Open-cycle MHD Generator Research Articles

ディスク形ＭＨＤ発電システムの制動抵抗による安定化の検討

Effects of installed SDR (System Dumping Resistors) on the stability of open-cycle disk MHD generator and synchronous generator system connected in parallel to power transmission lines are numerically studied. Usually the SDR is used to absorb the output energy of synchronous generator and to get stability of the power transmission system when faults occur in the A.C. power transmission lines.In this paper, we propose to apply the SDR in the D.C. lines between the MHD generator and the primary side of connected line-commutated inverters. We show that the SDR is effective for the system stability by a time dependent numerical analysis.

Performance analysis of commercial scale Ar–Cs disk MHD generator connected to electric power system with synchronous generator

Performance analyses of a commercial scale closed-cycle MHD disk generator are performed. A large scale MHD generator, superconducting magnet, inversion system and synchronous generator are designed. The MHD generator is operated with Ar–Cs plasma and connected to the ac power infinite bus through line-commutated inverters, while the synchronous generator is operated in parallel. The thermal input is 1000 MW, and the power output is 400 and 200 MW, from the MHD and synchronous generators. Fault analyses have found that rather large fluctuations within the MHD generator are induced by faults of the inverter and power transmission line, but control of the inverters can recover the MHD generation system to normal operation within 0.15 s. The feature of behavior of the MHD generator is the same with or without the parallel operation of the synchronous generator. The interaction between the MHD and the synchronous generators is small, and this feature is much different from the open-cycle MHD generation system, since the variation of output current of the closed-cycle disk MHD generator is much smaller compared with open-cycle MHD generators.

97/04707 Characterization of two modified lithium vanadate cathode materials in secondary lithium batteries: Yu, A. and Kumagai, N. Proc. Electrochem. Soc., 1997, 97-18 (Batteries for Portable Applications and Electric Vehicles), 215–232

Performance analyses of a commercial scale closed-cycle MHD disk generator are performed. A large scale MHD generator, superconducting magnet, inversion system and synchronous generator are designed. The MHD generator is operated with Ar–Cs plasma and connected to the ac power infinite bus through line-commutated inverters, while the synchronous generator is operated in parallel. The thermal input is 1000 MW, and the power output is 400 and 200 MW, from the MHD and synchronous generators. Fault analyses have found that rather large fluctuations within the MHD generator are induced by faults of the inverter and power transmission line, but control of the inverters can recover the MHD generation system to normal operation within 0.15 s. The feature of behavior of the MHD generator is the same with or without the parallel operation of the synchronous generator. The interaction between the MHD and the synchronous generators is small, and this feature is much different from the open-cycle MHD generation system, since the variation of output current of the closed-cycle disk MHD generator is much smaller compared with open-cycle MHD generators.

Two-dimensional stability of an open-cycle disk MHD generator: Effects of electrical boundary conditions

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

Parametric study of plant efficiency for an open-cycle steam-bottomed mhd plant using water gas-LPG mixture as fuel

The paper describes the cycle analysis for design and performance of a segmented electrode type open-cycle steam-bottomed MHD generator. Studies have been made to obtain train parameters to give maximum plant efficiency. The effects of the MHD generator length, the percentage of oxygen enrichment of the air (with and without preheating of the oxidant) on the plant performance have also been investigated. The optimum values of these parameters have been obtained for maximum plant performance.

Evaluation of fuel options for a commercial mhd plant in India

The choice of fuels for a commercial open-cycle MHD generator is not as simple as for a conventional plant. After the commissioning operations and the power runs of the Indian pilot MHD plant, the question of early commercialization is being debated. In this context, this paper looks at the spectrum of fossil fuels available in India and evaluates their relative suitability for commercial MHD generators. The attainable plasma temperature, electrical conductivity and the available fuel energy at the combustor outlet are taken as the comparison yardsticks. Standard operating parameters for commercial installations have been assumed. The comparison, which in the Indian context has been limited to coal-based fuels and natural gas, indicates the latter as the fuel of choice followed by gasified coal.

他励式インバータ負荷時の開放形ディスクＭＨＤ発電機の動特性

他励式インバータ負荷時の開放形ディスクＭＨＤ発電機の動特性

Two-dimensional laser-induced fluorescence-detection system for measurements of number density profiles of seed alkali atoms in MHD combustion gas plasmas

A thermally assisted laser-induced fluorescence (LIF) detection system is developed to measure two-dimensional spatial profiles of number density of alkali atoms seeded in an open-cycle MHD generator, especially in the boundary layer on channel electrodes. The spatial resolution of this system is evaluated to be 1.3 mm. To assess the system, the LIF intensity from Na atoms used as a seed tracer is measured in a laminar air-acetylene flame. The detected spatial profiles of the intensity show good agreement with those of the number density of sodium atoms measured by the spectral line absorption method. The LIF intensity near the surface of a cooled metal piece placed in the acetylene flame is also measured with this system as a preliminary experiment for applying it to the boundary layer on MHD channel electrodes.

Measurement of temperature, electrical conductivity and ion density of seeded combustion plasmas

The combustion products of a fossil fuel with an additive of low ionisation potential constitute the working medium in open cycle MHD generators. The most important parameters which have a direct bearing on the performance of MHD generators (apart from gas dynamic parameters) are: (a) plasma temperature, (b) electrical conductivity (c) charged particle density. In this paper, we have studied these characteristic parameters of a potassium seeded LPG-O 2 plasma as a function of stoichiometric coefficient, power rating of torch, seeding percentage in the plasma and water ballast on the seed solution. A few experiments were also done with caesium as seed. A suitable theoretical model developed has been used to cross-check the experimental results.

Interelectrode breakdown in MHD ducts

A simple model has been presented for the conduction of current between adjacent electrodes separated by an insulating wall and duct filled with conducting hot gases. Analytical expressions and calculations have been made for plasma initiated and insulator initiated breakdowns for the conditions prevailing in a typical open cycle MHD generator. The relative importance of the two types of breakdowns has also been evaluated.

The preparation and properties of strontium zirconate ceramics for channels of open-cycle MHD generators

Abstract A two-stage procedure of preparation of dense strontium zirconate ceramics capable of being used as electrically insulating material in MHD generators is described. A small addition of TiO 2 was introduced at the first stage to favour development of the properties, especially low apparent porosity, required for MHD purposes. The effect of TiO 2 on sintering temperature, phase composition and microstructure of the bodies is described. Properties of the resulting ceramics i.e. porosity, cold crushing strength, microhardness as well as electrical conductivity over the temperature range of 20–2000°C were measured. The results of successful testing of these ceramics in the channel of an experimental MHD generator are presented.

Comparative study of electrode voltage drops in MHD generators with and without ash in the combustion products

For estimation of the influence of slag layer on the electrode voltage drop, we have considered two identical open-cycle MHD generators with and without ash in the combustion products. Using the simple model of a slag layer with ohmic condution of current, we have evaluated the electrode voltage drop in a finitely segmented Faraday-type MHD generator with slagging electrodes. The electrode voltage drops in the presence of slag at different values of slag/plasma surface temperatures with and without slag for various values of Hall parameter and electrode wall temperature have been compared. It has been found that the presence of slag layer over the electrode surface with high slag/plasma surface temperature is more advantageous for lower electrode wall temperature and higher Hall parameter.

Power Conditioning and Control of Slagging MHD Generators

The operational characteristics of coal-fired open-cycle linear MHD generators are presented. The salient features of the loading and control requirements of Faraday and diagonal generators are analyzed and circuits that meet these requirements are presented. Consolidation and current control circuits are discussed, elaborating on the design considerations for operating them with MHD generators. Such circuits are shown to have relatively low losses, which results in higher than 98-99% efficiencies. Nomenclature DCW = diagonal conducting walls D V = voltage drop in consolidation circuits, V F(N) = installed volt/ampere factor of consolidation circuits for N consolidated electrodes, unitless / = cur rent, A n = number of electrodes shorted by slag TV = number of consolidated electrodes SCR = silicon controlled rectifiers V = voltage, V VF = Faraday voltage, V a = coupling impedance parameter (stiffness parameter), Q rj = efficiency

Effect of velocity profile models on the gasdynamic voltage drop in open-cycle mhd generators

In MHD generator channels, the actual gas flow is often approximated by a certain hydraulic flow model which requires an appropriate empirical velocity profile model. The existence of a general 1/m-power law for the velocity profile with m varying from 6 to 8 in small-scale MHD generator channels has been discussed. The effect of change in m giving rise to various velocity profiles on the gasdynamic voltage drop has been studied. It is found that the gasdynamic voltage drop is affected considerably by changing the power law for the velocity profile, demanding an appropriate velocity profile model for the analysis of data.

The preparation and properties of strontium zirconate ceramics for channels of open-cycle MHD generators

A two-stage procedure of preparation of dense strontium zirconate ceramics capable of being used as electrically insulating material in MHD generators is described. A small addition of TiO 2 was introduced at the first stage to favour development of the properties, especially low apparent porosity, required for MHD purposes. The effect of TiO 2 on sintering temperature, phase composition and microstructure of the bodies is described. Properties of the resulting ceramics i.e. porosity, cold crushing strength, microhardness as well as electrical conductivity over the temperature range of 20–2000°C were measured. The results of successful testing of these ceramics in the channel of an experimental MHD generator are presented.

Electrical conductivity of a seeded H2/O2 system

A H2/O2 system is suggested as a working fluid for an open-cycle MHD generator, and the conductivity of seeded combustion products of such a system has been investigated.

Transient Characteristics of Constant Velocity Faraday-Type MHD Generator

Transient characteristics of an open-cycle constant velocity Faraday-type MHD generator comparable to the size of Russian U·25 (MHD Experimental Generator at the Institute for High Temperatures, Moscow) are presented. Transient responses to start-up, shutdown and load changes of a subsonic MHD generator are numerically calculated solving unsteady magnetohydrodynamic equations. Results show that the MHD generator can attain another steady state within ten times the gas residence time for most of load changes. When loads locally change, shock waves occur to cause considerable fluid property change. The most dangerous transient characteristics are due to very large transient Hall fields at the start-up, which leads to breakdown between adjacent electrodes, particularly, the down-stream region of the generator. For local short-circuiting or load changes throughout the generator, no serious problems arise except for those associated with current density increase.

An investigation for minimum dimensions of oil‐fired MHD generator duct

The performance parameters for the open-cycle oil-fired MHD generator were examined. Those which minimize the generator duct length were numerically calculated. The analysis was made for both the constant-flowrate and the constant-Mach-number MHD generator ducts. The constant-Mach-number duct was found to have a shorter length, smaller variation of the optimum value with respect to the operating condition and a larger ratio of the cross-sectonal area between inlet and outlet. To limit the duct length to 15 m, it was found necessary to raise the magnetic field intensity by 1.73 times or to increase the conductivity of the fluid by 3 times. Since the heat loss from the duct wall in the 1000 MW generator was above 30% of the heat input, it was found necessary to improve the properties of the semi-hot wall to realize the MHD generator with high efficiency.

Transient Characteristics of Constant Velocity Faraday-Type MHD Generator

Transient characteristics of an open-cycle constant velocity Faraday-type MHD generator comparable to the size of Russian U·25 (MHD Experimental Generator at the Institute for High Temperatures, Moscow) are presented. Transient responses to start-up, shutdown and load changes of a subsonic MHD generator are numerically calculated solving unsteady magnetohydrodynamic equations. Results show that the MHD generator can attain another steady state within ten times the gas residence time for most of load changes. When loads locally change, shock waves occur to cause considerable fluid property change. The most dangerous transient characteristics are due to very large transient Hall fields at the start-up, which leads to breakdown between adjacent electrodes, particularly, the down-stream region of the generator. For local short-circuiting or load changes throughout the generator, no serious problems arise except for those associated with current density increase.

Simplified theory of nonuniform electrical conduction for an open cycle MHD generator with shaped magnetic induction

Simplified formulae were derived for the approximate evaluation of electrical performances of an MHD generator with nonuniform equilibrium plasma. In order to clarify the effectiveness of the propperly shaped nonuniform magnetic induction of type B ∞ n e , the transverse component B y was included in the formulation of the theory. It was shown that the terminal characteristics of the generator, such as the internal resistance, the motional emf, the current and the output power could be improved significantly under the shaped B z ∞ n e type of applied magnetic induction for wide ranges of electrodeand insulator wall temperatures, channel sizes and averaged intensities of the magnetic induction.