In the power generation, transformation, transmission, distribution and use of electricity in the line the size of the current varies, from a few to tens of thousands of amps.
In order to facilitate measurement, protection and control needs to be converted to a more uniform current, in addition to the line voltage is generally relatively high, such as direct measurement is very dangerous. The current transformer performs the function of current transformation and electrical isolation. For Pointer ammeter, the secondary current of current transformer is mostly amperage level (such as 5A, etc.) . For digital instruments, the sampling signal is generally of milliampere level (0-5V, 4-20mA, etc.) . The secondary current of the miniature current transformer is milliampere, which mainly acts as a bridge between the large current transformer and the sampling. The miniature current transformer is also called “instrument current transformer” . (“instrument current transformer” has a layer of meaning is a multi-current ratio precision current transformer used in the laboratory, generally used to expand the scope of the instrument.)