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If I plot a graph of primary voltage against primary current for an open-circuited transformer I get a curve. If I use my equivalent circuit to give me predicted values for this, it gives me a straight line which intersects the curve at 2 places: one intersection is at the rated voltage.

Why is it that the 2 graphs do not agree?

I have thought about it and am wondering if it has anything to do with the fact that the relative permeability of the core changes as it reaches saturation. This would change my graphs in the 'right direction' but I have read nothing about this kind of thing in any text book - but then I can't find this explained anywhere.

Is this idea correct, or is there some other reason for this?

Thank you very much to anyone who can give me any help,

it is much appreciated,

Chris