Principle of Transformer

In the lines of power generation, transformation, transmission, distribution, and power consumption, the currents vary greatly, ranging from a few amperes to tens of thousands of amperes. In order to facilitate measurement, protection and control, it needs to be converted into a relatively uniform current. In addition, the voltage on the line is generally relatively high, such as direct measurement is very dangerous. The current transformer plays the role of current conversion and electrical isolation.
For pointer-type ammeters, the secondary current of the current transformer is mostly ampere-level (such as 5A, etc.). For digital instruments, the sampled signal is generally milliampere (0-5V, 4-20mA, etc.). The secondary current of the miniature current transformer is milliampere, and it mainly serves as a bridge between the large transformer and the sampling.
Miniature current transformers are also called “instrument current transformers”. (The “instrument current transformer” has a meaning that the multi-current ratio precision current transformer used in the laboratory is generally used to expand the range of the instrument.)
The current transformer is similar to the transformer and also works according to the principle of electromagnetic induction. The transformer transforms the voltage and the current transformer transforms the current. The winding of the current transformer connected to the measured current (the number of turns is N1) is called the primary winding (or primary winding, primary winding); the winding (the number of turns is N2) connected to the measuring instrument is called the secondary winding (or the secondary winding) Winding, secondary winding).
The current ratio between the primary winding current I1 of the current transformer and the secondary winding I2 is called the actual current ratio K. The current ratio of the current transformer when it works at the rated current is called the current transformer rated current ratio, which is represented by Kn.
Kn=I1n/I2n
The function of the current transformer (CT) is to convert a primary current with a larger value into a secondary current with a smaller value through a certain transformation ratio for protection, measurement and other purposes. For example, a current transformer with a transformation ratio of 400/5 can convert an actual current of 400A into a current of 5A.