For the scalar potential formulation, you can use three different analysis methods: Reduced Scalar Potential (RSP), Difference Scalar Potential (DSP), and Generalized Scalar Potential (GSP). The type of model you are analyzing determines which method is best to use:
If the model contains no iron regions, or if it has iron regions but does not have current sources, use the RSP method. Do not use the RSP method when the model has both iron regions and current sources, because numerical cancellation errors may produce an inaccurate solution.
If you cannot use the RSP method, choose between DSP and GSP. The DSP method is available for models with "singly connected" iron regions, and the GSP method is for models with a "multiply connected" iron region.
A singly connected domain is an iron region that does not provide a closed iron loop to magnetic flux that a current source produces. A multiply connected domain provides a closed loop. (see Figure 5.1: Connected Domains) Figure (a) illustrates a singly connected iron domain (DSP method) and Figure (b) depicts a multiply connected iron domain (GSP method).
Mathematically, you can use Ampere's law in the iron region to check whether the domain is singly or multiply connected. According to Ampere's law, the closed contour integral equals the enclosed current, or magnetomotive force (MMF).
MMF =
H(dl)
In a singly connected domain, the MMF drop in the iron should approach zero as the permeability of the iron tends to infinity. Most of the MMF drop occurs in the air gap for a permeable core. In a multiple connected domain, a closed contour integral in the iron linking the coil produces a nonzero MMF for any value of permeability. All of the MMF drop in this case occurs in the iron core.