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I am trying to model a transformer using coupled electrical and magnetic circuits. SPICE has many advantages in assembling these circuits. I was able to model properly for an transformer with no load, although the solution is a little slow.

When I try to add a secondary to the transformer, the simulation is prohibitively slow.

Does anyone have any clue as to what the problem might be?

TR with no load

TR with secondary

Luiz Oliveira
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    Last image, right two circuits - no nodes have any reference to ground. That typically causes excessive GMIN stepping and slow results. Try adding a 1GIG resistor to ground. – rdtsc Jan 27 '21 at 18:31
  • Wow!! @rdtsc That was the problem... in this case, i could ground directy, as in the image 1. Thank you! – Luiz Oliveira Jan 28 '21 at 13:48
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    @rdtsc Hey hey hey! You stole my best tip there! – winny Jan 28 '21 at 18:35
  • That looks like an unnecessary convoluted way to represent a transformer. Have you conidered two coupled inductors? If nonlinearity is needed, use the Chan core. – a concerned citizen Jan 30 '21 at 00:26
  • @aconcernedcitizen, I was trying to model a 'topological-correct' transformer. In this models, some additional features can be modeled/checked, as flux densities in core limbs, yokes, tanks... also, some exotic connections can be done... zig-zag, phase-shift transformers... there is a lot of this in ATP... – Luiz Oliveira Jan 31 '21 at 13:48
  • @LuizOliveira Well, you know what you're doing, but I'd recommend using the simple voltage source instead of the behavioural one (as you did in your 2nd picture), and for simple constant*I(device) choose H or F sources, and, similarly, E or G for constant*V(node); it's likely you'll have better chances for convergence and get faster results. But, unless I'm wrong, your MUR(x) seems to be s/l/table(), and then REL(x,s,l)=l/s/MUR(x), which simplifies to table(). Also, you can accept your own answer, it helps future searches of the same topic, showing an acepted answer. – a concerned citizen Jan 31 '21 at 14:45
  • I tried recreating your first schematic, and it looks like you're trying to model a saturable transformer. Maybe it helps, maybe not, but there already is a nonlinear Chan core, and also a 3rd party library with the Jiles-Atherton model. If not, the behavioural inductor (Flux=<...>) can also be used to model simple saturable inductors. See the link I gave and the manual under LTspice > Circuit Elements > L. for more (if needed). – a concerned citizen Jan 31 '21 at 14:51
  • @aconcernedcitizen, thanks for the tips... about the MUR table, I was using it this way because I had the data for a specific configuration, now I have fixed it according to your suggestion. – Luiz Oliveira Feb 01 '21 at 13:22

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@rdtsc was right. If I ground the 2nd and 3rd circuits separetely, LTSpice finds a solution in an acceptable time, it is still not that fast, but this is probably due to non-linearity.

Luiz Oliveira
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