Language：English   Publishing type：Research paper (international conference proceedings)  

Electric power storage facilities for stabilization of the voltage and the frequency are necessary to interconnect wind power generations with power systems. However, conventional pumped storage generation systems can't combine with wind power generations because these can't work intermittently. Therefore we consider a new system featuring a pumped storage generation with the Archimedean screw. The Archimedean screw can hold water without electricity supplied, and can continue pumping while it is powered on. Therefore, the Archimedean screw enables the combination of the pumped storage generation and wind power generation. In this study, simulation has been done to examine the feasibility. © (2013) Trans Tech Publications, Switzerland.

DOI： 10.4028/www.scientific.net/AMM.260-261.50

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：TRANS TECH PUBLICATIONS LTD  

Renewable energy resources such as wind energy have a disadvantage that the quality of output power is lower than that of fossil fuel resources. To solve this problem, pumped storage power system with Archimedean screw is designed. The structure and principle of operation are introduced and the advantages and disadvantages are discussed according to the theory and the simulation. In this paper, comparison has been done by collecting and analyzing the data and simulated the system on different condition to show the differences of the two types of pumps working on the pumped storage system.

DOI： 10.4028/www.scientific.net/AMM.291-294.439

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE Computer Society  

Relay is a switch to break or to connect an electric circuit by an electromagnetic force. When a direct current is interrupted, an arc occurs between the relay contacts. And the relay may be destroyed by the damage of burning and/or melting. One method of the direct current interruption is commutation. A bypass circuit (commutation circuit) is constituted by connecting a commutation element to the relay contacts in parallel. The arc would not occur by diverting the circuit current to the commutation circuit when the contacts are interrupted. And then, the circuit current would decrease with the increasing of the resistance value of the commutation element by time. Finally, when another relay is opened, the circuit completely turns off without arcs. In this study, two cheap AC relays (the rating: 125V - 10A) and an IGBT as a commutation element are used. In addition, surge protection properties are measured when the circuit has an inductive load. As a result, the circuit current of DC 100V - 10A was interrupted with controlling surge voltage successfully. © 2013 IEEE.

DOI： 10.1109/ICEPE-ST.2013.6804365

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Publisher：Committee of Joint Conference of Electrical, Electronics and Information Engineers in Kyushu  

DOI： 10.11527/jceeek.2013.0_397

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：KOREAN PHYSICAL SOC  

Experimental studies of coaxial oversized backward wave oscillators (BWOs) are presented. The beam voltage is weakly relativistic, less than 100 kV. The slow-wave structure (SWS) consists of a rectangularly corrugated oversized hollow waveguide and rectangularly corrugated inner conductor and has a target operating frequency due to Cherenkov interaction is in the K-band. The coaxial SINS can have two surface waves caused by the inner and the outer corrugations. The oversized BWO operations under the influences of two surface waves are examined. The oscillation start voltage is decreased by introducing a rectangularly corrugated inner conductor, The output. power is increased greatly as compared with those without; the corrugated inner conductor. The inner corrugation improves the oversized BWO operation.

DOI： 10.3938/jkps.59.3573

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Language：Japanese   Publisher：電気学会  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Plasma Science and Nuclear Fusion Research  

Studies of slow cyclotron maser operation of a slow-wave device are presented. The beam voltage is weakly relativistic, less than 100 kV. The slow-wave structure is a periodically corrugated oversized waveguide for K-band operation. When using rectangular corrugation having a relatively small ratio of corrugation width to periodic length of about 20 %, the dispersion curve near the upper cut-off becomes flat and second harmonic slow cyclotron maser operation is observed in the low-energy region near 30 kV. Another type of combined resonance of Cherenkov and slow cyclotron interaction is also demonstrated in which an absolute instability is driven by the slow cyclotron interaction. By using sinusoidal corrugation and rectangular corrugation having a 50 % ratio of corrugation width to periodic length, amplification effects due to the fundamental and second harmonic slow cyclotron interactions are observed.

DOI： 10.1585/pfr.5.S1049

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Other Link： https://jlc.jst.go.jp/DN/JALC/00363491071?from=CiNii

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Plasma Science and Nuclear Fusion Research  

Studies of coaxial oversized backward wave oscillators (BWOs) are reported. The beam voltage is weakly relativistic (less than 100 kV). The slow-wave structure consists of a periodically corrugated oversized waveguide and periodically corrugated inner conductor, whose target operating frequency due to Cherenkov interaction is in the K-band. A starting energy exists for the coaxial oversized BWO as it does for a hollow oversized BWO. The coaxial slow-wave structure has two surface wave modes caused by the inner and outer corrugations. Operation based on these surface modes can be controlled by the beam diameter. The phase difference between the inner and outer corrugations has little effect on operation of the oversized BWO.

DOI： 10.1585/pfr.5.S2093

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Other Link： https://jlc.jst.go.jp/DN/JALC/00368733091?from=CiNii

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Plasma Science and Nuclear Fusion Research  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

An air-cooling system of a small capacity of several kilo-watts using only water refrigerant as a non-CFCs (Chlorofluorocarbon) technology is examined. The experimental device consists of two stages. The first stage is composed of a vacuum pump and a vacuum chamber of about 60 L in volume. The second stage has two heat exchangers (the exchanger located outside the vacuum chamber is a dummy cooling load) and a water circulating pump. An air-conditioner indoor unit or a heater is used as a dummy cooling load. The temperature and humidity characteristics are measured at each place. Consequently, the ability to cool the room air is ensured by an air-cooling system using only water refrigerant. A new vacuum pump, that can exhaust a large amount of water vapor, is developed and its properties are measured. It seems that the engine-based vacuum pump performance is sufficient to drive the air cooling system with water refrigerant.

DOI： 10.1299/jee.3.135

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Other Link： https://jlc.jst.go.jp/DN/JALC/00312923684?from=CiNii

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Plasma Science and Nuclear Fusion Research  

Studies on slow-wave devices with a novel disk cathode and two types of rectangular corrugation are reported. The beam voltage is weakly relativistic, which is less than 100 kV. A disk cathode can generate a uniformly distributed annular beam in the weakly relative region. Rectangular corrugation having the ratio of the corrugation width to the periodic length of 50 or 20% is used. Using the former, output powers of about 200 kW are obtained at around 100 kV. For the latter, the effect of slow cyclotron resonance is observed in the low-energy region of around 30 kV. Output powers of slow cyclotron masers are in the range of a few hundred W. The operation mode of a slow cyclotron maser can be controlled between axisymmetric and nonaxisymmetric modes by changing the end condition of rectangular corrugation.

DOI： 10.1585/pfr.3.S1078

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electrical Engineers of Japan  

Studies of an oversized BWO with a novel cathode and a rectangular corrugation are presented. The beam voltage is weakly relativistic, less than 100 kV. We propose to use a disk cathode made of metal only. The disk cathode can generate a uniformly distributed annular electron beam even in the weakly relativistic case. By using the annular electron beam, a weakly relativistic oversized BWO consisting of rectangularly corrugated cylindrical waveguide is demonstrated. The oscillation starting energy is about 60 kV for a 10-period rectangular corrugation. The maximum output power is estimated about 200 kW. The operation mode between axisymmetric and nonaxisymmetric modes can be controlled by changing the end condition of BWO.

DOI： 10.1541/ieejfms.127.681

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Language：Japanese   Publisher：電気学会  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Plasma Science and Nuclear Fusion Research  

We report an oversized K-band backward wave oscillator (BWO) operating above 20 GHz in the weakly relativistic region less than 100 kV. It is very important to prevent microwave from going into the beam diode, since intense microwaves will harmfully affect beam generation. A weakly relativistic oversized BWO is demonstrated using a Bragg reflector at the beam entrance of slow wave structure (SWS). The effect of the Bragg reflector on the BWO operation is examined, by changing the boundary condition at the beam entrance. The Bragg reflector improves the performance of the oversized BWO.

DOI： 10.1585/pfr.2.S1041

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

An electric brake by a three-phase short-circuit system used as the brake equipment of a small wind turbine damages the rotor blades by a rapid revolution stopping of the generator. Moreover, the generators windings may also be damaged by a large short-circuit current. In this paper, the electric braking circuit using the NTC thermistors (negative temperature coefficient resistors) is proposed as a braking system for a cheaper and safe stop of the small wind turbine. The effect under the natural wind condition is examined by the field test using a 500W small wind turbine. AS a result, it is clarified that the generator can decelerates gradually and reduce the burst current by using the braking circuit that composed of the NTC thermisitors.

DOI： 10.1109/PEDS.2007.4487813

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Language：Japanese   Publisher：電気学会  

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Language：Japanese   Publishing type：Research paper (other academic)   Publisher：Japanese Society for Engineering Education  

DOI： 10.20549/jseejaarc.2006.0_26

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

As a brake system for small wind turbine, mechanical brake and electric brake by the short circuit of 3-phase permanent magnet generator are used. However, an electric braking method may damage the rotor and/or blades by rapid stop of the generator revolution. Moreover, generator winding may also be damaged by large short-circuit current. In this paper, the electric braking method using NTC thermistors (negative temperature coefficient resistors) is proposed as a braking system for a cheaper and safe micro wind turbine.

DOI： 10.1109/EPEPEMC.2006.283437

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Language：English   Publishing type：Research paper (international conference proceedings)  

Triggered vacuum gaps (TVGs) can work for large current and high voltage in comparison with semiconductor devices, and have advantageous that are shown good switching characteristics for the wide working voltage range with no adjustment of the gap length. However, a switching time of TVG is strongly influenced by the main voltage polarity. It is called polarity effect. We found that a circuit of two parallel-connected TVGs generated a crowbar current automatically. When two TVGs used as a start switch and a crowbar switch, respectively, characteristics of the crowbar circuit of two parallel-connected TVGs was examined experimentally. In this paper, the pulse forming technology in the crowbar circuit which employing two TVGs is examined experimentally. It is clarified that the time to half value of the crowbar current is controlled by inserting a resistor or a capacitor. And the characteristics of the crowbar current are measured. © 2006 IEEE.

DOI： 10.1109/DEIV.2006.357275

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The triggered vacuum gap (TVG) is a closing switch for generating large current pulse and can work in the wide range of voltage for several kV to tens kV. Main electrodes are made of Ag-WC. One of main electrode has a hole for trigger electrode (Mo). The switching time is short, if the polarity of the holed-electrode is negative. It is called polarity effect. We devised a crowbar circuit using the polarity effect of the TVGs. The crowbar current of this circuit was investigated experimentally by varying applied voltage, inductance, capacitance, gap length of TVGs, and trigger current duration. A crowbar current, crest of which is 2.4 kA and 4.9/270µs for example, was observed. The probability of generating the crowbar current was more than about 90 %, in the following condition: the trigger current duration of 6.65 µs and the gap length of 2-6 mm. © 2003, The Institute of Electrical Engineers of Japan. All rights reserved.

DOI： 10.1541/ieejfms.123.443

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electrical Engineers of Japan  

The switching characteristics of a UV-laser triggered vacuum gap (ULTVG) with a metal target electrode were measured. The gap spacing of the diameter 85-mm copper electrodes was 1.6-mm. The target electrode of the 7-mm in diameter was placed in the hole (8-mm in diameter) of the cathode. The target electrode materials used in this work were Ti and Al. The target electrode and the cathode were connected electrically. An ultraviolet-pulsed laser beam was perpendicularly focused onto the grounded target electrode. The laser was third harmonic beam of Nd:YAG (wavelength 355-nm, energy 5mJ/pulse, beam diameter 2-mm). The operating voltage range for the target electrode ULTVG enlarged more than 11-21% compared with the copper electrode ULTVG and the switching time, 325 ns at 15 kV, was the same in the case of the copper electrode ULTVG.

DOI： 10.1541/ieejfms.122.440

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This paper presents results of a quench/recovery experiment for a BSCCO-2223/Ag composite tape in the presence or absence of a thin layer of solid nitrogen on each side of the tape. Voltage and temperature data were recorded for a 20-cm long BSCCO-2223/Ag tape operating in the range 20-55 K and subjected to a heat pulse of a 10-600 s duration applied over a short distance at its midpoint. The data clearly show that solid nitrogen is beneficial to the stability of high-temperature superconductors operating in this temperature range and subjected to transient heating disturbances. © 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4534(02)01120-6

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Language：English   Publishing type：Research paper (international conference proceedings)  

This paper presents experimental and numerical simulation results of a 2-section coil subjected to overcurrent pulses in the temperature range 20-60 K. The experiment simulates a high-temperature superconducting (HTS) magnet for electric devices such as fault-current limiters, transformers, motors, and power lines under fault-mode overcurrent pulses. Each section of the test coil is layer-wound with Bi-2223/Ag composite tape, 3.5-mm wide and 0.23-mm thick, with the outer section wound directly over the inner section. A pulse current exceeds the critical current of each conductor and may drive each section normal. A constant current that follows the pulse current leaves each section in three possible conditions: completely superconducting, recovering, and quenching. Simulation agrees reasonably well with experiment.

DOI： 10.1109/77.920208

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Language：English   Publishing type：Research paper (scientific journal)  

The switching time and arc-ignition probability of a sustained main discharge in a laser trigger vacuum gap were measured. The third harmonic beam of an Nd:YAG pulse laser (wavelength 355 nm, energy 5 mJ/pulse, power density 4×107 W/cm2) was used to trigger the gap. The main electrodes 85 mm in diameter were made of oxygen-free copper. The gap length was 1.6 mm and the experimental chamber was evacuated to about 1.3×104 Pa by a turbo-molecular pump. The UV beam from the laser was focused at normal incidence onto the grounded cathode. The switching time decreased and the arc-ignition probability increased with increasing applied voltage. The switching time was 326 ns at 15 kV with a circuit inductance of 107 μH. Its jitter was 24.8 ns. The advantageous results obtained with the UV beam are compared to the previously reported data on triggered vacuum gaps.

DOI： 10.1002/1520-6416(200008)132:3<8::AID-EEJ2>3.0.CO;2-7

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEE  

The switching time and the arc-firing probability of a self-sustaining discharge in UV-laser triggered vacuum gap (ULTVG) were measured. The third harmonic beam of Nd:YAG pulse laser (wavelength 355 nm, energy 5 mJ/pulse, power density 4×107 W/cm2) was used as a trigger for ULTVG. The UV-laser pulse injected perpendicularly onto the grounded cathode. The electrode materials were oxygen-free copper and aluminum. The electrodes had 85 mm in diameter. The gap length was 1.6, 1.9, 2.2 mm. The experimental chamber was evacuated to about 1.3×10-4 Pa by a turbo molecular pump. The range of the firing voltage in copper electrodes was higher than in aluminum. The jitter of the switching time in copper electrodes was smaller than in aluminum. The arc-firing probability decreased as the circuit inductance increased.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：John Wiley and Sons Inc.  

Both switching time and minimum firing voltage of a triggered vacuum gap employing a trigger electrode in the cathode and anode (double triggered vacuum gap) were measured. The double triggered vacuum gap was operated below 100 V independent of the high voltage main electrode polarity (positive or negative). This minimum firing voltage was lower than that of the conventional triggered vacuum gap. The switching time is approximately 0.5 μ in the range 3 to 18 kV. The conventional triggered vacuum gap has a trigger electrode that is placed at the center of the grounded main electrode. The polarity of the main electrode affected switching time characteristics. A trigger electrode was added to the high voltage main electrode. The double triggered vacuum gap was only slightly influenced by the polarity of the high voltage main electrode when both main electrodes were triggered at the same time.

DOI： 10.1002/eej.4391160609

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Axial density gratings with local rises in a plasma filled corrugated wall waveguide are experimentally found to be created by incident high-power microwaves. The density rises and the maxima of standing waves of the axial RF electric field are observed at the identical axial positions where the radius of the corrugated wall is minimum. A nonlinear plasma model to explain the physical meaning of the observed results is proposed.

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Other Link： http://dl.ndl.go.jp/info:ndljp/pid/10451599

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：電気学会  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

Field patterns and Poynting vectors of TM01 mode in sinusoidally corrupted waveguides are analyzed numerically. It is shown that a plasma column new the axis excludes the rf electric field lines towards the peripheral region, resulting in Poynting vectors in the axial direction there. The excitation of TM01 mode in corrugated waveguides is shown to be classified into two cases; surface and the volume waves. A possible physical explanation for the enhanced radiation observed previously from plasma filled backward wave oscillators is tried from the present results.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

The linear dispersion relation of low frequency electromagnetic plasma waves in a corrugated plasma waveguide is analyzed successfully for a particular model in which difficulties for satisfying Floquet theorem rigorously are overcome. The resultant absolute instabilities are investigated numerically in some detail.

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：電気学会  

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE PUBL B V  

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