*A current transformer (CT) is a device that measures the current in a circuit by producing a proportional current in its secondary winding.
*A CT can have different accuracy classes depending on its purpose. A 5P20 CT means that it is a protection class CT with an accuracy of 5% and an accuracy limit factor (ALF) of 20.
*This means that the CT can handle up to 20 times the rated primary current without saturating and with an error of less than 5%.
*For example, if the CT has a ratio of 1000/5 A, it can measure up to 20,000 A in the primary with an accuracy of 5%.
*Protection class CTs are used for applications such as overcurrent, earth fault, differential, and distance protection.
*They are designed to operate reliably under high fault currents and to isolate the secondary circuit from the primary circuit.