When one side of transformer add alternating current as U1, and the winding current is I1. The current will create alternating flux in iron core to connect with primary winding and secondary winding. According to the principle of electromagnetic induction principle, alternating flux will create electromotance through two windings. The size is in the direct proportion to the winding turns and maximum flux. The more turns of winding is high voltage, the less is low voltage.
If the secondary is connected to the load, the secondary coil generates a current I2, and thus the magnetic flux ф2, the direction of ф2 is opposite to ф1, which cancels each other out, so that the total magnetic flux in the core is reduced, thereby The primary self-inductance voltage E1 is reduced, and as a result, I1 is increased, and it can be seen that the primary current is closely related to the secondary load. When the secondary load current increases, I1 increases, ф1 also increases, and the φ1 increase partially complements the portion of the magnetic flux that is offset by ф2 to keep the total magnetic flux in the core constant. If the loss of the transformer is not taken into account, it can be considered that the power consumed by an ideal transformer secondary load is also the primary power drawn from the power supply. The transformer can change the secondary voltage by changing the number of turns of the secondary coil as needed, but cannot change the power that allows the load to be consumed. In fact, the conversion of electrical energy into magnetic energy, and then the conversion of magnetic energy into electrical energy output voltage is a relative voltage, but there is a voltage between the two lines, there is no voltage to the ground that also known as a safe voltage.