The working principle of the transformer
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. Therefore, the measuring instrument and the protection circuit are connected in series with the coil. 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 the no-load current I0=0 is assumed, the total magnetomotive force I0N0=0. According to the law of conservation of energy, 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 of the secondary current differs from the phasor of the primary current by 1800.
