by other equipment are almost opposite, and they cancel each other out.  In this paper, we classify equipment into six groups depending on the number of phases (i.e., single-phase or three-phase) and users' supply voltage. And the ratio of the contribution of each group to the fifth harmonic voltage is then quantitatively clarified. Time trends of the fifth harmonic current per kW and the effective power of each group are assumed by using measured data. The ratio of each group is assumed by making the time trends of the composite fifth harmonic current of all groups and the average of the fifth harmonic voltage as identical as possible. By comparing them with actual sales data from an electric power company, we confirmed the feasibility of the assumed ratios.

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Various evolutionary computation techniques have been applied to reactive power and voltage control. High penetration of renewable energies and deregulation of power systems require to shorten an interval of the control. One of the practical solutions for this problem is applications of parallel and distributed computing with dependability, which is an ability to keep sustainable control against various accidents. This paper presents evaluations of dependability for parallel particle swarm optimization based voltage reactive power control. Simulation results with IEEE 14, 30, 57, and 118 bus systems indicate high dependability of the method.

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The type of excitation systems mainly used for synchronous generators are the static excitation system and the blushless excitation system. The increase of single-unit capacity is remarkable nowadays. As single-unit capacity increases, its influence on the grid system makes a larger contribution in the case of a network fault. Therefore, it is desired to improve the accuracy of the equivalent circuit model for simulating the transient phenomena, including the excitation system. There have been many general characteristic explanations with two excitation systems. However there is no report has been published using actual model systems. The authors reported response and stability characteristics in 4-pole synchronous generator excitation system with actual generator model.

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The type of excitation systems mainly used for synchronous generators are the static excitation system and the blushless excitation system. In both cases, it is important to estimate the field characteristic. The authors derived about new knowledge three phase sudden short circuit and mismatched synchronizing using the electromagnetic transients program (ATP-EMTP). This paper studied these phenomena.

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Because of the rise of the global environment consideration, more attention is paid to the distributed generation using renewable energy sources like photovoltaic and wind power generation. However, the output fluctuates drastically according to the weather conditions like the insolation and the wind velocity. The fluctuation may have an impact on power demand and supply balance. Therefore, the daily operation and planning of a system with high penetration of the distributed generation is going to be very difficult than ever before. In order to study how difficult the demand and supply control will be, the model including a unit commitment, considering various constraints such as ramp rate and available generating capacity, is proposed. In this model, the frequency and the tie-line power flow fluctuation are calculated and used as indices to evaluate the effect of the introduction of renewable energy sources on the operation and planning of electric power system.

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Because of energy and environmental policies in the last decade, a lot of photovoltaic generations have been installed into power systems in Japan in recent years. In this situation, it is of great concern that disconnection of PV due to voltage drop caused by a system fault has an critical impact on power system stability. To avoid its disconnection, Fault Ride Through (FRT) requirement is applied for PVs. In this paper, PV power output control which improves transient stability of the power system with a huge amount of PVs is proposed and its effectiveness is confirmed by the numerical simulations.

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The installed capacity of photovoltaic (PV) systems has been increasing rapidly due to the enforcement of the feed-in tariff scheme in Japan. However, the reverse power flow from the roof-mounted PV systems could cause the voltage unbalance such as voltage-rises in distribution networks. As for the voltage stabilization with reactive power compensation, SVC (Static Var Compensator) has been installed in the high-voltage distribution network until now. On the other hand, the idea of installing the reactive power compensator in low-voltage distribution network is proposed as a promising alternative with its cost-effectiveness. This report proposes an evaluation method of the cost-effectiveness of the reactive power compensator at low-voltage side. We assumed following three installation schemes: (1) the compensator is installed at a consumer end where PV is installed; (2) the compensators are installed at consumer ends selected from all consumer ends; (3) the compensators are mounted at selected power poles. This method can select the most cost-effective scheme, reflecting the annual cost of the compensator as well as the degree of PV penetration.

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CEPCO's hybrid power system simulator consists of analogue models and hybrid models. The power system facilities are downsized as an analogue model, while the synchronous generators and the loads are modeled as an actual current source model through the amplifier and the digital model. In recent years, there is a growing interest in analyzing power system dynamic phenomena caused by a high penetration of distributed generations. Therefore, the multifunctional generator model which can simulate distributed generation has been developed.

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Heat pump water heater (HPWH) for household has been focused as a controllable load to compensate power fluctuation of renewable energy (RE) sources like photo voltaic (PV) cells, wind turbine (WT) and so on. HPWH should be operated without loss of user's convenience during power compensation. In this paper, HPWH model has been mode by use of a commercial HPWH with small change. The HPWH used in the study can be control the rotation speed of compressor by external signals, and it almost operates under the normal conditions as the HPWH without any change. Simulation studies have been done to evaluate loss of hot water demand by use of measured 60 hot water demands with power compensation control, and to evaluate the LFC capacity of the model gird with battery energy storage system. From simulation results, it is shown that The LFC capacity of the grid becomes large according to the capacity of HPWH, and loss of hot water demand under power control is relatively small and if several start-up/shutdown operation is allowed, the loss of hot water may be negligible small. The required energy for the hot water demand is almost the same value as mid-night operation.

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In recent years, rapid introduction of photovoltaic generation systems (PVs) causes voltage rise in distribution systems. In addition, residential PVs cause voltage unbalance in distribution systems, as these PVs are mostly single-phase connections. For these reasons, in order to control voltage in distribution system, it is important to suppress voltage unbalance. Voltage unbalance can be suppressed by power electronics equipment such as static var compensator, but it is high cost. So, the authors focus on static capacitor (SC), because SC is low cost compared to static var compensator.  In this study, the authors propose a new method of controlling single phase SCs to suppress voltage unbalance by estimating voltages after SCs control. And, we verify the effect of the method by experiments.

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The widespread use of photovoltaic (PV) systems may create voltage rise problem in future distribution system. In this paper, two different control methods; centralized and local for controlling consumer controllable load have been proposed to provide voltage control for distribution system with large penetration of PV systems. Heat pump water heater (HPWH) has been selected as a consumer controllable load due to its large thermal energy and flexibility in operating time. In centralized control, controller placed at the substation is responsible to control all node voltages within acceptable limit by controlling all HPWH's power consumption whereas in local control, node voltage is controlled by its own local controller. Optimal control parameters that determine HPWH power consumption are found in both methods and most appropriate time-varying power consumption for HPWH is obtained from node voltage and HPWH characteristics. The effectiveness of proposed voltage control methods has been evaluated in a model of the residential distribution system in Japan. It is considered that none of participating consumers in the proposed methods are affected with hot water shortage.

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This paper presents the fault location system for pulse radar method using FMCW radar technology at overhead HVDC line. This system operates that triggered off a line protection system (automatic mode) and/or user's control (manual mode), hence we can not only comprehend the fault location but also exploit the health check of transmission line. This proposed method is tested via experiments at the EPDC's Hokkaido-Honshu HDVC link and the CRIEPI Akagi testing center's 22kV distribution line. The applied test results corroborate the practical performance of fault occurrence at ground fault situation and break line situation.

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In Hokuriku Electric Power Company, surge arresters or distribution equipments, such as insulators with MO varistors and current-limiting arcing horns with a MO varistor, are installed on all high-voltage distribution poles in the area where a large number of lightning outages occurred. General distribution systems in Japan are isolated neutral systems, and if sparkover of insulators occurs only at one phase due to lightning-related overvoltages, a follow current will naturally disappear because of a small ground-fault current. Therefore, if the surge arresters are installed on only two phases, it is possible to prevent short circuits which cause phase-wire breakings. In the case of the two-phase arresters, sparkover of one phase without an arrester may reduce currents flowing through arresters of other phases, and may prevent failures of other phase arresters. However, this lightning protection effect has not yet been studied sufficiently. In this paper, we present that the lightning protection effect of distribution lines with non-surge arresters on one phase were obtained by experiments and EMTP simulations.

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The 26th Power and Energy Society Annual Conference was held on August 25 - 27, 2015 at Meijo University in Nagoya. The total number of technical papers was 386 which were presented at 44 technical sessions. On the afternoon of second day, a invited lecture, a panel discussion, a special lecture and a banquet were organized. The conference had a total enrollment of 1096. 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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