Excitation Coil Model

Excitation coils are widely used in electromagnetic applications such as motors, transformers, and inductors to generate magnetic fields.

Examples of Excitation Coils used in Electromagnetic Applications

A primary and secondary (wound) excitation coil in a transformer. Only half is shown due to usage of a symmetry plane	A transformer with a primary and secondary coil. Both coils are a thin wire wound many times around a core. (image credit: CC BY-SA 4.0)	A solenoid coil used in an actuator. The coil is wound around a core and generates a magnetic field when a current is applied. (image credit: CC BY-SA 3.0)

This model here allows the setup of various type of excitation coils and their excitation based on predefined parameters.

To add an excitation coil to simulation use first add the ExcitationCoilModel using:

from mufem.electromagnetics.coil import ExcitationCoilModel

coil_model = ExcitationCoilModel()
sim.get_model_manager().add_model(coil_model)

Then use CoilSpecification to describe the properties of each individual coil. A coil specification requires the specification of a coil type, a coil topology, and a coil excitation. Finally, add it to the model:

# from mufem.electromagnetics.coil import CoilSpecification

# coil = CoilSpecification(
#           name="Coil", marker=my_coil_marker, topology=my_coil_topology, type=my_coil_type, excitation=my_coil_excitation
#)
#coil_model.add_coil_specification(coil)

Coil Type

The following coil types are available for the time-domain magnetic model:

Supported Coil Types
Name	Type	Description
Stranded coil	Does not model individual strands but combines them to a single homogenized region. Applicable when the individual wires have a small diameter compared to the skin depth of the material otherwise modelling errors are introduced such as an underestimation of losses (AC losses).	Instead of modelling individual wire the coil is homogenized to a single body.

Coil Topology

Supported Coil Topologies
Name	Type	Description
Open coil	The coil is open, and the current enters and leaves the coil through boundary faces.	Example of an open coil with two boundaries.
Closed coil	The coil is closed, and the current circulates through the coil.	Example of a closed coil.

Coil Excitation

Supported Coil Excitations
Name	Type	Description
Current Excitation	The coil is excited through a current source.	An excitation coil excited through a current source.
Voltage Excitation	The coil is excited through an applied voltage.	An excitation coil excited through a voltage source.

Reports

Following reports are available for the time-domain magnetic model for visualization:

List of reports
Name	Type	Description
Coil Current Report	Scalar Value	Returns the applied current to the coil
Coil Resistance Report	Scalar Value	Computes the electrical resistance of the coil based on geometry and material.
Flux Linkage Report	Scalar Value	Computes the total magnetic flux linkage with the coil windings.
Magnetic Inductance Report	Symmetric Matrix	Computes the self- and mutual inductance matrix for a multi-coil system.

Coefficient Functions

Following functions are available for the time-domain magnetic model for visualization:

List of functions
Name	Type	Description
Unit Current Density	Scalar Field	The electric current density in the coil assuming a current of 1 A is flowing through the coil. \[\mathbf{\tau}\]
Flux Linkage	Scalar Field	The magnetic flux linkage function is defined as: \[\psi = \mathbf{A} \cdot \mathbf{\tau}\]
Electromotive Force	Scalar Field	The electromotive force function is defined as: \[\mathcal{E} = \dot{\mathbf{A}} \cdot \mathbf{\tau}\]