Wind energy conversion systems have been introduced to power system as one of decentralized energy resources. The generated power is generally controlled by pitch control system with feed back. However, the generated power is always changing because the generators are driven by fluctuating wind speed, and besides due to time lag of feed back signal based on large moment of inertia of wind turbines. Particularly, such tendency is remarkable in Japan, where wind power plants are built in mountainous and rough terrain, and this brings much wind turbulence. Hence, the power system with small capacity is affected in case of large power fluctuations. This paper presents a useful method to reduce power fluctuations by using feed forward control.

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This paper deals with the theoretical analysis and experimental investigation of a new optical DC voltage measuring system, in which two Pockels cells are located between a polarizer and an analyzer, and AC voltage is applied to one cell while DC voltage for measuring is applied to the other. Supposing a slight elliptical polarization occurred at no applied voltage when linearly polarized light passed through the Pockels cells without optical activity, the theoretical analysis of the measuring system was carried out. It clarified that the light intensity variation in the system could be compensated by dividing the AC normal component V(ω₀) of the output by the second harmonic component V(2ω₀), and V(ω₀)/V(2ω₀) was linearly proportional to the applied DC voltage, but it was not equalto zero at no applied DC voltage. Experiments were carried out by using Bi₄Ge₃O₁₂ (BGO) crystals longitudinally modulated with AC and DC voltage and showed that the characteristics of the DC component, V(ω₀), and V(2ω₀) of the output agreed well with the calculated results. Slightly rotating the y-z surface of the BGO about x axis, it was clarified that the phase difference caused by spontaneous birefringence in the BGO could be decreased to zero and linear DC voltage dependence of V(ω₀)/V(2ω₀) passed through the origin could be obtained at no apparent elliptical polarization.

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Voltage distribution for lightning surge in multi-cascaded transformer, that will be used for a converter transformer in self-excited DC transmission, was studied using model transformers. There was good agreement between measured data and calculated results. It was cleared that our calculation program have enough performance for estimating voltage distribution.
Maximum voltages in high-voltage windings for lightning surge were below 120% and transfer voltages to converting circuit were below about 5%. Therefore, there were no serious problems in cascaded transformers for lightning surge. However, their voltage distribution was not satisfactory when same transformers were connected in cascade. We clarified with simulation that the distribution could be improved by modifying every transformer's structure according to position in cascade connection.

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The improvement of the cooling-gas velocity distribution over the coil windings in SF₆ gas transformer is very important to get the high quality for designing.
In this paper, the application results of the reflective type ultra sonic wave method to measure the cooling gas distribution in the SF₆ gas transformer are reported.
This measurrement can be performed without disturbance of the gas flow by the presence of the sensors, and this method is proved to be more effective than the conventional fluid velocity measuring method. In this measurement, it is found that the velocity of gas flow at some locations in the transformer was not proportional to the volume of the input gas flow. It can be divided into three patterns corresponding to the location as follows.
(a) Gas velocity increases with the increase of the input gas flow amount.
(b) Gas velocity is constant regardless of the increase of the input gas flow amount.
(c) Gas velocity decreases with the increase of the input flow in the first, and changes to increase with the further increase of the input flow.
These characteristics are well compared to the computational results of gas flow analysis.

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For the purpose of improving the strengh of Ni/YSZ cermets, pre-sintered YSZ was applied to the cermets and relationship between pre-sintering conditions of YSZ, sintering conditions and properties of the cermet was investigated. Results revealed the bending strengh of the cermets can be increased by more than 10%, by using the YSZ pre-sintered at suitable condition. Pre-sintering has promoted the reaction between the primary particles in the YSZ granule, and resultantly suppressed the sinterability of YSZ. Pre-sintered YSZ granule was observed to maintain its spherical shape easily in the cermets. Conductivity was also improved, compared to that of conventional Ni/YSZ cermets which is made of raw YSZ. The reason for this phenomena is thought that Ni particles make a distinct conductive network in this new cermet. These cermets also provide adequate porosity.

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The influence of azimuthal non-uniformity of seed fraction on the plasma structure and performance in a non-equilibrium disk MHD generator is investigated with γ-θ two dimensional numerical simulation. It is found that locally high seed fraction causes mainly the non-uniformity in gas-dynamical properties, whereas locally low seed fraction develops the non-uniform plasma. Both locally high and low seed fractions reduce the generator performance considerably. These results suggest that the spatially uniform seed fraction should be required for high power generation.

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The inductively-coupled radio frequency plasma is now becoming gradually an important source with high-temperature and high-reactivity characteristics either for processing of new functional materials or for destruction of circumstance depleting substances. A wider plasma in space is required for higher rate and uniform processing as a future technique. Although a few MHz frequency has been usually used for the induction plasma, an attempt to expand the high temperature plasma fields was made by superimposing a lower frequency of 50-kHz magnetic fields on the D.C. plasma discharge as a small source plasma. Because the penetration depth such at low frequency field is as long as few hundreds mm, a wider plasma in radius is expected to be produced.
As a first step, we have investigated about the. operating condition at which a stable low frequency plasma is generated, based on the theoretical calculation include the time dependent rate egations for heat transfer and fluid flow in conjunction with Maxwell's electro-magnetic equations. Results showed that the necessary minimum power for expanding a small D.C. plasma toward a wider plasma of 100mm diameter by applying 50-kHz magnetic field is about 130kW at 0.1MPa pressure condition, and the power level is recognized to be within the available range in the existing high power oscillator system.
Measurements were carried out of the time variation of the spectral emission from the plasma immediately after superimposing the 50-kHz magnetic filed upon the small area plasma generated with D. C. power of 1.5kW at the pressure of 0.01MPa in Ar gas. At a low power level of about 60kW, the small plasma starts to expand in the radial direction, and finally, converged to a new wider plasma with 100mm diameter. FFT analysis of the oscillograph showed that during the transient state, a periodical fluctuation of the emission light occurs at a few tens of Hz reflecting the thermal time constant of a few tens of ms, besides of the power ferquency of 41.7kHz. The plasma temperature was estimated, by the spectroscopic line intensities from Ar neutral atoms, as 8, 000 to 11, 000K, and a uniformly distributed temperature field was successfully produced with applying the 50-kHz magnetic field, as expected.

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The audible noise which is produced by corona discharge from a transmission line conductor is composed of two major components, namely “hum noise” and “random noise”. Hum noise has a frequency of twice the power line frequency and is generated primarily in rain, fog, and highly humid environments. It is one of the major factors affecting conductor design of transmission lines for voltages above 500kV. In the case of flat ground, hum noise from each conductor bundle generates a complex standing wave near and perpendicular to transmission lines and the statistical characteristics are known. However, recently, bulk transmission lines tend to pass through the hilly areas and cross over ravines frequently. The slopes of the ravines cause multiple reflection of sound waves.
In this paper characteristics of spatial distribution for hum noise level in a ravine are described. The main results are that 1) the rate of increase of spatial mean level of hum noise against the slope of a V-shaped valley is 0.1 dB/degree and 2) the distribution of probability density for hum noise level can be approximately represented by a random walk model based on the random walk theory.

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Superconducting wires subjected to AC magnetic field dissipate losses. Recently developed AC wires with ultra-fine superconducting filaments and short twist-pitch have extremely low AC losses for the transverse field. However, AC losses of windings are mainly caused by longitudinal and azimuthal magnetic field components in AC superconducting apparatuses such as current limiters and transformers, the windings of which are subjected to relatively low transverse external field less than IT. Those non-transverse magnetic field components are produced by the wire transport currents and the external magnetic field. AC wires with low transverse field AC losses are not necessarily the wires with low AC losses caused by non-transverse magnetic field components. Technology for reducing the transverse field AC losses has been clarified but that for reducing the non-transverse field AC losses is not clear at the present state. To develop the technology for reducing the non-transverse field AC losses, it is important to analyze the relation between the loss characteristics and the configuration of the wire cross-section.
Energy dissipation of a superconducting wire subjected to external field with transport current is supplied from current source of the wire and the external field. We measured power supplied from the current source to various NbTi and Nb3Sn AC wires with different cross-section configurations and different twist pitches nder external AC magnetic field. We made an analytical model to evaluate the on-transverse field AC losses of the wires based on the experimental data. In the model, current density vs. electric field characteristics of the superconducting filaments are taken into account. The validity of the model is verified by comparing the calculated and measured results. In the paper, it is shown that the AC losses caused by the non-transverse field are evaluated by the analytical model and become much higher than those caused by the transverse magnetic field as the transport currents are close to the quench currents or critical currents. It is also shown that the losses are significantly dependent on the phase difference between the wire transport current and the back ground field and that our analytical model well explains the experimental results on the phase difference characteristics.

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In this paper, we proposed a circuit model of gas insulated shunt reactors for surge analyses in high frequency regions. The interleaved disk winding, widely used for high voltage windings, has resonance phenomena in the high frequency region and its series capacitance reduces above the resonant frequency. In order to simulate this phenomena, an equivalent circuit composed of three stage LC parallel circuits was proposed. On the contrary, the continuos disk winding are possible to be simulated by one stage LC parallel circuit because its series capacitance is almost constant through to high frequency region.
Impedance characteristics of a full scale model for a reactor winding were measured and the proposed circuit model was evaluated by comparing the measured results with the calculated ones. And it was verified that the proposed model could represent well the winding impedance up to 10MHz.

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Aging deterioration of transformers can be diagnosed by amounts of CO₂+CO and furfural decomposed from insulating papers. But, in case of breathing transformers containing an adsorbent in the insulating oil, CO₂ and CO gasses are exhausted through the breather and the furfural is almost adsorbed by the adsorbent. Therefore, in order to obtain the true values of each amount of CO₂+CO and furfural, some corrections for measured values are necessary.
Authors have noticed to acetone and furan as new indicators for the purpose of improvement of diagnostic for these transformers and carried out experiments on adsorption characteristics and solubility to insulating oils and dismantles and inspections of actual transformers etc.
We have confirmed as to following technical matters; there was a good relation between amount of acetone and retention average polymerization but furan was not detected at all in actual transformers; acetone is adsorbed by the adsorbent but the temperature fluctuation is low so that any correction of adsorption is not necessary; acetone solubility to insulating oil is so big that acetone can not be exhausted; acetone formation from oxidizing deterioration of insulating oil is small so negligible.
We consider that acetone is much desirable as a new deterioration indicator for breathing transformers containing an adsorbent in the insulating oil.

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IEC-TDG, a benchmark wave generator programme to be approved in IEC 1083-2, requires any impulse wave analysis software used in the approved test to determine wave parameters within specified margins. This is because the digital measuring technique has so far become more and more common, but unlike high voltage measuring techniques found in IEC60-1/2, there has been no recommendation with the software.
Authors developed a wave analysis code which, contrary to the conventional ones, determines the wave parameters by solving a set of non-linear equations directly, precisely and very quickly. This paper reports that by applying Levenberg-Marquardt method in determining the fitting curve, one can compute the parameters not only from ideal noise-free wave data but also from noisy ones. The effectiveness of the proposed technique is demonstrated using the IEC-TDG data.

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This paper investigates switching surge overvoltages due to a section switchgear between coils and a feeding cable, and surge overvoltages due to a ground fault in the feeding cable. The maximum overvoltage due to switchgear closing is about 25kV on the coil and 15kV on the cable sheath. The coil overvoltage becomes greater as a source voltage reaches its peak. The overvoltages due to switchgear breaking is dependent on a breaking current, and reaches 115kV on the coil and 15kV on the cable sheath when the current is 50A. The fault surge overvoltage is about 24kV on the coil which is smaller than the switching overvoltage. On the contrary, the cable sheath overvoltage reach 32kV which is the largest among various overvoltages investigated in the paper, and could result in sheath insulation breakdown. The coil overvoltage due to current breaking by a section switchgear may cause coil insulation breakdown when the breaking current is large. Both the coil and sheath overvoltages can be controlled to less than the insulation level by arresters.

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Though Photovoltaic power generation (PV) and wind power generation (WG) have advantages that energy are clean and infinite, they have a disadvantage that electrical output energy are unstable. The disadvantage causes them to need big energy storage device such as a battery and to increase their construction cost. A PV/WG hybrid system is effective for stabilizing output in specific locations that yearly profile of solar energy is different from that of wind energy. However, as the stability has a relation to a ratio of PV output energy fluctuation to WG output energy fluctuation, it is very important to clear the optimum ratio. The optimum ratio from the point of view of long-term stability for the output energy was cleared by simple simulations. And it was cleared that the optimum ratio changes from approx. 20 to 75% according to environment and that optimizing the ratio can reduce the battery capacity very much.

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In order realize a reliable, compct and economical converter station for HVDC transmission, applications of Gas Insulated Switchgears (GIS) for DC transmission lines are considered. The characteristics of DC gas insulation are different from those of AC. The behavior of metallic particles left in the enclosure is one of the largest differences. The accumulation of electrical charges on solid insulators is another essential factor in designing a DC-GIS. Also degradation of metal oxide arrester blocks under DC stress must be deliberated. Based on the fundamental studies, we developed the components of the ±500kV DC-GIS. Electrical and mechanical peformances of these components have been tested and proven to be satisfactory. Finally these components had been assembled into a full DC-GIS and subjected to a long-term voltage endurance test. In this paper, design philosophy of ±500kV DC-GIS, details of the components and the test results are described.

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The Influence of dust particles in closed cycle disk MHD generator driven with Ar+Cs working gas is evaluated numerically. A model of the nonequilibrium seeded plasma with dust particles is proposed. Electron number density decreases in the regimes of weakly ionized seed and noble gas due to the minglement of dust particles. It is confirmed from γ-θ two dimensional numerical simulations with the present model that the designed performance can be maintained below a critical amount of dust particles. When the amount of dust particles exceeds the critical value, however, discharge structre becomes nonuniform. As a result, the output power is markedly reduced.

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