Showing papers on "Magnetic circuit published in 1992"

Plasma accelerator with closed electron drift

Abstract: The closed electron drift plasma accelerator comprises an annular ionization chamber, an acceleration chamber on the same axis as the ionization chamber, an annular anode, a hollow cathode, a first DC voltage source, an annular gas manifold, a magnetic circuit, and magnetic field generators. A coaxial annular coil is placed in the cavity of the ionization chamber, is provided with bias conductive cladding connected, together with the electrically-conductive material of the inside faces of the walls of the ionization chamber, to the positive pole of a second voltage source whose negative pole is connected to the anode, and constitutes an additional magnetic field generator which, together with the other magnetic field generators, forms a magnetic field having a magnetic line of force with an “X” point corresponding to a magnetic field zero situated between the coaxial annular coil and the anode.

Finite element analysis in electromagnetic systems-accounting for electric circuits

Abstract: Two approaches for the numerical simulation of electromagnetic systems, accounting for electric circuit equations, are presented. First, the indirect coupled model, which permits the simulation of synchronous machines fed by controlled inverters with moderate calculation time is considered. Second, a direct coupled model where the magnetic and electric circuit equations (2-D or 3-D) are solved simultaneously is developed. This approach takes more calculation time but gives more precision. Applications concerning several electromagnetic systems are treated, and numerical results are compared with experimental ones to verify the validity of the models. >

Different finite element formulations of 3D magnetostatic fields

Abstract: Several finite-element formulations of three-dimensional magnetostatic fields are reviewed. Both nodal and edge elements are considered. The aim is to suggest remedies to some shortcomings of widely used methods. Various formulations are compared based on results for Problem No. 13 of the TEAM Workshops, a nonlinear magnetostatic problem involving thin iron plates. >

Models for induction machines with magnetic saturation of the main flux path

Abstract: A novel nonlinear pi -model for an induction machine operating in magnetic saturation has been developed. It is based on a magnetic circuit model of a rotor-stator tooth pair, with nonlinear elements representing the saturation in the rotor and in the stator. The model of a tooth pair is extended to a model of the machine by assuming an infinite number of infinitesimal teeth. The model is compatible with the Blondel-Park transformation. Experimental measurements on a wound rotor machine confirm the model. Operating conditions for optimal efficiency at high torque levels requiring operation in saturation are computed with the model. >

The bearingless electrical machine

Abstract: Electromagnetic bearings allow the suspension of solids. For rotary applications, the most important physical effect is the force of a magnetic circuit to a high permeable armature, called the MAXWELL force. Contrary to the commonly used MAXWELL bearings, the bearingless electrical machine will take advantage of the reaction force of a conductor carrying a current in a magnetic field. This kind of force, called Lorentz force, generates the torque in direct current, asynchronous and synchronous machines. The magnetic field, which already exists in electrical machines and helps to build up the torque, can also be used for the suspension of the rotor. Besides the normal winding of the stator, a special winding was added, which generates forces for levitation. So a radial bearing, which is integrated directly in the active part of the machine, and the motor use the laminated core simultaneously. The winding was constructed for the levitating forces in a special way so that commercially available standard ac inverters for drives can be used. Besides wholly magnetic suspended machines, there is a wide range of applications for normal drives with ball bearings. Resonances of the rotor, especially critical speeds, can be damped actively.

Computation of 3-D magnetostatic fields using a reduced scalar potential

Abstract: Some improvements to the finite element computation of static magnetic fields in three dimensions using a reduced magnetic scalar potential are presented. Methods are described for obtaining an edge element representation of the rotational part of the magnetic field from a given source current distribution. When the current distribution is not known in advance, a boundary value problem is set up in terms of a current vector potential. An edge element representation of the solution can be directly used in the subsequent magnetostatic calculation. The magnetic field in a DC arc furnace is calculated by first determining the current distribution in terms of a current vector potential. A 3-D problem involving a permanent magnet as well as a coil is solved, and the magnetic field in some points is compared with measurement results. >

A general purpose method for electric and magnetic combined problems for 2D, axisymmetric and transient systems

Abstract: The non-linear analysis of electrical devices is often limited by the complexity of the power supply. In effect, in the case of solid conductors, the voltage is required, while in the case of stranded conductors the current must be known. These restrictions are due to the nature of the field equations. A new formulation is proposed which allows the possibility to choose the power supply and choose any kind of connection between components. Two types of 'magnetic conductors' are considered: solid conductors, in which eddy current be induced and stranded conductors without eddy current. An equation combining the magnetic potential, the current and the voltage is established for each conductor. This equation is introduced into a conventional circuit analysis method. The magnetic field and circuit equations can be solved simultaneously in the resulting system. An implicit method is used to dicretize the equations in time. A Newson-Raphson linearization algorithm is used to handle problems that include materials with non-linear properties. This formulation is used in the commercial program FLUX2D. To illustrate one of the many applications, an A.C. electromagnet is studied.

Power generating apparatus

Abstract: An a.c. generator having a stator including an armature core and a polyphase output winding wound around the armature core. A plurality of rotors mounted on a rotary shaft to establish a first and a second field magnetic circuits are arranged in parallel with respect to the armature core. The first field magnetic circuit includes permanent magnets acting as a source of exciting magnetomotive force, while the second field magnetic circuit includes a field winding acting as a source of exciting magnetomotive force. The magnetic fluxes generated from the first and second field magnetic circuits penetrate the armature core inducing an output voltage across the polyphase output winding. The magnetic flux from the second field magnetic circuit is changed so as to increase or decrease the total magnetic flux penetrating the armature core thereby controlling the induced output voltage.

Characteristics and analysis of a thin film inductor with closed magnetic circuit structure

Abstract: A spiral inductor with closed magnetic circuit was fabricated by an RF sputtering machine and photolithography techniques. The inductance was twice as large as that of a reference sandwiched inductor. The authors analyzed the frequency characteristics of the proposed inductor from three points of view: inner current distribution, flux distribution, and eddy current in the magnetic film. The calculated results agree with the measured ones. It is demonstrated that the current distribution inside the inductors is mostly limited to within the area of the conductor up to several hundred megahertz. The frequency characteristics are influenced by the eddy current loss in the Permalloy film and the stray capacitance between the inductor and the ground plane. The permeability of the Permalloy film is less than that of its as-deposited state, but the closed magnetic circuit structure helps to reduce the influence of the demagnetizing field. >

Permanent magnet type dynamoelectric machine rotor

Abstract: A dynamoelectric machine rotor (13) comprising a plurality of substantially trapezoidal prism-shaped permanent magnets (16,17) mounted on a magnetic yoke (15). Each of the magnets (16,17) has magnetic pole faces in circumferential plane, side surfaces in a plane perpendicular to the rotary shaft (14) and a front and a rear skewed surface slanted in different directions with respect to a plane parallel to the shaft. The magnetic pole faces of the magnets (16,17) have alternating magnetic polarities in the circumferential direction, and the front and rear skewed surfaces of the neighboring permanent magnets are in parallel to each other. A ferromagnetic end material may be attached on the magnetic pole face of the magnets, and a ferromagnetic side material may be attached to at least a front and a rear skewed side surfaces of the magnets for increasing of the magnetization of the magnets by a stator flux. Also, slits may be provided in the magnetic yoke where the magnets are mounted for increasing a reluctance of a magnetic circuit passing through a common magnet.

Magnetic circuit analysis of a linear synchronous motor with permanent magnets

Abstract: The authors describe a magnetic circuit analysis of a permanent-magnet-type synchronous motor using the finite element method. The effect of the size of the permanent magnets on the static thrust characteristics is investigated, and a prototype machine is fabricated on the basis of the results. Measured values of the static thrust and normal force of the prototype machine have been compared with the calculated values obtained by the finite element method. >

Planar magnetic component technology-a review

Abstract: The materials and the fabrication of planar magnetic components for switch mode power supplies (SMPSs) and other applications are reviewed. The advantages and the disadvantages of such devices are introduced. The magnetic materials used in the devices, such as ferrite, amorphous metallic glass, and thin and thick magnetic films, are detailed. The devices have varying degrees of planarization-partially planar devices with magnetic cores and planar windings and truly planar devices for integrated magnetic circuits with planar windings and planar magnetics. Devices of both types reported in the literature since 1979 are reviewed. The design of the planar magnetic components must be optimized with respect to losses, and design issues which relate to electrical, thermal, and mechanical performance are discussed. >

Design of permanent magnet flat linear motors for standstill applications

Abstract: The authors examine planar linear permanent magnet motors and consider their operation at standstill. A method of finite element analysis (FEA) is used in which the use of several space phase-shifted force profiles accounts for the machine skew. The origin of the cogging forces, namely tooth and finite stator length effects, is explained. Results are given from a large experiment rig. It is shown that both cogging and electromagnetic forces compare well with the FEA. The authors conclude with a design survey using simple magnetic circuit theory considering the application of both NdFeB and ferrite magnets. Points on the graphs are validated by the FEA. >

A non-linear coupled 3D model for magnetic field and electric circuit equations

Abstract: The authors propose a 3-D numerical model in which the magnetic field and electric circuit equations in the absence of eddy currents are solved simultaneously. To consider the magnetic equations, use is made of a magnetic vector potential formulation with the gauge condition (A.w=0) which makes it possible to reduce the number of unknowns. To take into account the magnetic and electric nonlinearities, the Newton-Raphson algorithm has been used. Two applications have been considered: an iron core coil fed by sinusoidal voltage through a diode and a current transformer. For the latter example the results obtained from the simulation are compared with experimental ones. >

A fully integrated micromagnetic actuator with a multilevel meander magnetic core

Abstract: To generate and to confine a magnetic flux in the magnetic core and at the same time minimize coil series resistance, low-resistance meander conductors located in a single plane were interwoven with multilevel meander magnetic cores. This 'wrapped' solenoid (with the core wrapped around the conductor) was fabricated in a fully integrated fashion. A micromagnetic actuator was realized by incorporating a surface micromachined nickel-iron cantilever beam as part of the magnetic circuit of the core. The nickel-iron cantilever beam was 2.5 mu m thick, 25 mu m wide and 780 mu m long, and the magnetic circuit contained 17 turns of meander type solenoid coils. Tip deflection of 4 mu m in the vertical direction was achieved when a DC voltage less than 1 V (and resulting drive current of 600 mA) was applied to the coils. This fully integrated multilevel topology offers a variety of micromagnetic applications, which can be fabricated on the same substrate with an integrated circuit and actuated with low voltages. >

Linear electrodynamic machine

Abstract: A linear electrodynamic machine is disclosed having non-axisymmetric, interdigitating interfaces between moving and fixed magnetic circuit elements. The moving magnet elements may be of permanent magnet or electromagnetic construction, and in one embodiment constitute low reluctance elements moving relative to fixed energizing and output coils. Magnetic elements on a reciprocating plunger couple to fixed elements of a magnetic circuit in an interdigitating manner. Alternators and motors with non-axisymmetric, interdigitating interfaces are disclosed.

Computation of load performance and other parameters of extra high speed modified Lundell alternators from 3D-FE magnetic field solutions

Abstract: A combined magnetic vector potential, magnetic scalar potential method of computation of 3-D magnetic fields by finite elements, in combination with state modeling in the abc frame of reference, is used for global 3-D magnetic field analysis and machine performance computation under rated load and overload condition in an example 14.3 kVA modified Lundell alternator. The results vividly demonstrate the 3-D nature of the magnetic field in such machines and show how this model can be used as an excellent tool for computation of flux density distributions, armature current and voltage waveform profiles, and harmonic contents, as well as for computation of torque profiles and ripples. Use of the model in gaining insight into locations of regions in the magnetic circuit with heavy degrees of saturation is demonstrated. Experimental results which correlate well with the simulations of the load case are given. >

Finite element simulation of electrical motors fed by current inverters

Abstract: A method of examining electric machines coupled to static converters represented by a finite-element and a circuit type model is presented. This technique, based on a step-by-step process with respect to time for the simultaneous solution of the electrical circuit and electromagnetic field equations, is used for the working analysis of two permanent-magnet motors fed by a load commutated current inverter. The calculation and experimental results are compared in order to validate the proposed method. >

Magnetic reproducing head having a distributed-constant circuit type magnetic field detector

Abstract: A distributed-constant circuit type magnetic field detector which includes a magnetic member whose permeability varies with changes in a magnetic field applied thereto disposed at a point where a magnetic field is produced in a distributed-constant circuit excited with an electromagnetic wave and a detector for detecting a change in electromagnetic field distribution in the distributed-constant circuit produced by a variation in permeability of the magnetic member upon application thereto of a magnetic field to be detected.

A combined finite element-state space modeling environment for induction motors in the ABC frame of reference: the blocked-rotor and sinusoidally energized load conditions

Abstract: The combined finite element-state space (CFE-SS) modeling environment was used to predict the performance of a 1.2 hp, three-phase case-study squirrel cage induction motor under blocked rotor and typical load operating conditions. The nature of this CFE-SS environment allows one to rigorously account for the impact of space harmonics generated by the magnetic circuit, winding, and cage geometric, as well as layout peculiarities and magnetic saturation, on the current and torque profiles, and ohmic losses in the stator armature and cage. This includes the ability to predict the profiles of connector and bar currents. The results of the CFE-SS simulations compare favorably with blocked rotor and load experimental test data. Potential capabilities of this CFE-SS modeling environment, and its use in impacting motor design decisions, are discussed in the light of reported findings. >

Extra high speed modified Lundell alternator parameters and open/short-circuit characteristics from global 3-D-FE magnetic field solutions

Abstract: A combined magnetic vector potential, magnetic scalar potential method of computation of 3-D magnetic fields by finite elements is used for global 3-D field analysis and machine performance computations under open-circuit and short-circuit conditions for an example 14.3 kVA modified Lundell alternator, whose magnetic field is of an intrinsic 3-D nature. The computed voltages and currents under these machine test conditions were verified and found to be in very good agreement with corresponding test data. Results of the use of this modeling and computation method in the study of a design alteration example, in which the stator stack length of the example alternator is stretched in order to increase voltage and volt-ampere rating, are given. These results demonstrate the inadequacy of conventional 2-D based design concepts and the need for this type of 3-D magnetic field modeling in the design and investigation of such machines. >

An AC and DC current sensor of high accuracy

Abstract: A current sensor that can detect AC and DC currents with high accuracy of the same degree is presented. The detection characteristics are not degraded even when the sensor is exposed to large temperature variations and/or to external magnetic fields. The proposed sensor, which is named for the sensing principle it employs, will be referred to as the magnetic field controlled type or the zero magnetic field type of field and has the ability to fulfil the following specifications: (1) the sensor is a noncontacting type; (2) the operating frequency range covers from DC to several hundred hertz; (3) the dynamic range can be extended from several milliamperes to 100 A; (4) a detection accuracy of 0.01% full scale (FS) is guaranteed over the sensor's whole range; and (5) several sets of current sensor having the same detection characteristics are easily obtainable even if the B-H of the core to be used for each sensor is very different. >

Means for improving the opening response of a solenoid operated fuel valve

Abstract: Because of inherent delay in magnetic flux propagation in the magnetic circuit, the transient opening magnetic force on the armature does not build as rapidly as the injector driver circuit may be capable of commanding. This transient force is augmented without increasing the package size of the magnetic circuit. A fuel injector has a novel solenoid actuator magnetic circuit that has slots, convolutions, or the like dispersed in the surface of the magnetic circuit to provide increased surface area on the magnetic circuit in the direction of the lines of flux generated when the solenoid is energized along a path to the magnetic gap without increasing the overall size of the magnetic circuit. This increased surface area for the skin provides increased flux paths in the magnetic gap during the transient build-up of magnetic force across the gap, thereby improving the response of the armature upon opening. The slots/convolutions themselves and, especially, a novel arrangement of the slots/convolutions provide a resistivity increasing means for increasing the resistivity of the magnetic circuit by increasing the path length of the eddy currents that flow normal to the lines of flux in the magnetic circuit.

Faraday effect continuous circuit flux concentrating magnetic field sensor

Abstract: A general-purpose magnetic field sensor capable of sensitively measuring uniform magnetic fields includes a magneto-optic (Faraday-effect) sensor and a flux concentrator. Both the magneto-optic sensor and the flux concentrator have high magnetic permeability. The magneto-optic sensor is positioned in close proximity to the flux concentrator. The combination of the high-permeability magneto-optic material and the flux concentrator creates a magnetic circuit which efficiently concentrates the magnetic field into the magneto-optic sensor, and greatly enhances the measurement sensitivity. The preferred embodiment uses a pair of cylindrical flux concentrators in axial alignment. A sensing beam passes through a central axis hole in the cylindrical flux concentrators. The Faraday effect sensor is co-axially aligned with the holes in the cylindrical flux concentrators. The concentrators and Faraday effect sensor create a continuous flux concentrating magnetic circuit.

Circuitry changing or compensating electrical properties of current converter with magnetic field compensation - contains prim., sec. and measurement coils on core, Hall element in air gap feeding compensation current source controller

Abstract: The circuit contains a primary coil on the core (2) of a magnetic circuit with an air gap and switchable into a line carrying the measurement current. A secondary compensation coil (5), with an order higher winding count and mounted on the core, is connected to the output of a controllable compensation current source (6). The output of a Hall element (11) in the air gap is connected to the control input of the compensation source. A further coil (14) on the core is connected to an additional controllable current generator (15) whose control input (16) is driven by a measurement device (13) for the compensation current via a control and evaluation circuit (17). USE/ADVANTAGE - Measuring a.c. and d.c. Can be produced at low cost and all drift occurring during measurement can be compensated.

Analysis of a circuit breaker solenoid actuator system using the decoupled CAD-FE-integral technique

Abstract: A decoupled three-dimensional CAD (computer-aided-design) finite-element-integral method, combined with the Runge-Kutta method, is offered to determine the dynamic characteristics and design requirements of a circuit breaker solenoid actuator, when energized from a DC supply. The model couples the electric, magnetic, and mechanical systems of the device. The presented solution takes account of the nonlinear magnetic material properties, the dimensions of the magnetic circuit, the coil parameters, and load of the trip mechanism system. The predicted dynamic characteristics from the analysis correlate closely with the results from the test performed on the actuator and demonstrate the applicability of the proposed techniques to the optimization of circuit breaker actuator performance and electromagnetic solenoid design. >

Variable reluctance integral bearing sensor

Abstract: An integral variable reluctance sensor and bearing grease seal assembly (sensor assembly) has at least one magnet and an annular wire coil secured at the interior of a housing which seals an annular space between a dynamic inner race and a static outer race. The sensor assembly is characterized by a relatively large flux change and resulting large peak to peak periodic output due to exploitation of the outer race and housing as high permeance flux paths in the sensor magnetic circuit and an additive arrangement of plural magnets. Sensor output signal strength is variable in step with the number of magnets and output variations due to air gap variations are minimized by symmetrical distribution of the same. The sensor assembly is further characterized by a single dynamic seal and no moving parts.

Current sensor using a resonance directional magnetometer

Abstract: A current sensor using a resonance directional magnetometer which includes a magnetic circuit having a gap and a device supplying a voltage representative of a magnetic field produced in the gap by a current when the current passes through the circuit. The value of the field is a function of the intensity of the current. The device is a resonance directional magnetometer having a sample with resonant spins placed in the gap and exposed to a magnetic field having a polarization parallel to the field produced in the gap or coinciding with this field and a measuring device for exciting the resonance and detecting the excited resonance and for supplying a voltage representative of the amount of excited resonance.

Apparatus for testing documents having magnetic properties

Abstract: In an apparatus for testing test objects equipped with magnetic properties, the magnetic circuit with an air gap having a detector consists of at least a soft-magnetic material and a permanent-magnetic material, whereby the static magnetic field produced by the permanent-magnetic material penetrates the magnetic circuit. The air gap is preferably formed between an end of the soft-magnetic material and a pole of the permanent-magnetic material.