In this paper, the effect of Photovoltaic Power Generation system (PV system) on power plant mix is evaluated mainly from the viewpoint of economics, by using real data of the load and the solar radiation. For this purpose, first, we examine statistically the correlation between the PV system output and the load, as well as their periodic and random variation characteristics. Second, referring to the result of this statistical analysis, the probabilistic models of the load and the PV system output, in which these characteristics are properly reflected, are built. Due to these models, the load-probability distributions are derived for the power system with and without the PV system, respectively. Finally, we construct the optimal power plant mix with each of them, and investigate the effect of the PV system by comparing these results. Particularly, it is quantitatively demonstrated that the correlation characteristic between the load and the PV system output is a significant factor in evaluating the PV system. Further, economic indexes of the PV system are evaluated considering its penetration rate into the power system and also variation of the load characteristics.
The advantages and disadvantages of H∞ optimal control over LQ optimal control are investigated, when applied to a generator control system. The motivation of this study is that a variety of disturbances happen to the generator control system, which will become best when the system is designed by taking all these disturbances into consideration. In this study, ILG, clearing and reclosing in a power system connected to the generator, and changes in settings of terminal voltage and output of the generator are supposed as the disturbances, which will often occur in the generator control system.
A number of studies on the surge impedances of transmission towers and transmission lines when lightning struck have been carried out theoretically and experimentally. However, the theoretical studies could not always explain the experimental results. This paper derives new formulas of the surge impedances of the transmission towers and transmission lines for the lightning surge based on an electromagnetic field theory. A comparison of results calculated by the proposed formulas with the experimental results show nearly the same wave crest values and waveforms. It is not clear how much current flows into ground wires and the tower from the input current source. It is made clear that a large portion of the input current flows into the tower and a small current flows into the ground wires. This fact is very important to investigate lightning performance in the transmission towers and the transmission lines. The above results are useful to develope accurate models of the transmission towers and the transmission lines for the lightning stroke.
For the purpose of maintaining the power system security, the authors are developing an Integrated Security Monitoring and Control (ISMAC) system which consists of the three main functions: security monitoring, preventive control and emergency control. This paper focuses on the dynamic preventive control which deals with the transient stability immediately after the contingency has occurred. The proposed method is based on the transient stability assessment using the pattern recognition with two dimentional feature space; therefore we can obtain the preventive control strategy fast. An index which represents the severity of the contingency quantitatively (security index) is defined by the distance from a linear decision surface which devides a feature plane into stable and unstable region. Further, this method has also the advantage that it is possible to consider the effect of the control devices or damping to some extent and specify the operator demand for stabilization flexibly. The effectiveness of the proposed method is ascertained through numerical examples for model power systems.
Surge arresters and overhead ground wires have been equipped as principal measures to protect overhead power distribution lines from lightning. Surge arresters are installed to protect lines and apparatus with the primary aim of suppressing the overvoltage induced by nearby lightning strokes. Therefore, little attention has been paid to the prevention of backflashovers caused by direct lightning hits to overhead ground wires. However, for the further improvement of the performance of the power system, protection of distribution lines against direct lightning strokes needs to be investigated. The authors analyzed the protective effects of surge arresters against direct lightning hits to overhead ground wires using EMTP. We found by the analysis that power distribution lines could be properly protected from direct lightning hits to poles installed with surge arresters, irrespective of the distance between adjacent poles. As a result, it was found that the outages due to direct lightning strokes are mostly eliminated when surge arresters are installed on all poles.
An equivalent circuit to calculate lightning-induced voltages on a distribution line, linked to a numerical method to calculate the electric field associated with a return stroke, is proposed. The electric field is first calculated in the frequency domain by decomposing the return stroke channel into numerous electric dipoles, then it is synthesized to yield solution in the time domain. Under the condition for a line of infinite length over perfectly conducting ground, it is shown that the proposed equivalent circuit is identical to that proposed by Rusck, which has been widely used. In this paper, lightning-induced voltages on a line of finite length over perfectly conducting ground are analyzed by using the new model. The importace of the current wave generated by the vertical electric field at the termination of the line, which is newly taken into acount in this new model, is demonstrated. As a result, it is shown that the lightning-induced voltage on a line of finite length is greatly affected not only by the distance, but also by the direction to the return stroke.
Accurate estimation of the freguency bias of electric power systems is becoming more important in order to maintain system frequency within operating limits and to make the best use of generating and transmitting facilities. The freguency bias was supposed to use the data of the governor-cut test, but it was not the same as the data of normal operating conditions. This paper proposes that using frequency fluctuation data, total power generation data and tie-line power flow data, calculations be made from the input/output spectrum. It is not clear whether calculation outputs are right or not, so we investigated evaluation methods to confirm whether calculation outputs using observational data are correct. Some 400 calculation cases enabled us to evaluate calculation outputs. The estimation of the freguency bias (K) is expressed as the function of the standard deviation of frequency fluctuation (σ). Although this esimation is larger than the value of load frequency characteristics mentioned so far, it corresponds well with the value of generator-frequency characteristics calculated using generators' speed regulation.
The flashover characteristics of long air gaps submitted to switching surge voltages may be predetermined by use of a mathematical model of leader propagation. The present model is developed from each combinations of previous engineering models, and is also applied to positive rod to plane geometries with gap lengths up to 20m. However, four parameters to determine leader propagation with respect to our model are adjusted in the present calculation as so to fit experimental flashover voltages and calculated flashover voltages which depend on wave forms of the applied voltage and gap length. The calculations show that these parameters are only a function of gap length. Our combined engineering model used the parameters depending on gap length is easily able to predetermine the flashover characteristics of long air gaps with a microcomputer.
This paper comprehensively analyzes characteristics and economics of systems which treat municipal refuse and utilize its contained energy as the energy source to generate not only electric energy but also the heat energy for district heating and cooling. Investigated systems are the following two: (1) System-A which is composed of a plant to incinerate the municipal refuse and a cogeneration system with a bleeder/condensate turbine power generation unit, and (2) System-B which is the system proposed here, and is composed of a pyrolysis furnace for treating the municipal refuse, two-stage-cleaning process for refining generated pyrolysis gas, and a cogeneration system constructed by a combined cycle power generation unit using cleaned pyrolysis gas as its fuel gas. It was estimated that the maximum net power generating efficiency of System-B is 24.8%, and is higher by 63% compared to that of System-A. Economics of the systems have also been investigated, and it was shown that System-B, which is superior in the aspect of air pollution characteristics, is more economic than System-A, if the extra electric energy of the systems can be directly supplied to various facilities, being different with the case where it should be sold only to the electric company. Effects of changes in major social and technological factors which affect the economics of the two systems are also analyzed, and it was shown that possibility is considered to be high that the economics of System-B will become more advantageous than that of System-A in the future.
There are a number of possible applications of the technique whenever a computer or microprocessor is available for control of a windmill or a sub-system of it, and also for control of more complex wind turbine systems. To simulate or/and control windmill power system by control sequence, we need to obtain the accurate values of the system parameters previously. This paper describes a new method estimating windmill torque loss coefficients or torque coefficient of a propeller type windmill. In the method, time series data representing wind and windmill speed of a windmill power system are used for estimation. This paper is organized as follows; Paying attention to the energy flow of the propeller type windmill, we firstly discuss the mathematical windmill model and define the windmill torque loss coefficients, which are treated as a function of wind and windmill speed. Next, an estimation technique based on recursive estimation technique has been developed for determination of the values of these coefficients. We manifested the validity of the proposed method by estimated results used from both the simulated results and the experimental data for step or natural changes in wind speed.
The Pulverized and Intermixed Elements Sintering (PIES) method, which can eliminate the use of a powder consisting of fully reacted alloys, is successfully achieved for the preparing of n-type (Bi, Sb)2(Te, Se)3 based thermoelectric devices for the first time. Hence the PIES method can substantially reduce the manufacturing cost of thermoelectric devices such as (Bi, Sb)2(Te, Se)3 based one. It is proved that the solid solution formation of PIES device is occurred in the sintering process and in order to get the useful thermoelectric performance a strong intermixing force such as a large centrifugal force in a planetary ball mill is necessary by X-ray diffractometory and measurement of thermoelectric properties. The thermoelectric figure of merit of PIES devices is about 1.7×10-31/K at 300K, and there is plenty of room for improvement in the PIES method to obtain higher figure of merit.
To theoretically explain the experimentally obtained performance characteristics of nonequilibrium Faraday MHD generator such as the total output power and the value of each electrode current, the authors newly develop a quasi-two-dimensional time-dependent simulation code, in which not only the two-dimensional distributions of the electrical quantities but also the onedimensional distributions of the gas dynamical quantities are calculated and the interactions between the electrical and gas dynamical quantities are taken into account. In this paper, at first, the simulation results are compared with the experimental results and it is confirmed that the simulation code can predict the performance characteristics of the generator. Next, numerically obtained distributions of the electrical and gas dynamical quantities in the generator channel are described, where they were not sufficiently clear by the experiments because of the difficulty of their measurement, and the relations between the numerically obtained distributions and the experimentally obtained performance characteristics are also made clear.