Search

This paper presents a steady-state performance analysis of a stand-alone three-phase induction generator selfexcited with unbalanced capacitances and supplying unbalanced loads. Using the method of symmetrical components, the complex three-phase generator-load system is reduced to a simple equivalent passive circuit. A function minimization technique is employed to solve this equivalent circuit in order to determine the excitation frequency and magnetizing reactance. The proposed method enables practically all cases of unbalanced operation of the self-excited induction generator to be analyzed. Emphasis is next focused on single-phase loads and a special phase-balancing scheme, namely the modified Steinmetz connection (MSC), is investigated. It is shown that perfect phase balance of the SEIG can be obtained with an appropriate combination of excitation capacitances and loads. The theoretical analysis is validated by experiments on a 2.2 kW induction machine. Index Terms--Induction generators, phase balancing, Steinmetz connection.

By applying a radio-frequency (RF) electromagnetic field, the feasibility of improvement in the performance of a nonequilibrium disk-shaped magnetohydrodynamic (MHD) generator suffering from water vapor contamination in the working gas is investigated with [Tau]-[Theta] two-dimensional numerical simulations. Attention is paid to the relation between the behavior of MHD plasma in the presence of the RF electric field and the generator performance. The water contamination causes the strongly nonuniform and unsteady plasma, and deteriorates its performance. The fluctuations of the electron temperature and of the ionization degree of seed atoms are found to be suppressed by applying the RF electric field. As a result, the enthalpy extraction ratio and the isentropic efficiency of the generator improve. The ratio of the required additional joule heating by the RF electric field to the thermal input to the generator for the stabilization of the plasma and the improvement in the performance is estimated to be about 0.9%. Index Terms - Additional joule heating, inductively coupled plasma, nonequilibrium magnetohydrodynamic generator, water vapor contamination.

Isentropic efficiency of the nonequilibrium MHD power generator was studied by a shock tube driven disk generator. Cesium seeded helium was used as a working gas. From the measurements of Faraday current density distribution, it was possible to estimate the general tendency of Joule dissipation in the generator. The Joule dissipation did not decrease due to the occurrence of nonuniformity of the plasma when external load resistance was low, although it decreased with the decrease in the load resistance when the load resistance was high. The electrical efficiency increased with the increase in applied magnetic flux density. This fact is thought to be caused by high Hall parameter and the stabilization of the plasma due to high degree of seed ionization. Index Terms - Disk generator, high enthalpy extraction, isentropic efficiency, Joule dissipation, MHD power generation, nonequilibrium plasma.

In the present work, a time-dependent two-dimensional model based on a pressure scheme is presented. It is able to take real gas thermodynamics and loss mechanisms due to friction, heat transport, and turbulence into account. The MHD generation in a current-carrying nonuniform (STCC) regime has been studied by means of it. In order to see what the effects of the loss mechanisms on the STCC-MHD generation are, the results of three different approximations are compared. In the first case, the model analyzes the MHD operation in an ideal gas approximation without losses. In the second case, the ideal gas with losses is studied. In the last one, a combustion gas with loss mechanisms is considered. In all three cases, the same starting conditions and boundary conditions are assumed. Passing from the first to the second case, a reduction of the electrical power output of 20% is calculated. In the third case, with similar plasma conditions, small differences of the power output are obtained. In this case, the energy needed for the formation of the plasma nonuniformity results to be much larger than the energy used in the ideal gases. This is due to the specific heat of the combustion gas, which increases with the temperature. Index Terms - MHD generators, numerical analysis.

The IEEE Chinese Academy of Sciences has been developing a superconducting magnet system for MHD propulsion research. The large bore dipole magnet has a 205 mm inner diameter and a 60-degree circular saddle layer wound with 4T design central field and 830 mm length. The cryostat is 1,390 mm high, 1,300 mm long and has an outer diameter of 650 mm. It features a superconducting switch and a removable current lead.

The isentropic efficiency and the effective Hall parameter in a nonequilibrium disk MHD generator have been successfully evaluated on the basis of the experiments under high enthalpy extraction conditions. Special attention is devoted to measuring the exit total pressure and the Faraday current. The maximum isentropic efficiency achieved in the present experiments was 46% with the enthalpy extraction ratio of 31.6%. The experimentally obtained values of the effective Hall parameter covered a range of 2-3.

A numerical experiment in a plasma vane (current carrying plasma nonuniformity) MHD generator is presented. The numerical calculations are based on a time-dependent two-dimensional model. The gas constituting the plasma is assumed to be ideal. Viscosity and heat losses are neglected. In order to optimize the generator performance, a parametric analysis is carried out. The results of the calculations indicate that enthalpy extractions larger than 30% can be obtained.

Two dimensional calculations were carried out to clarify the behavior of boundary layer and its effects on performance of closed cycle MHD (CCMHD) generator and to investigate the relation between enthalpy extraction ratio and adiabatic efficiency. Calculation results suggest that the large Lorentz force causes propagation and separation of boundary layer where reverse current flows, because of small electromotive force. For large load resistance boundary layer becomes very thick and the eddy current arises in broad region. The push work of working gas against Lorentz force is effectively converted into electric energy under the condition at which the Lorentz force decelerates the working gas to Mach number in the range between 1.0 and 1.5 in this case of the generator. Stagnation pressure loss increases with load resistance until enthalpy extraction ratio takes maximum value. The entropy production due to Joule heating and viscosity increases with load resistance. The difference between the load resistances for which the enthalpy extraction ratio and the adiabatic efficiency take maximum value can be explained with the entropy production of Joule heating and viscosity.

The change in the circuit inductance of a pulsed MHD generator as the plasma sheet travels along the electrodes acts to increase the voltage produced in the generator. The paper explains how unconventional electrode arrangements enable this effect to be significantly magnified, thereby bringing about a considerable increase in the output that can be obtained.

A coupled electromagnetic and nonlinear structural analysis of a 4.5 tesla superconducting MHD dipole magnet is presented. The magnet design combines the latest in cable-in-conduit conductor (CICC) technology, a novel quasi-momentles support configuration, and finite element modeling to demonstrate the viability of this retrofit magnet concept. With the conductor participating as a major structural element, the support system is greatly simplified, and the overall cost and risk of the magnet system is reduced. Two and three-dimensional models are used to evaluate the concept and demonstrate how the full simulation is accomplished in one ANSYS computer run.

A saddle superconducting magnet for experimental MHD generator has been designed, constructed and tested. The magnet has [Phi] 44 cm warm bore, 103 cm effective magnetic length and 4 T central field. It consists of 17 layers, each layer has two circular saddle coils with 54.5 [degrees] segment cross section. The conductor is 2 mm X 10 mm NbTi monolithic provided by Supercon Inc.. The coils are assembled on the bore tube by spiral bandings. The performances and the test results of the saddle superconducting magnet will be presented in this paper.

The paper illustrates the activities developed in the frame of the Progetto Finalizzato 'Superconducting and Cryogenic Technologies: superconducting magnets for MHD'. The main objectives of the research activities are: the design and the construction of a superconducting prototype magnet (2m active length), and the reference design of a superconducting demonstrative magnet (8m active length), both for MHD applications. The magnets are designed to produce a 5T on axis field with 5% and 10% field uniformity in the cross section respectively, and with a field taper less than 0.15 T/m. The design and construction of high field superconducting magnets based on A15 materials is also developed. The study of commercial size MHD superconducting magnets (16 m active length), and the conceptual design of superconducting magnets for disk MHD generators are also included in the frame of the project.

In this paper the authors analyse the performance of a magnetohydrodynamic (MHD) linear generator excited by means of various saddle shaped superconducting (sc) coils. In particular the device has been excited using: a prototype magnet, a demonstrative magnet and a commercial size magnet. The various magnet shape and size determine a quite different distribution of the magnetic flux density along the channel. To show the effects of the magnetic field shape on the device behaviour, we have simulated the fluid by means of a three-dimensional (3D) lumped parameter network representative of all major physical phenomena. The equivalent network has been determined using an innovative approach with respect to the parameter evaluation. The reliability of the proposed model has been verified using experimental data. The aim of this paper is to show the importance of the device simulation in the magnet optimization design to quantify the effects of a non homogeneous magnetic field.

In this paper, the problem of power waveform synthesis using the PASC technique to produce a desired output from a single dc source is introduced. Although the specific example discussed here is for a diagonally connected magnetohydrodynamic (MHD) generator, the technique can be applied to any single terminal pair source, with appropriate modification in power extraction interface and computer control program to match source and load impedance characteristics. The method as discussed here, employs banks of pulse transformers, one bank per phase, in which the primaries are connected in parallel through a switch matrix to the dc source and two opposite polarity primaries per transformer are pulsed alternatively in time to produce an oscillatory output waveform. The timing sequence in which the primaries are injected with power from the source under switch control determines the resulting ac waveform. If a repetitive mono-polarity pulse waveform is desired, a capacitive interface network is used since it can support an average dc output component. The PASC process utilizes a switching array to connect/disconnect one or more dc sources in an overlapped fashion under computer actuation, along with error output signal feedback, to generate the control necessary to match the desired waveform as specified in the computer. The principal benefit of this system for the single output source diagonal MHD generator is that quantized sinusoids can be generated having low harmonic content and power factor control without the need for large and expensive filtering and VAR compensation such as is required for conventional inverters. After an introduction to the converter system topology for a single dc source along with the transformer representation employed, the simulation results for two and eight level PASC inverter systems are presented. Results for triangular synthesis and sinusoidal synthesis simulations are given for different load impedance to source impedance ratios. As expected the results indicate strong dependence on source impedance if the load to source impedance is not large. Uncontrolled output waveform results show very small total harmonic distortion.

This paper summarizes preliminary experimental and theoretical research that was directed toward the study of quasi-steady-state power flow in a large, unoptimized, multimegawatt coaxial plasma thruster. The paper addresses large coaxial thruster operation and includes evaluation and interpretation of the experimental results with a view to the development of efficient, steady-state, megawatt-class magnetoplasmadynamic (MPD) thrusters. Experimental studies utilized the Coaxial Thruster Experiment (CTX) facility at the Los Alamos National Laboratory. The unoptimized thruster, 1 m in length with inner and outer tungsten-coated electrode diameters of 0.37 and 0.56 m, respectively, was operated over a range of peak power levels (nominally 10-40 MW) in order to ascertain high-power performance scaling. In addition to pure self-field operation, an unoptimized applied magnetic field configuration, with adjustable flux densities, was used to form a rudimentary, annular magnetic nozzle. In this initial research, an accurate power balance was precluded due to the lack of spatial resolution of power deposition on the electrodes. However, the data, together with a calorimetric IR data reduction algorithm, did quantify energy flux deposition on electrode surfaces and provided a qualitative picture of global power flow and thruster performance. Highlights of this study include the observations that the measured longitudinal flow velocity of the propellant was in essential agreement with the prediction of self-field nozzle theory, achieving Alfvenic flow velocities of approximately equal to 10 to the fifth power m/s. Furthermore, radiative emission was a negligible power loss mechanism (

The problem of consolidating and inverting a number of dc sources is common in interconnecting arrays of batteries, fuel cells, solar cells, multi-electrode pair magnetohydrodynamic (MHD) generators, etc. This paper describes a general technique for performing such power processing when applied to the specific example of consolidation followed by three phase inversion, of a number of dc sources produced by a Faraday connected MHD generator. The method, as implemented in this paper, employs banks of pulse transformers, one bank per phase, in which the secondaries of each transformer have been connected in series and two opposite polarity primaries are pulsed from the dc sources. The sequence in which the primaries are pulsed determines the shape of the resulting ac waveform. The process, or method is called PASC for Pulse-Amplitude-Synthesis-and-Control, and utilizes a switching array to connect/disconnect one or more dc sources in an overlapped fashion under computer actuation, along with error output signal feedback, to generate the control necessary to match the desired waveform as specified in the computer. Although the principle benefit of this system is consolidation of diverse and isolated dc sources, it is shown that quantized sinusoids can be synthesized with low harmonic content precluding the need for expensive and inefficient filtering such as is required by conventional static inverters. A prototype single phase, 24 kVA, eight transformer system has been built and extensively tested. This system is described and representative experimental results are shown.

Given due consideration to the increasing use of Self Excited Induction Generators (SEIGs) in isolated power plants, an attempt is made to effect suitable design modifications in standard induction motor to improve its performance as SEIG. This paper explores the theory behind such improvements and sets the concept of voltage regulation in SEIG. Typical results of the sensitivity studies performed are presented and inferences are drawn to suggest guidelines for real design problem of such generators.

MAGNETOHYDRODYNAMIC (MHD) PROPULSION: USING MHD PROPULSION TO PROPEL A VESSEL. WILLIAM PANNELL Hollywood has glamorized the use of magnetohydrodynamic propulsion, but is it really possible? This project highlights the Lorentz [...]

Compact stellarator designs with modular coils and only two or three field periods are now available; these designs have both good stability and quasiaxial symmetry providing adequate transport for a magnetic fusion reactor. If the bootstrap current assumes theoretically predicted values a three field period configuration is optimal, but if that net current turns out to be lower, a device with two periods and just 12 modular coils might be better. There are also attractive designs with quasihelical symmetry and four or five periods whose properties depend less on the boot-strap current. Good performance requires that there be a satisfactory magnetic well in the vacuum field, which is a property lacking in a stellarator-tokamak hybrid that has been proposed for a proof of principle experiment. In this paper, we present an analysis of stability for these configurations that is based on a mountain pass theorem asserting that, if two solutions of the problem of magnetohydrodynamic equilibrium can be found, then there has to be an unstable solution. We compare results of our theory of equilibrium, stability, and transport with recently announced measurements from the large LHD experiment in Japan.

We present the structures of nonequilibrium-seeded plasmas in a closed-cycle magnetohydrodynamic generator. The features of cesium-seeded helium plasmas and cesium-seeded argon plasmas created in a swirl-flow mode operation are examined. The transition of the plasma-fluid structure controlled by seeding is closely coupled with the plasma stability and the flow configuration. Index Terms--Magnetohydrodynamic generator, plasma structure, swirl-flow mode.