A photovoltaic/wind/diesel generating system with a battery (PWD system) is discussed from a view point of total CO₂ gas emissions during life time. The total Emissions is the sum of the emissions occurring at manufacturing and operating. First, the manufacturing CO₂ emissions of the photovoltaic generator and the wind turbine generator are calculated by “the process analysis method”. The method considers the material used in each generator, its weight and its CO₂ emissions rate. On the other hand, the manufacturing CO₂ emissions of the diesel generator and the battery are calculated using “the interindustry (input-output) table”. Secondary, the PWD system is operated on a computer so that the fuel consumption of the diesel generator is minimum assuming that hourly series data of electric load, insolation intensity, wind speed and air temperature are known during a year. And CO₂ emissions occurring at the system operation is obtained from the annual fuel consumption of the diesel generator.
The result show that the CO₂ total emissions of the PWD system is lower than that of the conventional diesel generator system. The CO₂ total emissions has a minimum when photovoltaic/wind generating ratio is at 50/50. The CO₂ emissions of manufacturing decreases with increasing of the wind generating ratio from 100/0 to 0/100. The CO₂ total emissions decreases as the natural energy ratio increases. It is, however, saturated to about 60% when the ratio is more than 60%. And the CO₂ total emissions increases with increasing of the battery capacity. It is concluded that the PWD system plays an important role in decreasing considerably the CO₂ total emissions while the total system cost is high under the present price circumstances.

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A closest loadability limit (CLL) is considered as a most reliable index in the assessment and enhancement of voltage stability of a power system. Two kinds of methods, the iterative method and the direct N-R method, have been proposed so far, but the computation of CLL is known to be troublesome: The former method is quite time consuming and its convergence is sometimes disturbed due to the existence of multiple local CLLs, while the latter method is hardly useful unless a very accurate initial condition is available.
This paper proposes a new method to compute a CLL, consisting of three stages of computations. The first stage is to obtain a rough initial estimate of a CLL, where plural local CLLs if exist can be approximated by the multiple power flow solutions. The initial estimate is refined by the second stage computation based on a method similar to the conventional iterative method. The third stage is to obtain a direct solution by mean of the N-R method. The effectiveness of the proposed method is demonstrated using IEEE 14, 30, 57, 118 bus test systems.

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In recent years, the deregulation of the electricity industry aimed at achieving lower price of electricity is becoming a reality in many countries. In Japan, the introduction of the competition at the generation stage made it possible for independent power producers (IPP) to participate in the generation market at the bid-based wholesale level. An increase of non-utility-owned generators may reduce controllable resources for the utility such as spinning reserves. Therefore, when the security control is implemented only by the utility, the cost required for the control may become higher; this may result in higher electricity prices to consumers. Conversely, it is considered that the security cannot be maintained sufficiently using the same cost as usual.
The authors introduce “incentive prices” for leading the non-utility-generators to corporate in the security control. The incentive prices are prices when the utility purchases the power excluding the amount specified in a bidding from the non-utility-owned generators. It has temporal variation, which reflects the ever-changing demand location variation reflected the effect of network losses and constraints. This paper presents a method for determining the desirable incentive prices. Using the proposed method, the preventive control can be executed without exceeding a security cost required in the traditional situation.

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In this paper, we investigate a stability of voltage oscillation modes in longitudinal power systems equipped with static var compensators (SVC). These modes are usually stable, so they do not appear without external force. The conventional harmonic resonance is a phenomenon in which an oscillation mode is excited with a harmonic source. Hence, it is solved by removing the source with a harmonic filter. For this reason, a SVC is equipped with several filters. However, there is a possibility where an oscillation mode itself becomes unstable. If a mode is unstable, it can have a large amplitude without any harmonic source. Since it needs no harmonic source, its frequency is not limited to a harmonic frequency, but can have any value. The harmonic instability in direct-current transmission systems, is an example of such phenomena. PLL(phase locked loop) is considered to be effective to suppress the harmonic instability by SVC. However, no theoretical reason has been shown, yet. This paper clarifies the effectiveness of PLL based on a stability condition for the voltage oscillation modes. Frequency responses of a thyristor controlled reactor (TCR), a component of SVC, are largely influenced by existence of PLL. If PLL exists, the stability condition is always satisfied, and all modes are stable. Lastly, we perform numerical simulations to show the validity of our investigation.

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AFC control on BTB active power flow, which is in phase with frequency deviations both in Hokuriku AC power system and in the rest of the power system of middle and west Japan, can effectively reduce frequency fluctuations. In the first section of this paper, test measurement result of actual largescale power system fluctuation load is shown and dynamic fluctuation load model is derived from the study on the test result. Then we analyze effectiveness of this AFC control to suppress frequency fluctuation in the two AC power system through computations of static and dynamic simulations by using the derived model on MATLAB. Our simulation analyses reveal that effectivenss of frequency fluctuation suppression by the AFC control on BTB active power depends on the capacity scale of AC power system interconnected with BTB system: We conducted these computations on different states of power systems which represent summer-peak, winter-peak, typical spring-peak and summer-night. We confirmed that frequency fluctuation can be significantly reduced in the smaller capacity power system by setting larger AFC gain.

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As a power system is becoming larger and more complex, it has become more difficult for planning engineers to adjust outage works since the number of maintenance works has increased accordingly. For assisting planning engineers, the authors have developed a supporting expert system for outage work planning of electric power facilities. In this system, a suitable system configuration for a particular set of outage works is chosen out of the prepared system configurations which have been formed from the past operation records. However, in order to obtain feasible plans from the standpoint of adequacy in system configurations, it is necessary to consider the following three issues: (a) reducing the number of switching operations, (b) transition of system configurations from day to day, and (c) complete avoidance of supply shortage at N-1 contingencies. In order to achieve the above objectives, the authors have proposed an approach of generating system configurations under N-1 security constraints, which is based on the extended optimal switching power flow (EOSPF) and Tabu Search (TS) algorithm. However, since the proposed approach minimizes the objective function with respect to an N-1 security constraint violation, it is impossible to minimize switching operations for overall planning period.
In this paper, we propose a method of making up system configurations by means of a combination of (EOSPF+TS) and Genetic Algorithm (GA), in which the proposed method minimizes the number of switching operations for overall period while satisfying N-1 security constraints. In order to confirm the effectiveness of the proposed method, it has been applied to a 42-bus system with successful results.

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The microstructure and electric properties of new ZnO varistors containing both Bi₂O₃ and new additive, a rare earth oxide(R₂O₃) have been studied. The threshold voltage (Vs) of varistors containing R₂O₃ (ionic radius, r_i<0.95Å) showed 1.4 times as much as that of a based component without R₂O₃. Small particle, or R-phase, which contains the rare earth element, Zn, Bi, Sb, and Mn was observed at the ZnO grain boundary. High varistor voltage was probably achieved by the pinning effect of R-phase. New varistor elements for MOA (Metal Oxide surge Arrester) with a varistor voltage about twice that of conventional elements have also been developed by the optimization of additives and various sintering conditions. The size of arresters for GIS (for 66 to 500 kV) installed these new elements have been reduced by 40 to 60% in volume compared with the conventional type of arresters.

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This paper presents new developed noise reduction methods and results of partial discharge detection and measurements of electric power apparatus using digital signal processing techniques. We have examined noise diminution by the algorithm in laboratory based on measurements of PD signals in SF₆ gas and real noise as well as interference in practical HV and EHV substations. Consequently, the techniques, enabled us to reduce sinusoidal continuous noise considerably, so that they are promising for future application in actual HV substations.

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The production of non-equilibrium plasma and the fluid flow with the MHD interaction are examined experimentally with a shock-tube driven disk channel with no loading electrodes. For low magnetic flux density and low seed fraction, where non-uniform and unsteady plasma is generated, the static pressure decreases onotonically in the radial direction, although the pressure increases in the entire region of the channel in comparison with the value under no MHD interaction. For magnetic flux density and seed fraction above some critical values, a fairly uniform plasma is produced. The static pressure, however, is found to increase abruptly in the channel and the total pressure is considerably reduced at the location, where the abrupt pressure increase ocuurs. These facts imply that steady and uniform plasma should be produced without locally constricted strong Lorentz force to improve the adiabatic efficiency of a disk MHD generator.

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Imbalance of the current distribution in the multilayer high-T_c superconducting power transmission cable tends to result in serious problems, which means it increases the loss and deteriorates the transport current capacity of the cable. To solve this problem, a method to prevent the imbalance by adjusting the twist pitch angles of the superconducting tapes has been investigated. At first, a method to calculate the current of each layer for a multilayer coaxial cable has been proposed. Using the method, the twist pitch angles for the balanced current distribution were searched, and a simple relationship among them has been found out. Furthermore, a set of the twist pitch angles, which is decided by considering the bending strain tolerance of the superconducting tapes and the flexibility of the cable, has been indicated and discussed.

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Since ceramics resistor type NGR (Neutral Grounding Resistor) have been developed as new materials for power equipment, about 15 years have been passed. This paper describes cumulative application records of ceramics resistor type SFe gas insulated NGR and typical construction of 22 kV, 66 kV, 110 kV NOR, and monitoring methods measuring residual leakage current of 110 kV NGR depending on neutral unbalance voltage of power transformers and using thermal detection devices of ceramics resistors of 66 kV NOR.

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Response characteristics of a ZnO element generally used for surge arresters against very fast transients are hardly known. They have not only non-linear resistance characteristics but also dielectric ones. We have developed an analytical digital program to study internal resistive and capacitive currents of the element to very fast transient current based on Maxwell equations. And moreover, proposed equivalent circuit has been found to agree with the above theoretical method. This paper shows not only good agreement of theoretical method and equivalent circuit, but also new phenomena of skin and Ferranti effects on ZnO internal currents.

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The improvement in the performance of an MHD Generator in a blow-down facility by suppressing the seed deposition on the walls has been verified experimentally. In the previous experiments, where the generator with copper electrodes was used, the output power was reduced only at the early stage of the power generation run, even under the fixed operating conditions. This fact could be attributed to the deposition of seed material on the walls of the generator (water-cooled copper electrodes and insulator walls), because the wall temperature could not reach a high value at the early stage of the blow. On the basis of the experimental results, the anodes made of copper were replaced by those coated with stainless steel which has low thermal conductivity in the recent experiments. As a result, the decline in the output power at the early stage of the blow was markedly suppressed and the output power clearly depended on the seed fraction. Thus, the change in the material of anodes surface was confirmed to be useful for the improvement in the performance of the generator installed in the blow-down facility.

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For the stability of power systems, nonlinear control is thought to be desirable since generator has a strong nonlinearity. On the other hand, the authors have proposed an equilibrium point control for multi-machine power systems. This letter shows that in the case of nonlinear supplementary control input for AVR, the calculation of equilibrium points is simple, and the input gives fairly good control responses and a long critical clearing time through the numerical simulation of a one-machine model power system.

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The 500 kW wind generator was developed as one of NEDO's projects, and several tests on its performance have been made so far. Based on the measurement data, we performed the modeling of the NEDO 500 kW wind generator and have investigated a method to reduce power variations under fluctuating wind conditions in complex terrain. In a control system design of a wind generator, It is important to obtain effective wind speed to drive a wind turbine. This paper presents an estimating method of wind speed acting on a wind turbine using a wind generator itself. The result showed that estimating wind speed almost agrees measured wind speed.

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