Transformers can only be used with AC current
When current flows through a circuit an magnetic field is generated
If DC current is used the strength of this field will be constant
When AC current is used the field will increase and decrease in strength and change fields with change in the direction of flow of current
The strength of the magnetic field in a wire is not that strong but when placed in a coil shape increases drastically
If an similar coil is placed near this circuit the changing polarity and intensity of the magnetic field causes the electrons in the second coil to get disturbed and causes them to move
This movement is called as EMF (Electro Motive Force)
EMF is not generated with DC current is passed through the primary coil (Magnetic field is constant)
When these two coil are placed in free air there is significant loss to the magnetic field from the primary coil
To tackle this issue an Iron Core is place between the two coils that acts as a path for the magnetic fields to travel
Even with Iron Core there is some loss in the magnetic field in the form of Eddy Current
Eddy Current causes the current to swirl around the core which heats up the transform and the energy is lost as heat energy
This can be reduced by forming the core using laminated sheets of iron
Transforms are of two types:
Step Up : Increase the voltage. Reduce the current
Step Down : Decrease the voltage. Increase the current
The voltage can be stepped up and down by varying the amount of turns in the coil in the secondary side
High Voltage is easy to transform to long distances and hence the current that comes into the cities have high voltage
The transforms that we found in cities are generally consist of three phases
An very common configuration of three phase transform is the Delta-Star (Delta-Wye)