Daniel Weida

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.

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.

Three dimensional FEM electrical field calculations for EHV composite insulator strings

Numerical simulations play a key role in various fields of engineering as approach to verify and optimize functional properties for complex configurations which cannot be studied analytically, starting from the early stages of design even before construction of the first prototype. Numerical methods can be adopted to calculate electric field magnitude on the components of high voltage composite insulating strings: resulting data can be subsequently used to verify and if necessary to optimize the design of corona rings and field grading hardware, which constitutes a key feature especially for insulator sets operating at the highest voltage levels. Three dimensional Finite Element Method (3D-FEM) is a particularly suitable tool for such purposes since both symmetrical (mirror- or rotational-) as well as non-symmetrical geometries can be taken in account in the field calculation. Overhead Transmission Line (OHTL) composite insulator sets operating within and above EHV system voltages (>345kV) are always equipped with field grading hardware in order to reduce peak field stresses along the insulator string. String configuration (V-string, single or double suspension and tension sets etc.) geometry of conductor bundle, presence of metal structures in the vicinity like i.e. the lattice tower and cross arms as well as distance of insulator sets from the ground may have remarkable influence on the actual field magnitudes encountered under operating conditions. When all these details of geometry are considered, resulting geometry is typically neither mirror-nor rotational symmetric, thus complete study can only be performed by 3D-analysis. Beside an accurate knowledge of electric field magnitude around the insulator string, accurate information about critical field level is necessary in order to perform design evaluation properly. Stabile partial discharge on polymeric insulating materials (Silicone, EPDM, etc.) may generate long term degradation of material properties and consequent reduction of reliability in service. The simulation procedure in its main steps including modeling, meshing, numerical solving and post-processing is illustrated in the paper and some of the critical features are reported and discussed. Since the number of Degrees of freedom (Dof) growths quickly with model complexity, advanced modeling and simulation techniques for electrostatic or electro-quasistatic field distributions are necessary to perform bulk calculations in a reasonable amount of time. In this regard, a full 420 kV case study is presented.

Design of ZnO microvaristor material stress-cone for cable accessories

For the design of 20 kV cable accessories, a stress-cone with semi conductive ZnO microvaristors is examined using finite element method (FEM) simulations. It is virtually prototyped for various geometric design parameters and benchmarked by applying a test voltage. Based on the results, an optimal design is chosen and compared to standard cable accessories in virtual and experimental lightning surge tests in a high voltage laboratory.

Design of ZnO microvaristor end corona protection for electrical machines

For the stator winding of electrical machines, end corona protection arrangements including semi-conductive microvaristor lacquers are analyzed using finite element method (FEM) simulations. Those materials feature nonlinear resistive properties depending on the local electric field. Hence, electroquasistatic FEM simulations considering capacitive and nonlinear resistive material behavior are performed. End corona protection arrangements using semi-conductive materials are compared. The resulting voltage distributions, tangential electric fields and ohmic losses are presented.

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.

Design of cable accessories using ZnO microvaristor material based on FEM simulations

In this contribution, a stress-cone made of semi-conductive ZnO microvaristor material is analyzed using finite element method (FEM) simulations. The resulting electric fields and ohmic losses, which have an effect on the expected lifetime, are compared for various design parameters.

Effects of microvaristor material on the occurrence of partial discharges upon insulators in rain test

Finite element method (FEM) simulations of high voltage composite insulators including nonlinear field grading materials in rain test are presented. These silicone polymer materials are filled with ZnO microvaristors, which feature semi-conductive field-dependent material properties. The effects of adding layers to a composite insulator made of semi-conductive ZnO microvaristor material on the voltage resistance is analyzed using numerical simulations. The resulting homogenization of the electric field is compared for various ZnO layer setups in rain test.

Improved accuracy of electro‐quasistatic simulations of large‐scale 3D high voltage insulators with nonlinear material layers

Purpose – The purpose of this paper is to analyze the accuracy of finite element method simulations for high voltage equipment featuring resistive field grading.Design/methodology/approach – In such simulations, the order of the mesh used and the polynomial order of the ansatz functions are varied while maintaining mesh and simulation parameters. The resulting accuracy of the simulations is analyzed by an error convergence study which shows the relative errors against the number of degrees of freedom the computational time and the memory consumption.Findings – Simulation results of simplified benchmark geometry and applications to large‐scale 3D high voltage equipment are presented herein.Originality/value – The impact of the order of the mesh and the Ansatz functions are studied for realistic high voltage setups. The paper helps the user of simulation software to choose adequate simulation parameters.