A transformer is a device that changes AC voltage, current and impedance.

1. Energy transmission: the transformer can transmit electric energy from the primary side circuit to the secondary side circuit to realize electric energy transmission.

2. Voltage conversion: the step-up transformer can convert low voltage into high voltage for long-distance transmission; The step-down transformer can convert high voltage into low voltage, so as to transmit power from the power grid to users.

3. Impedance exchange: the impedance of the primary side and secondary side of the transformer can be different, that is, it has the function of impedance transformation.

4. Current conversion: the current at the primary side and secondary side of the transformer can be different, that is, it has current conversion function, which can change from large to small or from small to large.

5. Electrical isolation: the primary and secondary circuits of the transformer are electrically isolated, with only magnetic contact and no electrical connection. Isolation transformer is a special product.

6. Phase shifting: the simplest phase shifting method is that the two windings are connected by star and angle. If necessary, a phase-shifting winding can also be set at the primary side of the transformer for phase-shifting. There are three connection modes between phase-shifting winding and main winding, namely broken line, hexagon and extended triangle.

7. Measurement: in the measurement of voltage, current and electric power, instrument transformers (i.e. voltage transformers and current transformers) are widely used. The accuracy of transformer directly affects the measurement accuracy.

8. Coupling: transformer coupling has many applications in electronic circuits. It can not only realize signal transmission, but also has isolation function, which can reduce or eliminate interference.

In addition, there are some special-purpose transformers, many of which have specific functions. For example, electric furnace power transformer, welding power transformer, rectifier power transformer, etc. can be used for specific purposes.