Dispersed generations have been developed considering effective utilization of energy. Then a reverse power interconnection of generators is required to utilize power effectively. In Japan, “GUIDE LINE” was revised considering these situations. Then if a relay system which protects distribution systems and dispersed generators had two islanding detection methods (active and passive methods), the reverse power interconnection was made possible. Islanding detection method for synchronous generators have been developed (5) (6). However the previous methods do not take an active method into account and methods can not detect all islanding cases. Authors proposed two active islanding detection methods for synchronous generators. These two methods utilizes frequency deviation according to a active perturbation signal.
This paper presents an equivalent transformation technique for the proposed two methods. Theoretical basis, analysis, practical issues and implementation of the technique are described. The proposed technique was tested using a simulation and a field test plant.

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In recent years, enhancement of consciousness for energy saving and problem of environment are widely encouraging the installation of dispersed storage and generation (DSG) units such as co-generation and photo-voltaic generation. When a distribution line with the DSG is disconnected from the main source of utility, the DSG supplies power to the distribution line. The situation, namely islanding, creates various problems for the reliable and safe operation of the distribution line. Thus, the islanding must be immediately prevented by islanding protection equipment.
This paper describes an islanding protection scheme and the digital protection equipment for a synchronous generator. The proposed scheme detects an islanding of a synchronous generator from frequency fluctuation occurred by feeding a sinusoidal small reference voltage signal into the auto voltage regulator circuit of the generator. The authors have manufactured the digital protection equipment applying the scheme, confirmed the excellent performance by testing in an artificial distribution line. In the paper, a determining proceeding of the setting value of the equipment is described.

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By the amendment of electric utility industry law in 1995, independent power producers (IPP's) were allowed to enter the electric power market, and are to supply electricity from 1999. Many IPP's use coal or residual oil for electric power generation. However, because of high carbon-intensity of these fuels, the entry of such IPP's might influence the reduction in total CO₂ emission in Japan. This paper quantitatively evaluates the potential capacity of various types of IPP's with consideration for the reduction in CO₂ emission in the electric power industry on the basis of the optimal electric generation planning. The results show that the available incremental capacity of nuclear plants affects the maximum capacity and economic values of IPP's which use high carbon-intensity fuel. The optimal combinations of various types of IPP's in order to reduce generating costs of utility are also examined.

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In this paper, the operational applicability and the economical consequences of an electricity market model based on a discriminatory auction rule is analyzed and compared with a uniform price auction based one. The studied model is based on centralized optimization therefore, the operational constrains and costs are evaluated during the planning process. The existence of a system operating company, which might be a regional utility, with the duty to dispatch generators and the objective to minimize its payment is supposed. To ensure clarity in the scheduling decision process, during the dispatch operation, a sequential process based on a payment index is applied.

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Quantitative evaluation of power system reliability in planning stage is one of the effective approaches to realize more efficient facility investments. Especially, recent movements toward more effective utilization of existing facilities calls for precise evaluation of appropriate time of investments, and in this respect, reliability analysis based on a probabilistic method is expected to play an important role as one of the powerful planning tools.
This paper discusses reliability analysis of the specific portion of a trunk transmission network, which supplies bulk power to the metropolitan area. The sequential Monte Carlo method is applied in order to evaluate the effect of yearly demand profile and operation strategies on power system reliability.
Application of the developed tool to a model network revealed that the transfer capability of existing transformers may be increased in probabilistic sense without significant deterioration of reliability, indicating the possibility of investment deferral.
In this paper, effects of applying new short time overload rating on transmission facilities are also examined. Initial short time overload rating on transformers is adopted, which allows more overloads on transformers than conventional rating for relatively short period just after the faults. The reliability analysis showed that this new rating can decrease the opportunities of loss-of-load, and as a consequence, can be effective in improving probabilistic transfer capability of the transformer.

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The interference test is prescribed in the international standard, IEC60060-2 High-voltage test techniques, to convince that the induced noise in the low-voltage arm of an impulse measuring system is sufficiently small. However, the high-voltage arm of a measuring system also suffers some electro-magnetic noise, especially when a sphere gap is connected near the voltage divider, which is frequently used for the tests prescribed in the IEC.
This paper experimentally discusses the characteristics of the noise induced in the high-voltage arm of an impulse measuring system with a sphere gap, after the noise in the low voltage arm has been convinced to be small enough by the interference test.
Many voltage waves, which are obtained in our experiments and thought to be noise induced in the high voltage arm, may be understood without contradiction, if the main part of the noise is assumed to be induced through the capacitance connecting between the sphere and the high voltage arm of the divider.

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In diagnosis of faults by means of dissolved gas analysis for oil-immersed transformers in service, acetylene gas generated owing to faults accompanied with high temperature such as arc or partial discharge is designated as a characteristic gas. Even if small quantities of acetylene gas are detected, successive monitoring frequency for the transformer is generally increased.
It is reported that occasionally concentrations of acetylene gas dissolved in oil show decreasing behavior with operating time differing from other generated gases. Authors have taken notices of the behavior and made clear that it can be analyzed by the rate equation of first-order reaction, assuming that the behavior depends on a chemical reaction of acetylene gas to any material included in a transformer. We have had experiments using copper foils as a possible material reacting to acetylene and confirmed that the behavior of acetylene in transformers can be reproduced in a laboratory. We studied chemical bonds formed on the surface of the copper foil heated in oil dissolved acetylene gas using XPS. For exact calculations of quantities of acetylene gas generated abnormally, the reacting quantities of acetylene gas have to be taken in consideration.

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As power system in Japan are becoming larger and larger, measures against generator stability problems are expected to be more serious. On the other hand, in recent years researches on superconducting fault current limiter are moving forward in accordance with the advancement of superconducting technology. As regards to the problems of generator stability with superconducting fault current limiters, a lot of literatures exist, but they have a very few analyses in terms of instantaneous values. This paper analyzes the effects of the limiter in terms of instantaneous values on enhancement of generator transient stability and control of turbine shaft torque as well as control of fault current. Three types of fault current limiters are considered in this paper: i. e., resistance type, inductance type and resistance + inductance type. It is concluded in this paper that the resistance type fault current limiter is most effective for the three purposes stated above.

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Adjustable-speed pumped storage generating systems of large capacity have been newly installed in power systems with recent technologies of power electronics. These new generating systems contribute not only to frequency regulation of power system at night by means of input power change as results of rotor speed control, but also to enhancement of power system stability by fast control of voltage and power.
New analytical method based on extended Heffron-Phillips model was developed in order to support designing of power system stabilizer which is used to improve dynamic stability of the synchronous generators located in the vicinity of the adjustable-speed generating system. Systematic approach based on the new analytical method is shown with numerical examples, explaining how to construct the additional power system stabilizing controller as well as main controller of the adjustable-speed generating system.

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Since fault current tends to increase with electrical power demand, current-limiting technology for overcurrent have been investigated. As a promising candidate, superconducting fault current limiter (SC-FCL) is expected to be introduced into power system. It is one of the most important performance required for the SC-FCL to recover to a normal operating mode, i. e., superconducting state rapidly after current interruption. In this paper, the recovery time of a SC-FCL introduced into a distribution power system is discussed. To obtain the fundamental data, the recovery time of short Nb-Ti superconducting cables were measured. We developed a calculation method of the recovery time and it was confirmed that the calculated results agree with the measured ones. The recovery characteristics of a SC-FCL in a 6.6kV distribution system for the short-circuit fault near the substation. We considered 3 cycles and 17 cycles as the period from the fault occurrence until the current interruption. As a result, it is suggested that the superconducting cable length required to recover within high speed reclosing time of 0.3 sec are more than 270m and 480m for 3 cycles and 17 cycles respectively.

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The effects of diffuser shape and back pressure on the performance of closed cycle disk MHD generators are investigated with two dimensional numerical simulations taken account of boundary layer. The enthalpy extraction ratio decreases and fluctuates periodically with increase in the back pressure. The amplitude of power output fluctuation and the period depend on the volume of the inverse flow region. For the reduced height diffuser, the inverse flow region is supressed and the fluctuation becomes smaller than that for the constant height diffuser. When operated with a back pressure lower than an optimum value the diffuser does not work because of reacceralation in the diffuser. For the higher back pressure on the contrary, the inverse flow region propagetes into the MHD channel, then the enthalpy extraction ratio is reduced and the Mach number at the exit of MHD channel becomes lower than unity. For the optimum back pressure, high enthalpy extraction ratio is achieved and the adiabatic efficiecy at the diffuser exit is decreased by several percent from that evaluated at the MHD channel exit.

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Influences of back pressure on the discharge structure and the performance of a He/Cs nonequilibrium disk MHD generator are investigated with time dependent r-Φ two-dimensional numerical simulations. For load resistances higher than the designed value, the discharge remains stable and uniform in the azimuthal direction even for high back pressures, while the electron temperature varies in the radial directions. In spite of the stable discharge, however the generator performance is deteriorated by the low gas velocity and high static pressure due to high back pressures. For low load resistances, the discharge structure becomes nonuniform and unsteady due to the ionization instability. In this case, the influence of the back pressure on the generator performance is masked because the performance strongly depends on the discharge structure. It is found that the increase in the back pressure can make the discharge stable for load resistances slightly lower than the designed value.

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Structures of plasma and fluid flow in a nonequilibrium disk MHD generator driven with lOOMWth He-Cs working gas are examined with three dimensional numerical simulations. It is confirmed that the boundary layer is relatively thin and the main flow part remains under the condition of high enthalpy extraction with a uniform and steady plasma. For a low load resistance, nonuniform and unsteady streamer structure appears in the γ-φ plane due to the ionization instability caused by the partial ionization of seed atoms, and the structure holds in the height (z) direction for a large generator channel. It is clearly shown for a high load resistance that the boundary layer becomes considerably thick and separates, and the strong MHD interaction makes the structure like pseudo-shock waves, particulary in the upstream region of the generator. The structure of fluid flow is circular in the upstream region, while the flow is affected by the nonuniform and unsteady domain structure attributed to noble gas ionization in the downstream region.

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In the previously reported hydrothermal scheduling methods, emphasis is placed on the hydro scheduling and the thermal system is simply represented by a single equivalent unit which generates an economic schedule.
This paper presents a more detailed (thermal unit commitment involved) and efficient weekly power generation scheduling method of hydrothermal systems with pumped-storage plant. As the pumped-storage operation has a great influence on the unit commitment schedule, using power system's incremental fuel cost and unit's average fuel cost per kWh, firstly, the pumped-storage schedule is integrated into the thermal unit commitment schedule and then, optimal multireservoir hydro operation can be scheduled efficiently by the aggregation-decomposition method.
The effectiveness of the proposed method is ascertained through many simulations for a model system using a personal computer and due to its easiness of handling various constraints and an efficient calculation algorithm, it is considered to be a practical method for the large scale hydrothermal systems.

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Based on several experimental results, some hints are presented on the insulation design lor power caoies which are to be used under PWM inverter surge voltages. If there is no fear of water-tree deterioration, the peak voltage can be used as a design basis. However, if the cable is to be used under a wet condition, the number of voltage zero-crossings becomes important, since it highly enhances the water-tree deterioration.

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