Current transformer, taken out of context, is an instrument with mutual influence of two currents. So the question is, what is the function of current transformer? Measurement? Protection? Let's take a look at it together~~

I. function of current transformer

Current transformer, whose English name is current transformer and symbol is Ta, is an instrument composed of closed iron core and winding according to the principle of electromagnetic induction, which can convert primary current into secondary current. Its structure is as shown in the figure below. The number of turns of primary winding is small, which is in series with the circuit that needs to measure current, while the number of turns of secondary winding is large, which is in series with the measuring surface or protection circuit. When it is in operation condition, the secondary circuit of current transformer is closed (otherwise, safety hidden trouble will occur). The impedance of series coil of measuring surface or protection circuit is small, which makes its operation condition close to short Road.

II. Function of current transformer I -- for measurement

One of the functions of current transformer is to measure, which is often used to calculate or measure the current of equipment in operation. In the measurement of large alternating current, in order to facilitate the surface measurement and reduce the risk of direct measurement of high-voltage electricity, it is often necessary to use current transformer to transform it into a more unified current. Here, current transformer plays the role of current transformation and electrical barrier. The current transformer converts the high current into the low current in proportion according to the requirements. When measuring, the primary side of the current transformer is connected to the primary system, and the secondary side is connected to the measuring surface or relay protection equipment.

III. function II of current transformer -- for protection

The second function of current transformer is for protection. It is often used in cooperation with relay equipment. When the line is short circuited or overloaded, current transformer will send signals to relay equipment to block the defective circuit, and then achieve the purpose of protecting the safety of power supply system. The current transformer for protection is different from the current transformer for measurement. Only when the current is several times or dozens of times larger than the normal current, it can be used for operation. Moreover, it requires reliable insulation, large accurate limit coefficient, satisfactory thermal stability and dynamic stability.

IV. function of current transformer -- precautions

1. During the operation of current transformer, the secondary side is not allowed to open, and must adhere to the closed state. Once the secondary side is open, the magnetic flux and the secondary side voltage will be far beyond the normal value (up to thousands or even tens of thousands of volts), which is a great danger to the safety of operators and equipment.

2. The wiring method of current transformer shall follow the principle of series connection, that is, the primary winding is connected in series with the circuit under test, and the secondary winding is connected in series with the measuring surface or relay equipment.