Thorsten Steinmetz

Electro-quasistatic field simulations based on a discrete electromagnetism formulation

A finite-element formulation based on a discrete electromagnetism is developed to simulate electro-quasistatic fields on unstructured meshes. The presented formulation takes dielectric effects into account as well as nonlinear conductive effects. The implementation is based on discrete differential forms on an unstructured 3-D mesh. Numerical results of the simulation of a three dimensional high-voltage surge arrester consisting of linear and nonlinear materials are shown. An algebraic multigrid method is introduced as a preconditioner to nonstandard projected preconditioned conjugate-gradient linear system solver

Electro-Quasistatic High Voltage Field Simulations of Large Scale Insulator Structures Including 2-D Models for Nonlinear Field-Grading Material Layers

Resistive field-grading material is applied to nonceramic insulators. For the design of insulator structures, these resistive field-dependent and thus nonlinear material layers are considered as 2-D layers within 3-D transient finite element method (FEM) simulations of electro-quasistatic fields. The 2-D layer modeling approach is validated and compared to conventional 3-D layer modeling for various layer thicknesses. Numerical results for realistic structures are shown herein.

Simulation and Measurement of Lightning-Impulse Voltage Distributions Over Transformer Windings

This paper presents: 1) a novel method for accurate high-frequency modeling of dry-type transformer windings based on magnetic and electric field simulations for parameter extraction of the detailed equivalent circuit of the entire winding system; 2) a method for fast and accurate transient solution of the circuit differential equations that describe the voltage distribution over the winding system; 3) an efficient, cheap, and nondestructive low-voltage measurement system based on a self-developed lightning-impulse generator; and 4) verification of the simulation results by comparison with measurement.

Electro-Quasistatic High-Voltage Field Simulations of Insulator Structures Covered with Thin Resistive Pollution or Nonlinear Grading Material

In this paper, the effect of applying a thin mu-varistor material layer to composite insulator structure is presented for the rain test. In the finite-element-method (FEM) simulations, thin resistive layers are modeled as 2D surfaces instead of 3D volume bodies which helps to avoid problems within the geometric modeling process and moreover results in less degrees of freedom. Numerical simulations with this technique are presented for high voltage insulators with nonlinear field grading materials.

Efficient Symmetric FEM-BEM Coupled Simulations of Electro-Quasistatic Fields

Electro-quasistatic as well as electrostatic simulations of 3D high-voltage (HV) technical devices are presented using a symmetric coupled formulation of both the finite-element-method (FEM) and the boundary-element-method (BEM). This formulation allows for the specification of Dirichlet boundary conditions on the coupling interface. Accurate solutions can be achieved without the need of large spatial discretization domains. The use of the adaptive-cross-approximation (ACA) and a block Jacobi preconditioner for the linear system solver results in an efficient simulation scheme for numerical computations of electric field distributions of realistic 3D high-voltage devices.

Transient Full Maxwell Computation of Slow Processes

This article deals with finite element solution of the full linear Maxwell’s equations. The focus lies on the transient simulation of slow processes, i.e. of processes, where wave propagation does not play a role. We employ an implicit Euler method for time discretization of the A, φ-based Galerkin-formulation with Coulomb-gauge. We propose a novel stabilization technique that makes possible the use of very large timesteps. This is of supreme importance for efficient simulation of slow processes in order to keep the number of timesteps reasonably small. The greatly improved robustness in comparison with a standard formulation is demonstrated through numerical experiments. As an example we simulate the lightning impulse test of an industrial dry-type transformer.

Numerical Computation of Ohmic and Eddy-Current Winding Losses of Converter Transformers Including Higher Harmonics of Load Current

Two different numerical algorithms for computing the Ohmic and eddy-current winding losses of converter transformers are presented. The higher harmonic components of the nonharmonic electric current, generated by the rectifying part of the power electronic converter, are fully taken into account. The calculated numerical results are verified by comparison with measured results.

Investigations of no-load and load losses in amorphous core dry-type transformers

Amorphous metal core dry-type distribution transformers have a significant place in today power market since they exhibit 60–70% lower no-load losses when compared to the standard steel based transformers. At typical loading regimes these losses are the most significant ones for a distribution transformer. In order to improve the design and to shorten significantly the time to market of such products numerical analysis of the no-load as well as of the load tests are of paramount importance. The present manuscript describes the FEM based numerical analysis performed on a 1 MVA unit, in an industrial environment, with the emphasis on the importance of non-linear and anisotropic magnetic modeling as opposed to isotropic for the accurate computation of no-load losses. The choices for the analysis regime and the specific analysis tools are described in details - and results are given to prove the salient points of this particular design of a transformer.

Domains of validity of quasistatic and quasistationary field approximations

The electro-quasistatic and the magneto-quasistationary approximations to Maxwells equations are widely used to model slowly time-varying electromagnetic fields. An analysis based on characteristic times is presented which allows to decide if any of these approximations is valid for a given field problem. The domains of validity of both approximations are derived and visualized in a combined diagram.

Benefits of higher order elements for electrostatic simulations of large-scale 3D insulator structures

In finite element method (FEM) simulations of electrostatic fields of large-scale 3D insulator structures, second order elements are used instead of linear elements while maintaining mesh and simulation parameters. Additional nodes on the edges of the elements are adapted to more accurately reflect surface geometry. This results in a more accurate approximation through curvilinear higher order elements. In order to validate this approach, a simplified geometry with a known analytic solution is employed. Furthermore, simulation results of a large-scale 3D insulator structure with several million degrees of freedom are presented herein.