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The 21^st Power and Energy Society Annual Conference was held on September 1-3, 2010 at Kyushu University. The total number of technical papers was 376, and technical sessions were 53 (52 oral sessions and 1 poster session). An invited lecture, a panel discussion, technical exhibitions and two technical tours were organized. All events were very well attended and the final enrollment attained to 969 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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Nowadays, electric power systems confront many problems, such as environmental issues, aging infrastructures, energy security, and quality of electricity supply. The smart grid is a new concept of a better future grid, which enables us to solve the mentioned problems with Information and Communication Technology (ICT). In this research, a number of Heat Pump Water Heaters (HPWHs), one of the energy efficient-use customer equipment, and Battery Energy Storage System (BESS) are considered as controllable equipment for the frequency control. The utilization of customer equipment such as HPWH for power system control is one of the key elements in the concept of Ubiquitous Power Grid, which was proposed by our research group as a smart grid in Japanese context. The frequency control using a number of HPWHs with thermal storage of hot water tank is evaluated. Moreover, a novel statistical modeling of controllable HPWHs taking into account customers' convenience and uncertainty is proposed.

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The authors have been studying characteristics of equivalent circuit model. The authors paid attention to the flux saturation influence of large turbine generator. Now the authors examined the various equivalent circuit models using the finite element method (FEM) and electromagnetic transients program (ATP-EMTP).

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Power output fluctuation of high penetration photovoltaic power generation systems (PVSs) may cause negative impacts on the load frequency control (LFC) of an electric power utility. For the cost-effective mitigation, the proper evaluation of apparent electricity demand fluctuation is important, taking the power output of PVSs into account as a negative demand. If the actual power output patterns are independent among several points, the standard deviation (STD) of total power output fluctuation of PVSs located in several points can be estimated based on the addition theorem of variance. Moreover, the central limit theorem may be applied if the probability distribution of insolation fluctuation is the same among several points. As a fundamental study to apply the stochastic methods, this study evaluates the following two factors to determine the distance between two points with which the insolation patterns of two points can be considered as independent: 1) the coherence of insolation fluctuation for various combinations of two points with different distances, 2) the correlation diagram of two different STDs, i.e. the STD of ensemble average insolation fluctuation observed at two points and the averaged STD of each STD of insolation fluctuation at two points. The results suggest that the insolation fluctuation consisting of the cycles shorter than 30min can be considered as independent if the distance between two points is longer than 5km-10km.

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Power output fluctuation of photovoltaic power generation systems (PVSs) of high penetration may cause negative impact on the load frequency control (LFC) of existing electric power utility. For the cost-effective mitigation, the proper evaluation of power output fluctuation of PVSs dispersed in large-area is very important. Based on the independence in insolation fluctuation among various points, this paper discusses the practical usability of the standard deviation (STD) of total power output fluctuation of PVSs simply calculated as 1/√N value of STD at the representative point. The statistical evaluation using the insolation observed at 5 points within 25km × 25km reveals that STD with simplified calculation would be useful to evaluate STD of ensemble average of insolation on average for a certain period. Besides, the probability density of STD with simplified calculation is almost the same with that of STD of ensemble average for the period with large STD. As a result, the simplified calculation of STD would be useful for the stochastic evaluation of STD of ensemble average insolation among area at least 25km × 25km.

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Based on the independence of insolation fluctuations among various points, this paper estimates the standard deviation of total power output fluctuation of photovoltaic power generation systems (PVSs) of high penetration. In order to apply the simplified calculation of total insolation fluctuation property based on the independence, this study develops an area model consisting of a number of blocks, where the PVS power output pattern of the cycles shorter than a few ten minutes is considered as independent among blocks by considering the independency evaluation of insolation. This study evaluates the standard deviation of apparent electricity demand σ_A involving the PVS power output as a negative demand, by assuming that the standard deviation of power output fluctuation is the same for all blocks as a extreme case. The results suggest that σ_A may be as large as the original standard deviation of electricity demand, if the PVSs of mass penetration are dispersed in the large area according to the geographical distribution of existing residences.

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In the case of XLPE cables, there is the influence of the ion in the water trees as deterioration factors by the ones. Therefore we have analyzed the element by EDX so far, but it was the analysis technique that had difficulty with the distinction of the multi atomic ion. Therefore we developed ion analysis technique in the water trees including the multi atomic ion by Micro-FTIR, and utilize it as to analyzing the actual cables. In addition, we have investigated the harmfulness of each electrolyte detected from the actual cables.

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In recent years, much attention is paid to the nonlinear analysis method in the field of stability analysis of power systems. Especially for the multi-swing stability analysis, the unstable limit cycle has an important meaning as a stability margin. It is required to develop a high speed calculation method of stability boundary regarding multi-swing stability because the real-time calculation of ATC is necessary to realize the flexible wheeling trades. Therefore, the authors have developed a new method which can calculate the unstable limit cycle based on damping rate inversion method. Using the unstable limit cycle, it is possible to predict the multi-swing stability at the time when the fault transmission line is reclosed. The proposed method is tested in Lorenz equation, single-machine infinite-bus system model and IEEJ WEST10 system model.

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A generating plant can not energize longer transmission lines at once after blackout. The generating plant energize shorter transmission lines firstly, then circuit breaker turns on to connect other transmission lines through the transformer. Transient over voltage oscillation may occur in the transmission lines caused by the resonance of the transmission line. It is reported that the peak voltage exceeds more than 2p.u. when the non-sinusoidal wave voltage caused by saturation in the transformer core excites the resonated transmission line.
This paper describes the effect for preventing saturation of transformer by turning on contactors with appropriate resistors before main contactors of the 500kV circuit breaker. The first part presents the mechanism of preventing saturation in the transformer core by pre-resistor insertion of 500kV circuit breaker. The second part presents the expected effect in the actual power system simulated by analytical model using a transients simulation program, EMTP.

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A high voltage, large capacity power transformer is one of the most important equipment in electric power system. If a failure occurs in such a transformer, stable power supply may become impossible. In addition, efficient power system operation may become difficult because it takes long time to replace the transformer. To prevent failures that may occur, effective external diagnosis must be performed and the defective portions must be correctly identified. However, such anomalous phenomena are complicated in many cases, and their causes cannot be identified in some cases by using conventional techniques.
This paper reports a case study on the fault diagnosis of an oil-immersed power transformer that had a tendency to increase in the total combustible gas (TCG) during a regular operation. Specifying the faulty parts became possible by applying various case of Frequency Response Analysis (FRA) diagnosis though it was impossible by the electrical tests, DGA (Dissolved Gas Analysis), and so on. This transformer was disassembled to investigate the condition and was replaced without causing failure.

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Some MW-class PV power stations are now under construction and more PV power stations will be introduced in future. However, the penetration of PV power station may disturb a stable operation of the power system. The largest concerns are frequency variation and voltage variation caused by fluctuation of PV power station output. When these variations can not be eliminated by the conventional system operation and control schemes, installation of energy storage system might be needed. From this background, the authors have developed control method of battery system for fluctuation suppression of PV power station output. In this paper, battery capacity needed to satisfy the required fluctuation suppression level is estimated. In the estimation, two types of suppression control schemes; one can save the required power capacity and another can save energy capacity.

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Penetrating large amount of renewable energy sources into power system, battery energy storage performs an important role for smoothing their natural intermittency, ensuring grid-wide frequency stability, and suppressing voltage rise caused by reverse power flow. The ubiquitous power grid is one of the concepts as a smart grid in Japanese context, where the total battery capacity can be optimized by coordinating renewable energy sources, controllable distributed generators, and controllable loads on demand side, for example, heat pump based water heater with heat storage, and plug-in hybrid vehicle or electric vehicle with onboard battery, and so on. These controllable devices behave as an autonomous distributed smart storage by charging or discharging against the power system frequency measurement as paying attention to user convenience. In this paper, the effects of the autonomous distributed smart storage on load frequency control of the bulk power system are investigated. And the authors propose a simple coordinated control scheme to the spinning reserve of the thermal power generator.

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The life of a transformer is limited to the deterioration of its solid insulation. Winding conductors and other solid insulation materials in oil-immersed transformers have been insulated using cellulose products. For many years, manufacturers have met the needs of special applications by designing transformers using thermally upgraded materials to achieve lighter weight, higher power density and increased life. Recently, the effect of thermally upgraded insulation on diagnostic techniques such as gas-in oil analysis, and their indication of insulation degradation have been reviewed. This paper describes evaluations of the thermal degradation characteristics and decomposition reactions in mineral transformer oil of amine-impregnated thermally upgraded paper insulation. The thermal resistance of the thermally upgraded paper is evaluated by comparison with Kraft paper insulation. Further, aging degradation mechanisms of decompositional degradation of the thermally upgraded paper due to aging in mineral transformer oil are proposed.

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This paper presents the effects of introduction of residential polymer electrolyte fuel cell (PEFC) co-generation system with batteries in comparison with conventional systems that consist of a gas boiler and electric power from commercial grid, by computer simulation. The PEFC co-generation system in commercial use provides the average primary energy saving rate of 12.7% and CO₂ reduction rate of 15.4% with respect to the conventional system. Addition of 8.0-kWh batteries to the PEFC system results in limited improvements of 0.8 points and 0.9 points in the reduction rates, respectively, yielding 13.5% and 16.3%, when using a conventional operation planning method. A new operation planning method is proposed in order to make a precise control of charging and discharging the batteries. The average primary energy saving rate reaches up to 16.9% by the improvement of 4.2 points, and CO₂ reduction rate reaches up to 20.4% by the improvement of 5.0 points in the PEFC co-generation system with 8.0-kWh batteries using the new operation planning method. The new method can thus realize a substantial improvement in reduction rates. Furthermore, it is shown that the suitable battery module capacity for the residential PEFC co-generation system is 4.0kWh.

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Output power in photovoltaic systems changes steeply with the change of the solar irradiance and overall PV temperature. The change of output power has influence on the electric power quality of the system. This paper proposes a novel operational scheme of the residential distributed power generation system using solar cells and hydrogen-storage type fuel cells. In order to level the output power which changes steeply the fuel cells are connected to the PV system in parallel. Thus the generated power of all the system can be leveled. However, the hydrogen is required in order to generate electricity by the fuel cells. Therefore, the electrolyzer which is hydrogen manufacturing equipment is installed in the system. It is confirmed by the simulation that the distributed power generation system operates according to the proposed operational scheme and its system is available for residential supplies.

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There is possibility that lightning strokes to transmission lines with large peaks and/or long duration of currents cause arrester failures. Hence it is important to evaluate reliability of transmission lines considering arrester failures caused by lightning strokes.
Actually, arrester failures were caused by a winter lightning stroke to the tower top of one circuit transmission line. In this letter, the lightning stroke associated with the arrester failures is evaluated based on observation of electromagnetic field and analysis by EMTP simulation.

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