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# Interpretation of the role of current transformers -

by：Transmart     2023-01-09

A current transformer is an instrument that interacts with currents at both ends, so the question is, what is the function of a current transformer? Measurement? Protection? Let's take a look at it next~~ 1. The role of a current transformer - -Introduction Current transformer, the English name is Current transformer, the symbol is TA, it is based on the principle of electromagnetic induction, and it is composed of a closed core and a winding, which can convert a large current into a secondary small current. Its structure is shown in the figure below. The number of turns of the primary winding is small, and it is connected in series in the circuit that needs to measure the current, while the number of turns of the secondary winding is large, and it is connected in series on the measurement surface or the protection circuit. When it is in the working state, the current mutual inductance The secondary circuit of the device is closed (otherwise there will be a safety hazard), the impedance of the measuring instrument or the series coil of the protective circuit is very small, making its working state close to a short circuit. 2. The function of current transformer 1 - used for measuring One of the functions of current transformer is for measurement, often used for billing or measuring the current size of equipment in operation. When measuring a large alternating current, in order to facilitate surface measurement and reduce the risk of direct measurement of high voltage, it is often necessary to use a current transformer to convert it into a more uniform current. Here, the current transformer plays a role To the role of current conversion and electrical barrier. The current transformer converts high current into low current proportionally according to the requirements. When used for measurement, the primary side of the current transformer is connected to the primary system, and the secondary side is connected to the measurement surface or relay protection equipment. 3. The second function of the current transformer - used to protect the second function of the current transformer is for protection. It is often used in conjunction with relay equipment. When there is a short circuit or overload in the line, the current transformer will send The device sends a signal to block the defective circuit, so as to achieve the purpose of protecting the safety of the power supply system. The current transformer for protection is different from the current transformer for measurement. It can only work effectively when the current is several times or dozens of times larger than the normal current, and it requires reliable insulation and a large and accurate limit value. coefficient, with satisfactory thermal and dynamic stability. Fourth, the role of the current transformer - - Precautions 1. During the operation of the current transformer, the secondary side is not allowed to be open, and must be kept closed. Because once the secondary side is opened, the magnetic flux and the secondary voltage will far exceed the normal value (up to thousands or even tens of thousands of volts), which will cause great harm to the safety of operators and equipment. 2. The wiring method of the current transformer should follow the series principle, 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.
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