It is necessary to take the effects of mutual couplings into account when unbalanced faults are to be calculated in such as transient stability study.
When the method based on symmetrical co-ordinates is applied to faults calculation, it has been needed in conventional method to construct the zero sequence network configurated more complex than other networks so far. Then, the application of faults calculation including mutual couplings to the analysis on bulk power system model has been considerably difficult for long time.
This report presents the newly developed method to calculate the effects of mutual coupling in multi-faults calculation under same configuration and with no change for all sequence networks. The validity of proposed method was verified through the application to transient stability analysis for power system model.

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In this paper, a method of assessing dynamic stability of large-scale power system by Rayleigh's quotient, is proposed. One-machine infinite-bus systems show damping torque characteristics similar to diagonal components of operational transfer matrices for original multi-machine systems, which means that design of PSS with one-machine systems is exactly to control those components. An expression for damping constants of oscillation modes is derived based on an energy function and its time derivative for a simplified system representation. This expression clarifies that oscillations do not necessarily become unstable even if there are some generators with negative damping, and that effect of damping torque is determined by eigenvectors. The expression is generalized with Rayleigh's quotient, and a method of estimating eigenvalues of large-scale power systems is proposed. With this method, approximate eigenvalues are refined to accurate eigenvalues. Only a specified number of eigenvalue analyses are required irrespective of the number of generators, hence much calculation is saved. Lastly, this method is applied to a 107-machine system to verify its effectiveness.

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A converter-fed variable-speed generator-motor for a pumped storage power plant has been developed in order to contribute to the automatic frequency control on an electric power system during pumping operations, as well as to improve the efficiency of turbines during generating operation together with electric power stability. This system consists of a reversible pump-turbine, generator-motor, cycloconverter and control units. The rotor of the generator-motor, wich is coupled directly with the turbine runner, is normally operated at a rotating speed equal to the difference between the frequency of the electric power system and that of the rotor current. In the state that a fault has occurred in the secondary circuit of the generator-motor, the variable-speed generator-motor fault current differs from that of a conventional synchronous generator-motor.
This paper describes the fault current analysis results for the condition that a sudden short-circuit is made on the secondary side of the generator-motor, and collates the results with the EMTP simulation results.

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A converter-fed variable-speed generator-motor for a pumped storage power plant has been developed in order to contribute to the automatic frequency control on an electric power system during pumping operations, as well as to improve the efficiency of turbines during generating operation together with electric power stability. This system consists of a reversible pump-turbine, generator-motor, cycloconverter and control units. The rotor of the generator-motor, wich is coupled directly with the turbine runner, is normally operated at a rotating speed equal to the difference between the frequency of the electric power system and that of the rotor current. In the state that a fault has occurred in the secondary circuit of the generator-motor, the variable-speed generator-motor fault current differs from that of a conventional synchronous generator-motor.
This paper describes the fault current analysis results for the condition that a sudden short-circuit is made on the secondary side of the generator-motor, and collates the results with the EMTP simulation results.

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We propose an approach to one-day-thorough seven-day-ahead electrical load forecasting based on a realistic problem formulation which should contribute to more reliable and economic weekly power station operation. Generally, the load forecasting has the following problems: (1) Although the load is affected by various factors, like temperatures, in the load forecasting, it is impossible to consider all of them; (2) The relationships between the load and some factors are not clear, and often vary with time; (3) Uncertainties in forecasts of the temperatures sometimes make the results of load forecasting worse. They are very influential to the power station operation. While a number of methods have been proposed to solve the problems (1) and (2), there have been few attempts on the problem (3). We propose the following approach in this paper, taking these problems into consideration. Firstly, concerning the problem (1), we focus on such factors that have major influence on the load and whose values are obtainable on a weekly basis. The other factors are all regarded as stochastic and are not included in the forecasting model. Secondly, regarding the problem (2), we use a self-organizing approach where the algorithm itself finds the optimal model structure or the optimal set of factors to be included in the model day by day. And finally, addressing the problem (3), we propose a new performance index of model structures which can measure the balance between i) improvement of the load forecasting accuracy due to inclusion of a factor in the model and, ii) degradation caused by uncertainty or error in the factor included. Using this index, we construct a model which does not yield a large error in spite of errors in the temperature forecasts. Examples show that this approach improves the forecasted results when erroneous temperature forecasts are fed into the model, and verify its effectiveness.

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The transmission lines passing through a mountainous region are often struck by winter lightning, thereby, a number of double-circuit faults occur. Space charge might be responsible for this phenomena. Several investigations on flashover characteristics have been performed focusing on reduction of flashover voltage due to ionic space charge formed by corona discharge. In this paper, flashover characteristics of air gap within charged droplet cloud ejected from an airless nozzle using induction charging method are discussed. The droplets are charged in the range -200 to 200μ C/kg forming the the space charge density of approximately 13μ C/m³. The flashover voltage and the time lag to flashover were measured when 1.2×50μs lightning impulse voltage applied to a rod-sphere gap placed within the charged cloud. Flashover voltage for positive rod markedly increased within positive charged cloud by increasing the charge-to-mass ratio. The increase of flashover voltage was up to 80% in comparison with uncharged droplets. Flashover voltage for negative rod decreased about 20% in the cloud of either polarity. The results show that the presence of charged droplets in the air gaps affects dicharge process significantly.

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One of useful means to mitigate global warming is the energy conservation. The amount of energy consumption in industrial sectors is above 50% of total energy consumption in Japan. One of the ways of energy conservation in industrial sectors is the recovery of waste heat, of which the amount depends on the energy demand within and between connected factories.
The purpose of this paper is to investigate the energy conservation potential of so-called heat cascading of various energy consumption secotors. We have developed a heat combinat model of optimization type which integrates energy flows among processes of energy intensive industries so as to maximize the total energy-economic efficiency. We have treated mainly iron & steel, cement, paper & pulp and ethylene industries as core industries in combinats. Simulation results demonstrate effectiveness of heat cascading as one of useful means for future energy conservation.

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The authors propose a new calculation method of transient behavior of free electron density of the plasma in nonequilibrium MHD generator where cesium works as the seed atom. The method takes into account the minimum numbers of excited states and excitation and de-excitation paths which are sufficient to calculate free electron density in high accuracy. Calculation results obtained by the method, therefore, have almost the same accuracy as those obtained by the detailed calculation which takes more excited states into account, and also the method is simple enough to be incorporated in the time-dependent simulation code of performance of nonequilibrium MHD generator. Necessity of the proposed method is confirmed through the fact that there exists considerable difference between the calculated performances of nonequilibrium disk MHD generator obtained by the conventional quasi-one-dimensional time-dependent simulation code and obtained by the improved code in which the proposed method is incorporated.

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Results of experimental studies on behavior of a supersonic flow and of an nonequilibrium plasma in a disk MHD generator are presented. The experiments with cesium seeded argon were carried out under high MHD Interaction conditions. Effects of seed fractions on static pressure distributions, flow Mach numbers, electron temperatures and uniformity of discharge in the Disk MHD channel were investi-gated. The results have shown that the flow is kept supersonic throughout the disk MHD channel when a sufficient Joule heating exists in a supersonic nozzle and the seed is fully ionized. It was found that there was an optimum seed fraction at which the power output became maximum and at the same time, the seed was fully ionized. Furthermore, an almost uniform discharge due to the full ionization of seed was observed. It is noted that enthalpy extractions and adiabatic efficiencies were increased remarkably, and the highest enthalpy extraction of 26.5% was achieved for cesium seeded argon. However. adiabatic efficiencies remained still low owing to large pressure losses.

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The authors propose a new power control method which is suitable for the MHD power generation system which consists of nonequilibrium disk generator and line-commutated inverter. The thermal input of generator is controlled by changing the inlet stagnation pressure, whereas the seed mass flow rate instead of the inlet stagnation pressure is utilized as a manipulated variable of power control system. It is possible that the proposed method ran realize both high performance for part load operation and fast output power control of which time constant is much shorter than the response time of thermal input. Numerical simulations are carried out for the MHD power generation system connected to infinite bus and then it is confirmed that the system is stable and shows excellent power control performance.

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We investigated creepage discharge propagation characteristics on PET films by applying an impulse voltage in SF₆ gas under the influence of surface charging. Experimental results revealed that the impulse creepage discharges on the charged surface with -4 to -12kV extended to distance at maximum 20 times longer than the case of uncharged surface. It was also found that the flashover voltage V_FO had a power law dependence on the capacitance C_s of the sample, i.e. for C_s=11.3 pF/cm², V_FO decreased 2/3 as a result of charge formation with -12kV surface potential in comparison with uncharged case. Further, to discuss the mechanisms of creepage discharges with and without surface charges, measurements of light emission and current flowing through the back electrode were also performed when creepage discharge occurred. As a result, the existence of the surface charging proved to remove the pulsive component of the waveforms of the current and light emission on part of the wavetail. The results suggested that the surface charging causes the creepage discharge to extend to longer distance than for uncharged case.

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Relation between surface flashover voltages (FOV) and numbers (N) of voltage application was investigated under repeated impulse voltages by using a GIS spacer model of φ15/φ60 in diameter. Applied impulse voltages were standard lightning and switching impulse voltages. FOV for negative polarity was expressed as V∞N^-/n, where n was 124 for lightning and 134 for switching impulse. Polarity effect existed and FOV's were higher for positive polarity than for negative polarity. Moreover, polarity reversal tests were carried out, and voltage-number (V-N) characteristics were clarified to coincide with the relation for negative polarity described above.
Flashover characteristics were statistically analized and it was clarified that initial deffects caused the flashover. Finally, a mechanism was discussed and it was suggested that initial electrons played an important role of V-N characteristics.

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