With prevalence of high-specified equipment such as power electronics applied device, power quality problems are becoming concerned for both electric utilities and customers. This paper firstly describes what power quality problem is, and then, it outlines recent power quality technologies classified into those of immunity or emission side from the viewpoint of EMC concept, which is practical approach to consider these problems.
Recently, the basic framework of electric power systems has been changed significantly by deregulation of electric power industry. Also, distributed generators (DGs) such as renewable energy generations, co-generations, and energy storage systems have been introduced into the demand sides not only for saving energy and the global environment, but also for compensating voltage drops and supply interruption. In the future power systems, a lot of small-sized DGs will supply the electricity with existing large-scale generators under a competitive environment. In this context, it is desirable that DGs contribute to stable, reliable and economic operations by coordinating with existing large-scale generators. For example, power from large-scale generators could be leveled if DGs are operated during the peak period. Also, ancillary services such as frequency control, voltage control, and supply of reserve capacity could be executed by controlling DGs directly or indirectly. Under these circumstances, the authors have proposed a new power distribution system: Flexible, Reliable and Intelligent ENergy Delivery System (FRIENDS). This paper investigates some kinds of power supply systems which coordinate DGs with existing large-scale generators including the concept of FRIENDS and considering how DGs are managed. The effects of DGs which contribute to supply the energy and/or the reserve in every power system are evaluated.
We have recently proposed a new controller based on the equilibrium point analysis for model power systems. In this paper, first the Japanese standard one-machine infinite-bus system model is formulated, and the equilibrium points are analyzed. Next, complementary control inputs for AVR and GOV with limiters of the model system are determined on the basis of the analysis. Finally, it is shown that the unstable equilibrium point is eliminated by adding the proposed inputs, and then the critical clearing time can be improved in comparison with PSS of the standard model.
We have proposed nonlinear stability indices of power swing oscillation using normal form theory. The proposed indices are effective when there are several modes to be focused on. For each oscillation mode, the proposed indices indicate the characteristics of damping factor with regard to its amplitude change, and the stability region. In this paper, we apply the indices to autoparametric resonances between oscillation modes in longitudinal power systems. It is shown that we can evaluate stability of the power systems appropriately by modifying the proposed indices taking the autoparametric resonances into consideration.
If the economic activity in the commercial and residential sector continues to grow, improvement in energy conversion efficiencies of energy supply systems is necessary for CO2 mitigation. In recent years, the electricity driven hot water heat pump (EDHP) and the solar photo voltaic (PV) are commercialized. The fuel cell (FC) of co-generation system (CGS) for the commercial and residential sector will be commercialized in the future. The aim is to indicate the ideal energy supply system of the users sector, which both manages the economical cost and CO2 mitigation, considering the grid power system. In the paper, cooperative Japanese energy supply systems are modeled by linear-programming. It includes the grid power system and energy systems of five commercial sectors and a residential sector. The demands of sectors are given by the objective term for 2005 to 2025. 24 hours load for each 3 annual seasons are considered. The energy systems are simulated to be minimize the total cost of energy supply, and to be mitigate the CO2 discharge. As result, the ideal energy system at 2025 is shown. The CGS capacity grows to 30% (62GW) of total power system, and the EDHP capacity is 26GW, in commercial and residential sectors.
It is well known that the operation with low humidified reactants accelerates cell voltage loss of PEFC. On the other hand, the mechanism of the voltage loss is not clear. On this study, two kinds of cells which have different thickness membrane (15 and 30μm) were evaluated under operation with low humidified reactants to clarify the voltage loss mode. The study indicates that there are two different cell voltage loss modes. For 15μm cell (a thin membrane cell), the cell voltage decayed along with open circuit voltage decrease with H2 crossover increase. It is the case that H2 crossover depresses cell voltage. For 30μm cell (a thick membrane cell), the cell voltage decayed along with open circuit voltage decrease without H2 crossover increase. This decay mechanism of voltage loss without H2 crossover was focused to study. New methods for measuring humidity distribution and current distribution in a cell were introduced for further analyze. It is found that effective catalyst area loss in cathode catalyst layer could depress cell voltage.
A high speed vacuum circuit breaker (HSVCB) has been investigated. HSVCB makes high frequency current superimposed on a fault current so that the current is forced to be zero and is interrupted. Its interruption performance is considered to be dependent on a rate of change of the current (di/dt). As a fundamental research, we investigated the di/dt-dv/dt characteristics and the insulation recovery characteristic after interrupting the counter-pulse current for various contact materials of AgWC, CuW, and CuCr. The results revealed that the case where gap length is larger is better in a current interruption performance. Moreover, it was found that di/dt is not dependent on the insulation recovery characteristics, but the magnitude of interruption current influences greatly.
For the size reduction of electric power equipment, the electric field stress around solid insulators is to be carefully designed. This concern will be solved by the application of FGM (Functionally Graded Materials). In this paper, we investigated an application feasibility of FGM from numerical simulation, and the fabrication technique for gas insulated equipment. Finally, we could confirm the significant effect of FGM application for gas insulated equipment.
We have developed a High Gradient Magnetic Separation (HGMS) system to remove arsenic from geothermal water by using a superconducting magnet. We attained the reduction of arsenic concentration less than the effluent standard of 0.1mg/L and slightly larger than the environmental standard of 0.01mg/L in Japan. The system consists of a pretreatment process that adds extra magnetization to arsenic by chemical reaction, and a reciprocating HGMS filter using a superconducting magnet that extracts magnetized arsenic from the geothermal water. We improved efficiency of the pretreatment process with reusing the deposition and optimiizing chemical conditions. The reciprocating HGMS filter can reduce the time for rinsing the filter. We present the experimental results of the removal system and an estimate of a practical plant to supply hot water for public use on the basis of them.
Wind power generation is expected to become more important in the future distribution system. Although several prospective reports such as IEC 61400-24 and NREL SR-500-31115 indicate on insulation scheme and grounding design for lightning protection, it still seems that there are not many investigations on the problems. This paper therefore discusses lightning surge analysis using wind farm model with 2 or 10 ideal wind turbines. Changing parameters such as grounding resistance and lightning strike points, several cases were studied. As the result of the analysis using digital simulator ARENE, it is clear that the surge tends to propagate toward the end of a distribution line in a wind farm and there is possibility of insulation accidents at the other wind turbines when lightning attacks a wind turbine.
Applying anti-corrosion grease and aluminum clad steel (AC) wires to ACSR has adopted as general methods to prevent overhead transmission line conductors and/or wires from corrosion. However, there are some cases that ineffectiveness of those means are reported on some transmission lines passing through acid atmosphere in the vicinity of a factory exhausting acid smoke. The feature of the corrosion caused by acid atmosphere is to show a higher speed in its progressing as well known. As means against such acid corrosion, application of high purity aluminum, selective removal of inter-metallic compound in aluminum and plastic coating wires has been reported before, and each has both of advantage and disadvantage actually. In the former letter, we reported the new type of anti-corrosion grease that shows an excellent property against acid atmosphere as well as in a salty circumstance. Here presents a new type of anti-corrosion technology of applying high corrosion resistance aluminum alloy or zinc coatings on each component wires of a conductor that we succeed in developing through a serial study of anti-corrosion methods on overhead transmission lines.
Line surge arresters are installed mainly in the three phases of one side of double-circuit transmission lines to prevent double-circuit faults. In addition, there are some cases where arresters are installed in five phases or the six phases of those. Recently, the proportion of the arrester installation is rising remarkably. It is important to evaluate the rate of arrester failures due to the energy stress caused by lightning, because there is possibility that lightning strokes to transmission lines with large peaks and/or long duration of currents cause arrester failures. In this paper, we examine the lightning stroke current causing arrester failures and the frequency of the arrester failures in 77kV double-circuit transmission lines. Moreover, it is cleared that the optimal phase to omit an arrester is one lower phase for five phases installation of arresters.