The excitation current in transformer is the minimum amount of current required to produce magnetic flux in the transformer's magnetic circuit that is essential for normal operation of the transformer. It is also known as magnetizing current. The magnitude of excitation current depends on the transformer's design, manufacturing and working condition of the transformer.
The excitation current is an important parameter of the transformer because it affects the transformer's efficiency and voltage drop. The excitation current is made up of two components ( real component is losses and reactive component).
There are several methods that can be used to determine the excitation current which are open circuit test, short circuit test and inrush current test.