Synchronous switching controller (SSC) for gas circuit breakers (GCB) has been developed. SSC is able to close and open a GCB at the appropriate point on wave for minimizing the switching surges. This paper proposes the new synchronous switching algorithm to minimize the control delay time, and the control error for the desired point on wave. New algorithm for (1) detecting voltage and current zero crossing points and (2) predicting the next operation time of GCB is introduced. 145kV GCB with SSC built in new algorithm has been tested several condition. SSC performed well from-30 degrees C to 60 degrees C at various control voltage condition and the standard deviation from the taget phase is within 0.5msec. And the closing at two target points with voltage zero and peak works well in a capacitive load circuit at 145kV.

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This paper describes partial discharge (PD) inception and breakdown voltage characteristics of CO₂/N₂/SF₆ gas mixture under nonuniform field. These voltage characteristics were investigated with AC high voltage by changing the mixture rate of each gas of CO₂, N₂ and SF₆ gas and the gas pressure from 0.1 MPa to 0.6 MPa. It was found that adding a small amount of CO₂ gas into N₂/ SF6 gas mixture causes the drastic increase in the breakdown voltage: for instance, when the mixture rate of SF6 in N₂/SF₆ gas mixture is 50%, with 1% CO₂ addition the maximum breakdown voltage becomes 1.31 and 1.15 times higher than that of 50%N₂/50%SF₆ gas mixture and pure SF₆ gas, respectively. Moreover, those voltage characteristics of CO₂/N₂/SF₆ gas mixture were also investigated by changing the electric field utilization factor as well as by applying positive and negative standard lightning impulse voltages in order to enable to discuss the corona stabilization effect which seems to be one reason for drastically increasing the breakdown voltage. These results and breakdown mechanism of CO₂/N₂/SF₆ gas mixture were discussed on the basis of the corona stabilization effect and the dissociation energies of the component gases by observing PD light images, PD light intensities through a blue and red filter and PD current waveforms.

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The Ar inductively coupled thermal plasma (ICTP) including different environmentally-benign gases was established under the atmospheric pressure condition for the purpose of finding alternative gases for SF6 as an arc quenching medium in circuit breakers. Seven kinds of gases such as N₂, O₂, Air, CO₂, He, H₂ and Ar were used as an additional gas to Ar ICTP. The effect of the additional gases on the Ar ICTP was investigated to measure the radiation intensities of Ar lines and the temperature of the plasma. The result revealed that 3% CO₂ inclusion remarkably declined the radiation intensity and the temperature while other gas inclusions did not. This may indicate that CO₂ has high quenching capability of thermal plasma. Furthermore, a two-dimensional simulation was carried out to obtain the gas flow and temperature distributions in Ar ICTP including the different gases. The results showed that CO₂ inclusion caused the similar temperature decaying characteristics to the experiment.

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This paper shows the calculation of SLF interrupting performance for serially connected two Mayr-type arc models with different arc parameters by using EMTP-ATPModels. The arc model 1, assuming an air circuit breaker, has large arc time constant and large arc power loss. The arc model 2, assuming a vacuum circuit breaker, has small arc time constant and small arc power loss. The arc model 1 was impossible to interrupt 300kV-63kA-90% SLF by itself. However, by connecting thesearc models in series, it became successful in the interruption, even if the arc model 2 was reignited at low voltage at a few μs after current zero. These computations suggested that the serial connection of the two circuit breakers with different breaking characteristics would give a totally excellent circuit breaker by making the best use of advantages of each circuit breaker. EMTP-ATP Models was very useful to solve the arc models which are expressed by differential equations and coupled with the electric circuit.

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Effect of spatial distribution of airflow velocity on electron density of an arc around current zero was investigated in a flat-type arc quenching chamber. Varying the width of a nozzle inlet allowed to obtain different distributions of airflow velocities in the quenching chamber. For each of the nozzle inlet the profile of airflow velocity at the nozzle throat and the length of the vortex in front of an upstream electrode were calculated in the absence of the arc. Furthermore, an electron density around the current zero of an interrupting current at above-mentioned two locations was measured by means of the attention characteristic of 70GHz microwave. From the experimental and calculation results, distinct dependence of the electron density on the airflow velocity distribution was found.

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Optimal dosing target of 550kV gas circuit breaker (GCB) is investigated. In dosing operation of GCB, making voltage depends on dielectric and mechanical characteristics of GCB, therefore optimal closing target has to be determined by investigation of these characteristics. Optimal closing target and estimated making voltage are shown as functions of Rate of Decrease of Dielectric Strength (RDDS) and mechanical scattering of closing time of GCB. Closing characteristics of 2 break GCB are investigated considering a change of the dividing voltage of each pole. Synchronous closing of 550kV live tank GCB were tested with the optimum targets for minimum and maximum making voltage prospected by the functions. The EMC tests of the synchronous switching controller were also confirmed by switching test with 550kV circuit.

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Recently, electric power transmission/substation systems need to be extended and they tend to be more compact From the backgrounds of electromagnetic field environment, especially, magnetic field environment in and around electric power facilities becomes more important However, many factors must be considered to investigate it, such as complicated can conditions, configurations of conductors and ferromagnetic structures, and so on. For more precise investigation of magnetic field environment, we must understand the quantitative influence of conductors and ferromagnetic structures.
In this paper, we describe how the conductive and ferromagnetic materials influence the ELF magnetic field distribution. We carried out the measurement and finite element analysis of magnetic flux density distribution around an aluminum plate, a soft magnetic iron plate and a 1/40 reduced model of an actual transmission tower. From the result, we clarified the influence of conductors and ferromagnetic substances on the magnetic flux density distribution around them. Finally, we showed the effectiveness of finite element analysis to evaluate the magnetic field around actual power facilities.

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Recently, electric power apparatus tends to be operated under high voltage and larger capacity This makes the electromagnetic environment around the power system so complicated and then, precise measurement and analysis of electromagnetic field are intensely required. However, magnetic field in and around substations is influenced by many factors, such as power-line current conditions, configurations of conductors and ferromagnetic structures, and so on. For this reason, few studies on how such factors affected the magnetic field environment around power system have been reported. In this paper, we investigated the extremely low frequency (ELF) magnetic field environment in 77kV/6.6kV substation. We carried out the simultaneous measurement of the line current and magnetic field distribution in the substation on-site. Based on the current conditions, we could quantitatively characterize the magnetic field environment in 77kV/6.6kV substation. In addition, measurement of an elliptically polarized locus of magnetic field using amorphous wire 3-axis magnetic field sensor was discussed.

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Three-dimensional numerical simulations have been carried out for the shock tube driven disk MHD generator, where the effects of seed fraction and inlet stagnation pressure on the generator performance were examined. Numerical results agree well with the experimental results on the enthalpy extraction ratio near the optimum seed fraction. The isentropic efficiency predicted numerically, however, is higher than the experimental data, especially for the low seed fractions. The highest enthalpy extraction ratio and the highest isentropic efficiency are almost independent of the inlet stagnation pressure, although the optimum seed fraction becomes low with the increase of the stagnation pressure. It is found that the profiles of the loading parameter and the static pressure in the generator are almost unchanged under the condition for each optimum seed fraction, even under the different condition of the inlet stagnation pressure.

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The response of a nonequilibrium subsonic disk MHD generator to the fluctuation of seed fraction was examined with time dependent quasi-one-dimensional numerical simulations. When the seed fraction changes to a higher value step-likely, a temporary rise of the enthalpy extraction ratio is caused, and vice versa. For the pulse-like variation, the enthalpy extraction ratio settles after several hundreds of micro seconds, which can be determined by the response time of the MHD flow with reflected waves. For the sinusoidal fluctuation with the period of over _??_500μsec, the flow can follow the change of the seed fraction, and the enthalpy extraction ratio fluctuates largely. With the period shorter than _??_500μsec, the fluctuation of the enthalpy extraction ratio is reduced since the flow cannot respond. If the seed fraction fluctuates randomly, the time averaged enthalpy extraction ratio remains almost the ideal value, although the peak to peak value can increase.

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In recent years, many distributed generators are beginning to take a part in transmission network. Normally, these generators are connected to the power system regardless of the power supply capability of the transmission network. If many generators of this kind are connected to the system, power supply reliability of the transmission network may be decreased due to irregular power congestion, voltage problem, etc. From the above background, in this paper the authors propose a new method to find the optimal configuration of the transmission network by which power supply reliability can be increased from a viewpoint of voltage stability. Namely, this paper discusses a method to determine on/off status of power line switches so as to maximize the minimum bus voltage sensitivity to the total load increase. Since the “bus voltage sensitivity to the total load” shows a gradient of the active power-voltage curve for the specified bus at the current operational point, it can be used as an index of the voltage stability. The problem can be solved by employing tabu search. Several numerical examples are shown to demonstrate the validity of the method.

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This article deals with life cycle CO² emissions and dissemination strategies of photovoltaic (PV) systems for houses. For this purpose, we first proposed a novel concept of life cycle analysis, real-period-LCA. A mathematical model was established so as to estimate the life cycle inventories utilizing the input-output table. Then life cycle CO² emissions of photovoltaics and other power generation systems were estimated with this model. Estimated results indicated that life cycle CO² of PV systems were much less than those of fossil-fueled power generation systems when growth rate of the systems is zero per cent. However, the difference between PV and other power generation systems was shown to dramatically decrease as the growth rate increases.
Next we investigated appropriate dissemination strategies for the PV systems. Effects of mass production and subsidies to accelerate dissemination were taken into consideration in this analysis. In conclusion, we clarified a desirable strategy of disseminating PV systems so as to reduce CO² emissions. Namely PV systems should be increased with the appropriate economic incentives estimated in this paper. If this strategy were adopted, PV systems could be a promising technology in long term as an abatement option of global warming.

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