Solid, Stranded, and Parallel Current Sources

These types of sources specify the magnitude and phase of the AC current flowing through a conductor. Solid current sources model eddy and displacement currents in a solid conductor. The amount of eddy current and displacement current — as well as the amount of source current — are included in the total current you specify.

• Stranded current sources model current as being carried on strands within a conductor. They can be used to model conductors made up of many individual insulated turns, all small enough so that eddy currents can be neglected. Eddy currents and displacement currents are not computed inside the conductor. Either the total current or the current density may be specified. A uniform current density is assumed throughout the conductor, unless a functional current density is defined.
• Parallel current sources connect two or more conductors in parallel to an outside source. The total current flowing through all selected conductors (including eddy and displacement currents) is specified. However, the current flowing through individual conductors in the parallel group is unconstrained and its value is computed during the solution.

The differences between each type of AC current source are shown below:

For solid and parallel current sources, the current you specify is the total current in the conductor:

I_Total = I_Source + I_Eddy + I_Displacement

where:

• I_Total is the total current flowing through the source. It satisfies Ohm’s law with the potential seen by the source.
• I_Source is the current due to the potential difference generated by the external source. It is the current that the source would supply if you reduced the potential difference by the back EMF produced by the eddy and displacement currents in the conductor.
• I_Eddy is the eddy current induced in the conductor due to time-varying magnetic fields penetrating the conductor.
• I_Displacement is the displacement current due to time-varying electric fields in the conductor. It becomes significant only at very high frequencies.

For stranded current sources, the current you specify is the total source current (or source current density), I_Total = I_Source. Eddy current and displacement current effects are neglected.