In order to make use of solar energy instead of oil and coal, the authors have proposed a new driving system which is composed of two coupled induction machines with a photovoltaic array. One induction machine is driven by electric power of the photovoltaic array through a general-purpose inverter and the other induction machine is interconnected to the utility line. This system can generate a desired mechanical power even in fluctuating insolation and supply the surplus electric power of the photovoltaic array to the utility line.
In this paper, it is shown that the proposed method can be realized by using not only an induction-induction machine system but also an induction-synchronous one. The latter system can drive a mechanical load with a strictly constant speed and high efficiency. These parallel operation using two rotary machines have the advantage of decreasing the total loss compared to a one motor system when the no-load loss is less than a certain ratio of the load loss. Furthermore, this paper presents a practical method to measure the solar power, track the maximum power point and control the connection-disconnection of the photovoltaic array to the general-purpose inverter.

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The health effect of the weak current induced in the human body as a result of the interaction between human body and power frequency electric fields has been investigated. However, the current density inside the head part tissues of the human body exposed to the electric fields has little been discussed. In this paper, the finite element method is applied to the analysis of the current density distributions of the head part composed of scalp, skull, cerebrospinal liquid and brain tissues. The basic characteristics of the current density distributions of the brain in the head part of the axisymmetrical human model have been made clear.

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We have studied experimentally the shielding method of ELF magnetic field applied to the source of line conductors. For the single-phase line current, it appears to be difficult to achieve the effective shielding. On the other hand, for the balanced 3-phase conductors, including triangle and twisted configuration, a certain reduction of generated magnetic field was achieved by adjusting the configuration of conductors or by surrounding the conductors with cylindrical shielding materials made of ferromagnetic materials or non-ferromagnetic metals. Normalized characteristics between phase current, distance between source current and observation point, distance between phase conductors, and the pitch of twisted cable were derived. In addition, the effect of unbalanced current was also investigated.

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In a previous research for subsonic diagonhl type MHD generators, the authors have proposed a conceptual de-sign with relatively low Mach number in order to stabilize the MHD generator of commercial-scale and have shown that the MHD generator works stably under the constant current loading condition. In the present paper, effects of loading conditions on stability of the MHD generator are examined. A channel-length scale linear stability analysis and time-dependent calculations are carried out, where both gasdynamical boundary conditions and loading con-dition are taken into account. These analyses show that the MHD generator behaves stably under various loading conditions such as constant voltage loading condition and ohmic loading condition. Then the stability of the MHD generator connected with an AC power system is also analyzed by time-dependent calculations. The analysis show that the MHD generator stably provides the rated power to the AC power line.

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The decay rate of the MCFC stacks was analyzed with the decay rate of the single cells operated over more than 10, 000 hours. Out of 4-5 mV/1000hours of the decay rate of standard stacks, 0.4 mV was estimated as the contribution of the interfacial resistance because of the corrosion of cathode current collectors. Moreover, 0.8 to 1.6 mV/1000hours was attributed to the performance decay due to the dissolution of the NiO cathodes. The rest of the decay rate about 3 mV/1000hours was assumed as the effect of the electrolyte loss. Therefore, the reduction of the electrolyte loss was thought to be the most important counter measure to reduce the decay rate. 60% of the standard electrolyte loss was assumed to be the target to achieve the decay rate of 2 mV/1000hours. Moreover, using the Li/Na carbonate which has lower solubility of Ni and higher ionic conductivity, the target was expected to be 70% of the electrolyte loss of the standard stacks.

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Previous voltage stability studies have shown that typical OLTC controls can cause oscillatory behaviors as wel as reverse controls in tap changing operations due to interactions among multiple OLTC controls. These phenomena are undesirable from the viewpoint of both economy and security of power system operations.
In this paper, to avoid the above undesirable phenomena as well as to realize suboptimal voltage profile agains voltage instability, we proposes a new control method to coordinate numerous OLTC controls existing in transmissim and distribution networks. The method is based on the autonomous decentralized control scheme. A fundamenta theory and some techniaues for this control scheme are proposed.

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Investigations were carried out in order to develop a portable diagnostic equipment for gas circuit breakers with partial discharge detecting sensors attached to the exterior of their metallic tanks. It was shown that a surface current detector newly developed in the area of EMC performed better than a conventional type high-frequency antenna or a high-frequency current transformer coupled to a grounding wire. It was also proved that a band pass filter having a suitable frequency band is effective in improving S/N ratio. Finally, a good performance was assured to the prototype portable diagnostic equipment.

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New zinc-oxide elements with a varistor voltage about twice that of conventional ones have been developed by reducing the ZnO grain size with a new additive, which enable to halve the series number of elements in metal oxide surge arresters. The advanced arresters with these elements for GIS are compact by 40 to 60 % in volume compared with conventional ones.
These advanced MOAs increase the flexibility in positioning MOAs and optimizing the GIS layout. This paper describes the performance of the new elements, the specification and construction of the advanced MOAs and the results of typical evaluation tests.

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We have experienced many PAFC plants operation over ten years. In our operating experience, cell life is mainly restricted by operating mode, degree of hydrogen utilization and residual quantity of phosphoric acid. In this paper, we discuss details of life limiting factors, corrosion mechanism and examples of corrosion. As a result, those unexpected phenomena can be protected at initial stage if adequate detective methods are equipped.

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The analysis of dissolved gases in oil-filled electrical equipment can be put to good use as information on its natural ageing and faults. So it is important to determine accurate amount of these gases in oil for keeping normal operation of oil-filled electrical equipment. Dissolved gases such as CO, CO₂ and hydrocabons in standard oils containing N₂ and O₂ of 0.3_??_8vol.% and controlled at the temperature of 10°C, 25°C and 40°C were extracted by two methods and analysed with gas chromatography. One of these extraction methods was a vacuum piston method and the other was a stripping method.
It was found that in the case of the vacuum piston method, volume of CH₄ gas extracted from standard oils decreased with decrease of the total volume of N₂ and O₂ gas, and with decrease of the oil temperature. Another compositions of gas such as CO, CO₂, C₂H₂ and C₂H₄ showed the same tendency as that of CH₂. On the other hand, in the case of the stripping method, volume of CH₄ and other gases extracted from the same oil were not affected by the total volume of N₂ and O₂ gas and the oil temperature.

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In the standard mixed sensitivity weighting strategy for H∞ controllers, the designer can formulate desired requirements (desired loop shape) using frequency domain weighting functions. The ∞all pass∞ property of the optimal H∞ control laws ensures that the singular value Bode plots will precisely conform to those specified by the weighting functions. However, there is a serious drawback to this property; namely, the resulting standard H∞-PSS always cancels the stable poles of the plant (pole-zero cancellation). It is known that the cancellation of lightly damped poles can lead to poor robust stability and performance. In the case of multi-input H∞ controller, it becomes much more difficult to achieve good robust stability and performance.
In this paper, a design of H∞-PSS is proposed to prevent the pole zero cancellation phenomenon and increase the damping of weakly damped modes. The design method consists of applying the bilinear transform to a stable poorly damped nominal plant in order to transform it into a fictitious unstable plant suitable for the standard mixed sensitivity design approach. A combination of additive and multiplicative uncertainty representation was used to achieve the robust stability for a wide range of operating conditions. The PSS designed based on the proposed approach was compared with those based on the standard H∞ approach and the conventional method.
Simulation results show that the proposed PSS gives better performance and is more robust than the standard H∞-PSS and the optimally tuned conventional PSS.

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This paper describes an optimal TCSC (Thyristor Controlled Series Capacitor) control method which can be applied to local lines to suppress power flow deviations based on local information obtained at each bus. The background of TCSC, which is a typical equipment of FACTS, is requirement of increasing the transmissible power flow. To suppress system deviations for the system stabilization and for the effective use of existing equipment without new investments, the control methods of TCSC have been studied. However, the practical control method should have some conditions, which are the clock synchronization between collecting and using information for the control, and probability of the application for multi-machine systems.
The proposed method is based on the fact that the location of the contingencies can be estimated from only power flow deviations at local buses which are measured after the disturbance occurs. Because the power system has many variables, it is necessary to find the control method which decides optimal control of each TCSC. To solve this problem easily, optimal regulator theory is used. And a DC power flow calculation and a generalized inverse matrix are also used to make relation between the state variables and the power flow deviations.
The simulations with 4-machine 11-bus and 9-macnie 38-bus power system models show the effectiveness. The proposed method adequately controls the amounts of TCSC which are very close to those of centralized one. And it reflects small frequency deviations compared with that of uncontrolled method. The improved transient performance of frequency deviations are shown in the simulation tests.

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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 the purpose of assisting planning engineers the authors have developed a supporting expert system for outage work planning of electric power facilities. The proposed system is aiming to maintain high supply reliability when outage works are executed based on the combined use of three different security indicies. 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, 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 this paper, we propose a novel method of making up suitable system configurations by means of optimal switching power flow in DC model. In the optimal switching power flow, pivot operations on an LP like tableau is regarded to correspond to switching operations in a power system and thus it aims to obtain the optimal system configuration by minimizing some objective function. In the proposed method, the amoung of overloads in line flows is chosen as the objective function and thus a line switching is selected so that the overload reduces most. As to the consistency in transition of system configurations between the consecutive days, the tableau is augmented to include three days.

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The unit commitment problem is to determine an optimal schedule of what thermal units must he started or shut off to meet the anticipated demand; it can he formulated as complicated mixed integer programming prohlem with a number of equality and inequality constraints. This problem needs huge calculations for the large power system. There are various methods considering applications of neural network which have inherent characteristics of being able to find good solutions quickly.
In this paper, the authors present a neural network technique for determining the on/off state and also MW power output of each unit. Neural network of this method is formulated by Gaussian machine, The Gaussian machine have advantage of heing able to escape from a local minima by adding random noise of Gaussian distribution to input of neuron. Therefore, we can obtain the global minima independent on initial values. Furthermore, we also investigate an application of the simulated annealing and inequality neuron.
The effectiveness of the proposed method is clarified by numerical examples. It examines with the LR method.

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The 60 Hz system of our country forms a large longitudinal power system. The system is presently being doubled to increase transmission capacity. Its short-circuit current is increasing year by year, and will reach the breaking capacity in the near future. Under these circumstances, this paper makes theoretical considera-tions on the short-circuit current. First, we use a uniform model of the system, and derive an equation for the short-circuit current, which is easily obtained from reactances of two lines. One connects two substations, and the other connects a generator and a substation. The equation also applies to cases where two reactances vary with substation. Next, we derive a relation between short-circuit current and system capacity. If the ratio of the first reactance to the second one is small, the short-circuit current increases in proportion to the square root of the system capacity. If large, it increases in proportion to the system capacity. Hence, it, is effective to disperse power sources and to make the ratio small. Lastly, we derive an equation for short-circuit current at a connection point of two longitudinal power systems. The short-circuit current is one-two times as much as that of each system. The connecting line must be considerably long to suppress it.

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