the primary and secondary winding of potential transformer is magnetically coupled by a core. PT is used to further step down the system voltage to measurable value up to 63.5v, 100v or 110v as per standard of the equipment.
the typical class of accuracy of metering pt are 0.1, 0 2, 0.5, 1.0 and protection pt is 3p. The pts are offered in single phase or three phase version.