# Working principle of power transformer

##### author: KZ
20/09/2022

A transformer is a device that transforms AC voltage, current and impedance. It uses the principle of electromagnetic induction (the induced electromotive force is generated due to the change of magnetic flux. When a part of the conductor of a closed circuit moves to cut magnetic lines of force in the magnetic field, current will be generated in the conductor. This phenomenon is called electromagnetic induction). A transformer is an electrical appliance that transmits electric energy or signals from one circuit to another.
Transformer ---- static electromagnetic device
When there is AC current in the primary coil, AC magnetic flux will be generated in the iron core (or magnetic core) to induce voltage (or current) in the secondary coil. The transformer is composed of an iron core (or magnetic core) and a coil. The coil has two or more windings. The winding connected to the power supply is called the primary coil, and the other windings are called the secondary coil.
The phasor of the magnetic flux of the secondary winding is φ M, this magnetic flux is called the main magnetic flux
The coil connected to the power supply receives AC electric energy, which is called the primary winding.
The coil connected to the load sends out AC electric energy, which is called the secondary winding
Of the secondary winding of the primary winding
Voltage phasor U1 Voltage phasor U2
Current phasor I1 Current phasor I2
Electromotive force phasor E1 Electromotive force phasor E2
Number of turns N1 Number of turns N2
2. The ideal transformer is the assumption that no other losses are considered, and the actual transformer has a loss of several percent
If the voltage and the instantaneous value of the electromotive force of the primary and secondary windings change according to the sine law, then U1/U2=E1/E2=N1/N2
Regardless of core loss, according to the principle of energy conservation, U1I1=U2I2
From this, the relationship between the primary and secondary winding voltage and the effective va