Investigating R&D committee on “Survey results for the current specification and operation of protection relays in Japan, and trends in overseas technology” started in December, 2012 and published the technical report after 2 years activities. This technical report describes the results of a systematic survey particular to the protection relays used by each power utility in Japan written in accordance with the following outline;  (1) Specification of a typical protection relay system  (2) Basic concept of power system configurations including the protection relay and its operation  (3) Specification of overseas protection relay systems and trends in relevant standards  (4) Analysis of the differences between domestic and overseas protection relay technology  (5) Future direction of protection relay technology

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There is a danger of output suppression of high-penetration residential PV systems due to voltage increase. It is necessary to install new technology to prevent the occurrence of such phenomenon. Therefore, we focused our attention on heat pump water heaters (HPWHs). HPWHs are usually used to heat water during night time because electricity prices are cheaper than during the daytime for the load leveling in Japan. So they can be used as a countermeasure without additional cost if they are operated during the daytime. However, HPWHs do not have sufficient capacity to absorb inverse energy at each residence. Thus HPWH operation must be optimized to minimize output suppression loss. In this research, we selected four typical sunny days in spring, summer, autumn and winter. The optimal HPWH operation was calculated by numerical simulation. The optimal monthly HPWH operation was investigated using the weather forecast assuming actual operation in each season.

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It is an important issue to maintain voltage profile in distribution systems with a large number of distributed generators. To solve this problem, reactive power control of the distributed generator connected via a power conditioning system is effective. However, there is a possibility that the reactive power control leads to curtailment of active power output when capacity of the power conditioning system is not enough. Therefore, it is needed to compensate the economic disadvantage of the control collaborators in order to realize the cooperative voltage control method using the reactive power control. Hence, the authors developed a new real-time pricing method of reactive power supposing that all owners of the distributed generators behave based on economic rationality.

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Compensating the voltage within the appropriate range becomes difficult when a large number of photovoltaic (PV) systems are installed. As a solution to this problem, the installation of a low-voltage regulator (LVR) has been studied. In this paper, we propose a method for rapidly and accurately determining the line drop compensator method (LDC) parameters as a part of a voltage management scheme, which consists of prediction, operation, and control. In the proposed method, candidates of the appropriate LDC parameters are selected with low computational cost by using classifiers that learns the relation between power series data and the properness of LDC parameters. We performed numerical simulations to evaluate the validity from the viewpoints of computational time and classification accuracy for determination of the LDC parameters, and verified the voltage control performance of the proposed method.

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Flexible photovoltaic modules have received a great deal of attention for use in photovoltaic systems. At present, the most important issue to be resolved is the optimum shape of flexible photovoltaic modules for obtaining maximum power output. A design tool specifically tailored for the flexible photovoltaic module is required for this purpose. In the present study, a new method is proposed for estimating the power output of a cylindrically-shaped flexible photovoltaic module, taking into account the uneven irradiation and temperature that occurs for a curved surface. The average irradiation over the area of the entire module is used in the equation of the proposed method. The temperature is calculated based on the root mean square of the irradiation over the area of the entire module. The average and root mean square of the irradiation are calculated based on the directional dependence of the global horizontal irradiance. The estimated and measured power outputs are compared. The error rate of the total power output is 2.6%, and the mean absolute percentage error of the power output is 6.8%. The proposed method can reduce the amount of calculation to compare with a conventional method having the same mean absolute percentage error.

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The inverters which simulate the actual synchronous generators can continue to operate in grid disconnection. It is called virtual synchronous generator (VSG). In this paper, the VSG without phase locked loop (PLL) based on a current controlled inverter is proposed. The proposed controller is composed of impedance model, governor, AVR, damper model and rotor model. It can be synchronized with grid without PLL because it has synchronizing power. VSG parameter design method is provided by stability analysis. Finally, simulation and experimental results show that the proposed VSG can operate in disconnection from the grid. It can supply load after disconnection from grid.

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Observation of lightning current by using Rogowski coils started in February 2012 at Tokyo Skytree, which is a 634-m high freestanding broadcasting tower. Electromagnetic field waveforms are also observed by capacitive antennas at several tens of kilometers from the tower. Simultaneously observed lightning current and electric field waveforms are reproduced by using an electromagnetic model of a return stroke on lossy ground with the help of NEC-4. Electromagnetic field waveforms are reproduced by using an inclined lightning channel reconstructed from observed images. It turns out that the electromagnetic field waveforms are considerably affected by lightning channel geometry and ground conductivity.

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This letter deals with the problem which classifies the cause of the intermittent ground fault. In this letter, we focus on the difference of characteristic zero phase current waveform in both Gap ground fault and Cable ground fault, and propose the method to identify these cases based on a new feature value. Numerical examples show the effectiveness of the proposed method.

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