Transformers are capable of receiving AC power at one voltage and delivering it at another voltage.

In this way, they help achieve better transmission efficiency while transferring the power over longer distances.
In this explanation, we will go through the working and construction of a three-phase transformer by starting from its simplest form.

The basic working principle of a transformer is simple, electromagnetic induction. according to this principle of varying magnetic flux associated with a loop will induce an electromotive Force across it.
Such a fluctuating magnetic field can easily be produced by a coil and it alternating EMF system.
A current-carrying conductor produces a magnetic field around it.
With the fluctuating nature of the alternating current the magnetic field associated with the coil will also fluctuate.
This magnetic flux can be effectively linked to a secondary winding with the help of a core made up of ferromagnetic material.
This fluctuating magnetic field will induce an EMF in the secondary coils due to electromagnetic induction.
Since the turns are arranged in a series The Net EMF induced across the winding will be the sum of the individual EMS induced in each term.

Since the same magnetic flux is passing through the primary and secondary coils the EMF per turn for both the primary and secondary coils will be the same. The EMF per turn for the primary coil is related to the applied input voltage. As a result the induced EMF at the secondary coil is expressed as follows:
• This simply means that with fewer turns in the secondary than in primary one can lower the voltage.
• For the reverse case one can increase the voltage.
• But since energy is conserved the primary and secondary currents have to obey the following relationship.
• Three phase Transformers uses three such single phase Transformers, but with a slightly different coil configuration.
• Here the primary and secondary coils sit concentrically.
• Two more such windings are employed in a three-phase Transformer.
• Transformers with high power ratings generally employ a special kind of winding known as a disc type winding.
• We're separate discs windings are connected in series throughout outer and inner crossovers.
• The low-voltage windings are connected in a Delta configuration.
• And the high voltage windings are connected in a star configuration.
• Thus the line voltage further Rises to root 3 times at high voltage side. This also means that from a three-phase Step up Transformer. We can draw for output wires, three phase power wires and one neutral.
• High voltage insulated bushings are required to bring out the electrical energy.
• The core of the Transformer is made of thin insulated steel laminations.
• Such steel laminations are stacked together passion to form a three-phase limbs.
• The purpose of sin laminations is to reduce energy loss due to eddy current formation.
• The low voltage lighting  usually sit near the core.
• Various kinds of energy loss happens while transferring power from the primary to secondary coil. All these energy losses are dissipated as heat.
• So usually the Transformer is immersed in a cooling oil to dissipate the Heat.
• The oil dissipates the heat via natural convection
• Oil in the tank will expand as it absorbs the Heat. But conservator tank helps to accommodate for this volume change.