Introduction of fault current limiter (FCL) is expected as a promising candidate of short-circuit current suppression method in electric power system. However, there is so far no FCL put to practical use in actual electric power system. The present report describes problems to be solved for application of FCL. The current state and trends of research and development of FCL are also reported.

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A new circuit of parallel type voltage sag compensator is proposed in this paper. The proposed voltage sag compensator can reduce the necessary capacity of the energy storage capacitor for compensation by boost type power factor correction rectifier charging the capacitor during a voltage sag. As a result the proposed system can reduce the size and maintenances of the apparatus.
This paper shows principle and control system of the proposed circuit. Compensation characteristics were demonstrated by simulation and experiment.

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Application of a dispersed power supply system combined with a large scale photovoltaic system (PV), a fuel cell (FC) and an electric double layer capacitor (EDLC) is studied in this paper. This system is operated in autonomous mode, taking account of time delay characteristics of FC. The modified Euler type Moving Average Prediction (EMAP) model is improved using short time fast fourier transform (ST-FFT). The Adaptive Control type EMAP (AC-EMAP) model is introduced to reduce the capacity of EDLC. This system can meet the multi-quality electric power requirements of customers, and compensate voltage stability and uninterruptible power supply (UPS) function as well. Moreover, the required capacity of EDLC to compensate the fluctuation of both PV output and load demand is clarified by the simulation based on collaborative operation method by a prediction model using software MATLAB/Simulink.

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This paper proposes and analyzes a new simple real-time phase-estimation method for single-phase signals, which is based on a vector mapping theory of n-dimensional to 2-dimensional vectors. According to the analyses, the proposed mapping method can estimate instantly and properly the true phase of the signals that are contaminated by significant amplitude of noise and harmonics. The mapping method contains the conventional DFT method as a special case. In other words, it can be treated as a generalization of the DFT. Several simple realizations of the mapping method are also newly proposed as a single-input and two-output digital mapping filter in both non-recursive and recursive forms. The recursive realization being able to decrease drastically computing load utilizes the normal form that is robust to finite word length effects. As an application of the proposed mapping method, inverter-used power control system connected with a single-phase gird is shown. All analytical results are verified by numerical experiments and usefulness of the newly proposed mapping method is confirmed.

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This paper proposes a very short-term load forecasting technique in order to make Economic Load Dispatching Control (EDC) more effective. The controllable periodic term of EDC is made clear through power spectrum analysis of actual load and actual EDC outputs of the Kansai Electric Power Company. A real-time predictor is designed based on this result, and it can decrease the EDC error at almost the same level as the actual AR (Area Requirement: final error after EDC and LFC) through the year. In addition, it can be seen from the generation simulation by using this predictor that we can decrease the fuel cost and LFC margin.

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FRIENDS (Flexible, Reliable and Intelligent ENergy Delivery System) is a new concept for future power delivery system in which so-called QCC (Quality Control Center) plays an important role to realize the customized power quality services and to connect a large number of distributed generators to distribution systems. In FRIENDS, QCCs are connected as a network through distribution cables to realize a reliable power supply. In this paper, a method to find the optimal network configuration of FRIENDS is proposed. The method can minimize the sum of facility installation cost and operational cost (distribution loss) under the constraint that the expected power interruption cost is less than a predetermined endurable value. The solution algorithm is based on tabu search, and employs a sensitivity analysis to select efficient facilities to be installed or to eliminate constraint violations. In the algorithm, single and double faults of power distribution system are taking into account to calculate the power supply reliability or expected power interruption cost. Several numerical examples in real world are shown to demonstrate the validity of the algorithm.

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This paper describes how to smoothly restore the power system from blackout using a hydro power plant. Various kinds of abnormal phenomena could occur during the period of blackouts and restoration. Taking various possible abnormal phenomena into account, the authors first performed an analytical study of power system restoration processes using the proposed method with a simplified power system model consisting of a generator, some transmission lines and transformers. Based on this study, an actual power system test was then carried out. A transformer voltage goes to increase after its voltage application. This voltage increase causes an over voltage problem to a transformer. The authors are proposing practical countermeasures on the over voltage problem at restoration with a hydro power plant.

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Braking resistor is known to be a very powerful tool for transient stability improvement in electric power systems. Usually, in a large power system braking resistors are placed at each generator terminal bus which requires a high installation as well as operation cost. Also, heavy computation is required for the controllers used for the switching of the resistors. From these viewpoints, this paper directs to the study of installation of reduced number of fuzzy logic controlled braking resistors at suitable locations for transient stability enhancement. Groups of coherent generators in the power system are determined. Then one braking resistor is installed in each of the coherent group and at each of the remaining generator terminal bus. Thus, the number of braking resistors is reduced and hence the installation and operation cost as well as computational burden for the controllers are minimized. The suitable location for the braking resistor in each coherent group of generators is determined according to the values of the transient stability index as calculated for a 3LG (Three-phase-to-ground) fault at the points near the generators of the coherent group without considering the braking resistors in the system. The effectiveness of the proposed method is demonstrated through EMTP simulations for the IEEJ West-10 machine model system.

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In this paper, the authors evaluate the cost to secure the reserve capacity from the view point of ISO under the competitive environment. It is going on the deregulation of electric power industry now in Japan, and it is assumed that many companies will get into the generation category newly and energy market will be established. So we have to secure the reserve capacity enough to maintain the supply reliability after the deregulation. Generally, it is supposed that ISO should have the responsibility of securing the reserve capacity. Therefore, in this paper we propose two types of ISO security model, one is “Reserve market-based security model" and the other is “Commitment-based security model". The purpose in this paper is to compare with two models in terms of the cost for the supply security and research the better model for the customers.

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This paper aims to develop a single price auction model with AC transmission network, based on the principle of maximizing social surplus of electricity market. Specifically, we first formulate the auction market as a nonlinear optimization problem, which has almost the same form as the conventional optimal power flow problem, and then propose an algorithm to derive both market clearing price and trade volume of each player even for the case of market-splitting. As indicated in the paper, the proposed approach can be used not only for the price evaluation of auction or bidding market but also for analysis of bidding strategy, congestion effect and other constraints or factors. Several numerical examples are used to demonstrate effectiveness of our method.

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It is unavoidable for electric power companies to inspect and to maintain electric power facilities. Each work is generally called as an outage work due to suspending power supply to the relevant electric power facility. The power companies are expected to operate a power system retaining high power supply reliability even during outage works. Therefore, they need to make an outage work plan carefully, considering a great number of power system conditions and restrictions. Several studies in this area have been so far carried out by research organizations including power manufacture. Most of them are dedicated to obtain a feasible plan without considering power supply reliabilities because it is virtually impossible to find out the best plan with high reliability out of enormous combinations of system configurations. In this paper, the authors regard the outage work scheduling as a combinatorial problem of system configurations. We provide a framework to solve the problem and some results by numerical simulations in order to confirm the effectiveness of our study.

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Characteristic average power spectra in intervals from 25 to 100MHz are presented for electromagnetic radiation fields from some specific lightning events: preliminary breakdown processes, downward negative stepped- and dart- leaders, return strokes, K changes in cloud-to-ground lightning (CG) and in intra-cloud lightning (IC) flashes, and upward positive leaders in artificially triggered lightning flashes. The spectra are obtained by means of the Fourier transformation of wideband records of electric fields from lightning. Results show that the spectral patterns for these events are obviously dissimilar in the frequency band studied. The spectrum for the IC, the preliminary breakdown process and the K change usually peaks once around 60MHz, while that for the downward negative leader peaks initially around 60-70MHz then around 26MHz as the leader propagates down out the clouds. The spectrum for the upward positive leader in artificially triggered lightning, however, peaks at about 26MHz, whether the leader is propagating below or within the clouds. The dissimilarities in the spectral pattern in the range of 25-100MHz between different lightning events may imply that these events have dissimilar discharge mechanisms and provide a basis for identifying these different discharge events.

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Using high temperature superconductor, a Superconducting Fault Current Limiter (SFCL) was made and tested. Superconductor and vacuum interrupter as commutation switch are connected in parallel with bypass coil. When a fault occurs and the excessive current flows, superconductor is first quenched and the current is transferred to bypass coil because on voltage drop of superconductor. At the same time, since magnetic field is generated by current which flows in bypass coil, commutation switch is immediately driven by electromagnetic repulsion plate connected to driving rod of vacuum interrupter, and superconductor is separated from this circuit. Using the testing model, we could separate the superconductor from a circuit due to movement of vacuum interrupter within half-cycle current and transfer all current to bypass coil. Since operation of a commutation switch is included in current limiting operation of this testing model, it is one of helpful circuit of development of SFCL in the future. Moreover, since it can make the consumed energy of superconductor small during fault state due to realization of high-speed switch with simple composition, the burden of superconductor is reduced compared with conventional resistive type SFCL and it is considered that the flexibility of a SFCL design increases. Cooperation with a circuit breaker was also considered, the trial calculation of a parameter and energy of operation is conducted and discussion in the case of installing the SFCL to electric power system is made.

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The NbTi superconducting strands and cables for the field winding of 200MW class high energy density type superconducting generator are developed. They are composed of Cu/Cu-10wt%Ni/Nb-46.5wt%Ti superconducting strands and the 10kA (at 5T) class 9-strand compacted cables. The diameter of strands is 1.33mm, and the 9-strand compacted cables are 2.4mm thick and 6.0mm wide. In order to produce high current density NbTi strands, we made strands under the controlled aging heat treatments, the total and final strains, and the strains between heat treatments, by using large scale extruder. Moreover, in order to produce high stability and low A. C. loss NbTi strands and cables, the matrix ratio of strands and the cross sections of strands are optimized. The current density of NbTi filaments for the 4 times aging manufactured 1.33mm dia. strands was Jc = 3150A/mm² at 5T, 1150A/mm² at 8T. The critical current of the class 9-strand compacted cable is 10.7kA at 5T. The A. C. losses of the final compacted cables are less than 100kW/m³ at 5T, 5T/s, they are decreased to less than half of the target of the A. C. loss value (< 200kW/m³ at 5T, 5T/s). Compared with the strand (Cu ratio: 1.77), the minimum quench energy (MQE) of the strand (Cu ratio > 2) increased about 40% at the operation mode current of the superconducting generator.

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Photovoltaic (PV) systems have been introduced around Japan, and expected to diffuse more and more. As well as a lot of PV systems are installed; all of them have not been taken care after established. In fact, there are some troubles about PV operations behind owners of PV systems even if they are very few cases. It seems to be difficult to identify characteristics of PV systems 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 with main systems as usual. 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. As for evaluation, irradiation data are absolutely imperative item. An estimation method of irradiation by using external data is one of the essential studies. Therefore, developing the estimation method of irradiation is intended in this study.
In Japan, there are the weather observation stations which are Automated Meteorological Data Acquisition System (AMeDAS) and surface weather observation administered by Japan Meteorological Agency (JMA). In this method, it is essence that the irradiation data is alternated by estimated data from AMeDAS and actual measuring data from JMA. The data of them are appropriately each weather condition. Irradiation is estimated by AMeDAS data on fine days, and JMA data are alternated on the cloudy days. As a result, the proposed method can estimate irradiation less than 10% of error.

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