In a new competitive environment, it becomes possible for the third party to access a transmission facility. From this structure, to efficiently manage the utilization of the transmission network, a new definition about Available Transfer Capability (ATC) has been proposed. According to the North American ElectricReliability Council (NERC)’s definition, ATC depends on several parameters, i. e. Total Transfer Capability (TTC), Transmission Reliability Margin (TRM), and Capacity Benefit Margin (CBM). This paper is focused on the calculation of TRM which is one of the security margin reserved for any uncertainty of system conditions. The TRM calculation by probabilistic method is proposed in this paper. Based on the modeling of load forecast error and error in transmission line limitation, various cases of transmission transfer capability and its related probabilistic nature can be calculated. By consideration of the proposed concept of risk analysis, the appropriate required amount of TRM can be obtained. The objective of this research is to provide realistic information on the actual ability of the network which may be an alternative choice for system operators to make an appropriate decision in the competitive market. The advantages of the proposed method are illustrated by application to the IEEJ-WEST10 model system.
This paper addresses a new decentralized robust load-frequency control (LFC) design in a multi-area power system under deregulation based on bilateral policy scheme. In each control area, the effect of bilateral contracts is taken into account as a set of new input signals to modify the traditional LFC structure. The LFC problem is considered as a multi-objective control problem and formulated via a mixed H2/H∞ control technique, then it is easily carried out to synthesis the desired low-order robust controllers by solving standard linear matrix inequalities (LMI). A three-area power system example with possible contract scenarios and a wide range of load changes is given to illustrate the developed approach. The results of the proposed multi-objective control strategy are compared with pure H∞ design. The resulting controllers are shown to maintain the robust performance and minimize the effect of disturbances and specified uncertainties.
This paper presents the result of executing the conventional genetic algorithm (GA) and a new method to the voltage and reactive power control (VQC). The conventional GA can give the control process and improve the fitness with the practical control times. And, the method to cancel the limited deviation as early as possible is implemented. Moreover, the method to reduce the control times to the fitness as much as possible is proposed. The proposed method is integrated the tabu search (TS) into the conventional GA. The proposed method generates next generation’s individual with the crossover of the conventional GA and the neighborhood search of the TS. Therefore, the proposed method executes an effective search. As a result, the proposed method can obtain better fitness than the conventional GA in the same calculation times. The effectiveness of the proposed method is demonstrated by practical 15-bus and 118-bus systems.
This paper proposes a brand new method for transient stability analysis in power systems. The proposed method directly computes the critical trajectory for a given contingency to obtain the critical condition of the studied system. Although the method may be useful for general nonlinear dynamic systems, it is applied to the problem of obtaining a controlling UEP, unstable equilibrium point, which provides inevitable information for the energy function methods to assess transient stability. Namely, the proposed method effectively yields a critical trajectory on PEBS together with the controlling UEP, thus improving the conventional BCU method. The effectiveness of the proposed method is demonstrated in 3-machine 9-bus system and 6-machine 30-bus system.
Connection of a large number of the dispersed generators to distribution networks is not easy due to various technical considerations. Thus we have been trying to devise a concept for future electrical distribution systems with a lot of dispersed generators. In this work, it has been considered that each customer’s load and each generator’s active and reactive power should be controlled in order to stabilize and optimize the networks. Under this consideration, two control methods for future distribution systems are proposed, a cooperative control and an independent control. We have confirmed experimentally that the voltage regulation ability is higher with the cooperative control than with the independent control, especially in the cases of an eccentric load profile in a feeder and a heavy load.
This paper describes the effect of mutual leakage reactance in rotor circuit (Canay reactance) on analysis of generator transient characteristics. The authors derived a detailed equivalent circuit model for synchronous generator, and analyzed out-of-phase synchronizing phenomena (synchronizing with phase difference) of the generator by simulations using the electromagnetic transients program (ATP-EMTP), and compared the results with the experimental data.
A time domain simulation based preventive control method is proposed in this paper. To achieve excellent practicality of the proposed method, the author focused on improving economy of the resulted generation rescheduling, unlimited model application and calculation efficiency of the stability analysis. A new technique is proposed to improve accuracy of Transient Energy Margin estimation from time domain simulation results. A sensitivity analysis technique is employed for stability limit determination of generating power from TEM. Calculation efficiency is also improved by proposed contingency selection. The effectiveness of the proposed method is verified through a calculation example with IEEJ 10 machine power system model.
In recent years, there have been problems such as exhaustion of fossil fuels, e. g., coal and oil, and environmental pollution resulting from consumption. Effective utilization of renewable energies such as wind energy is expected instead of the fossil fuel. Wind energy is not constant and windmill output is proportional to the cube of wind speed, which cause the generated power of wind turbine generators (WTGs) to fluctuate. In order to reduce fluctuating components, there is a method to control pitch angle of blades of the windmill. In this paper, output power leveling of wind turbine generator by pitch angle control using an adaptive control is proposed. A self-tuning regulator is used in adaptive control. The control input is determined by the minimum variance control. It is possible to compensate control input to alleviate generating power fluctuation with using proposed controller. The simulation results with using actual detailed model for wind power system show effectiveness of the proposed controller.
In case of transmission lines along the sea coast, audible noise due to partial discharges may occur from insulators when contaminated with sea salt and wetted. From the consideration to residents, insulator washing has been performed periodically, but this results in increase in the maintenance cost. As a countermeasure to reduce the audible noise, semiconducting glaze insulator (DC resistance approx. 20MΩ) has been developed and used. However, in case of a very special environment with direct spraying of sea water in seaside districts, there seems to be some risk of thermal runaway because voltage concentration on very small number of insulator units in a string is possible and it may rise the temperature of those units up to the critical point. In this paper, the thermal runaway mechanism is clarified from view point of input and output energy of the semiconducting glaze insulator under contaminated and wetted condition. The surface temperature starting thermal runaway is estimated from various experiments. As a result, the high resistance semiconducting glaze insulator, which has higher thermal runaway withstand capacity and acceptable agreeable audible noise characteristics is developed and subjected to the field evaluation.
The International Space Station (ISS), which is scheduled to start the operation fully in early 2000’s, is being developed and assembled on orbit since 1998 with international cooperation of the USA, Russia, Europe, Canada, and Japan. Japan participates in this ISS program and will provide the Japanese Experiment Module (JEM, named “Kibo") which will be attached to the ISS core. Japan Aerospace Exploration Agency (JAXA), which is responsible for the JEM system development and integration, has been developed JEM Electric Power System (JEM EPS) as part of the Space Station Electric Power System (EPS). The International Space Station Electric Power System is the world’s largest orbiting direct-current (DC) power system. The ISS electric power is generated by solar arrays, and distributed to the each module in 120 Vdc bus voltage rating. When designing a large-scale Space Power System using direct current (DC), special attention must be placed on the electrical stability and control of the system and individual load on the system. For a large-scale Space Power System, it is not feasible to design the entire system as a whole. Instead, the system can be defined in term of numerous small blocks, and each block then designed individually. The individual blocks are then integrated to form a complete system. The International Space Station (ISS) is one of good example for these issue and concerns as a large-scale Space Power System. This paper describes the approach of the stability analysis for a large-scale space power network.
The purpose of this paper is to study an effect of offshoot branch connected rotary machines on a line selection protection relay. The motivation for this study stems from the fact that in a real power system with offshoot branch containing rotary machines like synchronous generators and induction motors, a case of mal-tripping of a line selection relay was observed. The main cause of this mal-tripping was thorough investigated through digital simulation followed by experimental verification carried out by connecting a real time simulator to the real world relay. It is found that the mal-operation of the relay was triggered by the combined dynamic characteristics of the rotary machines like synchronous generators and induction motors. Hence, the main result of this paper is that in case of a power system with an offshoot branch containing induction motors in addition to generators, it is very important to consider their combined dynamic characteristics in true sense, which hitherto has been more or less limited to generators only while conducting such relay settings/studies.
The national target for PV capacity in Japan is 4. 82, GW in 2010, and several PV Roadmaps until 2030 are also described. To achieve the target, several support programs, such as subsidization to capital cost, Green Credit by the Green Power Certification System, buy-back under the Renewable Portfolio Standard low, have been already introduced. Carbon tax is still under consideration, but there are several analyses about possible carbon tax. The purpose of this paper is to analyze PV system sales price and subsidy through buy-back which make photovoltaics cost-competitive with other energy technologies and make the target for PV capacity achievable by 2030 in Japan under an expected carbon tax. For the analysis energy system of Japan is modeled by using MARKAL. Based on the results of analysis, under 6000, JPY/t-C carbon tax, photovoltaics needs subsidy for a while even if we taking both fuel savings and Green Credit into account. For attaining the national target for PV capacity in 2010, photovoltaics needs more expensive buy-back than that in present, but after 2010 necessary buy-back decreases gradually. If 120, JPY/W PV system sales price is attained by 2030, photovoltaics becomes cost-competitive without any supports. Subsidy through buy-back becomes almost unnecessary in 2030, if we can reduce it less than 170, JPY/W. The total necessary buy-back meets peak in 2025. It is much more than ongoing subsidy to capital cost of PV systems, but annual revenue from the assumed carbon tax can finance the annual total necessary buy-back. This means if photovoltaics can attain the targeted PV system sales price, we should support it for a while by spending carbon tax revenue effectively and efficiently.
Harmonic interference by the high voltage distribution system is concentrated in phase advancing equipment of the customer, it arises, and it has lectured on various countermeasures. However, it seems to be the situation which can not be at present off guard. It is not possible to examine the higher harmonic countermeasure, when the flow of the higher harmonic is not grasped. It is indispensable that constitution of phase advancing equipment of the customer and the operational condition are known for the grasp. In this paper, the new method named “projective power factor angle convergent method" which estimated the capacity of phase advanced capacitor from observation result of receiving voltage and current was proposed. According to this method, there is hardly the constraint in the application for usual method, and the high estimation accuracy is obtained. In addition, it is possible to also easily estimate the total capacity of the condenser put into the identical feeder of a distributing substation output.
Lots of the chlorofluorocarbon (CFC) has been released to atmosphere, resulting that the ozone layer in the stratosphere has been destroyed by the released CFC. Therefore, air conditioners without using CFC have been required to be developed. One of the candidates for such air conditioners is a combined conditioner of the dehumidifying cell by the proton exchange membrane (PEM) and the air cooler by water evaporation. But, we need to understand the operating principle of the dehumidifying cell because the performance of existing dehumidifying cells are not cleared. In this study, first we measured the transmissibility and the electro-osmotic coefficient nd of water vapor through the membrane electrode assembly, the water vapor diffusivity through the diffusion electrode, and the mass transfer coefficient between the flow in channel and the diffusion electrode, as important factors to determine the dehumidifying performance. These factors were adopted in our analysis of the dehumidifying cell performance, where the conservation equations of mass and energy with an equivalent electric circuit of the cell are solved simultaneously. Calculated results can describe well the experimental dehumidifying performance. By using this simulation code we predicted the coefficient of performance (COP) of our novel air conditioner. Calculated COP’s for test cell are as small as 0.10 or 0.21, but could be 4 when we can get the PEM with high nd of 5.
If partial discharge occurs in high voltage apparatus, it is unfavorable in view point of its insulation reliability, because they might develop into its insulation degradation or its electrical breakdown. In order to raise the insulation reliability of an apparatus, it is important to detect a minute partial discharge with sufficient sensitivity, especially suppressing background noise. This paper deals with the waveform processing technology by the Daubechies wavelet transform to make relief of the partial discharge signal from a measured noise-containing signal. On this basic idea, here is discussed that the optimal Daubechies order and its level have a close relation with the detection impedance and the sampling interval of the measured signal. Since the partial discharge waveform measured with the detection impedance of parallel circuits of RLC tuned into a damped oscillatory pulse, it has been demonstrated that the Daubechies wavelet transform is effective in discriminating the partial discharge signal from the measured noise-containing signal. Moreover, by choosing suitably the Daubechies order and its level applied to the measured data, it has been clarified that even a minute glow corona which have been masked by the background noise, and also the streamer corona turns into clear appearance on the transformed wave with sufficient sensitivity.
The secondary batteries for the electric vehicle (EV) generate much heat during rapid charge and discharge cycles than the rated condition, when EV starts quickly consuming the battery power and stops suddenly recovering the inertia energy. During rapid charge and discharge cycles, the cell temperature rises significantly and may increase more than the allowable temperature. So we calculated the temperature rise of a small lithium-ion secondary battery during rapid charge and discharge cycles using our battery thermal behavior model, which we have developed being confirmed its validity during discharge cycle at the smaller current than the discharge rate of 1C. The heat source factors were measured by the methods described in our previous study, because the present batteries have been improved in their performance and have low overpotential resistance. The battery heat capacity was measured by a twin-type heat conduction calorimeter, and determined to be a linear function of temperature. Further, the heat transfer coefficient was measured again precisely by the method described in our previous study, and was arranged as a function of cell and ambient temperatures. The calculated temperature by our battery thermal behavior model using these measured data agrees well with the cell temperature measured by thermocouple. Therefore we can confirm the validity of this model again during rapid charge and discharge cycles.
In recent years, a wind turbine generator system is expected as one of clean energies to solve energy resources and global environmental problems. Those systems are installed in places with a strong wind. However, those places have also many winter lightning, which cause heavy damage to electric power facilities. Especially, these system in dozen of meter height are facing to severe problems such as an outage of the electric power and a maintenance check against lightning damage. In order to supply the stable energy, it is necessary to set up a lightning protection of the system. So, we developed the large diameter Rogowski coil, which can surround the steel pipe of the leg, and proved the performance by experiment. And using this Rogowski coil, we observed lightning current in some wind turbine generator systems in Japan. As the results of these observations, we got some observation data of lightning current, which struck the wind turbine generator system. This paper reports these observation techniques and results.