Voltage stability problem has been studied for long time as an important subject for secure power system operations. Various methods have been developed so far in order to analyze the complicated phenomena to predict and avoid voltage collapse. Recently, the complexity of the problem is increasing due to considerable change in power system circumstance under deregulated environment, where new types of instabilities such as immediate instabilities tend to increase; requirements for analyses are also changing. This article presents recent trend in voltage stability studies and development of analysis methods.
A CO2-capturing NOx-free H2O turbine power generation system is proposed in which middle pressure steam produced in a thermal power plant is utilized to increase generated power when demand for electricity is large. The proposed system can capture all the generated CO2 based on the oxygen combustion method and emits no NOx, so that it causes no urban and global environmental problems. A combined cycle power generation system with 200MW gas turbine power output is adopted as an example of a thermal power plant. It was assumed that 32 t/h of steam with 25kg/cm2 pressure produced at waste heat recovery boiler was utilized in the proposed system.It has been shown through simulation study that increase of power output by 11.8MW or 4.51% of the rated output is possible with no efficiency decrease. The amount of CO2 reduction is estimated to be 19600t/y.The unit cost of generated power is estimated to be 8.38yen/kWh, annual gross profit of the proposed system 271 million yen, depreciation year 4.87, and thus the proposed system is estimated to be economically feasible.
In this paper, it was assumed that a synchronous generator in a customer system was connected to a distribution system via the fault current limiter (FCL). We theoretically investigated the influence of the output power of the generator on the limiting effect of the fault current when the three-phase short-circuit fault occurs. It was shown that the fault current out of the customer system, limited by the FCL, rises with the output power of generator. It was found that the larger the output power is, the higher the fault current at the fault point is when the limiting resistance is less than 15Ω in the case of the resistive type FCL. On the other hand, the fault current at the fault point decreases with an increase in the output power for the limiting resistance more than 15Ω. By contrast, it was found that the suppressing effect on the fault current at the fault point due to the inductive type FCL hardly depends on the output power.
The idea of unbalanced power flow calculation was proposed many years ago. At that time, however, the needs for such techniques was not an argent issue. But modern power system networks are comprised of long untransposed transmission lines. Therefore, for some kind of analysis, it is now almost impossible to treat a system as though it were a symmetrical network. The aims of most previous studies were oriented to solve voltage/current imbalance in local or small system because local imbalance was a serious concern. This is still an important issue, but more recently our needs have become concentrated on practical bulk power systems, since principal EHV lines are entirely untransposed. Following such a background, we have developed a practical unbalanced load flow program. This program was developed for steady state analysis of large scale of practical networks under many possible unbalanced conditions.
This paper presents a novel method for optimal scheduling of hydraulically coupled power plants with operation constraints. In a hydro thermal power system, the operation schedule of hydro plants becomes more important to reduce the fuel cost of thermal plants, as the ratio of the hydro plants becomes larger. But hydraulically coupled power plants have some specific constraints depending upon the operations of the upstream plants, which makes the optimization problem more complicated. The proposed method is based on a decision process of an expert operation planner. First it calculates the most economical operation schedule without respect to the operation constraints of hydraulically coupled power plants. If this initial schedule violates the operation constraints of hydraulically coupled power plants, it is modified successively so as to dissolve each violation with most economical manner. The method is heuristic, but it can be widely applied to general problems as specify the river systems characteristics. Due to the above-mentioned method, the obtained schedule becomes easily acceptable because the intermediate schedules can be checked by the operation planners.
A fault current limiter (FCL) is extensively expected to suppress fault current, particularly required for trunk power systems heavily connected high-voltage transmission lines, such as 500 kV class power system which constitutes the nucleus of the electric power system. By installing such FCL in the power system, the system interconnection is possible without the need to raise the capacity of the circuit breakers, and it is expected that FCLs may be used in more efficient power system design. For these reasons, FCLs based on various principles of operation have been developed in the world. In this paper, we have proposed a new type of FCL system, consisting of solid-state diodes, DC coil and bypass AC coil, and described the specification of distribution power system and 66 kV class FCL model. Also we have proposed a 66 kV class prototype single-phase model and the current limiting performance of this model was evaluated using a short circuit generator.
Among several techniques of decomposition of dioxins offered by the present technology, possibility of application of atmospheric pressure arc was investigated. The treated substance was biphenyl due to a high risk involved while using pure dioxins during the experiment. The performance of hollow plasma reactor was investigated. In the experiment, discharge gaps' dimensions were from 5 to 20 mm, the source current ranged from 50 A to 150 A. Biphenyl was partly decomposed in a short time due to the high arc plasma temperature. Except the gaseous products, solid naphthalene and amorphous carbon were formed.
The purpose of this investigation is experimental research of many interruption performance for Molded Case Circuit Breaker (MCCB) currently used for the protection of a low voltage circuit. It is anticipated by interruption especially by high current many interruptions that the interruption performance will decrease. In order to investigate the performance change by many interruptions, it is important to grasp an interruption characteristic. The interruption experiment was conducted in large current for many times, and phenomena which are one of factors of the successes or failure of interruption, were observed. By carrying out the numbers of interruption it is shown that post-arc current begins to flow and duration of the arc is ten to a few hundred micro seconds. In order to explore relation between post-arc current and a decrease of an interruption characteristics, experiment conditions of post-arc current was investigated.
Polymer insulators have been used in worldwide because of some superior properties; light weight, high mechanical strength, good hydrophobicity etc., as compared with porcelain insulators. In this paper, effect of sample size on the aging characteristics in the salt fog test is examined. Leakage current was measured by using 100 MHz AD board or 100 MHz digital oscilloscope and separated three components as conductive current, corona discharge current and dry band arc discharge current by using FFT and the current differential method newly proposed. Each component cumulative charge was estimated automatically by a personal computer. As the results, when the sample size increased under the same average applied electric field, the peak values of leakage current and each component current increased. Especially, the cumulative charges and the arc discharge length of dry band arc discharge increased remarkably with the increase of gap length.
The radiant power emitted from a high temperature medium is useful for lighting and treatment of hazardous waste because it has a highly intense radiation. In this paper, we tried to measure the temperature and radiant power of DC free arc mixed with tungsten vapor between tungsten electrodes with a spectroscope and a power meter in air and calculate the radiant efficiency and radiant power density to know the fundamental relationship between the temperature and radiant power and to apply it to the lighting and plasma treatment. The radiant power was measured to be about 860—2, 100W at 30—70A in current, and the radiant energy was calculated to be about 27—43kJ at 35—55kJ in electrical input energy, and increases in proportion to the 1.06th power of the input energy. The temperature was measured to be about 9, 000K at 30 and 50A and to be 6, 400K at 70A. The radiant efficiency is up to 80%. The temperature was same value in different currents under 50A, even if the radius of free arc at 50A could be bigger than that at 30A. When the current is increased from 50A, the temperature is decreased. But the radiant power density is almost same value at 9, 000K(50A) and 6, 400K(70A) at mixture ratio of W: XW = 2.5%. So, it is assumed that the radiant power depends on the radius. The logarithmic slope of the current for the radiant power was lower than that in case of the wall-stabilized model and torch plasma, because the radiant power depended on the radius and temperature of the arc.
The behavior of supersonic flow under the energy exchange and the Lorentz force was studied analytically. The shock relations (MHD Rankine-Hugoniot relations) including the energy exchange and the Lorentz force were derived for the first time. The relations indicate that the shock wave strength can be weakened by the energy addition or the negative Lorentz force acting upstream and that the weakening of shock wave is always accompanied by total pressure loss. The relation between the isentropic efficiency and the enthalpy extraction of the MHD generator was derived using the MHD Rankine-Hugoniot relations, the interaction parameter and the electrical efficiency. The derived relation suggests that shock wave tends to appear at lower isentropic efficiency and this agrees with experimental results qualitatively. Effects of the energy exchange and the Lorentz force on velocity of propagation shock wave were also studied by one-dimensional numerical simulation. The results show that the reflected shock wave and the secondary shock wave appear under a certain condition. Furthermore, it is shown that the velocity of the propagation shock wave can be controlled by the energy exchange and the Lorentz force.
This paper is described on the fundamental performance of the disc type thermomagnetic engine. The disc type engine has been designed in order to decrease the eddy current braking loss. The performance characteristics such as power, torque and loss has been measured, and compared with that of the cylindrical engine in the condition of the same volume of the temperature sensitive magnetic material. The eddy current braking loss is 0.04W which corresponds to 1/30 the loss in the cylindrical engine at the rotation speed of 0.4rps with the maximum power output. The total loss including partial losses due to the friction, the hydraulic effect and the eddy current braking is 0.9W in the disc type engine and is 1.8W in the cylindrical engine. The total loss in the disc type engine is reduced to be 50% of the value of the total loss in the cylindrical engine at the same condition mentioned above. The maximum output power is 6.0W at the rotation speed of 0.4rps in the disc type engine which is about 1.6 times larger than that of the cylindrical engine. The eddy current braking loss in the disc type engine is 0.7% of the value of the maximum output power, which is negligible effect in this engine. The power per unit volume of disc has the maximum value at the disc width of 40mm. The clearance between discs is decided to be of 1mm due to keeping the working fluid flow condition at a constant. The rotor thickness includes with the clearance and the disc thickness. The power per unit rotor thickness also has the maximum value at the disc thickness of 0.5mm. The thermomagnetic engine with the optimum condition can be designed by using these results. When the permanent magnet fixes the size constant, the disc type engine generates high output power in comparison with the cylindrical engine at the point of effective use of magnetic field.
This paper presents on the result of voltage and reactive power control by use of the proposed method. The feature of proposed method is integration of genetic algorithm (GA) and tabu search (TS). This method obtains an excellent fitness at shorter calculation time than GA considering conventional control process. The effectiveness of this method is shown by a practicable 15-bus system.
Unstable output of the photovoltaic power generation system caused by insolating fluctuation is likely to give some unfavorable impact on the existing electric power distribution system (utility line). In order to mitigate the output fluctuation of PV, the modified moving average processing method is introduced. In this system, low frequency component of the net PV output is separated from high frequency component.
This paper proposes the new display system by windmill blade. The proposed method is a system by the visual afterimage phenomenon, using windmill blade in which the light emitter has been embedded. This system shows new effectiveness of the wind power generator system.