A current transformer is a device designed and manufactured based on the principle of electromagnetic induction, which can convert large currents into small currents under isolation conditions. It mainly consists of an iron core and primary/secondary windings. The primary winding consists of one or more turns, while the secondary winding typically has several tens to several thousand turns.

The use of current transformers is to connect the primary winding in series to the circuit of the measured current, and the secondary winding is connected to the instrument or control system. By using transformers with different ratios, a wide range of large currents can be converted into small currents that meet the needs of the instrument and control system, while also achieving isolation between strong and weak currents.

The current transformer has the highest accuracy within the range of 50% -120% of rated current; The smaller the load resistance, the higher the accuracy (except for standard current transformers with fixed loads); The larger the transformation ratio, the higher the accuracy, and the stronger the load capacity.

Special attention should be paid to the fact that the secondary circuit of the current transformer cannot be opened during use.

Current transformers can be divided into two categories in terms of usage, namely measurement current transformers and protection current transformers.