Plasma Fluid Flow Behavior and Power Generation Characteristics in a High‐Temperature Inert Gas Plasma Faraday MHD Generator

The plasma fluid flow behavior and power generation characteristics in a Faraday magnetohydrodynamic (MHD) generator using a high‐temperature inert gas (argon) plasma have been examined in a time‐dependent two‐dimensional numerical simulation. The inhomogeneous and unstable plasma at an inlet total temperature of 7000 K results in reductions and fluctuations in the output power. The plasma becomes homogeneous and stable as the inlet total temperature increases to 9000 K. One of the reasons for the suppression of ionization instability may be weakness of the dependency of the electrical conductivity on the electron number density, because the Coulomb collision of electrons becomes dominant during deviation from Saha equilibrium.     

Power Generation Experiments with a High Temperature Inert Gas Plasma Faraday Type MHD Generator

MHD power generation experiments have been conducted by using a single‐pulsed shock‐tunnel facility, where a high‐temperature inert gas (pure argon) at a fixed total temperature of 9000 K is introduced into a linear Faraday generator without seeding. The fluctuations in the output power and light emission from the plasma are found to be small, and the pure inert gas plasma seems to be rather consistently free of ionization instability. The output power is improved by increasing the magnetic flux density in near‐quadric fashion and the enthalpy extraction ratio does not depend on the inlet total pressure (11.2% to 12.9% for 0.063 MPa to 0.105 MPa). The generator performance obtained is competitive with or superior to that of existing seed plasma MHD generators.     

Numerical Simulation of Power Generation Characteristics of a Disk MHD Generator with High‐Temperature Inert Gas Plasma

The power generation characteristics of a disk magnetohydrodynamics (MHD) generator with high‐temperature inert gas (argon) plasma have been examined by a time‐dependent two‐dimensional numerical simulation. The numerical simulation results based on the experimental conditions show that the enthalpy extraction ratio (= electrical output power/thermal input) can reach above 10%, which surely supports the reasonability of the experimental results. Proper selection of working conditions, especially the inlet total gas temperature, is necessary, since the gas temperature dominantly determines the electrical conductivity in the generator, unlike the conventional seeded plasma MHD generator. It is also found that the plasma is not in the recombination process but in the ionization process, where the ionization degree moderately increases along the flow. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(3): 23–30, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21237     

Numerical Study on Periodic Structure Evolution of Output Power in MHD Generator by Using Pulse‐Assisted Ionization Discharge

A pulse‐assisted ionization discharge applied to a magnetohydrodynamic (MHD) generator is proposed as a technique to increase an electrical conductivity of working fluid. In this study, a periodic structure of output power in the MHD generator by using pulse‐assisted ionization discharge was evaluated. As a result, the discharge electrode length and the velocity of working fluid affect the discharge current distribution. The periodic structure of output power was observed in the several conditions. When the velocity of working fluid is roughly same as the sound speed, the periodic structure of output power was not observed.     

Numerical simulation of blow‐down closed‐cycle disk MHD generator

Numerical simulations of the closed‐cycle disk MHD generation experiment with Tokyo Institute of Technology's Fuji‐1 blow‐down facility are performed. In the calculations, the r–z two‐dimensional time‐dependent simulation code developed by the authors that can take the effect of water contamination into account is used, and the experimental conditions of Run A4109 operated by Disk‐F4 generator are selected as the numerical conditions. When the water contamination is the lowest level realized in the experiments, the simulation results coincide with the experimental results reasonably well, though there exist some discrepancies caused by inaccuracy of used basic plasma parameters, limitations of the two‐dimensional approximation, and so on. The voltage–current curve is almost linear, indicating that the MHD interaction is relatively weak and the flow field is mainly determined by the back‐pressure. The increase of the water contamination level results in decreased seed ionization rate at the generator channel inlet, leading to the steep deterioration of the generator performance. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(2): 46–54, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10335     

Characteristics of flow and plasma under high MHD interaction in nonequilibrium disk MHD generator using argon

Results of experimental studies on behavior of a supersonic flow and of a nonequilibrium plasma in a disk MHD generator are presented. The experiments with cesium seeded argon were carried out under high MHD interaction conditions. Effects of seed fractions on static pressure distributions, flow Mach numbers, electron temperatures and uniformity of discharge in the disk MHD channel were investigated. The results have shown that the flow is kept supersonic throughout the disk MHD channel when a sufficient Joule heating exists in a supersonic nozzle and the seed is fully ionized. It was found that there was an optimum seed fraction at which the power output became maximum and, at the same time, the seed was fully ionized. Furthermore, an almost uniform discharge due to the full ionization of seed was observed. It is noted that enthalpy extractions and adiabatic efficiencies were increased remarkably, and the highest enthalpy extraction of 26.5 percent was achieved for cesium seeded argon. However, adiabatic efficiencies remained still low due to large pressure losses.     

Plasma behavior in a non‐equilibrium disk MHD generator with a spatially non‐uniform seed fraction

The influence of azimuthal non‐uniformity of the seed fraction on plasma structure and performance in a non‐equilibrium disk MHD generator is investigated with a two dimensional r–θ numerical simulation. It is found that a locally high seed fraction causes mainly non‐uniformity of gas‐dynamical properties, whereas a locally low seed fraction develops a non‐uniform plasma. Both locally high and low seed fractions reduce generator performance considerably. These results suggest a spatially uniform seed fraction should be required for high power generation. ©1999 Scripta Technica, Electr Eng Jpn, 126(4): 48–54, 1999     

Transient response of closed‐loop MHD experimental facility

Transient responses of a closed‐loop MHD experimental facility from nonpower generation to power generation have been investigated by means of time‐dependent quasi‐one‐dimensional numerical simulations. For the long‐time continuous power generation experiment, the time required to obtain the steady state for the power generation is estimated to be approximately 20 hours. By increasing the electrical input power to the heater as an exponential function of time, the temperature increment of ceramics can be moderated. When the duration of the experiment is around 10 minutes, argon gas temperature at the exit of the heater hardly changes because of the large heat capacity of structure materials. It is found that the fluid disturbances are induced at the instant of the power generation and they propagate as they repeatedly reflect at the sudden change of duct shape. Since all of the induced disturbances attenuate approximately 0.4 second after the power generation, the time scale that the disturbances exist in the facility is estimated to be 1 second at most. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 158(1): 46–52, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20237     

The effect of an externally applied radio‐frequency electromagnetic field on the performance of a disk MHD generator

The effects of an externally applied radio‐frequency (rf) electromagnetic field on the nonequilibrium performance of a disk MHD generator were examined experimentally. As a preliminary experiment, plasma production by the applied rf electromagnetic field was attempted in the disk generator (Disk‐PIA), in which rf induction coils were embedded in the one‐side disk wall, under the conditions of no seeding, no flow, and no magnetic field. From the results of the preliminary experiment, it was confirmed that the argon plasma (～110 Torr) was produced uniformly in the azimuthal direction by the rf electromagnetic field even in the presence of exposed anodes in the faced disk wall and metallic support at the disk center. In MHD power generation experiments with the Disk‐PIA installed in the shock‐tube facility, the increase in the electrical output and more indiscrete discharge attributed to the rf electromagnetic field were verified with good reproducibility for the first time. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(4): 46–53, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10009     

Electron temperature measurement and performance of a nonequilibrium disk MHD generator

Electron temperatures of nonequilibrium cesium seeded argon plasmas in a disk MHD generator installed in a blow-down facility are measured spectroscopically, and the generator performance is discussed in relation to the electron temperature. The temperature is decreased from ∼9000 K to ∼3000 K when the seed fraction is increased from 1 × 10⁻⁴ to 3 × 10⁻⁴. For the seed fraction of about 2 × 10⁻⁴ corresponding to the maximum power output, the temperature is found to be 4000–5000 K and the temperature fluctuation becomes minimal. For the seed fraction around 2 × 10⁻⁴, the electrical conductivity evaluated from the temperature is almost independent of the temperature. These facts suggest that the plasma is almost in the full seed ionization regime. Partially ionized argon and cesium plasmas are dominant at seed fractions below 1.3 × 10⁻⁴ and over 2.3 × 10⁻⁴, respectively, which degrades generator performance. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 120(1): 16–22, 1997     

Behavior of magneto‐acoustic waves in a nonequilibrium subsonic disk MHD generator

The behavior of magneto‐acoustic waves in a nonequilibrium subsonic disk MHD generator was examined. The solution of the sixth‐order dispersion relation obtained by linearizing the set of MHD equations suggested that a magneto‐acoustic wave which propagates at a velocity of u_r ? a(u_r: radial fluid velocity, a: sound velocity) should be damped in subsonic flow. From time‐dependent quasi‐one‐dimensional simulations, it was verified that the pressure disturbance in the subsonic generator was damped at approximately the same rate as the value predicted by the linear theory. From a simplified analytical model, the mechanism of magneto‐acoustic instability with fully ionized seed was discussed, and the damping criterion for the magneto‐acoustic wave was clarified. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 142(4): 20–26, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10108     

大功率风力发电机转子温度场数值仿真

本文以一台1.5MW双馈风力发电机为例,研究发电机转子内流体流动与传热问题。根据发电机通风结构与传热的特点,建立转子1/8区域的三维求解模型,并采用CFD技术对求解域进行耦合求解,得出发电机转子内流体流动特点和温升分布规律。     

Voltage‐current characteristics of subsonic disk CCMHD generator

Voltage–current characteristics of a subsonic disk CCMHD generator are examined by time‐dependent quasi‐one‐dimensional numerical simulations. The output voltage is found to be almost constant for load resistances higher than the designed value, whereas the output current is kept almost constant for lower load resistances. It is confirmed that at high load resistances the subsonic flow is maintained in the whole generator, and a steady and uniform nonequilibrium plasma is realized. The connection of the low load resistances causes flow choking at the generator inlet, leading to the supersonic flow. Then shock waves and ionization instability occur in the generator. © 2000 Scripta Technica, Electr Eng Jpn, 130(4): 58–65, 2000     

Internally Self‐Sustaining Electric Power Generation

The electrical double layer capacitor‐electrostatic induction electric power generation system (EDLC‐ESIG) undergoes an electric cycle consisting of three steps: energy storage by electrostatic induction, power generation, and initialization by electromechanical coupling. An internally self‐sustaining electric power can be generated by repetition of cycles with periods of the order of seconds. The objective of this paper is to show the design of EDLC‐cell configuration for practical use to produce constant power output. On the basis of energy densities of the conventional EDLCs for energy storage, the volumetric power density has been estimated to be 450 W/L for the discharge time of 10 s. Possibilities of commercial applications of the EDLC‐ESIG system to vehicles and high power generations in central station have been considered with respect to the power densities of the EDLC‐cells consolidated into a generation system.     

Study of Low‐Voltage Ride‐Through Performance for Wind Power Generation with Doubly Fed Induction Generator

The introduction of wind power generation is increasing rapidly. The ratio of wind power generation to the total generation capacity is becoming higher and higher. When a phase‐to‐phase fault occurs in the power system, the frequency of the power system is lower due to disconnection of wind power generation with doubly fed induction generators (DFIG). Therefore, the power system might become unstable. This paper describes an LVRT (low‐voltage ride‐through) performance improvement scheme for wind power generation with DFIG. The wind power generator is disconnected from the grid in case of a power system fault. It is made to operate in isolation from the grid by controlling the inverters installed with the generators. After clearance of the power system fault, wind power generation is immediately reconnected to the grid. As a result, instability in the power system disappears. The performance of LVRT is confirmed by using the simulation software PSCAD/EMTDC. The simulation results show excellent results for the three‐phase short‐circuit fault with a voltage dip of 100%. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 185(1): 17–26, 2013; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.22423     

Fault analysis of the interconnecting system between a commercial‐scale subsonic diagonal‐type MHD generator and an ac power system

Fault analyses are performed for the interconnecting system between a commercial‐scale subsonic diagonal‐type MHD generator and an ac power system through a line‐commutated inverter. The behavior of the interconnecting system is first examined for the case of single misfiring of one thyristor in the inverter. In this case, the load current increases because the inverter system is short‐circuited. Following the theory of inverter commutation, the load current decreases to the rated value and the MHD generator is restored to the rated condition. Next, the cases of a single‐line ground fault and of a three‐phase short circuit fault are investigated. The line voltage decreases and thus the load currents increase after the fault. This increase of load currents destroys the design‐point flow of the MHD generator. Phase‐control angle control of the inverters is required in order to restore the rated operation of the MHD generator. © 2001 Scripta Technica, Electr Eng Jpn, 136(1): 29–36, 2001     

基于混合高温超导储能系统的电网动态功率补偿策略与试验

为实现高温超导储能系统(SMES)对电网功率波动的动态补偿,采用第1代铋系和第2代钇钡铜氧高温超导材料,设计并构建了过冷液氮温区运行、千焦级容量的混合高温超导储能系统。应用数字信号处理器和微控制器的双处理器形式,设计了LCL滤波的电压型SMES变流器的功率控制系统电路,基于空间矢量脉冲调制法(SVPWM),提出了SMES变流器对系统功率补偿的控制方法,并进行控制软件编程,实现对并网侧功率的动态监测和补偿策略的实时计算。最后应用SMES在一条200km输电线路上进行并网动模试验,针对电网负荷变化产生的功率波动状态,实现了毫秒级内对电力系统的快速功率输出和波动抑制,验证了超导储能系统对电网瞬时功率补偿策略和功率补偿变流装置的有效性。