bluuebunny/crossref_metadata_2025_split huggingface dataset:
One‐day‐ through seven‐day‐ahead electrical load forecasting in consideration of uncertainties of weather information
Authors: Miyake Takashi , Murata Junichi , Hirasawa Koutaro 
Published: July 2007

AbstractThis paper proposes an approach to one‐day‐through seven‐day‐ahead electrical load forecasting based on a realistic problem formulation which should contribute to more reliable and economic weekly power stations operation. Generally, the load forecasting has the following problems:

(1) although the load is affected by various factors, such as temperatures, in the load forecasting, it is impossible to consider all of them;
(2) the relationships between the load and some factors are not clear, and often vary with time; and
(3) uncertainties in forecasts of the temperatures sometimes make the results of load forecasting worse.
They are very influential in the power station operation. While a number of methods have been proposed to solve the problems (1) and (2), there have been few attempts to solve the problem (3).The following approach is proposed in this paper, taking these problems into consideration. First, concerning the problem (1), the focus is on such factors that have major influence on the load and whose values are obtainable on a weekly basis. The other factors are all regarded as stochastic and are not included in the forecasting model. Second, regarding the problem (2), a self‐organizing approach is used where the algorithm itself finds the optimal model structure or the optimal set of factors to be included in the model day by day. Finally, addressing the problem (3), a new performance index of model structures is proposed which can measure the balance between: i) improvement of the load‐forecasting accuracy due to inclusion of a factor in the model; and ii) degradation caused by uncertainty or error in the factor included. Using this index, a model is constructed which does not yield a large error in spite of errors in the temperature forecasts. Examples show that this approach improves the forecasted results when erroneous temperature forecasts are fed into the model, and verifies its effectiveness.
Power system stabilizing control by a superconducting magnetic energy storage with a high‐speed phase shifter
Authors: Uranaka Tsutomu , Mitani Yasunori , Tsuji Kiichiro 
Published: July 2007

AbstractElectric power demand has increased rapidly and this is expected to continue. Undamped power swings with low frequency tend to occur in large power systems with complex configuration. Therefore, several stabilizing control schemes, e.g., a power system stabilizer (PSS), have already been investigated.On the other hand, superconducting magnetic energy storage (SMES) is expected to be an effective apparatus in power systems since any SMES located in power systems is capable of leveling load demand, compensating for load changes, maintaining bus voltages and stabilizing power swings. The effectiveness of each function, however, depends upon the location of the SMES in the power system because output power from the SMES is distributed according to the impedance ratio of the transmission line at the SMES location. Therefore, it is difficult for SMES to serve two different purposes simultaneously.This paper proposes a combination of SMES with a high‐speed phase shifter (HSPS). The HSPS, which consists of a phase shift transformer and a set of power converters, is capable of controlling the power flow of the transmission line by adjusting the phase angle of a phase shift transformer. Therefore, it is expected that the combination of SMES and HSPS can realize a highly effective controller independent of its location. Numerical examples demonstrate that the proposed apparatus located far from a generator in a long distance bulk power transmission system is capable of stabilizing the power swing as effectively as the SMES located at a generator terminal. In addition, the effectiveness of both load change compensation and power system stabilization is confirmed numerically.
A parametrization of the discrete‐time two‐degree‐of‐freedom integral controllers with computation delays and its applications
Authors: Guo Hia‐Jiao , Ishihara Tadashi , Takeda Hiroshi 
Published: July 2007

AbstractUsing the observer‐based integral controller proposed by Isihara et al. as a basic controller, a state‐space parametrization of discrete‐time two‐degree‐of‐freedom integral controllers of combined general computation delays. The proposed parametrization can easily be obtained by using the solution of an LQG problem for a plant but not for a higher‐order extended system. In addition, the parametrization does not require constraints on the two free parameters. The role of the free parameters is clarified in connection with the basic controller. As applications of the proposed parametrization, the loop transfer recovery and the pole assignment using the free parameters are considered. A numerical example is presented to show the effectiveness of the proposed methods.
Performance of a 3000/6000 V, 1000 kVA class superconducting transformer developed for a prospective power transmission model system integrated under superconducting environment (PROMISE)
Authors: Tang Yue‐Jin , Shimizu Hirotaka , Kato Takeyoshi , Hayakawa Naoki , Yokomizu Yasunobu , Matsumura Toshiro , Okubo Hitoshi , Kito Yukio , Miyake Seiichi , Kumano Tomoyuki , Hatano Masayuki , Satoh Kazuhiko , Satoh Wataru 
Published: July 2007

AbstractA 3000/6000V, 1000 kVA class superconducting transformer (SC‐Tr) was developed for a Prospective Power Transmission Model System Integrated under Superconducting Environment (PROMISE). In this transformer, the core and superconducting windings are immersed in liquid helium and the major insulation is provided by the liquid helium. This paper describes both the design features and measured characteristics of the SC‐Tr. Fundamental characteristics of the SC‐Tr are obtained through no‐load, short‐circuit tests and quench experiments. The results of the no‐load test have verified that the SC‐Tr has the capability to withstand ac voltage of 3000/6000 V of 60 Hz without any partial discharge. The short‐circuit tests have proved that the SC‐Tr is capable of carrying ac current of 170 Arms without quench in the superconducting windings. Furthermore, in a real‐load experiment with the PROMISE, electric power of 3800 V‐460 kVA of 50 Hz in high‐voltage side is transmitted through this SC‐Tr.
Coordinated fuzzy logic control between SVC and PSS to enhance stability of power systems
Authors: Kihara Hidemi , Hiyama Takashi , Miyauchi Hajime , Ortmeyer Thomas H. 
Published: July 2007

AbstractThis paper presents a new switching control scheme for static var compensator (SVC) using fuzzy logic control rules to enhance the overall stability of electric power systems. In addition, the coordination with power system stabilizers (PSS) is also considered to achieve a wider stable region. An SVC is set on one of the busbars in the transmission system, where the real power flow signal is utilized at the location of the SVC to determine the firing angle of the thyristor switch. The switching control scheme is simple so as not to require heavy computation on the microcomputer based switching controller. The PSSs are also set on the generators in the study system. Simulation results show the effectiveness of the proposed fuzzy logic switching control scheme for the SVC. The coordination between SVC and PSS is also effective to enlarge the stable region.
Forecasting daily peak load by a deterministic prediction method employing Gram‐Schmidt orthonormalization
Authors: Mizukami Yuichi , Nishimori Toshiro , Okamoto Junko , Aihara Kazuyuki 
Published: July 2007

AbstractA technique for forecasting daily peak load in a utility power system is presented. After embedding time series data of daily peak load into a reconstructed state space, a nonlinear mapping is constructed by a local approximation method based on the orthonormal Gram‐Schmidt bases. This method utilizes only the past load data for short‐term prediction of the daily peak load, while many conventional methods make predictions with various kinds of data such as temperature and weather. The quality of prediction by the proposed method is as good as those with other prediction methods. Moreover, the results of short‐term prediction by this method are satisfactory even with data as small as 250 points.
Eddy current testing by upgraded microloop magnetic sensor array
Authors: Uesaka Mitsuru , Hakuta Kazumi , Miya Kenzo , Aoki Kazuhiko , Takahashi Ayumu 
Published: July 2007

AbstractA micro‐eddy current testing (ECT) probe, which consists of a planar microloop inductive magnetic sensor array and a pancake‐type exciting coil, was developed to upgrade the ECT technology, especially as it is used for inspecting steam generator tubing in a pressurized nuclear power plant (PWR). Eddy currents and resultant magnetic fields are perturbed due to a flaw in a conductor. The flaw is detected via perturbation of the electromotive force (EMF) and phase from the array. Flaws manufactured by electric discharge machining in INCONEL 600 planar specimens, the thickness of which was 1.25 mm, were detected and reconstructed by using stacked database and simplified algorithm. Even an outer‐edged 10 percent flaw could be detected. Measured EMF and phase signals were compared with numerical results obtained by using a three‐dimensional eddy current and field analysis code and then verified. The experiment confirmed that the spatial resolution of detection of the micro‐ECT probe is superior to that of the conventional pancake‐type ECT probe. Finally, it was demonstrated that it is possible to establish the same measurement speed using the micro‐ECT probe as it is by using the pancake‐type ECT probe.
Heating and acceleration processes of high melting point ceramic particles in pulsed plasma
Authors: Miyamoto Masahiro , Hikosaka Tomoyuki , Yamada Mamoru , Sakuta Tadahiro , Tago Masanari 
Published: July 2007

AbstractPlasma spraying is gradually becoming an important technique in the materials processing field, its primary feature being the ease by which the area or thickness of the deposited film can be controlled. High‐temperature plasmas to heat ceramic particles with a high melting point have in the past been generated by dc power sources. Applying a pulsed plasma using a high current of the order of tens of kA is proposed for the plasma spraying of refractory materials.Numerical analysis of the short‐time heating and acceleration of the particles showed that alumina particles 20 μ in diameter reach the complete melting state after a residence time of 83 and 9.6 μs and a flying distance of 5.8 and 0.5 mm, when the temperature of the pulsed plasma is assumed to be 10,000 and 20,000, respectively, with a constant plasma velocity of 200 m/s.Experiments are then performed using a specially developed plasma torch with a pulsed discharged current of 24 kA peak and a duration of 400 μs. This current is provided from a capacitor with a maximum stored energy of 14 kJ. The simultaneous, in‐flight measurements of the temperature, velocity, and size were taken for alumina particles injected into the pulsed plasma. Results show that the surface temperature of the alumina particles reached values as high as 2700 to 3300 K, which was considerably higher than the melting point. Particle velocity was found to be around 200 m/s, which is comparable to that of dc plasma. The experimental results confirmed the applicability of pulsed plasma for the spraying of refractory materials.
Power control of coupled nonequilibrium disk MHD generator and line‐commutated inverter system
Authors: Inui Yoshitaka , Ishikawa Motoo , Umoto Juro 
Published: July 2007

AbstractA new power control method is proposed which is suitable for the MHD power generation system which consists of nonequilibrium disk generator and line‐commutated inverter. The thermal input of the generator is controlled by changing the inlet stagnation pressure, whereas the seed mass flow rate instead of the inlet stagnation pressure is utilized as a manipulated variable of power control system. It is possible that the proposed method can realize both high performance for part load operation and fast output power control of which the time constant is much shorter than the response time of thermal input. Numerical simulations are carried out for the MHD power generation system connected to infinite bus and then it is confirmed that the system is stable and shows excellent power control performance.
Transient analysis of converter‐fed adjustable‐speed generator‐motor for the pumped storage power plant
Authors: Yanagisawa Tadahiro , Kageyama Takahisa , Okamura Kazuhiko , Kusunoki Kiyoshi , Taguchi Tadashi , Abe Michiyuki , Kaneko Hirokazu 
Published: July 2007

AbstractA converter‐fed adjustable‐speed generator‐motor for a pumped storage power plant has been developed in order to contribute to the automatic frequency control on an electric power system during pumping operations, as well as to improve the efficiency of turbines during generating operations together with stability. This system consists of a reversible pump turbine, a generator motor, cycloconverter and control units. The rotor of the generator motor, which is coupled directly with the turbine runner, normally is operated at a rotating speed which is equal to the difference between the frequency of the electric power system and that of the rotor current. In the state that a fault has occurred in the primary circuit of the generator motor, the adjustable‐speed generator‐motor fault current differs from that of a conventional synchronous generator motor.This paper describes the fault current analysis results for the condition when a sudden short‐circuit is made on the primary side of the generator motor, and collates the results with the field test and EMTP simulation results.
An efficient faults calculation method taking into account mutually coupled lines of power systems
Authors: Tanaka Kazuyuki 
Published: July 2007

AbstractIt is necessary to take into account the effects of mutual couplings when unbalanced faults are to be calculated in transient stability study.When the method based on symmetrical coordinates is applied to faults calculation, it has been necessary in the conventional method to construct the zero sequence network, the configuration of which is more complex than other networks so far. Then, the application of faults calculation including mutual couplings to the analysis on the bulk power system model has been considerably difficult for a long time.This report presents a newly developed method to calculate the effects of mutual coupling in multifaults calculation under the same configuration and with no change for all sequence networks. The validity of the proposed method was verified through the application of transient stability analysis for power system models.
Genetic algorithm‐based method for contingency screening in power systems
Authors: Saitoh Hiroumi , Takano Yutaka , Toyoda Junichi 
Published: July 2007

AbstractThis paper proposes an application of genetic algorithm (GA) to contingency screening in power systems. The contingency selected by the GA‐based screening method is the double line outage which has the risk of causing transient instability. Generally, the contingency screening problem including multiple outage can be interpreted as the combinatorial optimization one for searching the combination of single outages which makes the system insecure. Therefore, GA which is one of the probabilistic searches for combinatorial problems, is applicable for such contingency screening problems. In the GA‐based contingency screening method, a double line outage is represented as a chromosome. The fitness of the chromosome for environment is defined by using the transient energy function of power systems. The new procedure for avoiding the loss of important outage during contingency screening is developed and embedded in the proposed method by using the theorem of schema for GA. The validity of the proposed method is confirmed by applying it to a 6‐machine 30‐bus 40‐line system. The result shows that the GA‐based contingency screening has the potential for practical use.
Evaluation of influence of external magnetic disturbance on superconducting magnet taking conservation of linkage flux into account
Authors: Takechi Moriaki , Kuroda Sigenori 
Published: July 2007

AbstractExternal magnetic disturbance influences the quality of the image obtained with a magnetic resonance imaging (MRI) system because it causes magnetic resonance frequency drift. When a superconducting magnet in persistent current mode operation is exposed to external magnetic disturbance coil current varies to keep linkage flux constant. Conventional analysis is usually formulated with constant current and does not provide correct evaluation of drift of magnetic field in the magnet. This paper proposes a method of numerical analysis of magnetic field considering conservation of linkage flux in a superconducting magnet under a persistent current mode operation. This method is applied to evaluate drift of the magnetic field in a superconducting magnet for magnetic resonance imaging due to external magnetic disturbance. Analysis results show good agreement with the experimental results.
Multiple single‐phase PWM inverter by means of combination control
Authors: Ohnishi Tokuo 
Published: July 2007

AbstractA new multilevel inverter with simple circuit configuration and control is proposed here. The inverter is composed of a series connection of individual single‐phase inverters. The number of the output voltage levels depends on the number of the individual inverters in series and their output voltage level. The switching devices in the new circuit configuration can be reduced by using a common switching‐leg for the individual inverters. In this inverter circuit, the number of the levels is equal to 2m‐1 or 2m where m is the number of switching‐legs used.In the paper, a 15 level inverter using four switching legs (m = 4) is introduced. If the number of voltage levels is increased, smoother sinusoidal waveforms can be obtained directly and it is possible to control the output voltage almost continuously from zero to maximum without generating high‐voltage step changes as pulsewidth modulation techniques.The control principle, the circuit configuration and the characteristics of the output voltage control are discussed. The feasibility of the circuit is demonstrated by simulation and experimental results.
A basic study on power storage capacitor systems
Authors: Okamura Michio 
Published: July 2007

AbstractStorage batteries or pumped hydraulic power stations have been used to store electric energy. However, there are problems with storage batteries, e.g., long charging time, limited cycle life, low Coulomb efficiency, and inaccurate residual power meters. Because of these problems, practical power applications have not been achieved.To solve these problems, a complex system of capacitors and electronic circuits called the ECS (Energy Capacitor System) is proposed. The capacitor part of the ECS is a group of electric double‐layer capacitors of increased energy density. The circuits part is built around switching regulators. Although the capacitors alone are not capable of delivering stable output, the accompanying circuits compensate for various characteristics throughout the charge and discharge cycle.This combination of capacitors and electronic circuits increases the energy density by about 16 times that of the conventional electric double‐layer capacitors, close to the level of lead‐acid batteries but with lower output resistance and better voltage stability. The ECS inherently features short charging time, very long cycle life, and good Coulomb efficiency. The cells are completely sealed and made from materials which are not harmful to the environment.
Characteristics of flow and plasma under high MHD interaction in nonequilibrium disk MHD generator using argon
Authors: Tsuji Kiyoshi , Okubo Masaaki , Yamasaki Hiroyuki , Niwa Yoshimitsu , Kaneko Tetsuya 
Published: July 2007

AbstractResults of experimental studies on behavior of a supersonic flow and of a nonequilibrium plasma in a disk MHD generator are presented. The experiments with cesium seeded argon were carried out under high MHD interaction conditions. Effects of seed fractions on static pressure distributions, flow Mach numbers, electron temperatures and uniformity of discharge in the disk MHD channel were investigated. The results have shown that the flow is kept supersonic throughout the disk MHD channel when a sufficient Joule heating exists in a supersonic nozzle and the seed is fully ionized. It was found that there was an optimum seed fraction at which the power output became maximum and, at the same time, the seed was fully ionized. Furthermore, an almost uniform discharge due to the full ionization of seed was observed. It is noted that enthalpy extractions and adiabatic efficiencies were increased remarkably, and the highest enthalpy extraction of 26.5 percent was achieved for cesium seeded argon. However, adiabatic efficiencies remained still low due to large pressure losses.
Measurement method using coupled transmission lines for voltage transients on the distribution line
Authors: Kawamata Ken , Minegishi Shigeki , Haga Akira , Sato Risaburo 
Published: July 2007

AbstractIt is well known that voltage transients are caused by the operation of switchgears in a power system. The voltage transients travel along the power line as a traveling wave, and cause malfunction of electrical devices, communication systems, and the operational error of a control system.The voltage transients at the making operation of switchgear were examined to obtain the fundamental data for considering the immunity of communication systems used on a power system. However, it was difficult to observe the voltage transients using the potential transformer and the capacitance potential device because the transients were very rapid.Therefore, a measurement method using the coupled transmission line system is proposed to measure the high‐speed and high‐voltage transients, and the actual experimental results on the 6.9‐kV power system are presented. This method enables the measurement of high‐speed voltage transients in out of contact with the power system.
Discharge luminescence and discharge magnitude in treeing degradation
Authors: Ehara Yoshiyasu , Ito Tairo , Kishida Haruo , Sakai Takao 
Published: July 2007

AbstractThis paper describes results of the discharge luminescence and discharge magnitude measurements performed on the insulation materials exposed to partial discharge. Polymethyl methacrylate (PMMA) with an artificial needle shape void were used as the treeing specimens. The discharge luminescence is observed by image intensifier, and the luminous image is processed by computer. At the same time, the discharge magnitude distribution in relation to phase angle of the applied voltage was measured by a partial discharge measuring system. The mechanism of electric treeing was discussed by not only the measurement of the discharge pulses but also the local luminescence intensity of partial discharge.As a result, the luminescence intensity analysis showed the relation between tree growing length and void length when maximum luminescence intensity moved from the void area to the tree area. Both tree growth and maximum luminescence intensity at the tree area increase with constant ratio. The discharge luminescence intensity at the tree area increases significantly depending on the discharge magnitude in the specific phase angle area in positive and negative.