Interposing voltage or current transformers can be used to compensate for phase shift when the measurement point has a phase shift relative to the reference point.
An example of this could be the synchronizing circuit of a unit connected generator - in this case, PTs on the LV side of the unit transformer can be compared against PTs on the HV bus - you would need to compensate for the transformer phase shift in this case.
In regional transmission systems, there are many generators and loads and typically a numder of loops in the interconnected system that provide multiple paths for power flow.
“A phase shifting transformer is a device which, when connected to a transmission line, is capable of altering the effective phase-angle difference between the two ends of the line. Since power flow over a transmission line is closely related to the phase-angle difference between the line ends, phase shifting transformers allow the flow of power across a line to be adjusted.” [From:
