A large amount of radionuclides were spread by the accident of Fukushima Daiichi nuclear power plant in 2011. The situation of surrounding area of nuclear power plant is momentarily changing. In order to consider for decontamination or volume reduction of radioactive wastes, it is necessary taking into account not only the technical needs but also feelings of inhabitants, reduction of environmental load, reduction of the radiation exposure on workers and efficiency and cost of decontamination work. In this paper, the application possibility of superconducting magnetic separation system for decontamination and volume reduction was discussed compared with other technologies from above multidirectional viewpoint.

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At early stage of PV's (Photovoltaic) penetration, heavy leading power factor operation was adopted so that LV might be reduced within regulation (107V in Japan). However, such an excessive reactive power control claims additional capacity in PCS (Power Conditioning System). In addition, such a local control could not realize desirable voltage all over distribution network, and as the result, could not realize desirable voltage of the PV itself. Behind such a control procedure lies misunderstanding of distribution network. It must be noticed that impedance of distribution transformer is almost pure reactance and larger than MV and LV network impedance. Therefore, distribution transformer and its tap control are the most prominent elements in distribution network voltage regulation. In this paper, the reason why light and constant leading power factor operation of PVs is sufficiently effective for mitigating overvoltage and voltage fluctuation in distribution network (especially when combined with transformer tap control by vector-LDC: Vector-computed type Line [voltage] Drop Compensation) is clarified through analysis on aggregated network model and simulation on a realistic detailed network model. Moreover, the contribution to energy saving of this combination is demonstrated.

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This paper investigates capacities of a photovoltaic generation system and an electrolyzer in a proposed residential distributed generation system with a fuel cell vehicle. The evaluation is carried out in terms of the reduction rate of the power fluctuation and the operation cost in the five electricity price cases. By designing the rated capacity of the electrolyzer to be less than and near that of the photovoltaic generation system, an excessive capacity of the electrolyzer can be avoided. The operation cost of the proposed system is lower than that of the conventional system when the rated capacity of photovoltaic generation system is less than 5kW and the electricity price of sold power goes down. However, the operation cost increases as the electricity price of purchased power rises during the night. The reduction rate of 63.3% is achieved in the proposed system with a photovoltaic generation system of 5 kW and an electrolyzer of 4kW.

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In this paper, a cooperative control algorithm for multiple step voltage regulator (SVR) using correlation of measurement data of distribution line is proposed. Conventionally, the control time constant of a SVR placed on the feeder end side was set slower than a SVR placed on the substation side. The unnecessary tap movement of SVR was reduced by this setting. In this case, on the condition that “the photovoltaic power generation output of the feeder end fluctuates” and “only SVR of the end side works”, it is a problem that control of SVR becomes slow. By the proposed method, the SVR settled in end side of a feeder can change its tap rapidly only if the SVR settled in sending side of a feeder will not change its tap by using proposed method. The features of the method are followings: (1) to estimate tap change possibility of the sending side SVR using correlation model of both of the SVR, (2) only use local measurement data of the SVRs for tap change control. By the proposed method, unnecessary tap change operation and lag of tap control are reduced without communication networks.

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Recently in Japan, large-scale introduction of photovoltaics (PVs) has been under way. This development increases the likelihood of system voltage increase and fluctuations, which can be prevented by employing PV output prediction. In this study, we focus our attention on applying PV output prediction to system operation with the objective of system voltage control. In this paper, 30 minutes ahead prediction is assumed according to prior research with prediction error consideration. System voltages of 30 minutes ahead are estimated and are controlled in advance by using transformer taps and static capacitors. In this paper, voltage control is proposed for coordinating control, which is based on one of the games in the game theory, potential game. The validity of the proposed method is confirmed by running simulations using a modified IEEE 30 bus system. By applying the proposed method, both the voltage deviations and control counts improved considerably compared to a conventional method.

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Power output fluctuation of high penetration renewable energy such as photovoltaic 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. Estimation of a spatial and temporal cross-correlation function of the solar radiation intensity is inevitable for this analysis. Under this requirement, we propose a novel estimation method of the cross-correlation function. The proposed method allows, by using three pyranometers only, the accurate estimation of the cross-correlation function between any point and a point at which a pyranometer is installed. The accurate estimation is enabled by considering an anisotropic effect of wind directions in a “spatio-temporal attenuation model”. We confirmed the high accuracy of the proposed method by using practical data obtained from pyranometers installed in Sakai Solar Power Plant for its one year operation from January to December 2012.

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This paper proposes a network system architecture for next-generation wide-area monitoring, protection and control (WAMPAC) of power systems, featuring a wide-area Ethernet (L2-network) and time synchronization such as IEEE 1588 and other schemes associated with decentralized modular devices. Based on the architecture, a prototype WAMPAC system has been constructed and installed in an analog power system simulator to examine its communication performance, including time synchronism and show the validity of an actual application, wide-area integrated primary and backup protection with a current differential scheme. Fundamental analyses with respect to end-to-end transmission delay, system unavailability and scalability for double redundant current differential line protection systems with 4-repeater/5-span communication links were conducted to examine its applicability to an actual power system.

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Recently, with the increase in home electric appliances with power electronics devices, influences of harmonics are increasing. In order to investigate influences due to harmonics currents, grasp of waveforms for electric appliances in use in low voltage distribution system is important. In this study, four types of electric appliances were chosen as a single-phase load used on low voltage distribution system, and harmonic characteristics were measured. Measured data were compared with limits for harmonic emissions calculated by the standards of JIS C 61000-3-2 (Electromagnetic compatibility (EMC)-Part 3-2: Limits). Subsequently, average harmonic current characteristics profiles for four types of appliances were obtained. EMTP model for appliances using this profile was developed.

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Much of oil filled (OF) cable has been used for a long time for 66 to 500kV extra high voltage cable. Sometimes we can see extremely degraded oil (several tens % of tanδ, for example) in joint box etc, but even with that sever situation, an event such as thermal breakdown has not taken place up to the present in actually operated transmission lines.  The authors have reported the tanδ characteristics of oil impregnated paper with extremely high tanδ oil and the development of a simulation method of heat generation by dielectric loss in OF cable joint.  In addition to that, the degradation characteristics of actual OF cable system have been investigated. The degraded oil distribution in actual cable system seems to be balance in nearly 27 yeas. The temperature rise of joint box is quite small even with the extremely degraded oil (tanδ=204%). With the experimental results, the OF cable system tanδ distribution is estimated and the possibility of unexpected heat generation in cable which has been installed in the conduit pipe section is proposed.

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The Authors observe waveforms of lightning currents by Rogowski coils at Muregaoka wind farm in Kagoshima. We succeeded in observing three sets of the current waveforms of negative downward lightning flashes to a wind turbine on two summer seasons between 2013 and 2014. The mean location errors of those strokes observed by the JLDN are 557m and 316m for first and subsequent strokes, respectively. Information from sensors within 730km from lightning striking point was used in the case that location error was less than 400m. The mean errors of the peak currents estimated by the JLDN were -10% and +10% of the currents measured by the Rogowski coil for the first stroke and the subsequent ones respectively.

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