The working principle of the current transformer

Update date:2018-01-09 Source:maxge

The current transformer is an instrument that is used to convert a large current into a secondary side of a small current based on the principle of electromagnetic induction. The current transformer is composed of a closed core and winding. It has a small number of turns on one side of the winding and is strung on a circuit that needs to be measured.

Therefore, it often has all the current flowing through the circuit, and the number of turns of the secondary side winding is more. In the measuring instrument and the protection circuit, the current transformer is always closed in the work, so the impedance of the measuring instrument and the protective circuit series coil is small, and the working state of the current transformer is close to the short circuit. The current transformer is to convert a large current to a secondary side current to measure the secondary side.

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In power generation, electricity transmission, transmission, distribution and power lines, the current size is wide, from several to tens of thousands of security. In order to facilitate measurement, protection and control, it needs to be converted into a relatively uniform current. In addition, the voltage on the circuit is generally higher, such as direct measurement is very dangerous. The current transformer ACTS as a current transformer and an electrical isolation.

For the pointer type ammeter, the secondary current of the current transformer is mostly ampere grade (such as 5A, etc.). For digital instruments, the sampling signals are generally milliampere (0-5v, 4-20ma, etc.). The secondary current of micro current transformer is milliampere, which is the bridge between the main transformer and the sampling.

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Micro current transformer is also called "instrument current transformer". The "instrument current transformer" has the meaning that the multi-current transformer used in the laboratory is more than the precision current transformer, which is generally used to expand the instrument range.

The current transformer is similar to the transformer, which is based on the principle of electromagnetic induction. The transformer transforms the voltage and the current transformer transforms the current. The winding of the current transformer is called a winding; The winding of a measuring instrument is called a secondary wound.

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The current ratio of the current I1 and the secondary winding I2 of the current transformer is called the actual current ratio K. The current ratio of the current transformer in the rated current ratio is the rated current ratio of the current transformer, which is expressed by Kn.

The function of current transformer (CT) is to convert a large amount of current into a secondary current with a smaller value, which can be used for protection, measurement and other purposes. If the transformer is a current transformer of 400/5, it can convert the current of 400A to the current of 5A.


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