Definition of Ideal Transformer
An ideal transformer is an imaginary transformer which does not have any loss in it, means no core losses, copper losses and any other losses in transformer. Efficiency of this transformer is considered as 100%.
Ideal Transformer Model
The ideal transformer model is developed by considering the windings of the transformer are purely inductive and the core of the transformer is loss free. Also there is zero leakage reactance of transformer (reactance is the opposition to the flow of current from the circuit element due to its inductance and capacitance).
That means, 100% flux passes through the core and links with both the primary and secondary windings of transformer. Although every winding must have some inharent resistance in it which causes voltage drop and I2R loss in it. In such ideal transformer model, the windings are considered as ideal(fully inductive), that means resistance of the winding is zero.
Now if an alternating source voltage V1 is applied in the primary winding of that ideal transformer, there will be a counter self emf E1 induced in the primary winding which is purely 180o in phase opposition with supply voltage V1.
For developing counter emf E1 across the primary winding, it draws current from the source to produce required magnetizing flux. As the primary winding is purely inductive, that current lags 90o from the supply voltage. This current is called magnetizing current of transformer Iμ.
This alternating magnetizing current Iμ produces an alternating magnetizing flux Φ. The flux is proportional to that current which producing it hence the flux would be in phase with the current. This flux also links the secondary winding through the core of the transformer. As a result, there would be another emf E2 induced across the secondary winding, and this is mutually induced emf as shown in the figure below.