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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)?

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The magnetizing reactance decreases as the iron becomes saturated with increased voltage. The resistance increases as the current increase causes the winding temperature to increase.

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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.

As follow, an example of a characterisc permeabillity curve for a silicon iron: enter image description here

https://www.researchgate.net/publication/283131025_Some_important_effects_of_the_water_jet_and_laser_cutting_methods_on_the_magnetic_properties_of_the_non-oriented_silicon_iron_sheets

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V=LdI/dt + IRs such that when dI/dt reduces it is due to drop in L due to saturation and rise in Rs if self-heating. This may be tested with DC-CV, CC or Vac (CV or CC) to measure L depending on the size of the core and it’s current rating.

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