Construction of 275kV and 500kV substation in densely populated area is thought to be necessary in the future to keep stable supply of electricity. Using gas-insulated transformer is now considered for substations because gas-insulated transformers are non-frammable and non-explosive. Since completion of 77kV gas-insulated transformer in 1979, we have continued to research to develope gas-insulated transformers applicable to higher voltage level up to 500kV. As the results of the research, 275kV, 300 MVA liquid cooling type gas-insulated transformer has been developed. We introduce the abstruct of our study.

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High-voltage SF₆ gas-insulated switchgear was at first introduced as a power supply facility.
As its reliability and safety come to be recognized in service, the gas-insulated switchgear has evolved into a power receiving facility. This switchgear consists of a cubicle enclosure sealed with a low pressure SF₆ insulating gas and a long-life vacuum circuit breaker installed therein with devices and circuits integrated at higher density, the switchgear has achieved a substantial volume reduction of some 50% from the conventional one.
This paper introduced fundamental technologies such as low-pressure SF₆ gas insulation, gas-solid composite insulation and gas monitoring, and also gas-insulated vacuum switchgear for 66/77kV power receiving facilities.

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New RF coils of L-C-R connection loops type are proposed. One of the coils is only a bundle of μ order diameter isolated conductor, facing the both sides of the bundle ends each other for a capacity. The next characters were found by experiments. (1) This type coils show a sharp first resonance mode and few other modes are measured. (2) The complete proportional relation between the number of the conductors and the conductance of the bundle. (3) The ratio of the RF current resistance to the direct current resistance can be 1.
Variational principle for eigenvalue problem was considered for it. The loss due to the vortex current in the conductor itself when exposed in the magnetic field was calculated accurately. And it was found that when the diameter of the conductor is 1/3 of the high frequency skin depth δ, the vortex current is very small. The litz wire can be used below 10 kHz. But this coil can be used above 100MHz (δ_??_7μ), because this coil need not to be stranded.
For example, the turbulent heating at the axis of a tokamak plasma in μs order is possible, when a large amplitude stationary magnetosonic wave is excited by the magnetic piston of these coils array around the plasma. And the distance between the plasma and the coils can be large. The commercial nuclear fusion is thought to be possible.

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In order to clarify the grounding conditions for protecting workers on the de-energized circuit from induction due to the live circuit and the required current capacity of grounding conductor for a 1, 000kV double-circuit power transmission line, the phenomena caused by the electrostatic induction resulting from the live circuit are first discussed. The results are as summarized below.
(1) Even though both ends of the de-energized circuit are grounded, the electrostatic induction voltage grows larger in parabolic form as the distance from the grounding point increases. As such, this voltage then determines the safe working zone, which determines the electrostatic induction current I_g flowing through a worker and the electrostatic induction current I_g0 flowing through the grounding conductor.
(2) The electrostatic induction current I_g and I_g0 are determined by the voltage applied to the live circuit, grounding intervals on the de-energized circuit conductor conditions of the circuit and the phase configurations at the line.
(3) If a worker has an electric resistance of 1kΩ and touches any portion of the de-energized circuit, the current I_g will not exceed 1mA as long as the grounding intervals are less than approximately 9km.
(4) The value of the current I_g0 is proportional to the grounding intervals surrounding the relevant grounding point, regardless of the location of this point. This I_g0 current reaches a maximum of 10 A if the intervals are 100km.
(5) The calculation formulas used in considering the above are now in practical use for verification purposes on an actual power line of 500kV.

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A magnetic-field driven arc damaging inter-anode insulators in MHD generators is theoretically studied. Firstly a circular arc confined within an insulator is analyzed under the condition of no magnetic field. Next we propose a new model which describes the behaviors of magnetic-field driven arcs damaging insulator. The model is based on the following assumptions: (1) extra Joule's heat in the arc column due to applying the magnetic field causes the progress of the insulator damage, (2) Lorentz's force on the arc column balances with the aerodynamic drag due to the gas flow of the vaporized insulator, and (3) whole Joule's heat in the column is removed by the convection of the gas. The calculated results from this model are compared with the experimental results reported previously. There is good agreement between the calculated and experimental values in the relationships of both arc field and damaging rate vs. magnetic field, and damage width vs. arc current.

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The flow rate in a self-cooled transformer was difficult to be measured, because the driving force of the oil flow is very small. By this reason the characteristics of the flow rate distribution between windings have not been made clear. But by using the laser doppler velocimeter we now can measure this flow rate. Authors made the basic model which has vertical flat plate heaters and the larger scale disc winding model. The flow rate distributions between windings of these models are measured. On the other hand the flow rate distribution is calculated by using thermosiphone flow principle. The calculated value is compared with the measured value and both agree fairly well in heat flux range under which real transformer works. Then the characteristics of the flow rate distribution are made clear by using this calculation.

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This paper proposes a new estimation technique of dominant mode profile for dynamic security assessment and stability enhancement of a power system. The mode profile, which describes the distribution of the mode oscillation to the rotor speed responses of all mechines, can be obtained by using a newly developed filter, that is, a “Dominant Mode Filter (DMF)”. The DMF can be used in detecting the degradation of damping effect of the system and improving the stabilizing ability of a control device such as PSS. The basic concept of the DMF is based on the inherent characteristic of the power system network and the application of principal component analysis to a covariance matrix of the rotor speed fluctuations. The mode profile and the mode energy estimated by the DMF can be used for the following applications. One of them is to use the mode energy and the mode profile for on-line stability monitoring. Another one is a disturbance identifier to find out the location and the severity of a disturbance. The third application is the enhancement of stabilizing ability and adaptability of PSS.

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We have constructed CAE (Computer-Aided-Engineering) system of SF₆ gas circuit breaker (GCB) development and design. This system combines organically electrical field analysis, arc analysis, gas flow analysis, and so on, which can analyze dynamic interrupting phenomena.
The GCB interrupting phenomena are generally of two types, namely, small current interrupting phenomenon and high current interrupting phenomenon.
This CAE system integrates some of the analysis of interrupting performance which are small current interrupting, short-line-fault current interrupting, and terminal fault curret interrupting. We can almost use common data of every analysis and simulate interrupting performance of actual GCB during development steps.
This technology contributes directly to highly accurate development, shortened development steps, and further improvements in the reliability, interrupting performance, and functions of GCB. It helps to identify new problems encountered in upgrading GCB and in building important technologies for developing the new high power and high voltage GCB.

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Fine mesh divisions are essential to obtain accurate solutions of two dimensional AC magnetic field analysis. But it requires the technical know-how to find fine mesh divisions and moreover it is complicated to divide the analysis domain. So we have developed the adaptive mesh generator using equalization of energy variation of every element and applying the technical know-how to divide the conductor or magnetic material under consideration of the skin effect by the eddy current. And we have applied this adaptive mesh generator to the loss analysis of the infinite copper-plane, and we have obtained accurate solutions.

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