Wont self induction ruin the working of a transformer ?
While increasing voltage (AC) in the primary coil, wont there happen a self induction in the primary coil itself ?
$E_0 = -L \frac{dI}{dt} $
If there happens a change in current it should cause an emf. Even if the inductance is small. There happens a back emf in the coil.
Best Answer
The self-inductance of a transformer is the net inductive effect reflected onto the primary circuit by the transformer windings. Both the primary and secondary windings of a real transformer exhibit electrical resistance due to copper losses, and inductance due to magnetic flux leakage. Although most of the magnetic flux is confined to the core of the transformer, some flux links one winding without linking the other (leakage flux). The effect can be modeled as primary impedance and secondary impedance 'transposed' to the primary side of an 'ideal' transformer, along with the mutual inductance (magnetisation) and core losses (typically due to eddy currents and hysteresis).
The net effect on the current-voltage relationship through a transformer due to leakage flux is represented by a 'self-inductance'. In large power transformers, the winding resistance is generally large compared with the self-inductance, although the value of self inductance is generally not large compared to the mutual inductance, particularly at full load. When lightly loaded (<50%) the self inductance can have a noticeable effect in terms of a 'lag' between the applied voltage and the resulting current. This can be seen as 'undesirable' from an economic point of view, since it results in a low 'power factor'. This effectively means the full rating of the electrical transformer and related equipment (wires, switches, etc) are not being utilitized to their maximum capacity for transferring 'real' power, so there is some loss in efficiency.
On the other hand, the effect of self-inductance reduces the prospective fault currents. These are the potentially large electric current which flows when there is a fault, such as a short circuit between the line and earth ground. This reduces the need for large 'oversized' cables to handle a high fault current and also reduces the risk of possible damage caused by such currents.