Block label property in AC Magnetics

General

The tab "General" allows entering basic properties for the material: magnetic permeability and electric conductivity, and field sources values: total current, voltage drop or current density.

Permeability

Enter components of permeability tensor here, or leave None or blank to specify that the block with the corresponding label is excluded. To define two different components, first check the Anisotropic box. Choose Relative or Absolute to specify absolute values of permeability or relative to permeability of vacuum.

Dealing with nonlinear materials, instead of magnetic permeability you need to define the magnetization curve. To do it, check the Nonlinear box and QuickField will display the Edit B-H Curve dialog that allows to define the curve. To reopen the Edit Curve dialog later, click the Edit B-H Curve button.

Note. In AC Magnetics the magnetic flux density value at every field point depends on time. So, the magnetic permeability values do the same. To calculate the field values QuickField defines such equivalent time-independent magnetic permeability that the average magnetic field energy, (B·H)/2, for the period remains unchanged.

Defining a magnetization curve with the Curve Editor you specify the DC-based B(H) dependency and QuickField automatically recalculates the curve for the problem-defined frequency. The graph shows the original DC-based curve in green color while the curve recalculated for the problem-defined frequency is dashed red.

Conductivity

Enter the value of conductivity here or leave zero for non-conductive material.

The electrical conductivity of the material may depend on temperature. Dependency is given in tabular form and automatically be approximated by a spline. To specify the electrical conductivity, which depends on temperature, check the Function of Temperature check box, to get into the curve editor.

Enter a number or a formula into the Temperature field. The formula describes the temperature dependency on coordinates. Please note that all coordinates in a formula are given in meters no regards to length units you have choose for the problem.

You can import the temperature field from a coupled heat transfer problem. To do that create and solve a heat transfer problem based on the same geometry model, and link it to the problem.

When the imported temperature field and temperature given by a constant or a formula are both available, the imported temperature will be used.

Field Source

The ways you define field sources are different for conductors and non-conductive blocks. For solid conductors, you specify either applied voltage or total current. For non-conductive blocks and stranded conductors you always specify zero conductivity value and the field source can only be specified by total current or current density values.
You can specify coordinate-dependent current density phase and magnitude. To do it, enter the required formula in place of numerical value. Formulas are discussed in details in Working with Formulas section.
When total current or voltage is specified you can define several block labeled with this label (if any) as connected in parallel or in series. In the last case the total current over each conductor will be the same and distribution of the current density is subject to solve.

If the field analysis is performed with the electric circuit connected, then applied voltage or the full current for the solid conductor (with non-zero conductivity) can not be defined in the label properties window. Instead of it, include all the conductive blocks into electric circuit with voltage or current sources attached to them. Only the parallel or serial connection of the separate conductors with the same label assigned should be defined in the label properties window.

Coordinates

Have sense for anisotropic magnetics or compound (laminated) materials modeled as anisotropic. Specify Cartesian or Polar according to the class of symmetry of anisotropy.

Core Loss

The tab "Core loss" allows entering properties for the soft magnetic material, which are required to calculate the core losses in it. These parameters are optional. If no data entered, then with default zero values the core losses will not be calculated in the corresponding blocks. Entered parameters are considered to be in W/m3 units. W/m³.

There are two main causes for the magnetic material losses: ohmic losses generated by eddy currents, and losses caused by the cyclic reversal of the magnetization and proportional to the area of the hysteresis loop. If the non-zero conductivity is specified, then for this material eddy current losses are calculated automatically and there is no need to specify the loss coefficients separately.

Situation is different for the laminated cores, which are made of thin insolated ferromagnetic sheets. In the laminated cores the electrical conductivity should be set as 0, otherwise the eddy currents simulated with QuickField will be too large. However, even the small eddy currents generate the losses. They are usually taken into account using some empirical formula.

QuickField uses the empirical formula Bertotti for core loss calculation:

p = k_hf B² + k_cf²B² + k_e(f B)^1.5     (2)

Here B - magnitude of the module of the flux density vector per period, f - problem frequency, k_h, k_c, k_e - volume power loss coefficients for specific magnetic material. Default zero values of the loss coefficient will exclude the corresponding loss component from the calculations.

First term of the formula above corresponds to the hysteresis losses, second- to the eddy current losses, and third approximates the excess magnetic losses (not covered by first two loss types).

Specific loss coefficients for the given material are calculated outside QuickField by data fitting using the known or measured tables of the volume losses per flux density and frequency p_core = f(B, f). More details about the loss coefficient calculations may be found at www.quickfield.com > Glossary > Core loss coefficients