This paper presents an efficient method for dynamic stability in real-size power systems. Eigenvalue analysis based approaches have been studied to evaluate dynamic stability. The conventional methods require caluculating all the eigenvalue in evaluating dynamic stability. Among them, the QR method is widely-spread due to the high accuracy. However the method has a drawback that the method is not applicable to real-size systems with respect to computational time and storage. Recently, the S matrix method has been developed to overcome the problem. The idea of the method is based on mapping the most critical eigenvalue from s-plane to z-plane. As a result, the method requires caluculating the most critical eigenvalue rather than all the eigenvalue. Although the method is theoretically elegant, it has a numerical problem that it generates unnecessary fill-in elements and results in increasing computational time since the direct method is used in solving a set of linear equations. That becomes more significant with the system size. In this paper, an efficient indirect method is developed using a preconditioning technique. The proposed method has sucessfully applied to a 46 unit-187 bus system. The simulation results indicated that the proposed method is 30t and 5t faster than the QR and the S matrix methods, respectively.
A number of studies have been made on the hunting phenomena of synchronous machines. However, most of them have been concerned with the mathematical analysis based on equivalentcircuit models of machine and system, and experimental studies are quite rare. Besides, few papers have treated the phenomena from the viewpoint of internal airgap fluxes which actually govern the machine behaviors. This paper describes the experimental results on hunting phenomena of synchronous generators caused by a fast-acting AVR (Automatic Voltage Regulator) in a laboratory-model one-machine/infinite-bus power system. Changes of airgap fluxes in the process of hunting phenomena are measured by a search coil wound around a stator tooth top of the tested synchronous generator and are examined. The interaction is made clear between field fluxes and quadrature-axis fluxes both of which directly influence the hunting phenomena. The results obtained are confirmed by simulation studies. Thus, the relationship between system stability and machine fluxes is given a clearer understanding than before.
As concerns faults analysis in transient stability study, balanced fault condition such as 3-lines grounded has been adapted for long time in Japan. So transient stability software calculating only balanced fault has been utilized. However, with the advance of system protective control technologies such as multi-phase reclosing system for faulted transmission line, the stability software are needed which enable to calculate unbalanced faults including multiple faults conditions. This report presents the newly developed calculation method of system faults which enable to calculate unbalanced single or multiple faults with the addition of balanced faults, and the validity of presented method was shown through the comparison to the results of test simulator. Moreover the report describes how transient stability limits are difierent for various faults conditions.
A shielding theory which considers upward leaders from high structures is proposed to predict the characteristics of lightning strokes to high towers on the coast of the Sea of Japan in winter season. In this theory, it is assumed that when the electric field at the top of a tower exceeds a critical value by the charge in thunderclouds, an upward leader begins to develop and lightning strikes the tower. Calculated shielding characteristics of high towers are compared with field observations.
Interconections of dispersed generators like co-generation systems to distribution feeders can cause overvoltages to ground on substation bus lines during single-line-to-ground faults. These overvoltages are transient phenomena which exceed 1.73 pu and would occur at the feeder-circuitbreaker tripping. Significant point of causing the phenomena is existance of instantaneous openphases with single-line-to-ground faults. The open-phases are normal operation, because phases of three line currents on the circuit-breaker are different and don't trip exactly at the same time. The model of a distribution system involving generators is newly made for an analysis of the above problem. This model is used for a static analysis and a transient analysis. The static analysis is to clarify the system condition under which the zero-sequence voltage on substation bus lines reaches to the maximum amount. The transient analysis is to clarify the transient maximum voltage to the ground. The results of a transient digital simulation were corroborated by means of an analog simulator. The overvoltages to ground rarely cause iron-resonances due to the saturation of a GPT (grounding potential transformer). But they can be suppressed by means of a current-limiting resistor in a GPT.
Power transformers have been expected to work with safety and reliability during the long period over 30 years. Life expectancy of transformers depends upon the degree of deterioration of insulating materials, particularly conductor insulating paper. Many attempts have been made in recent years to estimate the degree of deterioration of transformers, no diagnostic techniques have been developed in practical use because of the difficulty to take the service conditions into account. It is well known that the color of materials changes according to its deterioration and colorimetry has not been studied on material deteriorations. According to the recent advances in instrumentation and data processing equipment, the color of materials has become easily to be measured qualitatively. So the basic investigation on colorimetry of insulating papers has been made to make the applicability to power transformers clear. Test results showed the strong correlation between the color difference and the deterioration of insulating papers. This paper mentions the effect of materials of papers and impregnating oils on colorimetry.
The alkali metal thermoelectric converter (AMTEC) utilizing the sodium ion conducting β″-alumina is a device to convert directly heat energy to electric energy. It is characterized by high conversion efficiencies, high power densities, no moving parts and low maintenance requirements. Because of these merits, AMTEC is one of the most promising candidate for aerospace power system, remote power station and dispersed small scale power station. In this paper, the experimental results of the series connected cells and the theoretical considerations about internal resistances have been reported. For the single cell, the open voltage of 1.37V and the maximum power of 7.89W and maximum power density of 0.40W/cm2 at the sodium temperature of 1, 077K have been obtained. For the series connected two cells, the open voltage of 2.60V and the maximum power of 12.3W at the sodium temperature of 1, 016K have been obtained. This power was about 90% of the sum power of two cells. This power decrease is due to the resistance of current collecting bus bar. It is necessary to optimize the current collecting bus bar considering the electrical resistance and heat conductance.
For global environmental protection, it is necessary to promote effective use of energy resources. As a method of attaining this purpose, it is also important to reduce heat loss during heat energy transport. In transferring heat energy by fluid, it is well known that the heat capacity of piping affects the heat loss at unsteady state. For the purpose of reducing heat loss from the piping, we tried to manufacture a piping made of only thermal insulation material, which we called a thermal insulation pipe (TIP). We proved its effectiveness by performing experiments of the thermal response at the transient state in comparison between a TIP and a piping which is composed of a metal pipe covered with thermal insulation material. Then we performed numerical calculations and simple analysis of unsteady state heat loss in both piping system. In this paper, we describe the effectiveness of the TIP from the major results of calculations.
This paper proposes a single phase utility interactive photovoltaic system using an IGBT current source PWM inverter with the two auxiliary IGBT's. With the two auxiliary IGBT's, a sinusoidal PWM can be performed easily because the waveform of the inverter DC voltage is made up of not only line and zero voltages but also half the line voltage. It has been experimentally verified that sinusoidal output current, power factor near unity and virtual maximum power can be obtained without any feedback control. Stable power condition can be obtained on starting or regardless of isolation change and line voltage transient because the system does not have any feedback control to interconnect with the utility line. The system behavior of malfunction has also been clarified and shown to have high reliability.