Equivalent Reactance

MAGNETIC LEAKAGE

Till now we have assumed that all the flux linked with the primary also links with the secondary. But in practice, the permeability of the core of the transformer is finite. All the flux linked with the primary do not link with the secondary. As shown in Figure 1.29(a), Φ_L1 and Φ_L2 induce emf e_L1 and e_L2 in primary and secondary windings respectively. Therefore, in effect, we can consider it as an equivalent inductive coil in phase with the winding shown in Figure 1.29(b).

EQUIVALENT REACTANCE

If X₂ be transferred to primary, let its referred value be X₂^′. We have
I₂²X₂=I₁²X₂^′
i.e.,
If X₁ be transferred to secondary, let the referred value be X₁^′ We have
I₁²X₁=I₂²X₁^′
i.e., 
The total reactance referred to as primary (X₀₁) is X_l + a²X₂ and that of referred to as secondary (X₀₂) is X₂+. The total reactance is known as equivalent reactance. It is denoted by
X₀₁=X₁+a²X₂ (1.18)