Question

How to find two phase of star connected system if one phase is given

Answer 1

See, you have to understand that merely interchanging phases won’t have any effect on the magnitude of the voltage. For instance ,from your example if we have a phase sequence RYB then the LINE VOLTAGE = root 3* phase voltage in star connected system=346.4 volts..Line voltage at R PHASE is taken as REFERENCE, therefore Y AND B PHASES will be LAGGING BEHIND R phase BY 120 AND 240 RESPECTIVELY.

Now, if we interchange R with Y The line voltage will be the same ! But now connection Y will still be lagging 240 from the reference phase R.

Moreover, if we do the same phase reversal at secondary, there will be phase angle change not magnitude change. They will be now 180 degree in opposition.