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There is a thing that i dont understand... If i measure winding resistance of the transformer primary winding - will result depend if secondary is shorted or open? If yes - why? I also attach the sheet from a book. enter image description here

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If you measure the primary winding resistance using DC then no, the state of the secondary does not have an effect. If, on the other hand you measure using AC then certainly, the secondary plays a role and the impedance seen at the primary contains primary impedance and referred secondary impedance.

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  • \$\begingroup\$ And the core losses (if those exist). \$\endgroup\$ – ercegovac Mar 12 '18 at 20:21
  • \$\begingroup\$ It is stated in the text excerpt in the question that all the losses are attributed to the ohmic resistance of the windings and that this is an approximation. I would hope that the text goes on to explain how the approximation can be improved. \$\endgroup\$ – Charles Cowie Mar 12 '18 at 20:28
  • \$\begingroup\$ @ercegovac no not really because the secondary is shorted in this sort of test conventionally hence the applied primary voltage is a small fraction of normal running voltages hence, core losses tend to be significantly small compared to copper losses and leakage inductance. \$\endgroup\$ – Andy aka Mar 12 '18 at 22:45
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Your book figure shows AC applied with secondary shorted will be the total winding resistance. With secondary it will open will be primary only.

To measure resistance on AC only the real component of current must be extracted, which is a small percentage of the reactive impedance. It is measured at some ~10%V such that current <=10% of rated current to prevent over heating often calibrated at 75'C or 85'C. Some rack mounted industrial instruments use a 10A constant current source for large XFMR's.

A DMM might use a 0.1mA or 1mA pulse integration method or a CC DC method which has error with Ic=LdI/dt until the core is saturated. An RLC meter may use 60Hz , 1kHz, 100kHz , and maybe 1MHz constant current source (CC)to measure impedance and separate R,L(f),Q results.

If saturating a transformer say with a LiPo cell dI/dt=V/L and then it rises rapidly to saturation and when constant will give the DCR or DC winding resistance. However the core will have energy stored and ought to be demagnetized with half the saturation time in the opposite polarity assuming it was neutral to begin with. Otherwise a variac is used to swing slowly up to max. and down to zero.

example of part 1 of DC method for primary or secondary only show I in Amps vs time in seconds for a large core with saturation beginning at 25s and ending at 50s.

enter image description here

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