The protection current transformer is used to reduce the currents in power systems, producing proportional currents in the unit’s secondary windings that remain isolated from the main circuit. In doing so, the protection current transformer allows the unaffected areas of the circuit to continue in operation.
This CT can be interpreted as a protection class CT having an accuracy of 5% over a current range of 10 times of normal primary current rating.
PS Class CT is also known as PX Class or simply Class X Current Transformer. It is special type of current transformer meant for protection purpose.