Working principle of current transformers

For a pointer type ammeter, the secondary current of the current transformer is mostly in the ampere level (such as 5A). For digital instruments, the sampled signal is generally in milliampere level (0-5V, 4-20mA, etc.). The secondary current of the miniature current transformer is in the milliampere level, mainly serving as a bridge between the large transformer and sampling.

Micro current transformers are also known as "instrument current transformers". ('Instrument current transformer 'has a layer of meaning, which refers to a multi current ratio precision current transformer used in the laboratory, generally used to expand the instrument range.)

Current transformers work similarly to transformers based on the principle of electromagnetic induction. Transformers transform voltage, while current transformers transform current. The winding of the current transformer connected to the measured current (with N1 turns) is called the primary winding (or primary winding, primary winding); The winding connected to the measuring instrument (with N2 turns) is called the secondary winding (or secondary winding, secondary winding).

The current ratio between the primary winding current I1 and the secondary winding current I2 of a current transformer is called the actual current ratio K. The current ratio of a current transformer operating at rated current is called the rated current ratio of a current transformer, expressed in Kn.

Kn=I1n/I2n

The function of a current transformer (CT) is to convert a larger primary current into a smaller secondary current through a certain transformation ratio, which is used for protection, measurement, and other purposes. A current transformer with a ratio of 400/5 can convert the actual current of 400A into a current of 5A.