The air-conditioner load is the most variable component of the system load of the Kansai Electric Power Company. As the magnitude of the air-conditioner load changes with the temperature and time, the voltage and frequency characteristics of the system load change significantly. The air-conditioner load is one of the most important load components that determine the aggregate bus load characteristics. I examined the voltage characteristics of the air-conditioner load.

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The control of power system networks will become more and more difficult due to installation of new facilities and uneven distribution of loads and generation. In particular, keeping voltage profile at desired value is becoming main problem in power system control because large voltage fluctuation at the substation bus occurs very frequently which makes the power system more and more unstable. In this paper, voltage reactive power controlling method based on time schedule control of shunt reactor and static capacitor is presented. This approach corrects the time schedule of voltage control equipment according to the fluctuation of voltage comparing with the result of power system state forecasting.
This approach is evaluated with small scale and whole power system, and the results show that this proposed method successfully reduces amount of voltage violation and transmission power loss comparing with real data.

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In the near future, many distributed generation systems, such as photovoltaic or wind power generation, will be interconnected to the electric power distribution systems of Japan. Therefore, we must make the best use of the distributed generation systems considering their influence on power quality, stability, and so on.
This paper investigates the influence of distributed generation systems on the voltage characteristics in distribution systems by a stochastic approach. Firstly, we calculate the node voltage fluctuations in a test distribution system using the stochastic power flow, and show that the voltage characteristics deteriorate after interconnecting distributed generation systems. Secondly, we formulate the problem of voltage characteristics improvement as the nonlinear optimization problem which has the following objective functions: 1) minimize the total voltage fluctuations throughout a distribution system; 2) regulate the node voltage at a specified value considering voltage fluctuations. These problems can be also solved using the stochastic power flow. The simulation results show that the node voltage fluctuations can be minimized by controlling the parameters regarding the reactive power of distributed generation systems, and the stochastic power flow is effective in calculating the practical value of reactive power of distributed generation systems in order to regulate the node voltage.

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In this paper, a new steam turbine power generation system utilizing waste heat from factories is proposed for leveling the electric power load. Hydrogen and oxygen, which are produced by using excess electric power at nighttime with electrolysis of water, are used in the proposed system as fuel and oxidant, respectively. It is assumed that the saturated steam produced by utilizing waste heat from factories is available for the system to use. Changes in power generation characteristics have been estimated by using a simulation model when both the temperature of the saturated temperature and turbine inlet temperature are changed. It has been shown through simulation study that the higher the saturated steam temperature the higher the electric energy saving efficiency and the smaller the generated power at daytime, and that the higher the turbine inlet temperature the larger the generated electric power at daytime and the smaller the electric energy saving efficiency. It has been shown, for example, that 4.78 MW of the net electric power can be produced with the electric energy saving efficiency of 98.8% when turbine inlet temperature is 400°, and temperature and quantity of the saturated steam is 140° and 22.6 t/h, respectively. This estimated value 98.8% is higher by 41.1% compared with the electric energy saving efficiency, 70%, of a pumping-up power generation system. Thus, the proposed system can be expected to become one of the high-efficient power generation systems for leveling electric power load.

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In recent years, many studies have been made to allocate NAS batteries in distribution substations for making good use of facilities and improving the load factor. Besides, it has been also hoped to utilize NAS batteries for the controls such as LFC and VQC, because NAS batteries can respond faster than existing generator units and can control active and reactive power outputs independently by the function of AC-DC converter systems. This paper presents a method for determining the optimal allocation and PQ output ratio of NAS batteries in order to improve voltage stability. The proposed method combines a sensitivity method with an OPF method, and can determine the allocation and PQ output ratio efficiently and optimally. Simulations are carried out for Ward & Hale 6-bus system and 73-bus distribution system to illustrate and verify the proposed method.

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Wavelet transform is one of the most efficient tools for analyzing non-stationary signals such as transients, and has been widely applied to solve numerous problems in power systems. This paper demonstrates a novel application of wavelet transform to identify the causes of ground faults in power distribution systems. The discrimination scheme which can automatically recognize the fault causes is proposed using artificial neural networks. The scheme can be separated into two stages, the time-frequency analysis of transients by wavelet transform and the pattern recognition to identify the causes of faults. By using the actual fault data, it is shown that the proposed method provides satisfactory results for identifying the fault causes. Moreover, the results obtained by this method are useful to explain the mechanisms of faults simultaneously.

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District Heating and Cooling energy supply system (DHC), which was widely spread in Japan to prevent air pollution by emission gas from boilers, has been recognized as an important district facility for supplying thermal energy as well as for saving energy and others.
This paper explored an optimization method applicable to select heating and cooling equipment in planning and designing of DHC. The proposed optimization method makes use of an extended dynamic programming (ExDP) algorithm developed by the authors, which is based on a best-mix algorithm applied to the power systems. The ExDP optimizes a nonlinear objective function under multiple linear constraints as a combinatorial problem.
Preliminary study by “ordinary” DP method resulted in showing an inevitable explosion of combinations due to the NP-hard. To cope with this difficulty, a judgement criterion to relax the combinatorial explosion was introduced by the authors. Consequently, the ExDP enabled to search an exact solution for the problem almost in real time. This means the ExDP paved a way for the optimization of the DHC problem, which had been unsolvable.

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Lead acid batteries present difficulty in estimating the remaining capacity because its deterioration is not detectable externally. Currently, the remaining capacity is measured by means of complete discharge. However, this method is not only time consuming but there is the possibility of causing damage to the performance of the battery itself. Although research for more simplified methods has been underway, hardly any results have been gained in accurately estimating battery remaining capacity.
We have been investigating various parameters to estimate floating charging battery capacity, and have found a very good correlation between the minimum value of a cell terminal voltage (minimum voltage) which appeared at the beginning of the discharge and the battery capacity. Examinations of past studies and experiment results showed that the generation of this minimum voltage was due to the temporal supersaturation of divalent lead ion (a discharge intermediate), which is attributable to lack of a lead sulfate crystalline nucleus. In addition, it was clarified that the correlation was good because it was a point at which we were able to measure the voltage without disturbance of the unstationary concentration polarization which occurred at the beginning of the discharge, and we could estimate battery capacity in short time with high accuracy by the new technique used this good correlation.

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In designing a Gas insulated bus (GIB) using N₂/SF₆ mixtures, there are many application problems such as the mixtures pressure to maintain the required dielectric and heat transfer performance. The problems on recycling SF₆ are also essential in applying N₂/SF₆ mixtures. In this paper, the minimum breakdown field strength at lightning impulse and temperature rise of conductor and enclosure have been measured for N₂/SF₆ mixtures. Considering the dielectric and heat transfer properties, we clarify the application problems of mixtures to a GIB and discuss the appropriate mixture ratio of SF₆ in designing the GIB comparable to the present dimension. And also the lowest limit of SF₆ content in a liquefied recovering method is theoretically estimated for the reference of practical SF₆ recovery from mixtures. It is important for the design to consider both breakdown phenomena including area effect of electrode and heat transfer properties of mixtures.

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The two types of epoxy molding resin combination systems for outdoor are found out by the examination of the silane coupling disposition to the filler and the coloring material based Grycidylester epoxy resin. These systems are tested by the high energy Xenon-arc accelerated weather-meter, and confirmed that these systems are better than Epi-bis type epoxy molding resin for 5 to 10 times at surface erosion depth, surface roughness and contact angle. And these systems are tested tracking and creep characteristics. The tracking characteristic is confirmed that these systems are equality or better than Silicone and EVA for polymer insulator. The creep characteristic is found out suitableness 30 years.
One of these epoxy molding resin combination systems is applied the outdoor separate type CT, and practical used since June 1999.

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Abstract - The sag in an overhead transmission line is very much influenced by the current in the conductor. Until recently, the current carrying capacity of a conductor has been determined by the deterministic approach. However, the probabilistic approach has become popular in recent times, and it is being applied in designing insulation, mechanical components, general electrical apparatus, etc. A new method, based on the probabilistic technique, is used to assess the sag in an overhead line in this paper. This is to avail another method, which looks more promising than the deterministic approach, and can provide utility companies as well as analysts a basis for comparison.
Recorded data on some climatic factors and transmission line current are used in our analyses.

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There have been reports on simultaneous measurements of the lightning current and the induced voltage on test distribution lines. The data in these reports are analyzed by a numerical model on the coupling of a lightning stroke and an overhead wire postulating several stroke models. The calculated induced voltage waveforms are compared with the actually measured waveforms, and the validity of each model of the lightning stroke is discussed.

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Unit step response characteristics of an impulse voltage measuring system are studied with the help of the Numerical Electromagnetic Code (NEC-2). An impulse voltage measuring system behaves as an antenna until a traveling wave makes several round-trips in the lead wire. Therefore, the response characteristics of a divider in this interval cannot be evaluated appropriately by the methods based on the circuit theory or the transmission-line theory. The NEC-2 code can analyze such dynamic electromagnetic field around a three-dimensional conductor system. In the present paper, the role of a shield ring is intensively investigated and is discussed on the basis of the analyzed results.

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Quasi-one-dimensional time-dependent numerical simulations of a supersonic nonequilibrium disk MHD generator are carried out for various load conditions by selecting the calculation region between the subsonic nozzle and
the diffuser. The generator studied is a large-scale type using cesium-seeded helium plasma with 100 MW thermal input and 40 MW electrical output. It is made clear that results of the conventional simulations, in which only the generation channel is analyzed, are valid and the present simulation is not exactly essential when the load resistance is lower than its nominal value. In high load resistance condition, the gas flow becomes subsonic all over the generator and the conventional simulations could not predict the existence of this phenomenon. The conventionally calculated result of almost constant load voltage in high load resistance region turns out to be false and the newly calculated load voltage gradually increases as the load resistance becomes high. These results mean the unreliability of the conventional simulations and indicate the necessity of the present simulation when the load resistance is higher than its nominal value.

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The authors are studying the method for a generating capacity lowering diagnosis of a photovoltaic module. In this paper, we propose one method for a generating capacity lowering diagnosis of a shaded photovoltaic module. We perfectly blinded the part of one cell in one module (36 cells) in order to investigate the influence of shadow on the generated power. The shading area was made to be 0, quarter (1/4), half (1/2) and whole (1) of one cell. The generated power without shadow is almost proportional to inradiance. Increasing the shaded area, the power decreases. It is possible to statistically show the range of the dispersion of the data by the 99% simultaneous confidence interval, assuming that the generated power is proportional to iuradiance. The data outside in the interval can be regarded as a different population from data within the interval. That is to say, the data of the outside in the 99% simultaneous confidence interval can be judged with any abnormality.

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The Numerical Electromagnetic Code (NEC-2), which is based on the method of moments, has been successfully used in lightning-related studies such as lightning surge analyses or lightning electromagnetic pulse (LEMP) calculations. These studies mainly deal with metallic structures over perfectly conducting ground, however, few of them take the influence of lossy ground into consideration although NEC-2 includes an option to simulate lossy ground. In the present paper, the accuracy of NEC-2 with the option simulating lossy ground is verified through comparison with the experimental results obtained at a reduced-scale model over lossy ground, before applying it to prediction of lightning-induced voltages on an overhead distribution line.

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A Rotary Phase Shifter (RPS) is proposed to maintain power schedule across tie-lines in interconnected power systems. Power flow can vary widely from the scheduled power due to the unbalance between generation and load that causes frequency fluctuations in interconnected power systems. The Rotary Phase Shifter which is basically a wound rotor induction machine can be placed between two interconnected power systems to control the power flowing from a non-utility-owned generation (NUG) to a large utility. The primary objective would be to maintain the power schedule across the interconnection by controlling the torque on the rotary phase shifter. A model of the RPS and a control strategy for it are presented. Experimental studies on a reduced scale two-area power system show that following a local disturbance, the rotary phase shifter allows the desired setting of tie-line flows regardless. of load conditions and the system as a whole operates in an optimal fashion.

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So called voltage conditioning is well known as an effective measure to rise vacuum dielectric breakdowns. An experiment was carried out to clarify this voltage conditioning phenomena. We tried to formulate the conditioning effect by an experimental equation. The test results showed that if the electrode surface was smoothed by an electrochemical buffing treatment, conditioning was completed earlier. The conditioning effect can be ended sooner by forming a melted layer, having a fine structure. It was classified that the conditioning effect was due to three factors: smoothing of the rough electrode surface by its melting due to breakdowns, formation of a melted layer and removal of adsorbed gas and contamination.

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Recently, it has become more necessary to consult lightning overvoltages at the consumer side. One cause of the consumerside overvoltages is due to transferred lightning surges from a distribution line via a pole-mounted distribution transformer. This paper presents a simulation methodology of the transferred lightning surges. Transient calculations were performed by the EMTP and compared with laboratory-test results.

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Influence of the switching characteristics of the voltage source over the output impulse voltage is investigated in the paper. Assuming various quasi-step voltages having the same response time as an input voltage in an impulse voltage calibrator, deviations of the output voltage's impulse parameters from the ideal lightning impulse voltage's are evaluated. It is clarified that, even with a slowly rising quasi-step voltage, there would be no measurable difference between deformed and ideal impulses.

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