With effectuation of Kyoto protocol to reduce CO2 discharging, conventional energy resources are gradually giving way to renewable natural generators. However their weak point of impossibility to control their output themselves will cause some problems with respect to power quality such as voltage and frequency fluctuation. In the meanwhile some kind of electrical energy storage devices like storage batteries, electric double layer capacitors, flywheels are put into practical use. This paper describes the combination of natural energy power and energy storing technologies to solve the power quality problem and to improve their generation values in use.
In this paper, a Voltage Magnitude Constrained OPF (VMC-OPF) algorithm to determine the reactive power injection from compensating equipment to load bus is developed. By introducing the proposed VMC-OPF to the real power related Unit Commitment (UC)(1), a novel daily UC method taking into account the reactive power to secure bus voltage magnitude is presented. The Transmission Access Charge (TAC) and Ancillary Services Charge (ASC) are included in the objective function for considering costs of using transmission network and supplying reactive power to maintain the voltage. Using the proposed UC, the difference between two schedules based on benefit maximization and cost minimization is also discussed. To demonstrate the effectiveness of the proposed UC method, we demonstrate various simulation results for a model power system of IEEE-118 bus system.
In power system, load drop can be observed following a severe fault. It is viewed as one of uncertain factors for the computation of control variable on a frequency stabilizing system for islanded system. The accurate estimation based on short-term actual power and voltage measurements of load just after clearing the fault is difficult since it contains a transient response due to load dynamic characteristic. We propose a new estimation method for load drop amount using a nonlinear dynamic load model. The method utilizes useful pieces of analysis information of load dynamic characteristics, which is derived from actual measurement data on a certain measure point, for effective online estimation. We also present numerical test results with real data of fault cases for validation and demonstrate the effectiveness of our method.
In the distribution system installed a Step Voltage Regulator (SVR), maximum capacity of distributed generators (DGs) is calculated where DGs are completely dispersed on distribution line. The calculation method is that maximum capacity of DGs is calculated under the restriction condition of upper (lower) voltage regulation value and allowable current value by using voltage and current profile which are expressed analytically based on power density model that the authors propose. As voltage control method of SVR, they consider existing SVR whose ratio of transformation is fixed to 1 if it detects reverse power flow, and reverse power flow type SVR which operates appropriately even if it detects reverse power flow. From calculation results on maximum capacity of DGs for power factor of DGs, it is found what the parameters like power factor of DGs, distribution of DGs, and magnitude of load influence maximum capacity of DGs. From calculation results on maximum capacity of DGs for length of system, it is found that restriction condition is classified two modes in existing SVR and four modes in reverse power flow type SVR respectively. Maximum capacity of DGs in the system with reverse power flow type SVR is larger than that in the system with existing SVR.
Harmonics bred from loads are mainly odd order because the current waveform has half-wave symmetry. Since the even harmonics are negligibly small, those are not generally measured in electric power systems. However, even harmonics were measured at a 500/275/154kV substation in Hokuriku Electric Power Company after removal of a transmission line fault. The even harmonics caused malfunctions of protective digital relays because the relays used 4th harmonics at the input filter as automatic supervisory signal. This paper describes the mechanism of generation of the even harmonics by comparing measured waveforms with ATP-EMTP simulation results. As a result of analysis, it is cleared that even harmonics are generated by three causes. The first cause is a magnetizing current of transformers due to flux deviation by DC component of a fault current. The second one is due to harmonic conversion of a synchronous machine which generates even harmonics when direct current component or even harmonic current flow into the machine. The third one is that increase of harmonic impedance due to an isolated power system produces harmonic voltages. The design of the input filter of protective digital relays should consider even harmonics generation in an isolated power system.
The electric industry has undergone a considerable change in the past decade throughout the world. The feature of change is to promote competition among utilities and to form active power market with reliable and less expensive electricity. Under these circumstances, stabilization and voltage stability problems of power system are very important. The power systems engineer is investigating the effect of the capacity of the braking resistor and the timing of insertion for the improvement of the stability level. In this paper, experiments are carried out the optimal size and switching of braking resistor and shunt capacitor etc. The studied system model for experiments consists of a single synchronous generator connected through two parallel transmission lines to an infinite bus.
This paper presents a new approach to optimal voltage and reactive power control based on a genetic algorithm (GA) and a tabu search (TS). To reduce time to calculate the control procedure, the parallel computation using Linux is executed. In order to obtain more effective and optimum parallel computation, the characteristic of the parallel processing algorithm used in the proposed method is to effectively utilize the Master operation of ordinary GA parallel processing. In other words, using the waiting time for transmission from the Slave to execute TS as Master. The effectiveness of the proposed method is demonstrated by practical 118-bus system.
For research and development of the solid oxide fuel cell (SOFC), it is very important to develop diagnostic tools that can grasp detailed cell performance characteristics. The a.c. impedance analysis is one of the indispensable methods for this purpose. The authors, therefore, perform time-dependent numerical simulations for a planar SOFC, and investigate its a.c. impedance characteristics caused by the variation of fuel gas partial pressure. It is made clear that the fuel gas flow in the SOFC works as a virtual capacitance and the Cole-Cole plot takes a form of almost perfect semicircle. The diameter of the semicircle in the Cole-Cole plot is the equivalent resistance originated in the change of the Nernst potential caused by the current change. In the case of the counter-flow type cell, this diameter is smaller in comparison with the co-flow type cell. The a.c. impedance characteristics also change depending upon the inlet gas temperature.
This paper proposes a new diagnosis method for short circuit faults in stator winding of motor based on Hidden Markov Model. Short circuit fault of a motor is one of the most probable faults in motor drive systems. When the fault occurs, the current waveform running in the motor is no longer sinusoidal which is observed in the healthy motor. The variation of the waveform in the faulty case depends on the location and degree of short circuit fault in the winding. In this paper, a Hidden Markov Model (HMM), which is widely used in the field of speech recognition, is exploited to capture and recognize the variation in the faulty current waveform. Thanks to the similarity between the speech signal and the current waveform, the HMM is highly expected to work as a robust fault diagnoser. Finally, the usefulness of the proposed diagnosis method is verified through some experiments using real faulty current waveforms.
Fuel cells (FC) can hardly react a hundred percent of fuel, because the cell potential becomes zero if all of the fuel is consumed at FC. Therefore a small amount of fuel is released from FC, even when pure H2 gas is used as fuel. If the space, where the exhaust H2 is released, is closed up such as the space of deep underground or undersea, the released amount of H2 may be restricted to an allowable level. The depleted H2 can be recovered by the hydrogen separation pump (HSP) such as proposed here. When we supply electricity to the polymer electrolyte by an external power source, H2 can easily be separated and pumped up from anode to cathode according to the principle of “concentration cell". In this study we have preliminarily tested the HSP, and our experimental results show that the HSP can work as a good separation and compression pump of exhausted hydrogen from FC. The typical cell potential was 100mV for HSP at our experimental condition of current density of 0.49A/cm2 and H2 treatment ratio of 98%.
R-z two dimensional numerical simulation with a large eddy simulation (LES) model has been carried out in order to clarify, for the first time, the typical MHD flow behavior and the performance of the disk MHD generator installed in the new closed loop experimental facility at Tokyo Institute of Technology. The results show thick separated flow regions in the generator channel both for non-MHD flow and MHD flow. The separated region influences the MHD interaction because of its low electrical conductivity. The MHD flow streamlines, however, tend to widen in the generator channel, with reduction of thickness of non-MHD flow separation. The typical performance of the generator have been predicted for several load resistances and seed fractions. The study is important to prepare as better as possible and to assure the success of the future MHD power generation experiment.
The use of various alcohols including methanol has been considered as the fuel of direct alcohol fuel cells (DAFCs). Thus far, the Pt alloys have mainly been studied as anode electrocatalysts for DAFCs. Pt itself is poisoned by chemical species produced during the alcohol oxidation. There exist many reports that the addition of Ru is effective for the alcohol oxidation. In this work, we prepared Pt-Ru co-sputtered electrode by changing Ru content, sputtering time and Ar pressure for the sputtering. By using the prepared electrocatalysts, relationships between sputtering conditions and electrocatalytic activity were measured for some alcohols.
SF6 gas has excellent dielectric strength and current interruption performance. For these reasons, it has been widely used for gas insulated switchgear (GIS). Today, such global environmental problems as global warming are important issues of concern. SF6 gas is known as a greenhouse gas with a long atmospheric lifetime, and has global warming potential of 23,900. SF6-free 72kV GIS was recently developed by using high pressure air and a gas/solid hybrid structure. But an alternating current disconnecting switch (DS) has yet to be not developed thus making this type of SF6-free 72kV GIS unsuitable for double bus-bar application. Consequently, the development of a high pressure air-insulated DS corresponding to bus-transfer current switching has been expected. The bus-transfer current is the highest among all current interruption requirements for the DS. To develop an alternating current DS, efforts must be made to reduce arcing damage to the electrode. This paper describes the fundamental characteristics of current interruption in the plain break type and the magnetic field driven type. Then, average arcing time of the magnetic field driven type was estimated by magnetic flux density. Finally, two types of DS which were a high speed plain break and a low speed magnetic field driven, were confirmed to comply with bus-transfer current switching requirements on JEC standard.
Impedance of cylindrical specimens of a soil having three different lengths is measured at frequencies ranging from 40Hz to 40MHz using two parallel electrodes in order to estimate and remove the effect of the contact impedance. Both conductivity and relative permittivity of the tested soil increase with increasing the moisture ratio. The conductivity of the soil having a moisture ratio of 5% is almost constant (about 3mS/m) at frequencies lower than 10MHz, and increases with increasing frequency beyond 10MHz. The relative permittivity of the same soil decreases with increasing frequency up to 10MHz, at which it is 7.
Gakain → Gakuin
Wrong:Department of Electrical Engineering & Information Technology, Faculty of Engineering, Tohoku Gakain University
Right:Department of Electrical Engineering & Information Technology, Faculty of Engineering, Tohoku Gakuin University