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Function And Principle Of Current Transformer
Jan 17, 2019

The main function is to convert the large current in AC circuit to a certain proportion of small current (the standard of our country is 5 amples), for measuring and relay protection only. In the process of power generation, substation, transmission and distribution, due to the difference of electrical equipment, the current often varies from tens of thousands of amperes to tens of thousands of amperes, and these circuits may also be accompanied by high voltage.

So in order to monitor and measure the circuit of these lines, and at the same time to solve the danger of high voltage and high current, it is necessary to use current transformer. The pincers for electricians, which are used to measure alternating current, are the "pincers" of the piercing current transformer.

II. Working Principle

The principle of current transformer is based on the principle of electromagnetic induction. The primary winding of current transformer often has all the current flowing through the circuit. When the current transformer works, its secondary circuit is always closed. Therefore, the impedance of the series coil of the measuring instrument and the protective circuit is very small, and the working state of current transformer is close to short circuit.

In an ideal current transformer, if the no-load current is assumed to be I 0=0, the total magnetic potential I 0N 0=0. According to the law of conservation of energy, the magnetic potential of primary winding is equal to that of secondary winding, i.e. I 1NI=-I 2N 2.

That is to say, the current of current transformer is inversely proportional to its turns. The ratio of primary current to secondary current I 1/I 2 is called the current ratio of current transformer. When the secondary current is known, the primary current can be calculated by multiplying the current ratio, and the phase of the secondary current is 1800 different from that of the primary current.