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The influence of an externally applied magnetic field on the characteristics and the transient behavior of the arc in a gas circuit breaker is examined by means of three-dimensional time-dependent numerical simulations. It is assumed that the gas circuit breaker has a ring-shaped permanent magnet and an arc is exposed to the externally applied magnetic field. Numerical results demonstrate that the rotation of arc induced by the Lorentz force produces a three-dimensional spiral structure of the arc. As a consequence of the rotation, the arc shrinks and the arc temperature decreases remarkably just before the time when the arc current is zero, so that applying the magnetic field increases the arc voltage. The numerical results also show that a swirling flow generated by the Lorentz force carries a thermal energy toward the thermal puffer room mainly by the convection during the high arc current phase, and as a result the pressure in the thermal puffer room increases. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

SUMMARY The purpose of this study is to examine the influence of the shape of the cross-section of a scramjet engine-driven experimental diagonal conducting wall (DCW)-MHD generator on generator performance by three-dimensional numerical analyses. We have designed MHD generators with symmetric square and circular cross-sections, based on an experimental MHD generator with an asymmetric square cross-section. Under the optimum load conditions, the electric power output reaches 26.6 kW for the asymmetric square cross-section, 24.6 kW for the symmetric square cross-section, and 22.4 kW for the circular cross-section. The highest output is obtained for the experimental generator with the asymmetric square cross-section. The difference in the electric power output is induced by the difference of flow velocity and boundary layer thickness. For the generator with the asymmetric square cross-section, the average flow velocity is highest and the boundary layer is thinnest. The compression wave is generated with dependence on the channel shape. The difference in the flow velocity and boundary layer thickness is induced by the superposition of the compression wave. © 2014 Wiley Periodicals, Inc. Electr Eng Jpn, 187(2): 9-16, 2014; Published online in Wiley Online Library (). DOI 10.1002/eej.22403 [ABSTRACT FROM AUTHOR]

Numerical analyses of the experimental-scale scramjet engine driven magnetohydrodynamics generator implemented in the Hypersonic Vehicle Electric Power System project have been carried out to clarify plasma behaviors and power generation characteristics. Three-dimensional numerical analyses have been performed under the two inlet conditions: one is the uniform inlet temperature condition, and the other is the nonuniform inlet temperature condition. Under the nonuniform inlet temperature condition, the generator performance approximately agrees with the experimental result. The tendency of the voltage loss is also reconstructed near the power takeoff electrodes though the voltage loss is smaller than that observed in the experimental result. The electric power output under the nonuniform inlet temperature condition is 40% smaller than that under the uniform inlet temperature condition. This is because the ratio of the Joule dissipation to the work by the Lorentz force increases owing to the decrease of active generator region as the current concentrates in the high-temperature region when the inlet temperature nonuniformity is considered. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

The present numerical study examines the possibility and usefulness of the control of weakly ionized plasma flow ahead of a space vehicle by means of the magnetic field for thermal protection in earth reentry flight under the flight conditions at the altitudes from about 72 to 48 km along the real earth reentry trajectory of the blunt body OREX, which was used for an earth reentry experiment in 1994. Numerical results show that the aerodynamic heating can be reduced by applying the magnetic field at the altitude above about 55 km where the weakly ionized plasma is produced behind the bow shock wave, and also that the reduction amount of the aerodynamic heating by applying the magnetic field becomes larger with increasing the altitude. At the altitude of about 60 km, where the aerodynamic heating had the peak value in the OREX experiment, the wall heat flux at the stagnation point and the total aerodynamic heating over the wall surface with applying the magnetic field of about 0.5 T are, respectively, 85% and 67% of their values obtained without applying the magnetic field. [ABSTRACT FROM PUBLISHER]

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 [ABSTRACT FROM AUTHOR]

Performance characteristics of self-excited pulsed MHD power systems are investigated with one-dimensional time-dependent calculations using a gas–liquid two-fluid model. First, the Russian pulsed MHD power system “Pamir-3U” is analyzed. The result of numerical simulations of hot-fire tests shows good agreement with the experimental data, confirming the validity of the mathematical model. Performance analysis of Pamir-3U reveals that the power output is approximately constant with the variation of load resistance, while the ballast resistor consumes a large amount of electric power. It is also shown that the system has been optimally designed to supply a large load current. Next, a new system yielding larger power output is proposed and analyzed. The obtained characteristics show that the new system can provide the maximum power output of 25 MW, which is 10 MW larger than that of Pamir-3U. © 2000 Scripta Technica, Electr Eng Jpn, 132(3): 30–37, 2000 [ABSTRACT FROM AUTHOR]

Numerical simulations of detailed time-dependent behavior are performed on a simulation model in which a coupled system of nonequilibrium disk MHD generator and line-commutated inverter is connected to an infinite bus through the transmission line, showing that continuous operation of the system is usually possible even when a power line fault occurs near the system. Then, time-dependent swing simulations are carried out on another simulation model in which the MHD/inverter system and a synchronous generator are connected in parallel to an infinite bus through the common transmission line, revealing that the rotor angle swing of the synchronous generator caused by the power line fault can be effectively suppressed by the fast output power control of the MHD/inverter system. © 1999 Scripta Technica, Electr Eng Jpn, 127(3): 13–24, 1999 [ABSTRACT FROM AUTHOR]

In previous research on subsonic diagonal-type MHD generators, the authors have proposed a conceptual design with relatively low Mach number in order to stabilize the MHD generator of commercial scale and have shown that the MHD generator works stably under constant-current loading condition. In the present paper, effects of loading conditions on stability of the MHD generator are examined. A channel-length scale linear stability analysis and time-dependent calculations are carried out, where both gasdynamical boundary conditions and loading condition are taken into account. These analyses show that the MHD generator behaves stably under various loading conditions such as constant-voltage loading condition and ohmic loading condition. Then the stability of the MHD generator connected with an ac power system is also analyzed by time-dependent calculations. The analysis shows that the MHD generator stably provides the rated power to the ac power line. © 1999 Scripta Technica, Electr Eng Jpn, 128(4): 16–24, 1999 [ABSTRACT FROM AUTHOR]

A preliminary analysis of two-phase flow in the pulsed MHD generator Pamir-3U is carried out. The two-fluid model for dusty gas flow is applied to treat the two-phase working body which consists of combustion gas and liquid particles of Al2O3. One-dimensional time-dependent calculations show that the velocity lag and the thermal lag between the two phases are large when the particle diameter is 15 μm. The lags become small when the diameter is small because the decrease of the diameter increases the momentum transfer and the heat transfer between the two phases. When the large Lorentz force develops a shock wave, the interaction between the two phases relaxes the shock wave. The increase of the particle diameter decreases the channel current and the power output because the increased diameter decreases the energy conversion from the liquid phase. © 1999 Scripta Technica, Electr Eng Jpn, 127(2): 15–23, 1999 [ABSTRACT FROM AUTHOR]

A conceptual design of a transonic disk MHD channel is carried out for a power generation system with liquefaction recovery of CO2. A previous study has shown that the subsonic disk MHD channel has rather poor performance and the supersonic disk channel yields sufficiently high power output, although its stability should be improved. The present paper proposes a transonic disk channel which can be stably operated with high power output. It is assumed that the transition between supersonic flow and subsonic flow is accompanied by a cylindrical shock wave in the channel. The transonic channel yields enthalpy extraction ratios of 20.2 and 22.9%, respectively, for thermal inputs of 1100 and 2000 MW, and is nearly equal to the performance of the supersonic channel. The stability of the transonic disk channel is examined by r-0 two-dimensional time-dependent calculations. The two-dimensional analysis shows that the transonic disk channel works stably with fewer load sections than the supersonic channel even when inlet perturbations are added. © 1998 Scripta Technica. Electr Eng Jpn, 122(2): 21–29, 1998 [ABSTRACT FROM AUTHOR]

Two-dimensional stability analyses for open-cycle supersonic disk MHD generators are carried out which take into account electrical boundary conditions. A method of r-θ two-dimensional linear stability analysis for supersonic disk MHD generators is proposed which examines the time growth rate of perturbations. The growth rate is determined by the characteristic equation which is derived from the electrical boundary conditions. Whether the perturbations grow or decay is judged diagrammatically in a way similar to the Nyquist method. A coal-fired outflow supersonic disk MHD generator of commercial scale is analyzed under several types of boundary conditions. The stability is much affected by the electrical boundary conditions and also by the azimuthal wavenumber of disturbances. Two-dimensional analysis has revealed an azimuthally nonuniform instability in one of the load sections of the generator, where no instability is found in the one-dimensional analysis. The analysis also shows that the instability can be suppressed by subdividing the load section with control electrodes. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 120(4): 23–30, 1997 [ABSTRACT FROM AUTHOR]

Design and stability analyses of MHD disk-type generators are carried out, which are applied for coal-fired electrical power generation system with CO2 recovery. Channels designed with subsonic flow show rather poor performance compared with supersonic flow channels. Inflow channels show better performance than outflow channels. The inflow channel gives enthalpy extraction ratios of 20.21% and 21.12% for thermal inputs of 1100 MW and 2000 MW, respectively, while the outflow channel operated with supersonic flow yields enthalpy extraction ratios of 17.92% and 18.12% when the magnetic flux density is 8 T. The open-cycle disk channels tend to become unstable at the exit region. It seems possible to stabilize the disk channels when operated with 8 T but seems difficult to stabilize them when operated with 10 T. © 1997 Scripta Technica, Inc. Electr Eng Jpn 119(1): 9–16, 1997 [ABSTRACT FROM AUTHOR]

A new power control method is proposed which is suitable for the MHD power generation system which consists of nonequilibrium disk generator and line-commutated inverter. The thermal input of the generator is controlled by changing the inlet stagnation pressure, whereas the seed mass flow rate instead of the inlet stagnation pressure is utilized as a manipulated variable of power control system. It is possible that the proposed method can realize both high performance for part load operation and fast output power control of which the time constant is much shorter than the response time of thermal input. Numerical simulations are carried out for the MHD power generation system connected to infinite bus and then it is confirmed that the system is stable and shows excellent power control performance. [ABSTRACT FROM AUTHOR]

Stability of large-scale coal-fired MHD channels is studied by (1) linearized stability analysis, and (2) time-dependent 1-D analysis. The channel length is 15 m with 600 electrode pairs, and the output power ranges from 220.6 MW through 258.7 MW. Linearized stability analyses show that the Faraday channels operated with fixed loading resistance are stable, whereas the two waves of u and u - a (u, a: gas and sound velocity) become unstable in the Faraday channel with fixed loading factor. Two waves of u and u - a are unstable in the diagonal channel with fixed loading current and the u + a wave becomes unstable in the diagonal channel with fixed electrode current. Time-dependent one-dimensional analyses indicate that the Faraday channels with fixed load resistance are smooth without growth of fluctuation. The diagonal channels with fixed electrode current are smooth with no fluctuation, though the linear theory indicates that the u + a wave is unstable. The diagonal channel with fixed load current suffers large disturbance along the latter half of the channel, being consistent with the linearized analysis which indicates that the u - a and u waves are unstable. [ABSTRACT FROM AUTHOR]

This paper presents the results of the analysis of three-dimensional mutual interaction between electromagnetic field and fluid of the subsonic Faraday-type MHD generator. [ABSTRACT FROM AUTHOR]

The article discusses the effects of electric arc behavior and electrode temperature on the current distribution and the location of arc spots in the boundary layer of magnetohydrodynamic generator. Based on numerical analysis, the potential distribution between electrodes drop dramatically across the boundary layer. If the wall temperature in the arc is high, the heat flux is concentrated on the laminar layer due to the presence of high effective thermal conductivity. The arc spots move in three-dimensional space.

The article discusses the operational characteristics of a power consolidation circuit for Faraday-type magnetohydrodynamic generator. The fundamental characteristics of Christmas tree type and Master/Slave type consolidation circuits are discussed, as well as the electrical nonuniformities caused by slag polarization. A schematic diagram of Christmas tree type power consolidation circuit with electrodes is presented.

The high-temperature ceramic electrode for an open-cycle MHD generator is now under intensive study but it can not be used in practice today. Presently available electrodes are of low-temperature type and made of copper. Currents of such low-temperature electrodes are carried in an arc discharge mode if natural gas or heavy oil is used as fuel. The current and voltage distributions around the electrodes often become very non- linear due to the effect of negative voltages current characteristics of the arc current.

The authors propose a new power consolidation-inversion-control system for the Faraday MHD generator using the voltage source PWM inverters. The dc output power for each electrodes pair of the MHD generator is at first inverted into three-phase ac power by a voltage source PWM inverter, and then the ac powers are consolidated by transformers. The proposed system does not need such expensive equipment as an ac filter or phase modifier and can independently and simultaneously control the active and reactive powers provided to the electric power system. Numerical simulations of the whole system, including the Faraday MHD generator, the proposed system can stably and steadily transit and control the electric power from the MHD generator to the electric power system. It is also confirmed that the proposed system can be independently and simultaneously control the active and reactive powers and can be used as a fast power controller. [ABSTRACT FROM AUTHOR]

This article discusses a study related to diagonal-type MHD generator interconnected to the transmission line through an inverter. Since an MHD generator produces a dc output power, it aust be connected to an ac system through an inverter. The inverter is classified into two types, line and forced commutation types, depending upon its commutation scheme. The forced-commutated inverter has been used little so far in the power application field. The progress of semiconducting power switches in capacity, switching speed and computer-based control techniques will help develop inexpensive reliable forced-commutated inverters.

Effects of the magnetohydrodynamics flow control on Earth reentry flight characteristics are examined by a coupled numerical analysis of the reentry flight trajectory and the magnetohydrodynamics flows with thermochemical reactions. Initial flight altitude and velocity of a blunt body with a nose radius of 1.35 m are 75.3 km and 7.2 km/s, respectively. Numerical results show that at high altitudes such as about 75 km, the main factor of the mitigation of wall heat flux by the magnetohydrodynamics flow control is the increase of the thickness of the shock layer by applying the magnetic field. At low altitudes such as about 55 km, on the other hand, the main factor of its mitigation is the decrease of flight velocity due to the change of flight trajectory by applying the magnetic field. It can also be found from a rough estimation that about 75 % of its mitigation amount at the altitude of about 60 km, where the aerodynamic heating is severest, is attributed to the decrease of flight velocity by applying the magnetic field. [ABSTRACT FROM AUTHOR]