1>Transformer is a static device.which transfer electrical energy from primary side to secondary side without change in input frequency and power of supply.Transformer works on mutual induction.

2>since it is static device it's efficiency is higher than other rotating electrical machine.

3>coupling between primary and secondary is through magnetic field. (no electrical inter connection between primary and secondary).

4> primary and secondary winding of transformer is not fixed but HV and LV side is always fixed.

5> when source is on LV side and load on HV side it called stepup transformer.

6> when source is on HV side and load on LV side it is called stepdown transformer