S. Salon

Applications of the hybrid finite element-boundary element method in electromagnetics

The concept of combining the finite-element method with the boundary-element method for electromagnetic problems is introduced. The general equations are derived, and examples are given for a number of two- and three-dimensional cases. These include both static and time-varying problems. >

The mutual inductance of two thin coaxial disk coils in air

This paper presents an efficient method for computing the mutual inductance between two thin coaxial disk coils in air. The derived principal semi-analytical expressions involve complete elliptic integrals of the first and second kind, Heumans Lambda function and three terms that have to be computed numerically. The presented method is compared to the filament method where both conductors are approximated by Maxwells filamentary coils. The mutual inductance values (for a chosen case) computed by both methods are in good agreement. However, the method presented in this work exceeds by far the filament method in its precision and computational efficiency. In another example, the computed mutual inductance is validated by measurement.

Coupling of Transient Fields, Circuits, and Motion Using Finite Element Analysis

The transient analysis of a coupled electro-mechanical system is undertaken. The system consists partly of spatial regions, which may support magnetic fields, that are modelled by finite elements. The regions may be attached to external electrical sources and circuits, and may also be capable of rigid body motion with respect to one another. A method for coupling the electric circuit transient equations, transient magnetic field finite element equations, and the transient mechanical motion equations is described. Only the external source variation is assumed to be known; all other field, circuit, and mechanical motion quantities are treated as unknowns and calculated. Equations for transient analysis of a general, 2-dimensional, planar, non-linear, voltage-excited system are derived in detail. The Galerkin formulation, time-discretization, and linearization of these equations are presented. The resulting global system of coupled electro-mechanical equations is assembled and investigated. Included are exam...

Internal faults in synchronous machines. I. The machine model

This paper discusses the construction of a mathematical model of a large synchronous machine suitable for analyzing internal phase and ground faults in stator windings. The method employs a direct phase representation, and uses conventional, and readily available, machine data. The methodology was validated by comparison with results obtained from independent finite element analyses.

Partitioning of synchronous machine windings for internal fault analysis

This paper discusses a technique for partitioning the stator windings of large synchronous machines, for application to internal fault analysis, and determining corresponding winding inductances. The method employs a direct phase representation, which is shown to reduce to the classical phase representation when the partitioned windings are collapsed.

New procedures for calculating the mutual inductance of the system: filamentary circular coil-massive circular solenoid

New and fast procedures for calculating the mutual inductance between a thin circular filament coil and a massive circular solenoid in air are presented. The coils are axisymmetric. These results are expressed over the complete elliptical integrals of the first and second kind, Heumanns Lambda function, and one term that has to be solved numerically. The numerical integration of this term is based on some numerical integrations to get the satisfactory accuracy and computational cost. These new expressions are accurate and simple to apply for useful applications. Also, another comparative method based on an approximation of the massive solenoid by Maxwells coils is given. The paper discusses the computational cost and the accuracy. Results obtained by the two approaches are in excellent agreement.

Calculating the external magnetic field from permanent magnets in permanent-magnet motors-an alternative method

We present an alternative method for calculating the magnetic field from a set of permanent magnets in a permanent-magnet motor. The method uses a cylindrical coordinate system to model the geometry of the structure enclosing the magnets. A Fourier series expansion yields an alternative to the more familiar multipole expansion given in spherical coordinates. The expansion is developed by using Greens function in cylindrical coordinates. A technique called charge simulation allows computation of an equivalent point charge distribution. Finally, Coulombs law is applied to express the magnetic scalar potential in a mathematically tractable form.

Nonlinear 3D magnetostatic field calculation by the integral equation method with surface and volume magnetic charges

The authors present a mathematical model for the 3-D nonlinear magnetostatic field based on integral equations with fictitious surface and volume magnetic charges. The solution is performed by the extended boundary element method including surface elements and volume elements. Examples of calculation for both linear and nonlinear magnetic systems are presented. The method has been shown to be accurate and efficient. >

Internal faults in synchronous machines. II. Model performance

For pt.I see ibid., vol.15, no.4, p.376-9 (2000). This paper applies techniques for analyzing internal phase and ground faults in the stator windings of large synchronous machines. A variety of internal fault conditions are considered, with results for a 75% ground fault presented, along with comprehensive data for a test machine. The methodology is validated by comparison with results obtained from independent finite element analyses.

Effects of slot closure and magnetic saturation on induction machine behavior

Reduction of the permeance variations due to slot openings can be achieved through the use of closed or semi-closed slots or magnetic slot wedges. A complete transient finite element model analyses the effects of slot closure in an induction motor. The analysis of the air gap flux density and magnetic force waves determined by the finite element model reveals two effects of stator slot closure: (a) a reduction of those flux density and force waves generated by stator slotting, which was expected, and (b) an increase in the amplitude of the flux density and force waves originating from saturation. >