Generally you  don't, or at least not directly.

What is actually measured is the relative phase of the voltage and current on all 3 lines, and then some post-processing is done, nowadays this is likely to involve analogue to digital conversions,  and some digital processing, but in years past, and probably still on exam papers,  it would have involved inductors and transformers with split windings to give phase shifts and then voltage or current addition or subtraction to in effect, perform the same as an analog computation using passive components.

Any set of realistic loads is mostly going to look like positive sequence current (i,e, a balanced, resisitve 3 phase load) with some out of balance terms as all 3 phases will not be carrying quite identical current and may not be perfectly at 120 degrees to one another.

Detection of a zero sequence current is a special case, and rather analogous to the current detection of a fault by a 3 phase RCD  - except that there are very good physical reasons that one does not route 3 high tension cables around the same magnetic core. Rather there are 3 current transformers, one per line, and the outputs (referenced to  a convenient low lower voltage)  are summed by interconnection, rather than a single chunk or iron. Basically the resultant is measuring the current that flows out down the 3 phase lines that is not cancelled when all 3 lines are summed

As the 3 lines have different capacitance to each other, and then to ground, or when all 3 are in parallel to ground (zero-sequence case) and the magnetic fields from any one core will also cause voltages in the others, the cable impedance are not quite the same for each configuration.

All  loads can be seen as a linear superposition of the various natural modes.

Mike.

You are absolutely right, however, the positive and negative impedance is to measure the relative value of volt and current between cable conductor and copper screen, and these values (real and magnitude) are representing the cable impedance in normal operation, while zero sequence impedance is representing the value during short circuit fault, that’s what i know but I'm always facing this dispute with many people that they are not understanding this concept or why we are measuring the impedance value for the cables.

You are absolutely right, however, the positive and negative impedance is to measure the relative value of volt and current between cable conductor and copper screen, and these values (real and magnitude) are representing the cable impedance in normal operation, while zero sequence impedance is representing the value during short circuit fault, that’s what i know but I'm always facing this dispute with many people that they are not understanding this concept or why we are measuring the impedance value for the cables.