What does a current transformer do
Jan 07, 2023| 1. Function
The main function of the current transformer is to convert the large current in the AC circuit into a certain proportion of small current (the Chinese standard is 5 amperes), which is used for measurement and relay protection. In the process of power generation, power transformation, power transmission, and power distribution, due to the different electrical equipment, the current often ranges from tens of amps to tens of thousands of amps, and these circuits may also be accompanied by high voltage.
Then in order to be able to monitor and measure the circuits of these lines, and at the same time to solve the dangers caused by high voltage and high current, current transformers are needed at this time. The clamp meter used by electricians is a device used to measure alternating current, and its "clamp" is a feed-through current transformer.
2. Working principle
The principle of the current transformer is based on the principle of electromagnetic induction. Its primary winding often has all the current of the line flowing through it. When the current transformer is working, its secondary circuit is always closed, so the measuring instrument and the protective circuit are connected in series. The impedance is very small, and the working state of the current transformer is close to a short circuit.
In an ideal current transformer, if it is assumed that the no-load current I0=0, then the total magnetomotive force I0N0=0, according to the law of energy conservation, the magnetomotive force of the primary winding is equal to the magnetomotive force of the secondary winding, that is, I1NI=-I2N2
That is, the current of the current transformer is inversely proportional to its number of turns, and the ratio of the primary current to the secondary current I1/I2 is called the current ratio of the current transformer. When the secondary current is known, the primary current can be obtained by multiplying the current ratio. At this time, the phasor difference between the secondary current and the primary current is 1800.