Saturation in Current Transformers

The saturation in current transformers is a characteristic feature of the properties of an equipment that operates with ferromagnetic induction. Your event is unavoidable if the TC operates in conditions above its nominal conditions.

It is then up to the designers to know the saturation curve of the equipment to well specify the TC for its field operation. The NBR 6856 prescribes that the manufacturer must provide the typical excitation curve for CT to protection service.

The CT saturation curve defines a satisfactory region for operation within its rated characteristics and according to the specifications of the circuit where it will operate. It is one of the elements used in the TC specification for its field operation.

The CT is commissioned to operate in a narrow range, in the initial region of the saturation curve. A well-designed CT over the nominal current, the working point lies in the linear range of the saturation curve, with the excitation current varying almost proportionally to the voltage developed in the secondary.

In this way the maximum error of relation of the TC will be within the mentioned class of accuracy. Laboratories that perform maintenance on current transformers must check the operating conditions of the equipment according to the data supplied by the manufacturer.