Detailed Electric Discharge Simulations

The Electric Discharge Module enables quick and easy setup of discharge models in 2D, 2D axisymmetric, and 3D domains.

The workflow is straightforward and typically follows these steps: Create or import the geometry; define the physics settings, boundary conditions, and initial values; set up the mesh; select a solver; and visualize the results. The meshing and solver settings are automatic, with the option for manual customization. All of these steps can be seamlessly performed within the COMSOL Multiphysics^® environment.

The module's functionality is centered around the Electric Discharge interface, which is designed to model discharges in a variety of media, including gases, liquids, and solid dielectrics. It features built-in charge transport models that solve transport equations fully coupled with Poisson's equation, accounting for chemical and physical processes like impact ionization, attachment, and recombination and adapting to the specific properties of each medium. Thanks to this built-in functionality, in most cases, users do not need to manually input chemical reactions or reaction rate data.

Discharges in Liquids

When modeling discharges in liquids, such as transformer oil used for electrical insulation, the Electric Discharge interface solves transport equations for electrons, positive ions, and negative ions. It includes typical processes such as field ionization, attachment, and recombination to represent the behavior of discharges in liquid media.

Surface Charge Accumulation and Relaxation

Modeling charge transport at dielectric interfaces is essential for many applications. Electric charges can accumulate at these interfaces, for instance, through corona discharge, and space charges may drift along the surface under the influence of an electric field. The Electric Discharge interface features a built-in dielectric interface capability that automatically handles surface charge accumulation and relaxation processes.

Electrode Boundary Condition

The electrode boundary condition is a central component in electric discharge modeling. Boundary conditions for electric potential and charge carriers can be specified within a single feature, enhancing the efficiency of the modeling process. The Electrode feature also includes built-in discharge current variables. The charge carrier boundary conditions include options for open boundaries as well as for defining flux, number density, or surface emission. Furthermore, the surface emission settings support secondary electron emission, field electron emission, and thermionic emission.

Customizable Discharge Chemistry

The Electric Discharge Module includes functionality for defining custom discharge chemistry, making it easy to set up models with complex chemical reactions. A dedicated feature simplifies the process of generating space-dependent models, enabling users to efficiently manage hundreds of chemical reactions in discharge simulations.

The module also offers flexibility for customizing transport equations beyond the built-in options for charge carriers. Those customized transport equations are solved in the Transport of Charge Carriers interface. It seamlessly couples with other physics interfaces, enabling the study of charge transport within electromagnetic and flow fields.

Capture Multiscale Dynamics

The dynamics of electric discharges span from sub-nanoseconds to milliseconds in time and from micrometers to meters in space, presenting challenges in resolving nanosecond-scale events over much longer time frames.

The Electric Discharge Module leverages advanced meshing and solving capabilities. Its adaptive meshing technique allows for variable mesh sizes, ranging from one micrometer to one meter, and for optimizing the number of degrees of freedom. Additionally, the solver's automatic time-stepping adjusts time steps across several orders of magnitude, enabling accurate capture of both short-term phenomena, such as Trichel pulses, and long-term effects, such as space-charge accumulation and relaxation.

Gas Discharges

The Electric Discharge interface models atmospheric and high-pressure gas discharges using fluid and local field approximations. In addition to solving transport equations for electrons, positive ions, and negative ions, the model incorporates processes like impact ionization, attachment, and recombination to accurately simulate gas discharges.

The built-in charge transport model, along with the module's included Electric Discharge material library (see section below), enables the simulation of essential discharge chemistry in gases such as air, without requiring manual input of chemical reactions. The gas medium can easily be switched by selecting a different option from the material library, such as SF₆, N₂, or CO₂.

Bipolar Charge Transport in Solids

For solid dielectrics, the Electric Discharge interface supports bipolar charge transport, solving transport equations for electrons, holes, and trapped charges. The model is fully coupled with Poisson's equation and accounts for trapping, detrapping, and recombination effects, providing detailed simulation of charge transport in solid materials.

Photoionization

Photoionization plays a critical role in positive electric discharges. The Electric Discharge interface includes a built-in photoionization model based on the radiative transfer method, enabling efficient computation of the photoionization rate. Up to seven exponential terms are available to approximate the photoionization process.

Connecting to Electrical Circuits

Built-in electrical circuit modeling functionality makes it possible to create lumped systems to simulate currents and voltages in electrical circuits. It supports the modeling of circuit elements such as voltage and current sources, resistors, capacitors, inductors, and other circuit components. Circuit models can also be connected to distributed field models in 2D and 3D. Additionally, circuit topologies can be imported and exported using the SPICE netlist format. These circuits can be combined with electric discharge physics models to simulate realistic loads.

Unique Numerical Stabilization Techniques

In electric discharge physics, species number densities can vary by several orders of magnitude over short distances. Traditional methods may result in unphysical negative values. To prevent this, the Electric Discharge interface uses a logarithmic formulation, ensuring that number density solutions remain strictly positive.

Additionally, the module includes numerical stabilization techniques to ensure the equations are solved with both accuracy and efficiency.

Material Library

Modeling electric discharges often involves specifying complex chemical reactions and material properties, which can be time-consuming. The Electric Discharge Module simplifies this with two built-in material libraries.

The Electric Discharge material library provides data for common gases, liquids, and solid dielectrics that is seamlessly integrated with charge transport models, enabling users to begin modeling without having to manually enter equations or data. The Equilibrium Discharge material library offers temperature-dependent properties (up to 25,000 K) for various gases, including density, heat capacity, thermal conductivity, dynamic viscosity, and volumetric emission rates.

Multiphysics Interfaces for Modeling Arc Discharges

The Electric Discharge Module can be used to model thermodynamic equilibrium discharges, such as electric arcs, where electrons and heavy species share the same temperature. The included Arc Discharge multiphysics interface uses a magnetohydrodynamic approach to describe the discharge as a single fluid with one temperature. This interface couples electromagnetics, fluid flow, and heat transfer, incorporating Lorentz force, electromotive force, enthalpy transport, Joule heating, and radiation loss.