Current Transformers - definition
Current Transformers - definition
A Current Transformer is a specialised measurement transformer whose function is to proportionally convert the values of large operating currents flowing in power circuits to levels that are safe and useful for measurement, protection and control devices. Its operation is based on the principle of electromagnetic induction, in which the primary winding, often single-coil, is incorporated directly into the current path, while the secondary winding, multi-coil, provides a reduced current value - normally scaled to 1 A or 5 A - depending on the ratio adopted.
Structurally, a current transformer consists of a closed-circuit magnetic core, usually made of ferromagnetic sheets with high permeability, around which the windings are wound. To ensure the accuracy of the representation of the rms value of the current, it is important to minimise angular and gear errors, which is regulated by an appropriate accuracy class defined by international standards (e.g. IEC 61869-2).
Current Transformers can be dry, oil or resin, and their selection depends on the rated voltage, environmental conditions and application requirements. Operation with an open secondary winding is not acceptable due to the possibility of induced overvoltages, which can lead to damage insulation and pose a risk to operator safety.
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