This paper proposes a new method of optimal FACTS devices allocation to be used in the preventive/corrective control (PCC) against voltage collapse. The new formulation takes into consideration the transition states that the power system may expose such as normal state and contingency states. For the severe contingencies that drive the system to voltage collapse, the corrective control is initiated by means of fast response of FACTS and load shedding to restore the system with small positive load margin, then the preventive control is carried out using all the fast and slow devices ensuring security margin and voltage feasibility. For this control strategy, FACTS allocation are determined based on the minimum cost for the installations and the operations.. The problem is formulated as a mixed integer nonlinear programming problem, which is solved using hybrid genetic algorithm/successive liner programming (GA/SLP) approach. The IEEE 57 bus system is tested to demonstrate the effectiveness of the proposed method.
This paper proposes a comprehensive model to examine future CO2 emission reduction and primary energy conservation through the installation of a cogeneration system (CGS) in commercial and residential sectors of Japan considering its long-term power generation mix. With the development of a CGS model and a long-term generation mix model on cost minimizing basis, Japan’s prospective power generation structure is figured out and the potential of CO2 emission reduction and primary energy conservation by a CGS is evaluated. With considerable uncertainty remaining concerning various assumptions made for the model analysis, following results are identified. (1) In all fuel price scenarios in power plants, the installation of CGS in commercial and residential sectors accomplishes the reduction of primary energy consumption. (2) In a standard fuel price scenario, the installation of CGS in commercial and residential sectors achieves the reduction of CO2 emission. In a low fuel price scenario which is the case current fuel prices continue for the future, however, CO2 reduction effect becomes decreasing compared to the standard fuel price scenario because of the dominant generation share of a LNG fired plant and a LNG combined cycle in future generation mix and these less carbon intensive plants replaced by CGS. In the case where nuclear power plant becomes competitive and increases its share in future generation mix, CO2 emission from energy system conversely increases by installing CGS in comparison with before installing, because electric power generation of CGS gradually replaces a nuclear power plant. These results suggest that the CO2 reduction potential by CGS introduction is cautiously evaluated taking into consideration the future power plant construction program in Japan.
Fuzzy logic control has been applied to various applications in power systems. Its control rules and membership functions are typically obtained by trial and error methods or experience knowledge. Proposed here is the application of a micro-genetic algorithm (micro-GA) to simultaneously design optimal membership functions and control rules for STATCOM. First, we propose a simple approach to extract membership functions and fuzzy logic control rules based on observed signals. Then a proposed GA will be applied to optimize membership functions and its control rules. To validate the effectiveness of the proposed approach, several simulation studies have been performed on a multimachine power system. Simulation results show that the proposed fuzzy logic controller with STATCOM can effectively and robustly enhance the damping of oscillations.
When an apparatus which should be diagnosed is near a neighboring heat source, it is difficult to distinguish the apparatus from the other heat source from only a thermal image, because there is no distance information. Therefore, we added distance information obtained with a stereo camera to temperature information obtained with an infrared camera, and developed a method of detecting a faulty apparatus on distribution poles using the infrared and stereo cameras. This method has four subcomponents: (1) generation of distance information with a stereo camera, (2) projection of distance information space onto temperature information space and integration of distance information and temperature information, (3) extraction of apparatuses on a thermal image, which is a visualization of temperature information, using distance information, and (4) detection of a faulty apparatus based on the local temperature gradient. We verified this method experimentally. The experimental result of using the new method indicated that by integrating distance information and temperature information, the effect of neighboring heat sources was removed and the faulty apparatus could be correctly detected.
This paper describes the temperature rise and the thermal stability of tank type power capacitors and a analyzing method of the stability and permissible overload factor using a computer. When capacitor is operated at high ambient temperature and under excessive high voltage, the temperature of the dielectric rises higher and in some cases the capacitor looses the thermal balance and finally breakdowns thermally. We measured the heat radiation coefficient and temperature rise of the capacitor, and clarified that the radiated heat calculated from the heat radiation coefficient and the area of the tank coincided with the generated heat calculated from the output of the capacitor and the loss factor of the dielectric. Furthermore we developed analyzing method of thermal stability and permissible overload factor of capacitors using a computer. By this analysis it becomes possible to know the permissible overload factor and the temperature of the capacitor dielectric without performing the temperature rise test which requires long time and much cost.
In recent year, non-conventional energy generation is coming up for effective use of natural energy, such as wind energy. Induction generators consisting squirrel-cage rotors are widly used as wind generators because of their salient features like robust rotor design, simple in the construction, maintenance free operation, etc. However these induction generators will draw large transient inrush current, several times as large as the machine rated current, the instant when they are connected to utility grid or restored after the fault clearance. Under such situations, there will be a severe voltage fluctuations in the power system. In this paper, we present transient analysis of induction generators before and after a three-phase fault conditions. Theoretical discission is developed to determine the initial phase angle and the time at which maximum transient currents flow in the system.
During disturbances in power system, turbine-generator shaft are subjected to mechanical stress caused by severe torsional torques. Shaft torque is proportional to the shaft twist, which is caused by angle difference between both ends. However, observing the angle difference in an actual generation system is difficult technically. On the other hand, measuring rotational speed of the shaft ends is relatively easy. Then if the shaft torque could be estimated effectively, it would be used in order to control the rotational speed for shaft torque reduction.This paper proposes a shaft torque excitation control for rotating machine by making use of an observer for the shaft torque. Firstly, the relationship between the observation signals and the accuracy of the estimation is discussed. Especially, the range of the error of actual values and measurement values of a turbine parameter are analyzed. Secondly, a shaft torque reduction control system is developed by using excitation control based on the estimate by identity observer.
This paper describes the characteristics of synchronous machines’ damper circuit on transient condition. The authors analyze load rejection case and starting condition in point of the transient reactance saturation by finite element method (FEM) and simulation using the electromagnetic transients program (ATP-EMTP).
This paper presents a practical method for OPF (Optimal Power Flow) with N-1 criterion, that can apply to a large power system.Though there are some OPFs which considers N-1 criterion, it is difficult to apply them to a large system.Because its calculation time and used memories increase rapidly as a scale of the system grows up.This paper suggests a formulation using power flow sensitivities to constrain power flows under assumed contingencies.This formulation reduces parameters in the OPF, and allows to cut down redundant constraints.The accuracy and effectiveness are probed through analyzing a large power system which consists of 185 generators, 1048 buses, and 1494 branches.
We have developed a digital real-time simulator of power electronics systems by using MATLAB/SIMULINK. This paper describes the modeling and the calculation accuracy of STATCOM models. Hence the simulator operates at a large time step of 50 μs, in order to improve simulation accuracy, a correction processing is implemented in the STATCOM model. Calculation accuracy of the real time STATCOM model is the same level as EMTDC results. We confirm stable operation of the developed simulator with connecting a commercial real time digital simulator (RTDS).
It is indispensable to accurately perform the short-term load forecasting of 10 minutes ahead in order to avoid undesirable disturbances in power system operations. The authors have so far developed such a forecasting method based on the conventional chaos theory. However, this approach is unable to give accurate forecasting results in case where the loads consecutively exceed than the historical maximum or lower than the minimum. Also, electric furnace loads with steep fluctuations have been another factor to degrade the forecast accuracy. This paper presents an improved forecasting method based on Chaos theory. Especially, the potential of the Local Fuzzy Reconstruction Method, a variant of the localized reconstruction methods, is fully exploited to realize accurate forecast as much as possible. To resolve the forecast deterioration due to sudden change loads such as by electric furnaces, they are separated from the rest and smoothing operations are carried out afterwards. The separated loads are forecasted independently from the remaining components. Several error correction methods are incorporated to enhance the proposed forecasting method. Furthermore, a consistent measure of obtaining the optimal combination of parameters to be used in the forecasting method is given. The effectiveness of the proposed methods is verified by using real load data for one year.
In relation to faults in overhead distribution lines due to the contact of animals, trees and etc., the authors have investigated the process of impulse breakdown of covered conductors in contact with bird nests. As a result, it was found that lightning surges lower than the operation voltage of arrestors cause the breakdown. In the distribution lines, prefab insulating covers are employed to protect the conductors from the contact problems. However, the reliability has not been found clearly. In the present study, the authors investigated the design and evaluation of the insulating covers. Then the degradation of conductor covers and the prefab insulating covers and the lightning surges lower than the operation voltage of arrestors were taken into account.
Recent progress of long YBCO coated conductors is remarkable and coils wound of YBCO conductors will be developed in near future. YBCO coated conductors that are made by deposition of thin YBCO film on high resistance metal substrates such as Hastelloy and nickel tapes are highly resistive when they are quenched. Therefore, measures for stabilization and quench protection are more important for YBCO conductors than for Bi/Ag sheathed tapes which have low resistive silver matrix. Though HTS conductors working at liquid nitrogen temperature are hard to be quenched, the conductors still have possibilities of quenches due to local defects for example. We studied necessary amount of copper stabilizer to protect the YBCO conductors in coils from damages caused by hot spots due to quenches. In the work we numerically calculated maximum hot spot temperature of a YBCO conductor quenched by a local disturbance during the sequence of quench detection and energy dump. In the analysis, necessary amounts of copper to keep the maximum hot spot temperature below a threshold are calculated. Based on the analysis, optimum conductor design is discussed to obtain safe and high current density conductors.