I have an x-ray closed transformer and I only can access to the primary terminals. I want to measure the inductance of the primary and to know how this loaded secondary influences it.
Turns ratio squared inversely defines the secondary inductance and load impedance is transferred the same way when mutual coupling is assumed to be high.
So If Lp = 1 H and n = 10:1 Ls = 1/10^2= 0.01 H.
With load switched off you can measure Lp with an RLC meter and compare with V, I scope readings.
With load switched on , you may measure the power factor and inrush current as well as the crest factor on peak current to Average. But it ought to have active power factor correction if it is relatively new.
The easiest method is to use a current transformer or a neutral ground resistor for 50mV drop with coax and compare the ratios of Vin/In.