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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 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 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]

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]

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.

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.