I did an experiment where I varied the test voltage and determine the values of the resistance and magnetising reactance of the core. What I noticed is that their values actually vary (not constant). Ideally speaking, shouldn't their values be constant regardless of the test voltage (while they vary in practice)?
The point is: we calculate the paremeters of equivalent circuit as ideally and in a specific contour conditions. But the core is made with non-linear material, and the losses have exponential bahavior in some regions of operation. Because it, these parameters are not constants with all applied conditions.