This paper aims to introduce recent topics about the control technique of power electronic equipments for power system. the control technique is explained from the view points of the power system control, the local system control and the converter control. The installation of STATCOM in Japan and UPFC in Korea are mentioned as the examples.
The Advanced Power System Analyzer “APSA” was developed for planning and evaluation of future network developments in 1989 as one of the largest practical power system simulator in the world. We realized digital generator models, low loss/high frequency response transmission line and transformer models and etc under this project. And “APSA” has unique operation systems to set up and start up aided by computer system as same as computer analysis. This paper introduces memories of the development work by engineers.
This paper presents estimation techniques of machine parameters for two windings power transformer using design procedure of winding structure. Especially, it is very difficult to obtain machine parameters for transformers in customers' facilities. Using estimation techniques, machine parameters could be calculated from the only nameplate data of these transformers. Subsequently, EMTP-ATP simulation of the inrush current was carried out using machine parameters estimated by design procedure of winding structure and simulation results were reproduced measured waveforms.
This paper analyzes the performance of Nepalese Electricity Supply Industry (ESI) by investigating the relative operational efficiencies of the generating stations as well as the Distribution Centers (DCs) of the Integrated Nepal Power System (INPS). Nepal Electricity Authority (NEA), a state owned utility, owns and operates the INPS. Performance evaluation of both generation and distribution systems is carried out by formulating suitable weight restriction type Data Envelopment Analysis (DEA) models. The models include a wide range of inputs and outputs representing essence of the respective processes. Decision maker's preferences as well as available quantitative information associated with the operation of the Decision Making Units (DMUs) are judiciously incorporated in the DEA models. The proposed models are realized through execution of computer programs written in General Algebraic Modeling Systems (GAMS) and the results obtained are thus compared against those from the conventional DEA models. Sensitivity analysis is performed in order to check the robustness of the results as well as to identify the improvement directions for DMUs. Ranking of the DMUs has been presented based on their average overall efficiency scores.
In this paper, we studied how to forecast next-day hydropower energy expected output based on the past rainfall record in the reference area. Tank model, which has been conventionally applied for this type of forecast has been improved by employing Kalman Filter stepwise estimation, to accommodate seasonal and yearly variations of rainfall water runoff conditions. Our Kalman Filter Tank Model (KF-Tank Model) yielded a broader choice of parameters while maintaining acceptable level of average forecast errors of about +/-0.05[PU] per forecast period. Further, it is shown that the error correction mechanism of the KF Tank Model can remain robust for snow-falling and snow-melting seasons, without calling for parameter revisions of the model.
DC microgrid is a novel power system using dc distribution in order to provide a super high quality power. This dc system is suitable for dc output type distributed generations and energy storages. In this research, we assumed one type of the dc microgrids for residential houses (apartment house or housing complex). Each residence has a distributed generation such as gas engine or fuel cell. Those cogenerations are connected to the dc power line, and the electricity from the generations can be shared among the residences. The hot water from the cogeneration is used in each residence. We constructed an experimental system based on this concept in our laboratory. We have studied the fundamental characteristics and the quality of the supplied power to the loads against several fluctuations or faults. Experimental results demonstrated that the system could supply high quality power to the loads against a sudden load variation and a voltage sag of the utility grid. Afterwards, we moved the experimental system to an experimental apartment house (NEXT21). We studied the quality of the supplying power by using practical power line, and confirmed that the system was also able to supply a power to home appliances stably.
In high voltage aerial distribution systems, the insulated wires are supported by the insulator with the binding wire at the electric light pole. When a lightning strike happened in the neighborhood of the aerial insulated wire in a power distribution system, the inductive lightning surges invade to the central line of the wire. Then, the creeping discharges develop along the wire surface from the binding wire tip in the same time as the flashover of the insulator at a supporting point of the wire. If the wire insulator has weak points such as the pin-holes, the disaster near the wire supporting point may occur with a melting of wire due to the punch-through breakdown. To prevent such accidents, it is important to clarify the mechanism of the creeping discharge along the insulated wire which caused by the lightning strike. The polarity of creeping discharges is decided by the polarity of inductive lightning surges, and the developing length and aspect of the discharge are greatly different by the discharge polarity. The developing of these creeping discharges is attributed to complicated behaviors of the positive and negative electric charges. In the present study, we examined in detail the developing process of positive creeping discharge along the wire surface by using a high speed image converter camera. This paper describes the developing mechanism of positive creeping discharge based on the experimental results.
The SPS (Space Solar Power Satellite/Station) will be clean base-load power station in space. It will be hugest space system and we need high efficient, huge, high accurate, light weight and inexpensive phased array for the SPS in order to transmit energy generated in space from space to ground. We have proposed and developed a phase controlled magnetron (PCM) with injection locking and PLL technique for the high efficient, light weight and inexpensive phased array. It has still weak points; (1) it contains approximately 10% power loss at circulator for injection locking, (2) we need phase shifter in each PCMs for the phased array. In order to solve the weak points, we propose a magnetron phased array with mutual injection locking. For the magnetron phased array, we only use two PCMs with phase shifters and the other components are self-oscillated and mutual injection locked magnetrons. In this paper, we propose new formula for the magnetron phased array with mutual injection locking. We also show experimental results of beam direction control with the magnetron phased array with mutual injection locking.
Pressure Retarded Osmosis (PRO) power generation system is a hydroelectric power system which utilize permeation flow through a semi-permeable membrane. Permeation flow is generated by potential energy of salinity difference between sea water and fresh water. As membrane cost is expensive, permeation performance of membrane must be higher to realize PRO system. We have investigated Reverse Osmosis (RO) membrane products as semi-permeable membrane and measured permeation volume of a few products. Generation power by membrane area calculated from permeation volume is about 0.62W/m2. But by our improvements (more salt water volume, spacer of fresh water channel with a function of discharging concentrated salinity, extra low pressure type of membrane, washing support layer of membrane when generation power reduces to half), generation power may be 2.43W/m2. Then power system cost is about 4.1 million yen/kW. In addition, if support layer of membrane makes thinner and PRO system is applied to the equipment that pumping power on another purpose is avairable (wastewater treatment plant located at the seaside, thermal and nuclear power plant or sea water desalination plant), generation power may be more. By these improvements PRO system may be able to realize at the cost close to photovoltaic power system.
Recently, the focus of lightning protection measures for distribution lines has moved from a nearby lightning stroke to a direct lightning stroke. Studies of direct lightning stroke countermeasures are generally carried out by digital simulations using the EMTP (Electro-Magnetic Transients Program). Thus, components of a distribution line must be modeled appropriately in the EMTP for accurate simulations. The authors have previously clarified the surge response of a distribution line by pulse tests using a reduced-scale distribution line model. In this paper, first, the results of the pulse tests are simulated in the EMTP using a conventional model which represents a distribution pole by a single lossless distributed-parameter line model, and comparisons with the test results show that transient overvoltages generated at the insulators cannot accurately be reproduced by the conventional model. This indicates that a special treatment is required to represent the transient response of a distribution pole and wires. Then, this paper proposes new EMTP models of the pole and wires which can reproduce the transient overvoltages at the insulators. The parameter values of the proposed models can be determined based on a pulse test result.
For distribution lines in Japan, protection measures against lightning induced overvoltages have been taken and can be considered almost complete. The focus of lightning protection measures has moved to overvoltages due to direct lightning strokes. Studies of such overvoltages require simulations using the EMTP (Electro-Magnetic Transients Program), and components of a distribution line must be modeled appropriately in the EMTP simulation environment. The authors have proposed an EMTP model of a distribution line in a separate paper. This paper consists of two parts. The first part presents surge characteristics of a distribution line obtained by measurement using an actual-scale test distribution line. Especially, the result reveals noteworthy characteristics of the surge impedance of a reinforced concrete pole and the wavefront-time dependence of insulator voltages. The second part presents validation of the distribution line model previously proposed by the authors. The validation shows that the distribution line model accurately reproduces the measured voltage and current waveforms for various wavefront times of injected currents.
This paper presents a combination system of wind power generator and hydrogen generator. In the proposed system, Doubly-Fed Synchronous Generator (DFSG) is used as an adjustable speed wind generator, and an electrolyzer is connected to its terminal for hydrogen generation, which is controlled by power electronic converters. Output power from the wind generator is smoothed and supplied to the power system as well as to the electrolyzer to generate hydrogen under a cooperative control of the wind generator and the electrolyzer. The performance of the proposed system is investigated by simulation analyses, in which simulations are performed by using PSCAD/EMTDC.
Results of experimental study on transient phenomena of the closed cycle disk MHD generator are described in this paper. The transient phenomena were caused by a step-like change of load resistance during a test time of the shock-tube driven disk MHD generator. The load resistance was changed by using an IGBT (Insulated Gate Bipolar Transistor) installed in a load circuit. When the load resistance was changed from 0.096Ω to 2.5Ω, an overshoot of the Hall output voltage and of the Hall electric field was observed, and a large fluctuation of static pressure was also observed. At the same time, a spike-like increase of cesium recombination continuum and line spectrum appeared just after the load change. Results of the quasi-one dimensional numerical simulation have indicated that the observed overshoot was caused by the following phenomena: 1) a steep reduction of the Hall current and a steep increase in both the Faraday current and the electrical conductivity, and 2) a slow reduction of gas velocity due to the enhanced retarding force. Furthermore, the measured spike-like increase of radiation intensity was ascribed to an increase of electron temperature and electron number density by a steep increase of Joule heating.
Threshold level of electric shock perception caused by electrostatic induction generated by 50Hz alternative current has been studied. The results are summarized below. When the surface of an insulator is wet with hydrophilic condition, the surface acts as a conductor under electrostatic induction, and one may perceive electric shock when he/she touches the surface. In conclusion, the minimum threshold perception voltage is about 1000V (r.m.s) when one touches the surface, pinching a copper coin in order to lower the resistance. However, the threshold level of perception is not concerned with the voltage or the amount of the electric discharge but a peak value of the current flowing through a subject, furthermore, the length of electric discharge time is also infuluenced. And a peak value of the current is about 1500mA.
A large number of distributed generators (DGs) are expected to be installed in distribution systems. In this letter, we propose an estimation method for unknown output of DGs connected to a distribution system. This method enables estimation of DG-outputs by analyzing a power flow data measured at one spot using independent component analysis (ICA) and discrete wavelet analysis.