Open Cycle-Ocean Thermal Energy Conversion (OC-OTEC) system has a merit to use a heat exchanger of direct contact type without a heat transfer tube. Therefore, it is expected that capital cost of OC-OTEC is reduced by use of this simply designed heat exchanger. However, non-condensable gas are released in a system, because in a direct contact evaporator, the steam driving a turbine is generated by surface sea water including air, and existing air causes the reduction of system performance. From above point of view, we carried out experimental study on operating characteristics and the effect of structure of a heat exchanger and an existing of non-condensable gas on the performance of the direct contact heat exchanger in an experimental apparatus of barometric type OC-OTEC.
As the results, the performance of the direct contact evaporator is to be satisfied. However, we can not get the satisfied results in a direct contact condenser. Therefore, we conduct the further experiments through the improvement of the structure of condenser and the control of the existing of non-condensable gas. Finally, we defined that the major factor affecting the system performance is the existing of non-condensable gas, but its effect can ignore when its concentration is below 8%.

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An Open-Cycle Ocean Thermal Energy Conversion (OC-OTEC) system has the potential of producing electricity and fresh water in comparison with a Closed-Cycle OTEC (CC-OTEC) system. In Electrotechnical Laboratory (ETL), a test equipment simulating the heat and mass transfer phenomena on the OC-OTEC system was made and the fluctuations of the pressure and temperature in the system were measured. This study examines theoretically the power output characteristics of the OC-OTEC system producing fresh water and the CC-OTEC system. Therefore, the specifications of shell-and-tube condenser using smooth tubes were decided refering the size of the experimental equipment. And, as the type of the evaporator was adopted the flash method with the spout for the OC-OTEC system, the nucleate boiling method using smooth tubes for the CC-OTEC system. For both systems, the dependences of power output were investigated as a function of water temperature, water flow rate and concentration of noncondensable gas. In consequence, the desirable conditions of application were clarified for each system.

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An instantaneous power failure due to a galloping have a great influence on power consumers, so studies on a galloping have been done even today. Our study differs from other ones on the points that non linear three dimentional simultaneous equations of conductor movement can be solved directly using numerical calculation and simulations can be performed easily. In this paper, firstly, we explain the double conductor method which strictly deals with boundary conditions at the point where an inter-phase spacer is attached. Then, fundamental characteristics are made clear through simulations. These results showed the effectiveness of our method. And also the numerical calculation in case of an inter-phase spacer attaching are developed. Simulation results showed that a clearance between phases can be maintained even in severe conditions.

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A difficult problem is encountered when the ground resistance of a large grounding system is measured by the fall-of-potential method. The problem is that a horizontal curve section does not exist with a fall-of-potential curve. In this case it is difficult to estimate the ground resistanse from the fall-of-potential curve.
In this paper, a method for determination of potential probe position to estimate the ground resistance of horizontal electrodes (counterpoise and mesh), is proposed when the horizontal curve section does not exist. First the exact potential probe position is obtained in two-layers ground case. Second, in three-layers ground case, three-layers ground is replaced with two-layers ground by some procedures, and the potential probe position for the three-layers ground is taken as the position for the replaced two-layers ground. Error extent of the ground resistance from the replacement is estimated. Third in four-layers ground case, the procedures for replacement of four-layers ground with two-layers ground are described, and error extent of the ground resistance from the replacement is estimated also in this case. Last, for the case where the ground configuration is not clear, another method is proposed and error extent is described.

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The problem to supply electric power stably has been more important year by year since electric power system has become large and complex, and many stabilizing equipments have been set up. Therefore, the research on, for example, decentralized system and nonlinear control with analytic approach is strongly desired.
In the decentralized control proposed by the authors, a step for considering the robustness of the system and finding efficiently feedback gains of AVR. GOV plays an important role. The aim of this paper is to propose “equilibrium point control”, in which the feedback gains can be determined by observing equilibrium points of the system. First, a model system and the swing equation are explained. Next, the equilibrium point control is introduced and an approach for considering limiters of AVR.GOV is represented. Finally, after summing up the results, it is summarized that the proposed control is simple and flexible for considering the robustness and limiters.

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The desirable capacity of future energy storage facility in power system in Japan is discussed in this paper, putting emphasis on future new electric demand/supply factors such as CO₂ emission problems and social structure change. The two fundamental demand scenarios are considered; one is base case scenario which extrapolates the trend until now and the other is social structure change scenario. The desirable capacity of the energy storage facility is obtained from the result of optimum generation mix which minimizes the yearly expenses of the target year (2030 and 2050). The result shows that the optimum capacity of energy storage facility is about 10 to 15%. The social structure change and demand side energy storage have great influences on the optimum capacity of supply side storage. The former increases storage capacity. The latter reduces it and also contributes to the reduction of generation cost. Suppression of CO₂ emission basically affects to reduce the storage capacity. The load following operation of nuclear plant also reduces the optimum storage capacity in the case it produces surplus energy at night. Though there exist many factors which increase or decrease the capacity of energy storage facility, as a whole, it is concluded that the development of new energy storage technology is necessary for future.

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A large-scale power system usually consists of several subsystems. This property makes it possible to improve the efficiency of the stability analysis of the power system by utilizing decentralized and hierarchical processing. Under the decentralized and hierarchical analysis scheme, stability analysis would be performed in each subsystem. Consequently, it is advantageous to find the relation between dynamics of subsystems and those of the whole interconnected system. In this paper, novel methods to evaluate the dynamical relation between the subsystems and the whole system for the decentralized and hierarchical eigenvalue analysis are proposed. The dynamical relation is described by using the eigenvectors of subsystems and those of the whole system. A locality index for eigenvalues of subsystems and a new method to evaluate the relation between the eigenvectors of subsystems and those of the whole system are proposed. The relation between the global oscillatory modes of the whole system and the oscillatory modes of subsystems which have large participations in the global oscillatory modes of the whole system can be obtained from the reduced order eigenvalue problem by the proposed methods. The effectiveness of the proposed methods are illustrated using numerical examples.

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This paper describes an estimation method of the amount of power drop after severe generation outage. When a large amount of generation outage occurs, the system frequency goes down to unacceptable frequency level. Frequency drop affects not only customers but generation systems unfavorably. So adequate and quick load-shedding must be carried out to prevent spreads of accidents. In order to perform the load-shedding policy effectively, the amount of the generation outage must be precisely estimated in the short time. So far, several methods have been proposed to estimate the power outage amount by means of the measurement of the decaying frequency variations which are obtained at each local bus. These methods are easily to apply but can not be expected to bring a good result in real power system operations because of noises included in decaying frequency variations.
In order to cope with this problem, a new estimation method based on an estimation method of dominating differential equation is proposed in this paper. For the improvement of the precision of the estimation, the supplementary informations such as a sine wave included in the decaying frequency deviations are incorporated in the equation.
Simulation studies on a model power system consisting of five generating stations and four load points show that the methods is encouraging.

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A CO₂-capturing power generation system utilizing waste heat was proposed for increasing electric power generated in the daytime. In the system, relatively low temperature saturated steam is produced by using industrial waste heat at nighttime and is stored in a steam accumulator (AC). At daytime the steam from the AC is used as the working fluid of a gas turbine power generator in which generated CO₂ is captured based on the method of oxygen combustion. The system has no process of compressing the working fluid gas, that is the process to be extremly power consuming one. Hence the system has high power generation efficiency. The generated CO₂ can be captured by using oxygen combustion method, so that high CO₂ capturing ratio near 100% as well as no thermal NOX emission characteristics can be attained. It has been shown through a case study of using waste heat generated in a urban waste incineration plant that the proposed system has total net exergetic efficiency of 31.1% and that the power generation efficiency is 51.1%, when the amount of utilized waste heat is neglected, being higher than 17.5% compared with that of the conventional power plant with the efficiency of 43.5%.

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We have developed a shell type superconducting transformer for experiments using Nb₃Sn superconducting cables. The designed capacity is 667kVA (single phase), the voltage is 440/220V, the current is 1515/3030A and the percent impedance is 16%. Main features of the design are as follows. (1) Magnetic field in superconducting coils are decreased by increasing the number of high-low coil groups. (2) Large scale superconducting cables are not needed by increasing the number of high-low coil groups. (3) Epoxy impregnated coils are used to withstand electro-magnetic force at 120 Hz. The Nb₃Sn basic strand was manufactured by the internal tin diffusion process. The cable consists of insulated 7 sub-cables, and the sub-cable consists of 7 strands.
The transformer excites to primary (HV) coil that secondary (LV) terminal is shorten. The result was that primary current reached 1618 A_rms with no quenching, and the reached capacity corresponds to 712 kVA.

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This paper describes the mechanism of creepage discharge propagation on charged dielectric surface in SF₆ gas. Experimental results revealed that the surface charging having the opposite polarity to the applied impulse voltage increased the discharge extension length by enhancing the electric field strength at the discharge head. The charging potential of -12kV for the 1mm-thick PMMA sample doubled the mean step length and halved the pulse interval of stepwise discharge propagation. The influence of the charged surface on creepage discharge propagation was interpreted in terms of two processes: (a) streamer propagation and (b) streamer-to-leader transition based on the precursor mechanism.

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A new fault location system using optical current transducers to detect faulted sections in the bus bars of directly grounded 275kV substations has been developed. This system detects fault current by combining optical current transducers with wound type CTs. The new type optical current transducer applies a bulk type Faraday sensor to the combination of a windings around a magnetic iron core and a solenoid coil. The optical current transducer was capable of current measuring over 50kA. A current differential discriminator combining an optical current transducer and an wound type CT, verified the operational performance with 40kA currents. The intended level of fault detection performance was obtained. Based on these results, a system is being made for actual application in 275kV substations.

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Up to now, the quantitative characteristics of stationary electric contacts in electrical apparatus have been given by means of some calculation, based upon an artificial model of the current flow lines which highly simplifies the treatment. However, by this model it has been unable to calculate the static characteristics of the electric contacts in which the current flows complexly. We have developed a new analytical method by which the flux distribution is obtained after the current distribution in the current carrying parts is analyzed by the 3-D finite element method with edge elements. In this paper, the accuracy of the Holm's method based on a simplified contact model is examined by comparing with the calculations of electromagnetic repulsion forces by our method. In addition, the influences of the position of the contact point and the bridge length between contact members on the repulsion force are quantitatively clarified. These results, which can not be calculated by the Holm's method, are useful in the design for circuit breakers, switches, etc.

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This paper describes the fundamental characteristics of the residual voltage and the relationship between irradiation dose and residual voltage in electric power cable using in nuclear power generating station. The residual voltage of unirradiated cable increases with time, tending to saturate. The saturated value of residual voltage is nearly proportional to bias voltage. This result supports that the residual voltage of cable is caused by depolarization. From theoretical and experimental investigation we found that the residual voltage is not influenced by cable size and length. This is important merit of residual voltage as the nondestructive diagnosis. When dose is more than 500kGy, the residual voltages exhibit a peak. As the irradiation dose is increased, the peak moves to the shorter time. Therefore, we can know the degree of radiation degradation from the location of the peak.

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