Potential transformer or PT can have the same construction as any normal transformer. It has primary & secondary winding. The number of turns in primary windings is greater than the number of turns in the secondary winding because it is a step-down transformer.

In the power system, the role of the current transformer is to change the large current into the small current, isolate the secondary loop connected to the relay and measuring instrument from the high voltage system of the primary current, and convert the primary current to the secondary current value of 5A or 1A standards.