A transformer is a static electromagnetic device specially intendedto transform primary current system to secondary current system but with same frequency and features, like voltage and current.
When we see a transformer we will find a core made of sheet with windings which are coupled electromagnetically and also electrically.
A double-wound transformer consists of two windings, triple-wound has three and multi-wound has more than three windings.
Transformers are categorized as single-phase, three-phase and poly-phase as per the type of current. Poly-phase transformers can be defined as a transformer with allthe phase windings interconnected at the same voltage.
The winding of transformer in which current is travelling is called primary winding and the winding which receive this energy is known as secondary winding. In these windings the energy of alternative current is being passed.
The winding associated to the circuit with the advancedvoltage is known as high-voltage winding and the winding with the lower voltage is known as the low-voltage winding.
A tapped transformer is something whose windings are fixed with special taps for altering its voltage or current ratio.
The transformer core along with the windings is submerged in a tank of transform oil in order to resist the adverse effects of air on it. Such transformers are Oil Transformers. Other transformers are Dry Transformers.