Superconducting generator (SCG) with superconducting field winding has many advantages such as small size, light weight, high generation efficiency. A prominent advantage is to improve power system stability owing to lower synchronous reactance compared with the conventional generator. High response excitation type SCG has a rotor with thermal radiation shield without damping effect; it can enable very rapid change in field current and the magnetic flux due to the change of the field current can reach the armature winding quickly. The excitation power is large and has a rapid change enough to affect the conditions of power system in self-excited operation of the generator. This effect is equivalent to the effect of a superconducting magnetic energy storage (SMES), then so-called “SMES effect", and it is expected to contribuite to transient stabilty improvement. In this paper, excitation control system design for high response excitation type SCG in consideration of SMES effect is proposed for improving power system dynamics by employing eigenvalue sensitivity. The SMES effect is considered to couple with the power system as a nonlinear load. The control performance of the proposed excitation control system is examined in IEEJ East 10-machine and West 10-machine systems. It is made clear that the SMES effect of SCG is utilized effectively and results in both transient and dynamic stability improvement. However, the performance depends on the locations of SCGs and fault contingencies.

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This paper deals with numerical analysis of behaviors for cooperative and competitive systems operated in the super distributed environment. Since the behavior is dictated by a complicated interaction of electric power outputs produced by numerous dispersed generators, the study is focused on the macroscopic behavior as well as the microscopic behavior of numerous dispersed generators based on the stability analysis of the Hopfield neural network. Some simulation results using a typical energy system model make it clear that maintenance of supply-and-demand balance becomes difficult when customers with a dispersed generation system cannot obtain sufficient information from their neighborhood.

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Taking the distributing woody biomass supply into account, this paper assesses the potential of a co-firing of woody biomass in utility's coal power plant from the both energy-saving and economical view points. Sawmill wastes, trimming wastes from fruit farms and streets, and thinning residues from forests in Aichi Prefecture are taken into account. Even though transportation energy is required, almost all of woody biomass can be more efficiently used in co-firing with coal than in a small-scale fuel cell system with gasification as a distributed utilization. When the capital cost of fuel cell system with 25% of total efficiency, including preprocess, gasification and power generation, is higher than 170× 10³yen/kW, almost all of thinning residues can be more economically used in co-firing. The cost of woody biomass used in co-firing is also compared with the transaction cost of renewable power in the current RPS scheme. The result suggests the co-firing of woody biomass in coal fired power plant can be feasible measure for effective utilization of woody biomass.

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The authors have proposed the Flexible, Reliable and Intelligent ENergy Delivery System (FRIENDS) as a concept of future electric power systems. The concept of FRIENDS takes into account the deregulation of the electric power industry and progress of technologies such as power electronics, distributed generators (DG), distributed energy storage systems (ESS), information and communication. One of the most important characteristics of FRIENDS is that new facilities called Quality Control Centers (QCC) are installed between distribution systems and electric consumers.
This paper presents a methodology for DSM based on a real-time pricing system through the information and communication network in FRIENDS. The economic use of DG and ESS in QCC is also considered in the proposed DSM. The sigmoid logistic function is used for modeling the real-time pricing system and a couple of parameters in the function are optimized by the Genetic Algorithm so that the profit of QCC is maximized. The effectiveness of the proposed DSM is ascertained by evaluating the profit or the load factor of QCC through simulations using model systems.

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In Japan electricity market will open on 1st April 2004. Electric utility, Power Producer and Supplier (:PPS) and Load Service Entity (:LSE) will join to the electricity market. LSEs purchase electricity based on Market Clearing Price (:MCP) from electricity market. LSEs supply electricity to the customers contracted with the LSEs on a certain electricity price, and one to the customers introduced Energy Storage System (:ES) on a time of use pricing. It is difficult for LSEs to estimate whether they have incentive to promote customers to introduce ES or not. In this paper, it is evaluated the reduction of LSEs' purchasing cost from electricity market and other LSEs' purchasing cost by introducing customers ES. It is clarified that which kind of customers has the effect of decreasing LSEs' purchasing cost and how much MCP of whole power system the demand-side energy storage systems change. Through numerical examples, this paper evaluates the possibility to give the cost merit to both customers with energy storage systems and LSE by using a real data of yearly MCP.

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Effective utilization of renewable energies such as wind energy is expected instead of the fossil fuel. Wind energy is not constant and windmill output is proportional to the cube of wind speed, which cause the generated power of wind turbine generators (WTGs) to fluctuate. In order to reduce output power fluctuation of wind farm, this paper presents a output power leveling control strategy of wind farm based on both average wind farm output power and standard deviation of wind farm output power, cooperative control strategy for WTGs, and pitch angle control using a generalized predictive controller (GPC) in all operating regions for WTG. The simulation results with using actual detailed model for wind farm systems show effectiveness of the proposed method.

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In order to analyze the potential gradient of ground surface of grounding system installed in buildings, the hemispherical grounding simulation system has been designed and fabricated as substantial and economical measures. Ground potential rise (GPR) has been measured and analyzed for shapes of a mesh grid grounding electrode by using the system. The system is apparatus to have a free reduced scale for conductor size and laying depth of a full scale grounding system. When a current flows through a grounding electrode, the system is constructed so that a shape of equipotential surface is nearly identified a free reduced scale model with a real scale model.
The system was composed of a hemispherical water tank, AC power supply, a movable potentiometer, and test grounding electrodes. The water tank was made of stainless steel and its diameter was 2m. AC power supply produced earth leakage current. GPR was measured by a moving probe of a potentiometer horizontally. The test grounding electrodes were fabricated through reducing grounding electrode installed in real buildings such as a mesh grid type, a combined type and so on. GPR has been measured in real time when a test current has flowed through grounding electrode. GPR was displayed in two-dimensional profile and was analyzed for shapes of a grounding electrode. When a mesh grid type was associated with a rod type and auxiliary mesh electrodes were installed at the four sides of mesh grid grounding electrode, GPR was the lowest of all test grounding electrodes. The proposed results would be applicable to evaluate GPR in the grounding systems, and the analytical data can be used to stabilize the electrical installations and prevent the electrical disasters.

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It is very effective to enhance the robustness of control over the faults occurred in power system in order to realize stable and reliable power supply. The sliding mode control based on the Variable Structure System (VSS) theory is paid attentions as one of the promising robust control scheme. In the sliding mode control, the structure of the control system is changed across the hyper plane (switching plane) in state space so that the state variables of the system are kept on the hyper plane.
This paper proposes a novel control method of generator's excitation system in which the concept of sliding mode control is employed. More specifically, the proposed method switches the reference voltage used in AVR according to the sign of switching function. This paper also discusses the systematic design procedure of the optimal hyper plane. Performance and effectiveness of the proposed control method are investigated through both numerical studies and experimental tests using the single-machine infinite-bus system simulator. Both results show that the proposed control method can damp the transient swing caused by a fault effectively.

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This paper addresses a new method to design a PI-based load-frequency control (LFC) with communication delays. First the LFC problem is reduced to a static output feedback control synthesis for a multiple delays system, and then the control parameters are easily carried out using robust H_∞ control technique. A 3-control area power system example is given to illustrate the proposed control methodology and the results are compared with the H_∞-based delay-less control system design.

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Recently, the assessment of control area performance has become an important subject in interconnected power systems. The North American Reliability Council (NERC) has adopted the control performance standards CPS1 and CPS2 for this purpose since 1997. However, the characteristics of these indices are not fully known.
This paper investigates the performance of CPS through analysis of two-area systems. Major dynamic elements of interconnected systems affecting the frequency are taken into account to investigate responses of the system against load disturbance. The analysis of CPS2 shows that, when two systems are interconnected, the smaller system tends to require more effort of control against load disturbance to keep the standard depending on condition.

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This paper proposes parallel connected transformers operation constrained optimal power flow. Usually, taps of parallel connected transformers are adjusted to be the same ratio to reduce transformers' load losses. Moreover, shunt capacitors and shunt reactors connected with parallel connected transformers are not used at the same time. It's supposed that increase of constraint on optimal power flow causes computing probrem, for example increasing time for computing, so the constraint about parallel connected transformers are not considered in the conventional optimal power flow. When an objective function much related to reactive power compensation is applied to the conventional optimal power flow, we can get a suitable solution for power system operation. However when an objective function not related to reactive power compensation is applied to the conventional optimal power flow, we cannot get suitable solution. The proposed method adjusts tap ratio of transformers and phase shifting equipment (power capacitor and shunt reactor) to be suitable for power system operation whatever objective function is applied. In addition, the proposed method can reduce the calcurate time.

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Wind turbine generators and PV system generate fluctuating power condition. Therefore, the fluctuating power causes frequency and voltage fluctuations. To solve this problem, we propose a new power supply system with using renewable energy in isolated island. The feature of this system is to use an aqua electrolyzer and fuel cell. The operation of suggested system absorbs fluctuating power of renewable energy. Furthermore, the proposed system is able to generate reactive power and active power with using three-phase inverter. The effectiveness of the proposed power supply system is shown through simulation results in this paper.

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This paper describes the surface breakdown characteristics of the silicone oil which has the possibility of the application to innovative switchgear as an insulating medium. At the first step, we have experimentally studied on the impulse breakdown characteristics of the configuration with a triple-junction where a solid insulator is in contact with the electrode. The test configurations consist of solid material (Nomex and pressboard) and liquid insulation oil (silicone and mineral oil). We have discussed the experimental results based on the maximal electric field at a triple-junction. As the second step, we have studied the configuration which may improve the surface breakdown characteristics by lowering the electric field near the triple-junction.

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The adhesive coated non-oriented electromagnetic steel sheet is well known to be effective in realizing high efficiency, high power motors with compact size and low noise. The authors developed newly adhesive coated grain oriented electromagnetic steel sheets. Then, a gapped iron-core type reactor having a new iron-core structure is developed using the adhesive coated steel sheets. By adopting the adhesive coated grain oriented electromagnetic steel sheets to the leg of the reactor, the fastening studs of the laminated electromagnetic steel sheets, which are required in conventional reactor, and the through hole for the fastening studs could be omitted. This enabled us to simplify the structure and reduce the core diameter. On the other hand, we examined the magnetic flux distributions and local loss distributions in the yoke by the detailed magnetic field analysis to utilize the grain oriented electromagnetic steel sheet with bolt-less construction, and realized the reduction of dimensions and weights due to the increase of magnetic flux density. The reactor developed has such features of smaller size, lighter weight and lower noise level.

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Lightning current distribution in a directly hit building is studied by using a simple equivalent circuit and an electromagnetic model. Numerical Electromagnetic Code (NEC-4) is employed for numerical electromagnetic analysis. Error in portion of lightning current into wiring, which is calculate by the electromagnetic model, is estimated to be less than 4%. Portions of lightning current into wiring on the top floor and the first floor are largest. Although they are larger for a higher building, they are almost constant if the number of floors of the stricken building is more than five. They are smaller when there are more vertical conductors, or length of wiring is longer.

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Water tree is one of the degradation aspects of XLPE cables used for under-ground distribution or transmission lines. We have developed the loss current method using 3rd harmonic in AC loss current for cable diagnosis. Harmonic components in loss current arise as a result of the non-linear voltage-current characteristics of water trees. We confirmed that the 3rd harmonic in AC loss current had good correlation with water tree growth and break down strength. After that, we have applied this method to the actual 66kV XLPE cable lines. Up to now, the number of the application results is more than 120 lines.
In this method, it is sometimes said that the degradation signal (3rd harmonic in loss current) is affected by the 3rd harmonic in the test voltage. To indicate and solve this problem, we investigated the extent of influence by 3rd harmonic in the test voltage, and found the rule of the influence. As a result, we developed a new technique of harmonic-noise reduction in loss current method that enabled a more highly accurate diagnosis and confirmed the effectiveness of this new technique by simulations and experiments with actual cables.

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For the size reduction of electric power equipment, electric field stress around solid insulators is to be increasing, therefore carefully be considered. The application of FGM (Functionally Graded Materials) will be effective solution for this concern. In this paper, we investigated an application feasibility of FGM, from both an experimental approach and numerical simulation. Finally, we could confirm the significant effect of FGM application for gas/solid composite insulation system. The estimation method developed in this paper is also effectively applied to the insulation performance around triple junctions in SF₆ gas.

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Solid Oxide Fuel Cell (SOFC) can be composed by solid components, and high power generation efficiency of a whole cycle is obtained by using high temperature exhaust heat for fuel reforming and bottoming power generation. Recently, the low temperature SOFC, which runs in the temperature range of around 600°C or above, has been developed with the high efficiency of power generation. On the other hand, multi-stage power generation system has been proposed by the United States DOE. In this study, a power generation system of two-stage SOFC by series connection of low and high temperature SOFCs has been studied. Overpotential data for low-temperature SOFC used in this study are based on recent published data, and those for high temperature SOFC arhaihe based on our previous study. The analytical results show the two-stage SOFC power generation efficiency of 50.3% and the total power generation efficiency of 56.1% under a standard operating condition.

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This paper describes technology required for advanced intelligent voltage and reactive secondary control systems enabling co-ordination of voltage control between main and local power systems. Firstly, the paper describes the general structure of a power system control and the concept of a proposed autonomous voltage and reactive power control system. Then, the paper comments on the inadequate behavior of voltage and reactive power control systems, such as up-and-down fluctuations, which sometimes occur during off-peak load times, and explains the reasons for voltage fluctuations. The capacity of distributed generation is increasing in accordance with deregulation of electric supply. In order to enhance voltage stability of power system, the voltage control system requires the more detail information and data of its local network systems, such as local demand forecast, distributed generation and characteristics of power systems. The paper briefly describes two previously developed intelligent component functions, namely, flexible feed forward control to prevent voltage fluctuation, and on-line acquisition of voltage characteristics by neural network technology. The paper describes local demand forecasting one or two hours in advance by the NN method. This method is also applicable to the forecast of the total demand of a power system.

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SF₆ gas has excellent dielectric strength and interruption performance. For these reasons, it has been widely used for gas insulated switchgear (GIS). However, use of SF₆ gas has become regulated under agreements set at the 1997 COP3. So investigation and development for GIS with a lower amount of SF₆ gas are being carried out worldwide. Presently, SF₆ gas-free GIS has been commercialized for the 24kV class. Air or N₂ gas is used as insulation gas for this GIS. On the other hand, SF₆ gas-free GIS has not been commercialized for 72kV class GIS. Dielectric strengths of air and N₂ gas are approximately 1/3 that of SF₆ gas. So to enhance insulation performance of air and N₂, we have investigated a hybrid gas insulation system which has the combined features of providing an insulation coating and suitable insulation gas. We have developed the world's first 72kV SF₆ gas-free GIS.
This paper deals with key technologies for SF₆ gas-free GIS such as the hybrid insulation structure, bellows for the high pressure vacuum circuit breaker, a newly designed disconnector and spacer and prevention of particle levitation. Test results of 72kV high pressure air-insulated GIS with the vacuum circuit breaker are described.

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Impedance spectroscopy of Z(ω) is often used in the electrochemical field to analyze electrode reactions and to calculate transient responses. Our previous study measured the overpotential resistance for our thermal behavior model to calculate the temperature rise of Nickel/metal-hydride battery or Lithium-ion battery during charge and discharge cycles. However, the Z(ω) measured by AC impedance meter did not agreed with the ones induced by charge/discharge characteristics. Therefore, we focus on the impedance measurement method by Takano et al, who obtained Z(ω) for Lithium-ion battery at wide frequency region by the Laplace transformation of both signals of the voltage-step input and its current response. We have extended this method to the Laplace transformation of current-step or current-pulse input signal and its voltage response signal to get Z(ω) for any charge/discharge current of Nickel/metal-hydride battery or Lithium-ion battery. We can get almost the same Z(ω) by the three different methods, and the measured Z(ω) does not depend on both charge/discharge current and the state of charge or the charge input. Moreover, Z(ω) including Warlbulg impedance at low frequencies gets near the overpotential resistance that can estimate well the battery temperature rise in our battery thermal behavior model.

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Although power semiconductor devices such as IGBTs and GTOs have been widely used for high power industrial applications, turn-off losses of those devices due to the current tail characteristics dominate their total switching losses. A soft switching technique is very effective in cutting down the switching losses.
We have proposed an energy storage system using a current-source inverter (CSI) and a zero-current switching bi-directional DC-DC converter with a simple L-C resonant circuit in our previous works. However, based on those works, the CSI circuit is turned on and off with a hard switching technique. Improvements of efficiency and performance of CSI are indispensable to implement the proposed system.
This paper proposed a soft-switching bi-directional circuit topology. The switching losses of CSI are reduced by adding a commutation circuit. In order to verify effectiveness of the proposed system, the system is analyzed in terms of the characteristics of switching losses and conversion efficiency, through a theoretical approach and computer simulations based on an instantaneous value analysis model.

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Beside photovoltaic (PV) systems are recently expected to introduce around Japan, almost all of them have not been taken care after established since PV systems are called maintenance free. In fact, there are few troubles about PV operations behind owners of PV systems because characteristics of them cannot be identified completely such as the ideal output energy. Therefore, it is very important to evaluate the characteristics of them. For evaluating them, equipments of measuring are required, and they, especially Pyrheliometer, are expensive as much as owners of the PV system cannot equip usually. Consequently, An evaluation method which can reveal the performance of operation such as the performance ratio with a very few kinds of data is necessary. In this paper, proposed method can evaluate performance ratio, shading losses, inverter efficiency losses by using only system output data items. The adequacies of the method are indicated by comparing with actual data and field survey results. As a result, the method is intended to be checking tool of PV system performance.

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In this paper, the novel standby mode operation of series type SMES (Superconducting Magnetic Energy Storage) for voltage sag compensation is presented. In the proposed control scheme for standby mode, the power losses are minimized and voltage drop is mitigated. The series type SMES is bypassed during the normal weather. During the adverse weather, the series type SMES can compensate voltage sags instantaneously. Simulations of standby mode operation and voltage sag compensation demonstrated the validation of the proposed control scheme.

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Voltage of power distribution line will be increased due to reverse power flow from grid-connected PV systems. In the case of high density grid connection, amount of voltage increasing will be higher than the stand-alone grid connection system. To prevent the over voltage of power distribution line, PV system's output will be restricted if the voltage of power distribution line is close to the upper limit of the control range. Because of this interaction, amount of output loss will be larger in high density case. This research developed a quantitative analysis method for PV systems output and losses to clarify the behavior of grid connected PV systems. All the measured data are classified into the loss factors using 1 minute average of 1 second data instead of typical 1 hour average. Operation point on the I-V curve is estimated to quantify the loss due to the output restriction using module temperature, array output voltage, array output current and solar irradiance. As a result, loss due to output restriction is successfully quantified and behavior of output restriction is clarified.

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In order to study the characteristics of copper wire according to the variation of fusing current, melting process of wire has been analyzed and the analysis of structure has been performed. Melting process was taken with HSIS (High Speed Imaging System) at a rate of 500 frames per second. A flash of light was seen at the center of the wire during melting process and a lot of small beads were scattered from the center to the outside of the wire. In the analysis of metallurgical structure, small dots grew into dendrite structure by overcurrent. Dendrite structure appeared in case that the values of current increase rate are lower than 2.5[A/sec], and the structure grew more according to the larger fusing time. Therefore, the growth of dendrite structure was related to the fusing time (current increase rate per time). The shorter the fusing time was, the narrower the melted areas were. SEM (Scanning Electron Microscope) and EDX (Energy Dispersive X-ray Spectrometer) analysis showed that oxygen is included in black dots of dendrite structure. An empirical equation was derived based on the experiments of fusing current, and the relationship among Preece, Onderdonk and the empirical equation was analyzed. The results will be applicable to the cause analysis of electrical fire because fusing time and fusing current can be calculated through the metallurgical analysis.

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The temperature of secondary batteries may increase above allowable limits and deteriorate its performance, during rapid charge and discharge cycles. Therefore, assessing thermal behavior of battery is essential. On the other hand, rectangular parallelepiped shape batteries are supposedly going to be used more commonly for cars and electrical devices because of their better space efficiency. Then, we constructed a two dimensional Cartesian coordinates battery thermal behavior model for a prismatic lithium-ion secondary battery during rapid charge and discharge cycles. It was extended from one dimensional cylindrical coordinates model, which had been developed and experimentally verified. As parameters of the numerical model, battery heat source factors such as overpotential resistance, entropy change, heat transfer coefficient and heat capacity have been measured. The radiation thermometer was used for obtaining battery surface temperature variance and distributions. Battery temperature generally increases as charge and discharge cycle proceeds, nevertheless temperature drops were observed at begging of low rate charge cycle and vicinity of SOC=0.8 in discharge cycle. Our modified model could predict these phenomena and agreed well with experimental results. Then the reliability of our numerical model and measuring techniques of heat source factors are confirmed each other.

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The introduction of Distributed Flexible Network Photovoltaic (DFNPV) system is going towards solving the shortcomings of stand-alone systems in remote areas. Three types of configurations of DFNPV system are studied: star, loop, and mesh. Each configuration has many subsystems, which are assumed to have the similar characteristics and location, and consist of PV panel, DC/DC converter, and dc load.
Comparative study had been carried out from the viewpoint of power losses in wires, wire length, and initial cost. First of all for estimating the size of DFNPV system within acceptable voltage drop, relations between wire length, power loss, wire cost, and cable types are discussed. The problem in DFNPV System is to find the best location of the battery bank from a many viewpoints, minimum extension cost and minimum losses in wires. This paper describes how to optimize the best location of the common battery bank from the viewpoints of the cost of power losses and the extension cost. The results of optimizing configurations show that a star configuration for initial installations is most effective, in future expansion; loop network is more cost effective. In addition, the economic study shows the final cost advantage of DFNPV system, for three types of configurations over stand-alone ones.

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The maintenance control of oil-immersed transformer based on dissolved gas analysis of insulation oil is carried out according to the Electric Technology Research Association report “The maintenance control of oil-immersed transformer". According to this diagnostic method, it is possible to discriminate between discharge mode and overheating mode. But in the overheating mode, it is difficult to judge the abnormality of an iron core group and the one of a winding group exactly. As for the cause of the gas occurrence of the overheat mode, the wrong point of the iron core occupies most. However, it has the difficulty of the countermeasure in the maintenance spot. Because it had to cope with it urgently when there was a wrong point in the winding group.
So, we did the experiment of the gas occurrence using actual models of winding and iron core, and could know the characteristics of the gas occurrence. The estimated precision improvement of the overheating point inside the transformer could be attempted, by adding the way of diagnosing which these characteristics were used for to the Electric Technology Research Association method.

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Accurate modeling of a pole-mounted distribution transformer is important in assessing lightning performance on a medium-voltage line. In this paper, equivalent circuits of 10kVA, 20kVA and 30kVA transformers for analysis of lightning overvoltage on a medium-voltage line are proposed based on measured primary-side admittance. The validity of equivalent circuits is ensured by comparison of measured responses of investigated transformers with calculations obtained by using the proposed equivalent circuits. The responses of transformers to lightning ovrevoltage dependent on their capacity are also studied.

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